BIOCHEMISTRY FLASH CARDS

Acidic dissociation

1. General expression: HA is the acid (proton donor) and A- is the conjugate base (proton acceptor):

2. An acid dissociates in water to yield a hydrogen ion (H+) and its conjugate base

3. A base combines with H+ in water to form its conjugate acid

k1[HA] = forward rate, k-1[H+][A-] = reverse rate

Measures of acidity

1. pKa· When forward & reverse rates are equal, acidic dissociation constant, Ka, is defined by:o k1/k-1 = [H+][A-] / [HA] = Ka· Expresses the STRENGTH OF AN ACID· pKa = -log[Ka]· Strong acid has pKa of W2 (H+ binds loosely to conjugate base)· Weak acid has a pKa of D10 (H+ binds tightly to conjugate base)2. pH· Henderson-Hasselbalch equation: pH = pKa + log [A-]/[HA]· A measure of the ACIDITY OF A SOLUTION· pH = -log[H+]· Neutral solution has a [H+] of 10-7 à pH = 7· Acidic solution has a [H+] > 10-7 à pH < 7· Alkaline solution has a [H+] < 10-7 à pH > 7

Buffers and Buffering capacity

1. A solution that contains a mixture of a weak acid and its conjugate base2. It resists changes in [H+] on addition of acid or alkali3. The buffering capacity of a solution is determined by the acid-base concentration and the pKa of the weak acid· Maximum buffering effect occurs when: o [weak acid] = [conjugate base]· When the buffer effect is at its maximum:

o pH of the solution = pKa of the acid4. Buffering effect is seen on a titration curve for a weak acid· The shape of the curve is the same for all weak acids· At the midpoint of the curve, the pH = pKa· The buffering region extends one pH unit above and below the pKa

What acid-base pair is an effective buffer in physiologic fluids?

What acid-base pair is the principal buffer in plasma and extracellular fluid (ECF)?

1. What acid-base pair is effective buffer in physiolog fluids?· H2PO4- and HPO42- 2. What acid-base pair is the principal buffer in plasma and ECF?· CO2-H2CO3-HCO3- system (carbon dioxide-carbonic acid-bicarb)· CO2 + H2O –carbonic anhydraseà H2CO3 ßà H+ + HCO3-· Note: carbonic anhydrase converts CO2 to H2CO3 in RBCs· In this system, CO2 is an acid, so H-H equation is:o pH = 6.1 + log [HCO3-] / (0.0301)PCO2· This system is effective around physiologic pH of 7.4, even though the pKa is only 6.1, for 4 reasons:o Supply of CO2 from oxidative metabolism is unlimited, so effective concentration of CO2 is very higho Equilibration of CO2 with H2CO3 is very rapido CO2 removal by lungs allows for rapid changes in [H2CO3]o Kidney can retain or excrete HCO3-, thus changing the concentration of the conjugate base

Acid-Base Disorders:Acidosis and Alkalosis

1. Acidosis· Occurs when pH of blood and ECF falls < 7.35· Results in CNS depression· When severe, can lead to coma and death· Respiratory acidosis: pCO2 ↑ as a result of hypoventilation· Metabolic acidosis: [HCO3-] ¯ as a result of the addition of an acid stronger than H2CO3 to the ECF2. Alkalosis· Occurs when pH of blood and ECF is >7.45· Leads to neuromuscular hyperexcitability· When severe, can result in tetany· Respiratory alkalosis: pCO2 ¯ as result of hyperventilation· Metabolic alkalosis: [HCO3-] ↑ as a result of excess acid loss (e.g., vomiting) or addition of a base (e.g., oral antacids)

Diabetic ketoacidosis

1. Combination of high blood levels of ketone bodies and a metabolic acidosis2. Pathogenesis· Uncontrolled insulin-dep DM (type 1) à ¯ glucose utilization, hyperglycemia à ↑ fatty acid oxidation· ↑ fatty acid oxidation à excessive production of acetoacetic and 3-hydroxybutyric acids and acetone (ketone bodies)· Acids dissociate at body pH and release H+ à metabolic acidosis3. Clinical picture

· Dehydration· Lethargy· Vomiting· Drowsiness· Coma

4. Therapy: correct the hyperglycemia, dehydration, & acidosis· Insulin – to correct the hyperglycemia· Fluids (physiologic saline) – to treat dehydration· In severe cases: sodium bicarbonate – to correct acidosis

Amino acids grouped by the properties of their R-groups

1. Aliphatic, nonpolar (hydrophobic) · Glycine· Alanine· Valine· Leucine· Isoleucine· Proline

2. Aromatic, nonpolar

· Phenylalanine· Tyrosine· Tryptophan

3. Sulfer-containing

· Cysteine· Methionine 4. Hydroxyl, mildly polar (uncharged, hydrophilic) · Serine· Threonine

5. Basic, polar

· Lysine· Arginine· Histidine

6. Acidic, polar

· Aspartic acid· Asparagine· Glutamic acid· Glutamine

Secondary structures of proteins and collagen

1. Secondary structure = arrangement of H bonds between peptide nitrogens & carbonyl oxygens of different amino acids2. Helical coils· Hydrogen-bonded nitrogens & oxygens are on nearby amino acids· Right-handed alpha helix – most commono Alpha-keratin in hair and nailso Myoglobin – has several alpha-helical regions· Proline, glycine, and asparagine – “helix breakers”3. Beta sheets (pleated sheets) – may run parallel or antiparallel· Hydrogen bonds between residues on neighboring peptide chains4. Left-handed helical strands· Wound into a supercoiled triple helix in collagen· Collagen – major structural protein in the bodyo Primary structure: repeating glycine-X-Y sequenceso X and Y are freqeuntly proline or lysineo Contains hydroxyproline & hydroxylysine

Protein Denaturation Agents

1. Extremes of pH (e.g., strong acid or alkali)2. Ionic detergents (e.g., sodium dodecylsulfate/SDS)3. Chaotropic agents (e.g., urea, guanidine)4. Heavy metal ions (e.g., Hg++)5. Organic solvents (e.g., alcohol or acetone)6. High temperature7. Surface films (e.g., as when egg whites are beaten)

Sickle cell anemia

1. Caused by mutant sickle cell hemoglobin (Hgb S)· Hydrophobic valine replaces hydrophilic glutamate at position 6 of the beta-chain of normal

hemoglobin A (Hgb A)2. Sickle cell disease· Individuals with homozygous genotype (SS)· Have only Hgb S in their RBCs· Symptomso Severe anemia: deoxy Hgb S produces fibrous precipitates à formation of sickle cells à shorter life span à severe anemiao Acute episodes of vaso-occlusion – “sickle cell crisis”Þ Sickle cells can’t pass thru capillaries à vasocclusionÞ Disabling pain that requires hospitalization3. Sickle cell trait· Individuals with heterozygous genotype (AS)· Have both Hgb A and Hgb S in their RBCs· Symptoms

o Usually asymptomatico Episodes of hematuria

Scurvy

1. Defective collagen synthesis resulting from a vitamin C (ascorbic acid) deficiency2. Consequences of abnormal collagen

· Defective wound healing· Defective tooth formation· Loosening of teeth· Bleeding gums· Rupture of capillaries

3. Ascorbic acid is required for hydroxylation of proline and lysine during post-translational modification of collagen4. Pathogenesis· Hydroxylating rxn requires hydroxylase, O2, & Fe2+· Vit C is required to maintain iron in its oxidation state (Fe2+)· Hydroxyproline forms H-bonds that stabilize collagen helix· Symptoms of scurvy are thus the result of weakend collagen when these hydrogen bonds are missing

Free energy change

1. The quanitity of energy from chemical reactions that is available to do work (DG)2. The DG of a rxn A + B ßà C + D is:· DG = DG0’ + RTln ([C][D]) / [A][B])o where DG0’ is the standard free-energy change (when concentrations of all reactants and

products are 1M and pH = 7), R is the gas constant (1.987 cal/molK) and T is the absolute temperature3. When the rxn has reached equilibrium:· DG0’ = –RTlnKeq

Thermodynamic spontaneity: Exergonic and Endergonic Rxns

1. Exergonic rxns are spontaneous (rxn goes to the right)· Keq > 1· DG0’ is negative· Final concentration of the products, C and D, is greater than that of the reactants, A and B2. Endergonic rxns are nonspontaneous (rxn goes to the left)· Keq < 1· DG0’ is positive· Final concentration of the reactants, A and B, is greater than that of the products, C and D3. Note: DG0’ CANNOT predict spontaneity under intracellular conditions· Intracellular spontaneity is a function of actual concentrations as well as Keq, DG, NOT DG0’

Enthalpy, entropy, and free-energy change

1. Enthalpy (DH)· The amount of heat generated or absorbed in a rxn2. Entropy (DS)· Measure of the change in randomness or disorder of system· ↑ when a salt crystal dissolves, when a solute diffuses from a more concentrated to a less concentrated solution, and when a protein is denatured· ¯ when a complex molecule is synthesized from smaller substrates3. Free-energy change (DG)· Is related to enthalpy and entropy as follows:o DG = DH - T DS (where T = absolute temp in Kelvins)

Catalysts and the Rate of Reaction

1. Rate of reaction· The DG0’ provides no info concerning the rate of conversion from A to B· When A is converted to B, it first goes through an energy barrier called the transition state, A-B±· The activation energy (DG±) = energy required to scale the energy barrier and form the transition state· The greater the DG±, the lower the rate of the rxn converting A to B2. Catalysts (mostly enzymes) result in a:· Lower DG±· Faster reaction rate

Michaelis-Menten equation

1. Describes the kinetics of enzyme rxns2. In enzyme-catalyzed rxns:k1 k3E + S ßà ES à E + Pk2· Where E=enzyme, S=substrate, P=product, k1-3 = rate constants3. Velocity (v) of product formation is related to [ES]:o v = k3[ES] where k3 is also called kcat4. Michaelis-Menten eq predicts velocity if [enzyme] is constant:

· Where Vm = max velocity & Km is the Michaelis constant5. Km = [substrate] at which v = ½Vm ([S] = Km)6. A plot of velocity versus [S] is a rectangular hyperbola

Lineweaver-Burk Equation

1. Form of the Michaelis-Menten eq, which is sometimes known as the double-reciprocal equation:1 = Km + [S] = Km x 1 + 1v = Vm[S] Vm [S] Vm

2. The slope is Km/Vm3. The Y-intercept = 1/Vm4. The X-intercept is –1/Km

Enzyme Regulation:How doe Inhibitors affect the Lineweaver-Burk plots?

1. Competitive inhibitors· ↑ apparent Km· Vm remains the same· ↑ slope· X-intercept has smaller absolute value· Y-intercept is unchanged2. Noncompetitive inhibitors· ¯ Vm· Km unchanged· ↑ slope· X-intercept is unchanged· Y-intercept is larger3. Uncompetitive inhibitors (bind only to ES complex)· Both Km & Vm are different à lines on the plot are parallel

Allosteric regulation of enyzmes: Definition, How do they affect Km, and Example of Hexokinase

1. Low-molec wgt effector binds to enzyme at a specific site other than active site (the allosteric site) & alters its activity2. Allosteric enzymes usually have >1 subunit and >1 active site· Active sites that interact cooperatively: velocity vs, [S] = sigmoid· Binding of 1 substrate facilitates binding of substrate at other sites3. Effectors may have a + or – effect on activity· Positive effectors ¯ the apparent Km· Negative effectors ↑ the apparaent Km4. Example: muscle hexokinase· Hexokinase catalyzes 1st rxn in use of glucose my muscle cells:o Glucose + ATP à glucose-6-P + ADP· Hexokinase has a low Km compared to blood [glucose], so it is saturated and operates at its Vm· When glycolysis slows down, gluc-6-P accumulates à gluc-6-P allosterically inhibits hexokinase (keeps gluc-6-P in balance)

Other mechanisms of enzyme regulation:1. Induction/repression of enzyme synthesis2. Covalent modificataion3. Protein-protein interaction

1. Induction/repression of enzyme synthesis· Cytochrome P450 enzymes in the liver (degrade and detoxify drugs) are induced by the drugs themselves2. Covalent modificataion· Phosphorylase (enzyme that breaks down glycogen) is activated by phosphorylation of a specific hydroxyl group· This phosphorylation is stimulated by hormones that elevate blood glucose, such as glucagon and Epi3. Protein-protein interaction between enzyme & regulatory protein· Pancreatic lipase (digests dietary fat) is assisted by colipase· Colipase anchors lipase to the surface of fat droplets

Mechanism and Treatment of Methanol & Ethylene glycol Poisoning

1. Mechanism of poisoning· Toxicity is caused by the action of their metabolites· In both cases, the 1st oxidation is carried out by alcohol dehydrogenaseo Methanol à formaldehyde + formic acidÞ Eyes very sensitive to formaldehyde à blindness

o Ethylene glycol à glycoaldehyde, oxalate, and lactateÞ Deposition of oxalate crystals in kidney à kidney failure2. Treatment· Initial infusion of ethanol à competitive substrate à displaces methanol or ethylene glycol from active site of alcohol dehydrogenase· Prevents continued production of toxic metabolites

Citric acid cycle:Location, Pathway, and Initial Substrate

1. Location· Mitochondria (found in all cells except RBCs)2. Pathway· It is the final common pathway of oxidiative metabolism3. Initial Substrate: Acetyl Coenzyme A (ACETYL CoA)· Condenses with oxaloacetate (OAA) to begin the cycle4. Where does acetyl CoA come from?· The catabolism of carbs, fats, & proteinso Glucose catabolism eventually produces pyruvate à acetyl CoA via pyruvate dehydrogenaseo Fatty acids generate acetyl CoA via b-oxidationo Some amino acids are degraded to acetyl CoA

What are the products of one revolution of the citric acid cycle?

1. 2 CO2 (most CO2 from metabolism)2. Regeneration of one mole of OAA3. 3 NADH & 1 FADH2 à 11 ATPs (via oxidative phosphorylation)4. 1 GTP à 1 ATP

TOTAL OF 12 ATPs/acetyl CoA

Describe the anaplerotic rxns that provide OAA and other citric acid cycle intermediates

1. Pyruvate carboxylase in the liver & kidney:· Pyruvate + ATP + HCO3- ßà OAA + ADP + Pi2. Phosphoenolpyruvate (PEP) carboxykinase in heart and skeletal muscle:· PEP + CO2 + GDP ßà OAA + GTP3. Malic enzyme in many tissues:· Pyruvate + HCO3- + NAD(P) ßà Malate + NAD(P)+4. Glutamate dehydrogenase in the liver:· Glutamate + NAD(P)+ + H2O ßà a-ketoglutarate + NAD(P)H + NH4+

Regulation of the citric acid cycle

1. Step: Acetyl CoA + OAA à citrate· Enzyme: citrate synthase· Inhibitors: ATP (↑ Km), long-chain acyl-CoA2. Step: Isocitrate + NAD+ àa-ketoglutarate + NADH + CO2· Enzyme: isocitrate dehydrogenase· Allosteric activator: ADP· Inhibitors: ATP, NADH3. Step: a-ketoglutarate + NAD+ + CoASH à succinyl CoA + NADH + CO2· Enzyme: a-ketoglutarate dehydrogenase (note: requires same cofactors as the pyruvate dehydrogenase complex)· Inhibitors: succinyl CoA, NADH

Electron Transport Chain (ETC) & Oxidative Phosphorylation(BOTH in MITOCHONDRIA)

1. ETS: electrons pass from NADH or FADH2 to ultimately reduce O2 and produce H2O2. Oxidative phosphorylation: uses energy derived from flow of electrons thru ETS to drive synthesis of ATP from ADP and Pi

NADH dehydrog. = Complex I, Succinate dehydrog. = Complex II (where FADH2 enters – not pictured here), Cytochrome bc1 = Complex III, Cytochrome oxidase = Complex IV

Chemiosmotic hypothesis

1. Describes coupling of electron flow thru ETS to ATP2. Respiratory complexes as proton pumps:· As electrons (e-) pass thru complexes I, III, & IV, hydrogens are pumped across inner membrane to intermembrane space· The [H+] in the intermembrane space ↑ relative to matrix· This generates a proton-motive force as result of 2 factors:o Difference in pH (DpH)o Difference in electrical potential (Dy) between the intermembrane space and the mitochondrial matrix3. ATP synthase complex (complex V)· Hydrogen ions pass back into the matrix thru complex V, and in doing so, drive the synthesis of ATPo Passage of pair of e- from NADH to O2 à 3ATPo Passage of e- pair from FADH2 to O2 (bypass I) à2ATP

Uncouplers and Inhibitors of ETS

1. Uncoupling· Carry H+ across inner mit membrane w/o going thru complex V· This short-circuits the proton gradient and uncouples electron flow from ATP synthesis· Energy, instead of used to make ATP, is dissipated as heat· Uncoupling agents:o Dinitrophenol (2,4-DNP) – former diet drugÞ Caused blindness (retina has ↑ rate of oxidativ metblism)o Thermogenin – helps to maintain normal body tempÞ Found normally in brown fat of newborn mammals2. Inhibitors (via blocking e- flow thru complexes or direct action)Complex I Amobarbital (barbiturate), Rotenone (insecticide), Piericidin A (antibiotic), AmytalComplex II Antimycin A (antibiotic)Complex IV Cyanide, Hydrogen sulfide, Carbon monoxideATP synthase Oligomycin

Carbohydrate digestion and absorption

1. Digestion· Disacharides (sucrose),oligosacharides (dextrins),& polysacharides (starch) are cleaved into monosaccharides (glucose, fructose)· Starch: storage from of carbs in plantso Hydrolyzed to maltose, maltotriose, and a-dextrins by a-amylase in saliva and pancreatic juice· Disaccharides & oligosaccharideso Hydrolyzed to monosaccharides by enzymes on the surface of epithelial cells in the small intestine2. Absorption· Monosaccharides absorbed directly by carrier-mediated transport· These sugars (primarily glucose) travel via portal vein to liver for:o Oxidation to CO2 and H2O for energyo Storage as glycogeno Conversion to triglyceride (fat)o Release into general circulation (as glucose)

Glycogen metabolism

[Glycogen: carb storage, found chiefly in liver & muscle]1. Glycogenesis (glycogen synthesis)· Activated substrate: Uridine diphosphate-glucose· Glycogen synthase adds to nonreduc end of chains in a-1,4 links· Branching enzyme amylo (1à4) to (1à6) transglycosylase creates branches w/a-1,6 linkages· Stimulator: insulin (via dephosphorylation in muscle, liver, & fat)· Inhibitors: glucagon (liver), Epi (muscle & liver), phosphorylase (liver), cAMP, Ca2+ (muscle)

2. Glycogenolysis (glycogen breakdown)· Phosphorylase releases units of glucose 1-P from nonreducing end· Phosphoglucomutase converts glucose 1-P to glucose 6-P· Debranching system releases glucose residues from a-1,6 bonds · Stimulators: sames as inhibitors of glycogenesis· Inhibitor: insulin (via dephosphorylation in muscle, liver, and fat)

Glycolysis:Location, Anaerobic and Aerobic

1. Location: cytosol in most tissues of the body2. Anaerobic (without oxygen)· Glucose à 2Lactate + 2ATP· Characteristic of skeletal muscle after prolonged exercise· Lactate dehydrogenase converts pyruvate to lactate3. Aerobic:· Glucose + 6O2 à 6CO2 + 6H2O + 36-38 ATP· Charactersitic of the brain· NADH produced is oxidized by the mitochondrial ETS· ATP is generated by oxidative phosphorylation

Describe the first step in glycolysis

1. Phosphorylation – involves rxn of glucose in presence of hexokinase OR glucokinase to form glucose 6-phosphate· Hexokinase is found in the cytosol of most tissues:o Low specificity (catalzyes phosphorylation of a wide variety of hexoses)o Low Km (it’s saturated at normal blood [glucose])o Inhibited by glucose 6-P (prevents cells from accumulating too much glucose since phosphorylation traps glucose inside cells)· Glucokinase is present in the liver & pancreas (b-cells):o High specificity for glucoseo High Km (above the normal blood [glucose])o Inhibited by fructose 6-P (ensures glucose will be phosphorylated only as fast as it is metabolized)

What happens in the “2 phases” of glycolysis?

1. In the first phase (5 reactions):· 1 mole of glucose is converted to 2 moles of glyceraldehyde 3-P· 2 moles of ATP are consumed for each mole of glucose2. In the second phase (5 reactions):

· Two moles of glyceraldehyde 3-P are oxidized to 2 moles of pyruvate· 4 moles of ATP and 2 moles of NADH are generated for each mole of glucose

What do the following do:1. Glycerol phosphate shuttle2. Malate-aspartate shuttle

NADH produced in the cytosol DOES NOT pass through the mitochondrial inner membrane, but is instead “shuttled” in by:1. Glycerol phosphate shuttle (most tissues)· Transfers electrons from cytosolic NADH to mitoch FADH2· It generates 2 ATP/cytosolic NADH = 36 moles of ATP/glucose2. Malate-aspartate shuttle (heart, muscle, & liver)· Transfers electrons to mitochondrial NADH· It generates 3 ATP/cytosolic NADH = 38 ATP/glucose

Gluconeogenesis

1. Occurs primarily in the liver & kidney2. Synthesis of glucose from small noncarb precursors (such as lactate and alanine)3. Involves the reversible rxns of glycolysis4. To bypass nonreversible steps of glycolysis, separate rxns occur:· Conversion of pyruvate to PEP bypasses pyruvate kinase· Conversion of fructose 1,6-bisphosphate to fructose 6-phosphate by fructose 1,6-bisphosphatase bypasses phosphofructokinase· Conversion of glucose 6-P to glucose by glucose 6-phosphatase bypasses hexokinase5. Glucose from gluconeogenesis is released into the bloodstream for transport to tissues such as the brain and exercising muscle6. Gluconeogenic substrates:

· Lactate· Pyruvate· Glycerol

· Substances that can be converted to oxalacetate via the citric acid cycle (such as amino acid carbon skeletons)

Cori cycle

1. Shuttling of gluconeogenic substrates between RBCs and muscle to liver, allowing muscle to function anaerobically (net 2 ATP)2. Lactate from exercising or ischemic muscle is carried by the circulation to the liver and serves as a substrate for gluconeogenesis

3. The liver releases the resynthesized glucose into the circulation for transport back to the muscle

Regulation of glycolysis

1. All are the irreversible steps:· Fructose 6-P à fructose-1,6-BP via phosphofructokinaseo Stimulators: AMP, fructose 2,6-BP (in liver)o Inhibitors: ATP, citrateo Rate-limiting step· D-glucose à glucose-6-P via hexokinase/glucokinase*o Inhibitors: glucose-6-P· PEP à pyruvate via pyruvate kinaseo Inhibitors: ATP, alanineo Stimulators: fructose-1,6-BP (in muscle)· Pyruvate à acetyl CoA via pyruvate dehydrogenaseo Stimulators: CoA, NAD, ADP, pyruvateo Inhibitors: ATP, NADH, acetyl CoA2. Induced by insulin

Gluconeogenesis regulation

1. All are the irreversible steps:· Pyruvate à OAA via Pyruvate carboxylase (mitochond)o Requires biotin, ATPo Activated by acetyl CoA· OAA à PEP via PEP carboxykinaseo Requires GTP· Fructose-1,6-BP à fructose-6-P via Fructose-1,6-BPase· Glucose-6-P à glucose via Glucose-6-phosphatase2. These enzymes are only found in liver, kidney, intestinal epithel3. Muscle cannot participate in gluconeogenesis4. Hypoglycemia is caused by a deficiency of these key enzymes5. Induced by glucocorticoids, glucagon, cAMP6. Suppressed by insulinPnemonic: Pathway Produces Fresh Glucose

Pyruvate dehydrogenase complex

1. Contains 3 enzymes that require 5 cofactors:· Pyrophosphate (from thiamine)· Lipoic acid· CoA (from pantothenate)

· FAD (riboflavin)· NAD (niacin)2. Reaction:· Pyruvate + NAD+ + CoA à acetyl-CoA + CO2 + NADH3. The complex is similar to the a-ketoglutarate dehydrogenase complex (same cofactors, similar substrate and action)4. Cofactors are the first 4 B vitamins plus lipoic acid:

· B1 (thiamine; TPP)· B2 (FAD)· B3 (NAD)· B5 (pantothenate à CoA)· Lipoic acid

Pentose phosphate pathway

1. Sites: lactating mammary glands, liver, adrenal cortex – all sites of fatty acid or steroid synthesis2. Begins with glucose 6-P3. The irreversible oxidative portion generates NADPH· NADPH needed for: fatty acid and cholesterol (steroid) synthesis, maintaining reduced glutathione inside RBCs4. The reversible nonxidative portion rearranges the sugars so they can reenter the glycolytic pathway5. Ribose 5-P, which is needed for nucleotide synthesis, can be formed from glucose 6-P by either arm6. Major regulatory enzyme: glucose 6-P dehydrogenase – · Glucose 6-P à 6-phosphogluconolactone7. Stimulators: NADP+, insulin8. Inhibitors: NADPH

Sucrose and Lactose Metabolism

1. Sucrase converts sucrose to glucose and fructose· Hexokinase can convert fructose à fructose 6-P (muscle, kidney)· Fructose enters glycolysis by a different route in the liver· Dihydroxyacetone phophate (DHAP) enters glycolysis directly· After glyceraldehyde is reduced to glycerol, it is phosphorylated and then reoxidized to DHAP2. Lactase converts lactose to glucose + galactose· Galactokinase converts galactose à galactose 1-P· Galactose 1-P ààà glucose 1-P à glycolysis

Glycogen Storage Diseases

Result in abnl glycogen metabolism & ↑↑ glycogen in cellsDEFFECT TISSUE SIGNS, ETC.Von Gierke’s(type I) Glucose 6-P Liver & kidney Hepatomegaly, Failure to thrive, Hypoglycemia, Ketosis, Hyperuricemia, HyperlipidemiaPompe’s (type II) a-1,4-glucosidase Lysosomes, All organs Failure of heart & lungs Death <2 yoCori’s(type III) Debranch enzyme Muscle & liver Similar to I, but milderAnderson(type IV) Branching enzyme Liver & spleen Liver cirrhosis, death <2 yMcArdle (type V) Phosphorylase Muscle Painful muscle cramps w/exerciseHers’ (type VI) Phosphorylase Liver Similar to type 1, but milderType VII Phosphofructokinase Muscle Similar to type VType VIII Phosphorylas kinase Liver Mild hepatomegaly, mild hypoglycemia

Hereditary enzyme deficiencies in lactose and sucrose metabolism

1. Hereditary enzyme deficiences in sucrose metablism:· Fructokinase deficiency à essential fructosuriao Benign disorder· Fructose 1-P aldolase deficiency à hereditary fructose intoleranceo Characterized by severe hypoglycemia after ingesting fructose (or sucrose), jaundice, cirrhosis2. Inherited enzyme deficiencies in lactose metabolism:· Lactase deficiency à milk intoleranceo Develops in adult life (age-dep) or hereditary (blacks, Asians)· Galactokinase deficiency à mild galactosemiao Early cataract formation· Galactose 1-P uridyltransferase deficiency à severe galactosemia (AUTOSOMAL RECESSIVE)o Cataract, hepatosplenomeg, growth failure, retardation, deatho Treatment: exclude galactose & lactose from diet

Pyruvate dehydrogenase deficiency

1. Pyruvate dehydrogenase deficiency à neurologic defects2. Causes backup of substrate (pyruvate & alanine), resulting in lactic acidosis3. Treatment: ↑ intake of ketogenic nutrients (Lysine & Leucine are the only purely ketogenic amino acids)

Glucose-6-phosphate dehydrogenase deficiency

1. X-linked recessive2. Background:· G6PD is the rate limiting enzyme in HMP (hexose monophosphate) shunt, which includes the

pentose phosphate pathwy (which yields NADPH)· NADPH is necessary to keep glutathione reduced, which in turn detoxifies free radicals and peroxides3. Manifestations of disease:· ¯ NADPH in RBCs à hemolytic anemia4. Pathogenesis:· Poor RBC defense against oxidizing agents (fava beans, sulfonamides, primaquine) and antituberculosis drugs5. More prevalent among blacks6. Heinz bodies: altered Hemoglobin precipitates w/in RBCs

Lipid digestion

1. In mouth:· Medium-chain triacylglycerol (TGs) are hydrolyzed by lipase· Continues in stomach, producing a mix of diacylglycerols & FFAs2. In the duodenum:· Lipids are emulsified by bile salts (made from cholesterol in liver)3. In small intestine:· Emulsified fats are hydrolyzed by pancreatic lipase· Phospholipids are hydrolyzed by phospholipase A· Cholesterol esters are hydrolyzed by cholesterol esterase4. Mixed micelles form, which contain:

· Fatty acids· Diacylglyc· Monoacyl· Phospholipi· Cholesterol· VitA,D,E, K· Bile acids

5. Micelles absorbed in small intestine à further metabolized à · Medium-chain TGs are hydrolyzed· Medium-chain fatty acids (8-10 carbons) pass into portal vein · Long-chain fatty acids (>12 carbons) are reincorporated into TGs· TGs go into chylomicrons à lymphatics à circulation via thoracic duct

How are lipids transported to tissues?

1. Lipids are transported to tissues in the blood plasma primarily as lipoproteins:· Spherical particles w/a core that contain varying proportions of hydrophobic triacylglycerols & cholesterol esters· Outer layer of cholesterol, phospholipids, and specific apoproteins

Lipoprotein absorption

1. Exogenous lipid (from intestine), except for medium-chain fatty acids, is released into the plasma as chylomicrons· Chylomicrons contain a high proportion of TGs· TG is hydrolyzed to FFAs and glycerol by lipoprotein lipase on the surface of capillary endothelium in muscle and adipose tissue· The cholesterol rich chylomicron remnants travel to the liver, where they are taken up by receptor-mediated endocytosis (RME)2. Endogenous lipid (from liver) is released into blood as VLDLs· VLDL TG is hydrolyzed by lipoprotein lipase to FFAs and glycerol, yielding low-density lipoproteins (LDLs)· LDLs are removed from circulation by RME in tissues that contain LDL receptors (tissues that need cholesterol, but mostly in liver)· LDL cholesterol:o Inhibits HMG CoA reductase (RLS in cholesterol synthesis)o Down-regulates LDL receptor synthesis à ¯ LDL uptake· High density lipoproteins (HDLs) are made in the liver

Lipoprotein functions and associated apolipoproteins:Chylomicrons

1. Delivers dietary triglycerides to peripheral tissues and dietary cholesterol to liver2. Secreted by intestinal epithelial cells3. Excess causes pancreatitis, lipemia retinalis, eruptive xanthomas4. Associated apolipoproteins:· B-48 mediates secretion· As are used for formation of new HDL· C-II activates lipoprotein lipase· E mediates remnant uptake by liver

Lipoprotein functions and associated apolipoproteins:VLDL

1. Delivers hepatic triglycerides to peripheral tissues2. Secreted by liver3. Excess causes pancreatitis4. Associated apolipoproteins:· B-100 mediates secretion· C-II activates lipoprotein lipase· E mediates remnant uptake by liver

Lipoprotein functions and associated apolipoproteins:LDL

1. Transports hepatic cholesterol to peripheral tissues2. Formed by lipoprotein lipase modification of VLDL in peripheral tissue3. Taken up by target cells via RME4. Excess causes atherosclerosis, xanthomas, and arcus corneaa (senilis?)5. Associated apolipoproteins:· B-100 mediates binding to cell surface receptor for endocytosis

Lipoprotein functions and associated apolipoproteins:HDL

1. Mediates centripetal transport of cholesterol (i.e. reverse cholesterol transport, from periphery to liver, i.e. transports cholesterol from periphery to liver)2. Acts as a repository for apoC & apoE (which are needed for chylomicron and VLDL metabolism)3. Secreted from both liver and intestine4. Associated apolipoproteins:· A’s help form HDL structure· A-I in particular activates LCAT (which catalyzes esterification of cholesterol)· CETP mediates transfer of cholesteryl esters to other lipoprotein particles

Pneumonic: HDL is Healthy, LDL is Lousy

Oxidation of fatty acids

1. Occurs in mitochondrial matrix. The overall process is:RCH2CH2COOH b-oxidation CH3COSCoA Citric acid cycle CO2+ H2O2. Fatty acids must first be activated to their acyl CoA thioesters· Long-chain (LC) fatty acids (>12) activated in cytosol à LC acyl CoAs are shuttled into mitoch matrix by carnitine transport syst· MCFAs pass directly into the mitoch & are activated in the matrix3. Fatty acyl CoA is then oxidized to CO2 and H2O by b-oxidation:· Continues in cycle until it’s completely converted to acetyl CoA· Each cycle generates 5 ATPs via ETS and 12 ATPs via combined action of citric acid cycle and ETS· Terminal 3 carbons of odd-numbered fatty acids yield propionyl CoA as the final product, which can:o Enter the citric acid cycle (after carboxylation to succinyl CoA in a 3-rxn sequence requiring biotin and Vit B12)o Be used for gluconeogenesis

Ketogenesis

1. The formation of acetoacetate and b-hydroxybutyrate from metabolism of acetyl CoA in the liver2. Reaction:· Acetyl CoA + acetoacetyl CoA à hydroxymethylglutaryl CoA (HMG CoA)· HMG CoA à acetoacetate and acetyl CoA· Acetoacetate à b-hydroxybutyrate (requires NADH)3. How is acetoacetate used in the body?· Extrahepatic tissues (especially heart) can activate acetoacetate at the expense of succinyl CoA and burn acetoacetyl CoA for energy· Glucose-starved brain can use acetoacetate for fuel (b/c its freely soluble in blood and easily crosses the BBB)

Fatty acid synthesis

1. Carried out by fatty acid synthase, a cytosolic complex2. Primary substrates: · Acetyl CoA: formed in mitoch, mainly by pyruvate dehydrogenaseo It’s transported to cytosol by citrate-malate-pyruvate shuttle· Malonyl CoA: formed by biotin-linked carboxylation of actyl CoA3. The acetyl and malonyl moieties are transferred from the sulfur of CoA to activate sulfhydryl groups in the fatty acid synthase4. 7 cycles lead to production of palmityl:enzyme, which is hydrolyzed to yield products – palmitate & fatty acid synthase5. Palmitate is the precursor for longer & unsaturated fatty acids· Chain-lengthening occurs in the mitoch and ER (C16àC18àetc)· Desaturating system is also present in the ERo Requires NADPH and O2o Inserts double bonds no further than 9 carbons from the carboxylic acid group

What do the limitations of the desaturating system result in?

1. The limitations of the desaturating system impose a dietary requirement for essential fatty acids (those w/double bonds >10 carbons from the carboxyl end)· Lineoleic acido Precursor for arachidonic acid (which is beginning of cascade that synthesizes prostaglandins, thromboxanes, and eicosanoids)· Linolenic acids

Glycerolipid synthesis

1. This process is carried out by the liver, adipose tissue, and the intestine2. Pathways begin w/glycerol 3-P, which is mainly produced by reducing dihydroxyacetone phosphate w/NADPH3. Succesive transfers of acyl groups from acyl CoA to carbons 1 and 2 of glycerol 3-phosphate produce phosphatidate, which can then be converted to a variety of lipids:· Triacylglycerol (from transfer of acyl group from acyl CoA)· Phosphatidyl choline & phosphatidyl ethanolamine (from transfer of base from its cytidine diP/CDP derivative)· Phosphatidylserine (from exchange of serine for choline)· Phosphatidylinositol (from reaction of CDP-diacylglycerol with inositol)

Sphingolipid synthesis

1. Begins with palmityl CoA and serine· Produces dihydrosphingosine and sphingosine2. Sphingosine can then by acylated to produce ceramide· Additional groups may be added to the C1-OH of ceramides

Cholesterol synthesis

1. Cholesterol is made by the liver and intestinal mucosa from acetyl CoA in a multistep process2. Key intermediate = HMG CoA· HMG CoA reductase: regulatory enzyme that catalyzes HMG CoA + NADPH à mevalonic acid· Increasing amounts of intracellular cholesterol lead to inhibition of HMG CoA reducate and accelerated degradation of the enzyme3. Overall reaction:Acetoacetyl CoA + acetyl CoA –HMG CoA synthase à HMG CoA –HMG CoA reductase à mevalonic acid àààcholesterol

What are the fates of the products of cholesterol synthesis?

1. Mevalonic acid· Precursor of a number of natural products called terpenes, which include vit A, vit K, coenzyme Q, and natural rubber2. Cholesterol · Converted to steroid hormones in the adrenal cortex, ovary, placenta, and testes· Majority is oxidized to bile acids in the liver· 7-dehydrocholesterol is the starting point for synthesis of vit D

Lipid malabsorption

1. Leads to excessive fat in the feces (steatorrhea)2. Occurs for a variety of reasons:· Bile duct obstructiono ~50% of dietary fat appears in the stools as soaps (metal salts of LCFAs)o Absence of bile pigments leads to clay-colored stoolso Deficiency of the ADEK vitamins may result· Pancreatic duct obstructiono Stool contains undigested fato Absorption of ADEK vitamins is not sufficiently impaired to lead to deficiency symptoms· Diseases of the small intestine (e.g., celiac disease, abetalipoproteinemia, nontropical sprue, IBD)

Hyperlipidemias

1. Familial hypercholesterolemia· Results from defective LDL receptors· Findings: severe atherosclerosis, early death from CAD· Tx: HMG CoA reductase inhibitors (“statins”)2. Hypertriglyceridemia· Can result from either overproduction of VLDL or defective lipolysis of VLDL triglycerides· Findings: cholesterol levels may be mildly ↑3. Mixed hyperlipidemias· BOTH serum cholesterol & serum triglycerides are ↑· There is both overproduction of VLDL and defective lipolysis of triglyceride-rich lipoproteins (VLDL and chylmicrons)· There is a danger of acute pancreatitis

Inheritied defects and deficiencies that disrupt fatty acid oxidation

1. Inherited defects in the carnitine transport system, which have widely varying symptoms:· Hypoglycemia· Muscle wasting w/accumulation of fat in muscle· Feeding fat w/medium-chain triacylglycerols (e.g., butterfat) is helpful in some cases, b/c MCFAs can bypass carnitine transport system2. Inherited deficiencies in the acyl CoA dehydrogenase, the most common being medium-chain (C6-C12) acyl CoA dehydrogenase deficiency· Hypoketotic hypoglycemia and dicarboxylic aciduria occur, with vomiting, lethargy, and coma· This is believed to account for the condition called “Reye-like syndrome”

Sphingolipid Storage Diseases

Disease Accumulated Substance Clinical ManifestationsTay-Sachs Ganglioside GM2 Mental retardation (MR), blindness, red spot on macula, death by 3rd yrGaucher’s Glucocerebroside Hepatosplenomeg, bone erosion, MRFabry’s Ceramide trihexoside Rash, kidney failure, lower extremity painNiemann-Pick Sphingomyelin Hepatosplenomegaly, MRGloboid cell leukodystrophy Galactocerebroside MR, myelin absent(also called “Krabbe’s” disease)Metachromatic leukodystrophy Sulfatide MR, metachromasia, nerves stain yellowish brown w/crystal violetGen gangliosidosis Ganglioside GM1 MR, hepatomegaly, skeletal abnormalitiesSandhoff’s Ganglioside GM2, globoside Same as Tay-Sachs, but more rapid courseFucosidosis Pentahexosylfuco-glycolipd Cerebral degeneration, spasticity, thick skin

Urea Cycle

1. Converts NH4+ (which is toxic, esp to CNS) to urea2. Occurs in the liver3. Urea is excreted in the urine4. NH4+ + CO2 –carbamoyl phosphate synthetase I àcarbamoyl P + ornithine –ornithine transcarbamoylase àcitrulline + aspartate + ATP –argininosuccinate synthetase à argininosuccinate –argininosuccinate lyase à fumarate +arginine + H20 –arginase à UREA + ornithine

Urine byproduct

How does detoxification of NH4+ occur in peripheral tissues?

1. In most tissues:· Glutamine synthetase incorporates NH4+ into glutamate to form glutamine, which is carried by circulation to the liver· In the liver, glutaminase hydrolyzes glutamine back to NH4+ and glutamate2. In skeletal muscle:· Glutamate dehydrogenase and glutamate-pyruvate aminotransferase à incorporate NH4+ into alanine· Alanine is carried to the liver, where transdeamination results in converstion of alanine back to pyruvate and NH4+

Hyperammonemia

1. May be caused by insufficent removal of NH4+, resulting from disorders that involve one of the enzymes in the urea cycle2. Signs and Symptoms· Blood NH4+ concentrations above the normal range (30-60 mM)· Mental retardation, seizure, coma, and death3. Enzyme defects· Low activity of carbamoyl P synthetase or ornithine-carbamoyl transferase à [NH4+] in blood & urine ↑↑ à NH4+ intoxication· Defective argininosuccinate synthetase, argininosuccinase, OR arginase à blood levels of metabolite preceding defect ↑↑ o NH4+ levels may also rise4. Treatment· Restriction of dietary protein· Intake of mixes of keto acids that correspond to essential amin acid· Eating benzoate & phenylacetate: alternate path for NH4+ excretion

Carbon skeletons of amino acids

1. Amino acids can be grouped into families based on the point where their carbon skeletons enter the TCA cycle2. AcetylCoA/Ketogenic fam(blue:keto-& glucogenic; red:ketogen only)· Isoleucine, leucine, lysine, phenylalanine, tryptophan, and tyrosine· Phenylalanine à tyrosine via phenylalanine hydroxylase· Tyrosine is starting compound for:

o Epi and NE, T3 and T4, Dopamine, Melanin

3. a-Ketoglutarat fam (arginine,histidine,glutamate,gluatmine,proline)· Histidine – precursor of histamine· Glutamate – excitatory neurotransm, can be converted to GABA4. Succinyl CoA family (isoleucine, methionine, valine)· Methyl of methionine participates in methylation rxns as S-adenosylmethionine (SAM)5. Fumarate family (phenylalanine and tyrosine)6. Oxaloacetate family (asparagine and aspartate)7. Pyruvate fam (alanine,cysteine,glycine,serine,threonine, tryptophan)

Essential amino acids

1. Isoleucine2. Leucine3. Lysine4. Phenylalanine5. Tryptophan6. Histidine7. Methionine

8. Valine9. Threonine

Phenylketonuria (PKU)

1. Results from a deficiency of:· Phenylalanine (Phe) hydroxylase OR· Dihydropteridine reductase2. Findings· ↑↑ Phe in the blood (hyperphenylalaninemia)· Phe builds up to toxic concentrations in body fluids, resulting in CNS damage with mental retardation· ↑↑ Phe inhibits melanin synthesis à hypopigmentation3. An alternative pathway for Phe breakdown produces phenylketones, which spill into th eurine4. In those affected, tyrosine is an essential amino acid5. Treatment: restricting dietary protein (phenylalanine)

Albinism

1. No tyrosinase (1st enzyme on pathway to melanin)2. Have little or no melanin and are:· Easily sunburned· Very susceptible to skin carcinoma· Photophobic b/c of lack of pigment in iris of eye

Homocystinuria

1. May result from several defects:· Cystathionine synthase (CS) deficiency· ¯ affinity of CS for its coenzyme, pyridoxal phosphate (PLP) (may respond to megadoses of pyridoxine/vit B6)· Methyl tetrahydrofolate homocyst methyltransferase deficiency· Vit B12 coenzyme deficiency (may respond to vit B12)2. Finding: homocysteine accumulation in blood, appears in urine3. Pathologic changes· Dislocation of optic lens· Mental retardation· Osteoporosis and other skeletal abnormalities· Atherosclerosis and thromboembolism4. Pts unresponsive to vitamin therapy may be treated with:

· Synthetic diets low in methionine· Betaine (trimethylglycine) – alternative methyl group donor

Maple-syrup urine disease

1. Results from a deficiency in the branched-chain 2-keto acid decarboxylase2. Findings: branched chain keto acids derived from isoleucine, leucine, and valine appear in the urine, giving it a maple syrup-like odor3. Elevated keto acids cause severe brain damage, with death in the first year of life4. Treatment· A few respond to megadoses of thiamine (vitamin B1)· Those that don’t: synthetic diets low in branched-chain amino acids

Histidinemia

1. Deficiency in histidine-a-deaminase (the 1st enzyme in histidine catabolism)2. Characterized by elevated histidine in blood plasma and excessive histidine metabolites in urine3. Symptoms:· Mental retardation and speech defects (both are rare)4. Treatment: not usually indicated

Origin of the atoms in the purine ring

PURINE nucoleotide synthesis

De novo synthesis:1. Inosine monophosphate (IMP), AMP, & GMP inhibit PRPP synthetase2. Committed step: conversion of PRPP to 5’-phosphoribosyl-1-amine· PRPP activates glutamine PRPP amidotransferase· Inhibited by end products (IMP, GMP, AMP) of the pathwayPurines made by salvage of preformed purine bases:1. Involves 2 enzymes:· Hypoxanthine-guanine phophoribosyltransferase (HGPRT)o Comp inhibited by IMP and GMP· Adenine phosphoribosyl transferaseo Inhibited by AMP

Regulation of purine synthesis

1. Regulation provides a steady supply of purine nucleotides2. GMP and AMP inhibit 1st step in their own synthesis from IMP3. Reciprocal substrate effect: GTP is a substrate in AMP synthesis, and ATP is a substrate in

GMP synthesis· Balances supply of adenine and guanine ribonucleotides4. Interconversion among purines ensures control of their levels· AMP deaminase converts AMP back to IMP· GMP reductase converts GMP back to IMP· IMP is the starting point for synthesis of AMP and GMP

Origin of the atoms in the pyrimidine ring

De novo pyrimidine synthesis

1. In mammals, 1st 3 steps occur on one multifunctional enzyme called CAD, which stands for the names of the enzymes· CO2 + glutamine – CAP synthetase II à carbamoyl-P (CAP) · Synthesis of dihydroorotic acid is a 2-step process:o Committed step: aspartate + CAP –aspartate transcarbamoylase à carbamoyl aspartateo Carbam aspartate –dihydrorotaseà dihydroorotic acid + H2O2. Dihydroorate forms UMP· Dihydroorate ßà orotic acid· Orotic acid + PRPP à orotidylate (OMP)· Decarboxylation of OMP à uridylate (UMP)· These 2 steps occur on 1 protein (if defected: orotic aciduria)3. Synthesis of remaining pyrimidines involves UMP· Phosphorylation of UMP à UDP + UTP· Addition of amino group from glutamine to UTP à CTP

Regulation of pyrimidine synthesis

1. CAP synthetase II regulation· Inhibited by UTP· Activated by ATP and PRPP2. CTP itself inhibits CTP synthetase

Salvage of pyrimidines

Accomplished by the enzyme pyrimidine phosphoribosyl transferase, which can use orotic acid, uracil or thymine, but NOT CYTOSINE

Deoxyribonucleotide synthesis

Formation of deoxyribonucleotides (for DNA synthesis) involves reduction of sugar of ribonucleoside diphosphates:1. Ribonucleotide reductase

· Leads to reduction of ADP, GDP, CDP, or UDP to deoxyribonucs· Its reducing power is from 2 sulfhydryl groups on thioredoxin· Using NADPH + H+, thioredoxin reductase converts oxidized thioredoxin back to the reduced form· Regulation – controls the overall supply of deoxyribonucleotideso Rxn proceeds only in presence of nucleotide triphosphateo dATP: allosteric inhibitoro Other deoxynucleosides interact w/enzyme to alter specificity2. Thymidylate synthase· Catalyzes formation of dTMP (deoxythymidylate) from dUMP· Coenzyme: N5, N10-methylene tetrahydrafolate (regenerated after each rxn by dihydrofolate reductase)

Nucleotide degradation

1. Purine degradation (product: Uric acid is exreted in urine)· Sequential actions of 2 groups of enzymes (nucleases and nucleotidases) lead to hydrolysis of nucleic acids to nucleosides· Deaminase converts adenosine/deoxyadenosine to deoxy-/inosine· Purine nucleoside phosphorylase splits inosine and guanosine to ribose 1-P and free bases hypoxanthine and guanine· Guanine is deaminated to xanthine· Hypoxanthine & xanthine –xanthine oxidaseà uric acid 2. Pyrimidine degradation (products = b-amino acids, CO2, NH4+)· Degraded to free bases uracil or thymine· A 3-enzyme rxn (reduction, ring opening, deamination-decarboxylation) converts uracil to CO2, NH4+, and b-alanine and thymine to CO2, NH4+, & b-aminoisobutyrate· THUS: urinary b-aminoisobutyrate is an indicator of DNA turnover (may be ↑ during chemo or radiation therapy)

Disorders caused by deficiencies in enzymes involved in nucleotide metabolism

Hereditary orotic aciduria Orotate phosphoribosyl transferase and/or OMP decarboxylase Retarded growth,Anemia Synthetic cytdine or uridine (UTP formed acts as inhib of carbamoy-P synthetase II)Purine phosphorylas deficiency ↑ purine ¯ uric acid formation Impaired T-cell function SCID Adenosine deaminase T- & B-cell dysfunction w/early death from infection Gene therapyLesch-Nyhan HGPRT (deficient or absent) ↑↑ purine synthesis, hyperuricemia, severe neuro problem (spastic, MR, self-mutilation) Allopurinol - ¯ deposition of sodium urate crystals, but doesn’t ameliorate neuro symptoms

Anticancer drugs that interfere w/nucleotide metabolism

1. Hydroxyurea· Inhibits nucleoside diphosphate reductase (enzyme that converts ribonucleotides to

deoxyribonucleotides)2. Aminopterin and methotrexate· Inhibit dihydrofolate reductase (enzyme that converts dihydrofolate to tetrahydrofolate)3. Fluoredeoxyuridylate· Inhibits thymidylate synthetase (enzyme that converts dUMP to dTMP)

Gout

1. May result from a disorder in purine metabolism2. Is associated w/hyperuricemia3. Primary gout: overproduction of purine nucleotides· Mutations in PRPP synthetase à loss of feedback inhibition by purine nucleotides· A partial HGPRT deficiency à less PRPP is consumed by salvage enzyes à ↑ PRPP activates PRPP amidotransferase4. Secondary gout· Due to radation therapy, CA chemo (b/c they ↑ cell death)5. Treatment: allopurinol· Xanthine oxidase catalyzes oxidation of allopurinol to alloxanthine, which is a potent inhibitor of the enzyme· Result: uric acid levels fall, hypoxanthine & xanthine levels rise (is OK, b/c they don’t form crystals)

Energy expenditure (3 components)

1. Basal energy expenditure (BEE)· “resting energy expenditure”· Energy used for metabolic processes at rest· Represents >60% of total energy expenditure· Related to the lean body mass2. Thermic effect of food· Energy required for digesting and absorbing food· Amounts to ~10% of energy expenditure3. Activity-related expenditure· 20-30% of daily energy expenditure

Caloric yield from foods and what % they should be in diet

1. Carbs: 4 kcal/g· 50-60% of caloric intake2. Proteins: 4 kcal/g· 10-20% of caloric intake (0.8 g/kg body weight/day)

3. Fats: 9 kcal/g· No more than 30% of caloric intake4. Alcohol: 7 kcal/g

Fats:Essential fatty acids, Deficiency, and Excess storage

1. Essential fatty acids (EFAs):· Linoleic acid· Linolenic acid2. Deficiency· Mainly seen in low-birth-weight infants maintained on artificial formulas and adults on TPN· Characteristic system: scaly dermatitis3. Excess fat· Stored as triacylglycerol

Marasmus vs. Kwashiorker

Marasmus KwashiorkerInsufficient food, including both calories and protein Starvation with edema often due to protein deficient dietDepleted subQ fat Pitting edemaFlaky paint dermatosis: dark patches on skin that peelLiver ketogenesisàbrain&heart fuel Large liver due to fatty infilatrationMuscle wasting (break ¯ protein for gluconeogenesis & protein synthes) Muscle wasting less severeFrequent infections Frequent infectionsLow body temp Micronutrient deficiencies Other nutrient deficienciesSlowed growth(<60% expected wgt) Growth failure(>60% expected wgt)Death when energy & protein reserves exhausted Poor appetitie (anorexia)Watery stools w/undigested foodMental changes (apathetic)

Vitamin A

1. Functions:· 11-cis-retinal – prosthetic group of rhodopsin· Beta-carotene – antioxidant – NOT TOXIC at high doses· Retinyl phosphate – mannose acceptor/donor in glycoprotein synth· Retinol & retinoic acid – regulate tissue growth & differentiation2. Deficiency signs and symptoms:· Night blindness, Xerophthalmia (cornea keratinizes: Bitot spots)

o Leading cause of child blindness in 3rd world nations· Follicular hyperkeratosis (rough, tough skin)· Anemia· ¯ resistance to infection· ↑ susceptibility to cancer3. Toxicity (prolonged ingestion of 15,000-50,000 equivalents/day)· Bone pain, scaly dermatitis, hepatosplenomegaly, nausea, diarrhea4. Clinical usage: For acne and psoriasis

Vitamin D

1. Functions: regulation of Ca+ metabolism· Stimulates synth of Ca+-binding protein à aids absorption· In combo w/PTH, ↑ blood Ca+ by:o ↑ bone demineralization by stimulating osteoblastic activityo Simulates Ca+ reabsorption by distal renal tubules2. Sources:· Major: skin (UV: 7-dehydrocholesterol à Vit D3/cholecalciferol)· Diet (vit D3) and foods fortified w/vit D23. Activation· Liver: Vit D3 à 25(OH)D3 · Kidney: 25(OH)D3 à active 1,25(OH)2D3 (stimulated by PTH)4. Deficiency· Rickets (kids): soft bones, stunted growth· Osteomalacia (adults): pathologic fractures· Bone demineraliz may also result from vit D à inactive forms by steroids5. Toxicity: (hyperCa+, metast calcification, bone demineraliz, kidney stones)· Seen in sarcoidosis (epithelioid macroph convert vit.D to its active form)

Vitamin E

1. Function · Protection of membranes & proteins from free-radical damage· Includes isomers of tocopherol:o Tocopherol + free radicals à tocopheroxyl radical à vit C reduces tocopheroxyl radical à tocopherol is regenerated2. Deficiency· Secondary to impaired lipid absorption (cystic fibrosis, celiac disease, chronic cholestasis, pancreatic insufficiency, abetalipoproteinemia)· Signs & Symptoms:o Ataxiao Impaired reflexeso Myopathy

o Muscle weaknesso Hemolytic anemia (b/c of ↑ fragility of RBCs)o Retinal degeneration

Vitamin K

1. Function· Post-translational carboxylation of glutamyl residues in Ca+-binding proteins: factors VII, IX, & X2. Deficiency (↑ PT, ↑ aPTT, but nl bleeding time)· Impaired blood clotting à ↑ bruising, ↑ bleeding· Causes:o Fat malabsorptiono Drugs that interfere w/vit K metabolism (warfarin)o Antibiotics that suppress bowel flora3. Vitamin K in infants· Neonates are born w/low stores of vit K· Vit K crosses placental barrier poorly· Newborns given single injection of vit K· High doses: anemia, hyperbilirubinemia, kernicterus

The B vitamins

1. B1 = Thiamine2. B2 = Riboflavin3. B3 = Niacin4. B5 = Pantothenate (pantothenic acid)5. B6 = Pyridoxine (pyridoxamine, pyridoxal)6. B12 = cobalamin

Thiamine (vitamin B1)

1. Thiamine pyrophosphate (TPP): required for nerve transmission & is coenzyme for several key enzymes:· Pyruvate & a-ketoglutarate dehydrogenase(glycolysis, TCA)· Transketolase (pentose phosphate pathway)· Branched-chain keto-acid dehydrogenase (valine, leucine, isoleucine metabolism)2. Deficiency leads to beriberi, which occurs in 3 stages:· Early: loss of appetite, constipation, nausea, periph neuropathy, irritability, fatigue· Moderately severe: Wernicke-Korsakoff syndrome (mental confusion, ataxia, ophthalmoplegia)· Severe (in addtion to polyneuritis):

o Dry: atrophy & weakness of muscleso Wet:edema,high-output cardiac failure,pulm congestion

Riboflavin (vitamin B2)

1. Function:· Converted to re-dox coenzymes FAD & FMN2. Deficiency signs & symptoms:· Angular cheilitis· Glossitis (red and swollen tongue)· Scaly dermatitis (esp at nasolabial folds & around scrotum)· Corneal vascularization

Niacin (vitamin B3)

1. Function:converted to redox coenzymes NAD & NADP2. Deficiency· Causes:o Hartnup diseaseo Malignant carcinoid syndromeo INH· Mild deficiency: glossitis· Severe deficiency: pellagra – the 3 D’so Dermatitiso Diarrheao Dementia3. High doses· Vasodilation (very rapid flushing)· Metobolic changes: ¯ blood cholesterol & LDLs

Vitamin B6 (pyridoxine, pyridoxamine, & pyridoxal)

1. Function· Coenzyme involved in transamination (e.g., ALT & AST), decarboxylation, and trans-sulfuration (rxns of amino acid metabolism)2. Deficiency (inducible by INH)· Mild: irritability, nervousness, depression· Severe: periph neuropathy, convulsions, occasional sideroblastic anemia· Other symptoms: eczema, seborrheic dermatitis around ears, nose, and mouth; chapped lips; glossitis; angular stomatitis

3. Clinical usefulness:· High doses: tx homocystinuria (defective cystathione b-synthase)

Vitamin B6: Pantothenic acid

1. Function· Essential component of coenzyme A (CoA) and of fatty acid synthase· Cofactor for acyl transfers2. Deficiency (very rare)· Vague presentation, little concern to humans· Dermatitis, enteritis, alopecia, adrenal insufficiency

Biotin

1. Function· Covalently linked biotin = prosthetic group for carboxylation enzymes (e.g. pyruvate carboxylase, acetyl CoA carboxylase) (NOT decarboxylations)2. Deficiency (rare)· Signs and symptoms:

o Dermatitiso Hair losso Atrophy tongue papillao Gray mucous membo Paresthesa,muscle paino Hypercholesterlemiao ECG abnormalities

· Causeso Antibiotic use (since intestinal bacteria make biotin)o Eating Avidin (raw egg whites)Þ Binds biotin in a nondigestible formÞ If you eat >20 eggs/day

Folic acid

1. Function· Polyglutamate derivatives of tetrahydrofolate serve as coenzymes in 1-carbon transfer rxns:o Purine & pyrimidine synthesiso Thymidylate synthesiso Conversion of homocysteine to methionineo Serine-glycine interconversion

2. Deficiency· Signs & symptoms:o Megaloblastic anemiao Neural tube defectso ↑ blood homocysteine – associated w/atherosclerotic disease· Can be caused by several drugs:

o Methotrexate (chemo)o Trimethoprim (antibact)o Pyrimethamin(antimalari)o Diphenylhydantoin (anticonvulsant)o Primidone (anticonvuls)

Vitamin B12 (cobalamin)

1. Functions· Coenzyme for methylmalonyl CoA à succinyl CoA (methylmalonyl CoA mutase) in propionyl CoA metabolism· Coenzyme for methyl transfer between tetrahydrofolate & methionine (homocysteine methyl transferase)2. Deficiency:· Signs & Symptoms:o Megloblastic anemiao Paresthesia, optic neuropathy, subacute combined degenerato Prolonged deficiency à irreversible nervous system damage· Causes:o Intake of no animal products (vegans)o Achlorhydria, ¯ intrinsic factor (impaired absorption)o Malabsorption (impaired pancreatic function, sprue, enteritis, D. latum, absence of terminal ileum/Crohn’s)3. Use Schilling test to detect deficiency

Vitamin C (ascorbic acid)

1. Functions· Coenzyme for re-dox rxns, including:o Post-translational hydroxylation of proline & lysine in maturation of collageno Carnitine synthesiso Tyrosine metabolismo Catecholamine neurotransmitter synthesis· Antioxidant· Facilitator of iron absorption2. Deficiency· Signs & symptoms:

o Mild: capillary fragility w/easy bruising & petechiae (pinpoint hemorrhages in skin), ¯ immune functiono Severe: scurvy (¯ wound healing, osteoporosis, hemorrhage, anemia, swollen gums, teeth may fall out)

ySymptoms of Mineral Deficiencies

Mineral Deficiency-Associated ConditionsCalcium ParesthesiaTetanyBone fractures, bone painOsteomalacia (as in vit D deficiency)Iodine GoiterCretinismIron AnemiaFatigue, tachycardia, dyspneaMagnesium Neuromusc excitability, paresthesiaDepressed PTH releasePhosphorus (as phosphate) Deficiency rarely occursZinc Growth retardation & hypogonadismDry, scaly skinMental lethargyImparied taste & smell, poor appetite