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REVIEW REVIEW of of

CARBOHYDRATESCARBOHYDRATES

CARBOHYDRATESCARBOHYDRATES Hydrates of carbon [Hydrates of carbon [CCnn((HH22OO))mm]]

PolyPolyhydroxyaldehydehydroxyaldehyde or poly or polyhydroxyketonehydroxyketone, or , or substance that gives these compounds on hydrolysissubstance that gives these compounds on hydrolysis

Most abundant organic compound in the plant worldMost abundant organic compound in the plant world

Chemically made up of skeletal Chemically made up of skeletal CC,,HH which is usually which is usually 2x the number of C, highly variable number of 2x the number of C, highly variable number of OO, , occasionaloccasional NN && SS

Linked to many lipids and proteinsLinked to many lipids and proteins

FUNCTIONS of FUNCTIONS of CARBOHYDRATESCARBOHYDRATES

Storehouses of chemical energyStorehouses of chemical energyGlucose,starch, glycogenGlucose,starch, glycogen

Structural components for supportStructural components for supportCellulose, chitin, GAGsCellulose, chitin, GAGs

Essential components of nucleic acidsEssential components of nucleic acidsD-ribose, 2-deoxy-D-riboseD-ribose, 2-deoxy-D-ribose

Antigenic determinantsAntigenic determinantsFucose, D-galactose, D-glucose, N-acetyl-D-Fucose, D-galactose, D-glucose, N-acetyl-D-

glucosamine, D-acetyl-D-galactosamineglucosamine, D-acetyl-D-galactosamine

SPECIFIC CARBOHYDRATESSPECIFIC CARBOHYDRATESMonosaccharidesMonosaccharides

GlucoseGlucose ( (dextrose, grape sugar, blood sugardextrose, grape sugar, blood sugar)) Can be stored as glycogenCan be stored as glycogen Most metabolically important monosaccharideMost metabolically important monosaccharide

FructoseFructose ( (levuloselevulose))

GalactoseGalactose ((brain sugar)brain sugar)

MannoseMannose Targets lysosomal enzymes to their destinationsTargets lysosomal enzymes to their destinations Directs certain proteins from Golgi body to lysosomesDirects certain proteins from Golgi body to lysosomes

DisaccharidesDisaccharidesSucroseSucrose ((table sugar, cane sugartable sugar, cane sugar, ,

saccharosesaccharose) ) glucose & fructose glucose & fructose linkedlinked αβαβ1-21-2

LactoseLactose ( (milk sugarmilk sugar) ) glu & gal glu & gal linkedlinked ββ 1-4 1-4MaltoseMaltose ((malt sugarmalt sugar) ) 2 glucose 2 glucose linked linked

αα 1-4 1-4 TrehaloseTrehalose ( (mycosemycose) ) 2 glucose 2 glucose linked linked

αα 1-1 1-1 GentiobioseGentiobiose ( (amygdaloseamygdalose) ) 2 glucose 2 glucose

linkedlinked ββ 1-6 1-6CellobioseCellobiose 2 glucose 2 glucose linked linked ββ 1-4 1-4

CLASSES OF CARBOHYDRATESCLASSES OF CARBOHYDRATESNumber of CNumber of C

Triose, tetroses, pentose, hexose, heptuloseTriose, tetroses, pentose, hexose, heptulose

Number of saccharide unitsNumber of saccharide units Monosaccharides, disaccharides, oligosaccharides (2 to 10 Monosaccharides, disaccharides, oligosaccharides (2 to 10

units), polysaccharidesunits), polysaccharides

Position of carbonyl (C=O) groupPosition of carbonyl (C=O) group AldoseAldose if terminally located if terminally located KetoseKetose if centrally located if centrally located

Reducing propertyReducing propertyReducing sugars Reducing sugars (all monosaccharides)(all monosaccharides)Nonreducing sugars Nonreducing sugars (sucrose)(sucrose)

STRUCTURAL PROJECTIONS OF STRUCTURAL PROJECTIONS OF MONOSACCHARIDESMONOSACCHARIDES

FISCHERFISCHER by Emil Fischerby Emil Fischer ((Nobel Prize in Chemistry 1902Nobel Prize in Chemistry 1902))

2-D representation for showing2-D representation for showing the configuration of a stereocenterthe configuration of a stereocenter

Horizontal lines project forward Horizontal lines project forward while vertical lines project towardswhile vertical lines project towards the rearthe rear

DD ( (RR or or ++) or ) or LL ( (SS or or --))

HAWORTH HAWORTH by Walter Haworthby Walter Haworth

((Nobel Prize in Chemistry 1937Nobel Prize in Chemistry 1937))

A way to view furanose (5-membered ring) and A way to view furanose (5-membered ring) and pyranose (6-membered ring) forms of pyranose (6-membered ring) forms of monosaccharidesmonosaccharides

The ring is drawn flat and viewed through its edge The ring is drawn flat and viewed through its edge with the anomeric carbon on the the right and the with the anomeric carbon on the the right and the oxygen atom on the rearoxygen atom on the rear

ANOMERIC CARBONANOMERIC CARBON

CHAIR & BOAT CHAIR & BOAT CONFORMATIONSCONFORMATIONS

AMINO SUGARSAMINO SUGARS

REDUCING PROPERTYREDUCING PROPERTY

KetoseKetose

EnediolEnediol

AldoseAldose

AldonateAldonate

H

H – C – OH

C = O

R

OH-

OH-

Oxidizing agent

HO H

C

C

R OH

O H

C

H C OH

R

O O-

C

H C OH

R

AABBOO ANTIGENS ANTIGENS

N-acetyl-N-acetyl- D-galactose D-galactose N-acetyl-N-acetyl-

D-galactosamineD-galactosamine D-glucosamineD-glucosamine

FucoseFucose

D-galactose D-galactose D-galactoseD-galactose N-acetyl-N-acetyl-

D-glucosamineD-glucosamine

FucoseFucose

D-galactoseD-galactose N-acetyl-N-acetyl- D-glucosamineD-glucosamine

FucoseFucose

TYPE ATYPE A

TYPE BTYPE B

TYPE OTYPE O

POLYSACCHARIDESPOLYSACCHARIDESSTARCHSTARCH

Storage carbohydrate in plantsStorage carbohydrate in plants

Two principal parts are Two principal parts are amyloseamylose (20-25%) & (20-25%) & amylopectin amylopectin (75-80%) which are completely (75-80%) which are completely hydrolyzed to D-glucosehydrolyzed to D-glucose

AmyloseAmylose is composed of is composed of continuous, unbranchedcontinuous, unbranched chain of chain of 4000 D-glucose4000 D-glucose linked via linked via αα 1-4 bonds 1-4 bonds

AmylopectinAmylopectin is a chain of is a chain of 10,000 D-glucose10,000 D-glucose units linked units linked via via αα 1-4 bonds but 1-4 bonds but branchingbranching of 24-30 glucose units is of 24-30 glucose units is started via started via αα 1-6 bonds 1-6 bonds

GLYCOGENGLYCOGEN

Energy-reserve carbohydrate in animalsEnergy-reserve carbohydrate in animals

Highly branched containing approximately Highly branched containing approximately 101066 glucose units linked via glucose units linked via αα 1-4 bonds & 1-4 bonds & αα 1-6 bonds1-6 bonds

Well-nourished adult stores 350 g. of it Well-nourished adult stores 350 g. of it equally divided between the liver and equally divided between the liver and musclesmuscles

CELLULOSECELLULOSEPlant skeletal polysaccharidePlant skeletal polysaccharide

Linear chain of 2200 glucose units linked Linear chain of 2200 glucose units linked via via ββ 1-4 bonds 1-4 bonds

High mechanical strength is due to High mechanical strength is due to aligning of stiff fibers where hydroxyl form aligning of stiff fibers where hydroxyl form hydrogen bondinghydrogen bonding

ACIDIC POLYSACCHARIDESACIDIC POLYSACCHARIDES Also called mucopolysaccharides (MPS) or Also called mucopolysaccharides (MPS) or

glycosaminoglycans (GAG)glycosaminoglycans (GAG)

Polymers which contain carboxyl groups and/or Polymers which contain carboxyl groups and/or sulfuric ester groupssulfuric ester groups

Structural and functional importance in connective Structural and functional importance in connective tissuestissues

Interact with collagen to form loose or tight networksInteract with collagen to form loose or tight networks

ACIDIC POLYSACCHARIDESACIDIC POLYSACCHARIDES HYALURONIC ACIDHYALURONIC ACID

Simplest GAGSimplest GAG Contains 300-100,000 repeating units of Contains 300-100,000 repeating units of D-glucuronic D-glucuronic

acid and N-acetyl-D-glucosamineacid and N-acetyl-D-glucosamine Abundant in embryonic tissues, synovial fluid, and the Abundant in embryonic tissues, synovial fluid, and the

vitreous humor to hold retina in place vitreous humor to hold retina in place Joint lubricant & shock absorberJoint lubricant & shock absorber

HEPARINHEPARIN Heterogeneous mixture of variably sulfonated chainsHeterogeneous mixture of variably sulfonated chains Stored in mast cells of the liver, lungs and the gutStored in mast cells of the liver, lungs and the gut Naturally-occurring anticoagulant by acting as Naturally-occurring anticoagulant by acting as

antithrombin III and antithromboplastinantithrombin III and antithromboplastin Composed of two disaccharide repeating units A & B;Composed of two disaccharide repeating units A & B;

A is A is L-iduronic acid-2-sulfate linked to 2-deoxy-2-sulfamido-D-L-iduronic acid-2-sulfate linked to 2-deoxy-2-sulfamido-D-galactose-6-sulfategalactose-6-sulfate

BB is is D-glucuronic acid beta-linked to 2-deoxy-2-sulfamido-D-glucose-D-glucuronic acid beta-linked to 2-deoxy-2-sulfamido-D-glucose-6-sulfate6-sulfate

HEPARAN SULFATEHEPARAN SULFATE

CHONDROITIN SULFATECHONDROITIN SULFATE Most abundant in mammalian tissuesMost abundant in mammalian tissues Found in skeletal and soft connective tissuesFound in skeletal and soft connective tissues Composed of repeating units of Composed of repeating units of N-acetyl galactosamine sulfate linked N-acetyl galactosamine sulfate linked

beta1-4 to glucuronic acidbeta1-4 to glucuronic acid

KERATAN SULFATEKERATAN SULFATE

DERMATAN SULFATEDERMATAN SULFATE Found in skin, blood vessels, heart valves, tendons, aorta, spleen Found in skin, blood vessels, heart valves, tendons, aorta, spleen

and brainand brain The disaccharide repeating units are The disaccharide repeating units are L-iduronic acid and N-L-iduronic acid and N-

acetylgalactosamine-4-sulfate with small amounts of D-glucuronic acidacetylgalactosamine-4-sulfate with small amounts of D-glucuronic acid

GLYCOLYSISGLYCOLYSISThe specific pathway by which the body The specific pathway by which the body

gets energy from monosaccharidesgets energy from monosaccharidesFirst stage is ACTIVATIONFirst stage is ACTIVATIONAt the expense of At the expense of 2ATP2ATPs s glucose is glucose is

phosphorylatedphosphorylatedStep #1Step #1formation of glucose-6-phosphateformation of glucose-6-phosphateStep # 2Step # 2isomerization to fructose-6-phosphateisomerization to fructose-6-phosphate

Step # 3Step # 3Second phosphate group is attached to yield fructose-Second phosphate group is attached to yield fructose-

1,6-bisphosphate1,6-bisphosphate

Second stage is CSecond stage is C66 to 2 molecules of C to 2 molecules of C33

Step # 4Step # 4Fructose-1,6-bisphosphate is broken down into two C3 Fructose-1,6-bisphosphate is broken down into two C3

fragmentsfragments glyceraldehyde-3-phosphate (G-3-P) and glyceraldehyde-3-phosphate (G-3-P) and

dihydroxyacetone phosphate (DHAP)dihydroxyacetone phosphate (DHAP)

Only G-3-P is oxidized in glycolysis. DHAP is converted Only G-3-P is oxidized in glycolysis. DHAP is converted to G-3-P as the latter diminishes. to G-3-P as the latter diminishes.

ATP-YIELDING Third stageATP-YIELDING Third stage Step # 5Step # 5

Glyceraldehyde-3-phosphate is oxidized to 1,3-Glyceraldehyde-3-phosphate is oxidized to 1,3-bisphosphoglycerate; hydrogen of aldehyde is bisphosphoglycerate; hydrogen of aldehyde is removed by NADremoved by NAD++

Step # 6Step # 6

Phosphate from the carboxyl group is transferred Phosphate from the carboxyl group is transferred to the ADP yielding ATP and 3-to the ADP yielding ATP and 3-phosphoglyceratephosphoglycerate

Step # 7Step # 7

Isomerization of 3-phosphoglycerate to 2-Isomerization of 3-phosphoglycerate to 2-phosphoglyceratephosphoglycerate

Step # 8 Step # 8 Dehydration of 2-phosphoglycerate to Dehydration of 2-phosphoglycerate to

phosphoenolpyruvate (PEP)phosphoenolpyruvate (PEP)

Step # 9Step # 9Removal of the remaining phosphate to yield Removal of the remaining phosphate to yield

ATP and pyruvateATP and pyruvate

Step # 10Step # 10Reductive decarboxylation of pyruvate to Reductive decarboxylation of pyruvate to

produce ethanol and COproduce ethanol and CO22

REACTIONS OF GLYCOLYSISREACTIONS OF GLYCOLYSIS

STEPSTEP REACTIONREACTION ENZYMEENZYME REACTION REACTION TYPETYPE

ΔΔG in G in kJ/molkJ/mol

11 Glucose + ATPGlucose + ATP G-6-P + ADP + HG-6-P + ADP + H++

HexokinaseHexokinase Phosphoryl Phosphoryl transfertransfer

-33.5-33.5

22 G-6-P G-6-P F-6-P F-6-P Phosphoglucose Phosphoglucose isomeraseisomerase

IsomerizationIsomerization -2.5-2.5

33 F-6-P + ATPF-6-P + ATP

F-1,6-BP + ADP + HF-1,6-BP + ADP + H++

Phosphofructo-Phosphofructo-kinasekinase

Phosphoryl Phosphoryl transfertransfer

-22.2-22.2

STEPSTEP REACTIONREACTION ENZYMEENZYME REACTION TYPEREACTION TYPE ΔΔG in G in kJ/kJ/

molmol

44 F-1,6-BP F-1,6-BP DHAP + GAP DHAP + GAP AldolaseAldolase Aldol cleavageAldol cleavage -1.3-1.3

55 DHAP DHAP GAP GAP Triose Triose phosphate phosphate isomeraseisomerase

IsomerizationIsomerization +2.5+2.5

66 GAP + Pi + NADGAP + Pi + NAD++ 1,3-BPG + NADH + H1,3-BPG + NADH + H++

GlyceraldehydeGlyceraldehyde-3-Phosphate -3-Phosphate DehydrogenaseDehydrogenase

Phosphorylation Phosphorylation coupled to coupled to oxidationoxidation

+2.5+2.5

77 1,3-BPG + ADP 1,3-BPG + ADP

3-phosphoglycerate +ATP3-phosphoglycerate +ATP

Phosphoglycer-Phosphoglycer-ate kinaseate kinase

Phosphoryl Phosphoryl transfertransfer

+1.3+1.3

88 3-phosphoglycerate 3-phosphoglycerate 2-phosphoglycerate2-phosphoglycerate

Phosphoglyce-Phosphoglyce-rate mutaserate mutase

Phosphoryl shiftPhosphoryl shift +0.8+0.8

99 2-phosphoglycerate 2-phosphoglycerate

PEP + HOHPEP + HOH

EnolaseEnolase DehydrationDehydration -3.3-3.3

1010 PEP + ADP + H+ PEP + ADP + H+ pyruvate + ATP pyruvate + ATP Pyruvate kinasePyruvate kinase Phosphoryl Phosphoryl transfertransfer

-16.7-16.7

CITRIC ACID CYCLECITRIC ACID CYCLESTEPSTEP REACTIONREACTION ENZYMEENZYME PROSTHETPROSTHET

IC GROUPIC GROUPREACTION REACTION

TYPETYPEΔΔGGoo in in kJ/kJ/

molmol

11 acetylCoA + oxaloacetateacetylCoA + oxaloacetate + + HOHHOH

citrate + CoA + Hcitrate + CoA + H++

Citrate Citrate synthasesynthase

CondensationCondensation -31.4-31.4

2a2a Citrate Citrate cis-aconitate + HOH cis-aconitate + HOH AconitaseAconitase Fe-SFe-S DehydrationDehydration +8.4+8.4

2b2b Cis-Aconitate + HOH Cis-Aconitate + HOH isocitrateisocitrate

AconitaseAconitase Fe-SFe-S HydrationHydration -2.1-2.1

CITRIC ACID CYCLECITRIC ACID CYCLESTEPSTEP REACTIONREACTION ENZYMEENZYME PROSTHETPROSTHET

IC GROUPIC GROUPREACTION REACTION

TYPETYPEΔΔGGoo in in kJ/kJ/

molmol

33 Isocitrate + NAD+ Isocitrate + NAD+

αα-ketoglutarate + CO-ketoglutarate + CO22 + +

NADHNADH

IsocitrateIsocitrate

Dehydro-Dehydro-genasegenase

DecarboxylatiDecarboxylation & oxidationon & oxidation

- 8.4- 8.4

44 αα-ketoglutarate + NAD+ CoA -ketoglutarate + NAD+ CoA

succinyl CoA + COsuccinyl CoA + CO22 + +

NADHNADH

αα--ketogluta-ketogluta-rate rate dehydro-dehydro-genase genase complexcomplex

Lipoic acid, Lipoic acid, FAD, TPPFAD, TPP

Decarboxyla-Decarboxyla-tion & tion & oxidationoxidation

-30.1-30.1

55 Succinyl CoA + Pi + GDP Succinyl CoA + Pi + GDP

succinate + GTP + CoAsuccinate + GTP + CoA

Succinyl Succinyl CoA CoA synthet-synthet-asease

Substrate-Substrate-level level phosphoryla-phosphoryla-tiontion

-3.3-3.3

CITRIC ACID CYCLECITRIC ACID CYCLESTEPSTEP REACTIONREACTION ENZYMEENZYME PROSTHETPROSTHET

IC GROUPIC GROUPREACTION REACTION

TYPETYPEΔΔGGoo in in

kJ/kJ/

molmol

66 Succinate + FAD (enzyme-bound) Succinate + FAD (enzyme-bound)

fumarate + FADHfumarate + FADH22

(enzyme-bound)(enzyme-bound)

Succinate Succinate dehydro-dehydro-genasegenase

FAD, Fe-SFAD, Fe-S OxidationOxidation 00

77 Fumarate + HOH Fumarate + HOH L-malate L-malate FumaraseFumarase HydrationHydration -3.8-3.8

88 L-malate + NAD+ L-malate + NAD+ oxaloacetate + NADH + Hoxaloacetate + NADH + H++

Malate Malate dehydro-dehydro-genasegenase

OxidationOxidation +29.7+29.7

REGULATION OF TCA CYCLEREGULATION OF TCA CYCLE Pyruvate

Acetyl CoA

Citrate

Isocitrate

Α-Ketoglutarate

Succinyl CoA

Succinate

Fumarate

Malate

Oxaloacetate

- ATP, acetyl CoA & NADH

- ATP & NADH

+ ADP

- ATP, succinyl CoA & NADH

Α-KGD

ICD

BIOSYNTHETIC ROLES BIOSYNTHETIC ROLES

OF TCA CYCLEOF TCA CYCLE Pyruvate

Acetyl CoA

Citrate

Isocitrate

Α-Ketoglutarate

Succinyl CoA

Succinate

Fumarate

Malate

Oxaloacetate

Aspartate

Other amino acids,

purines & pyrimidines

Porphyrins, heme,

chlorophyll

Glutamate

Other amino

acids & purines

Fatty acids, sterols

NOTES TO REMEMBERNOTES TO REMEMBER

The unusual thing about the The unusual thing about the structure of N-structure of N-acetylmuramic acidacetylmuramic acid compared to other compared to other carbohydrates is the carbohydrates is the presence of a lactic acid presence of a lactic acid side chain.side chain.

Cell walls of Cell walls of plantsplants are are cellulosic cellulosic (polymer of (polymer of D-glucose);D-glucose); bacterialbacterial cell walls consist mainly cell walls consist mainly of of polysaccharide crosslinked to peptide polysaccharide crosslinked to peptide through murein bridgesthrough murein bridges; and ; and fungalfungal cell walls cell walls are are chitinouschitinous ( (polymer of N-acetyl-polymer of N-acetyl-ββ-D--D-glucosamineglucosamine))

Glycogen and starch differ mainly in the Glycogen and starch differ mainly in the degree degree of chain branchingof chain branching..

EnantiomersEnantiomers are nonsuperimposable, are nonsuperimposable, mirror-mirror-image stereoisomersimage stereoisomers differing configuration differing configuration on all carbonson all carbons while while diastereomers diastereomers are are nonsuperimposable nonsuperimposable nonmirror-image nonmirror-image stereoisomers differing only on two stereoisomers differing only on two carbonscarbons..

Fischer projection of glucoseFischer projection of glucose has has 4 chiral 4 chiral centerscenters while its while its Haworth projectionHaworth projection has has 5 5 chiral centerschiral centers. .

Sugar phosphateSugar phosphate is an is an ester bondester bond formed formed between a sugar hydroxyl and between a sugar hydroxyl and phosphoric acidphosphoric acid..

A A glycosidic bondglycosidic bond is an is an acetalacetal which can which can be be hydrolyzed to regenerate the two hydrolyzed to regenerate the two original sugar hydroxylsoriginal sugar hydroxyls..

A A reducing sugarreducing sugar is one that has a is one that has a free free aldehyde groupaldehyde group that that can be easily can be easily oxidized.oxidized.

Major Major biochemical roles of glycoproteinsbiochemical roles of glycoproteins are are signal transductionsignal transduction as hormones, as hormones, recognition sites for external moleculesrecognition sites for external molecules in in eukaryotic cell membranes, and eukaryotic cell membranes, and defensedefense as as immunoglobulins.immunoglobulins.

L-sorbitolL-sorbitol is made by is made by reducing D-glucosereducing D-glucose. .

Arabinose Arabinose is a is a ribose epimerribose epimer, thus, , thus, its its derivatives derivatives ara-Aara-A and and ara-Cara-C if if substituted substituted for ribosefor ribose act as act as inhibitors in reactions of inhibitors in reactions of ribonucleosidesribonucleosides..

Two best precursors for glycogenTwo best precursors for glycogen are are glucoseglucose and and fructosefructose..

CelluloseCellulose because of the because of the ββ- bonding- bonding is is linear linear as to structure and as to structure and structural structural as to role while as to role while starch starch because ofbecause of αα-bonding-bonding coils coils with with energy storageenergy storage role. role.

The The highly branched nature of glycogenhighly branched nature of glycogen gives rise to a gives rise to a number of available glucose number of available glucose molecules at a timemolecules at a time upon hydrolysis to upon hydrolysis to provide energy. A provide energy. A linearlinear one provides one provides one one glucose at a timeglucose at a time..

The enzyme The enzyme ββ-amylase-amylase is an is an exoglycosidase exoglycosidase degrading polysaccharides from the ends. The degrading polysaccharides from the ends. The enzyme enzyme αα-amylase-amylase is an is an endoglycosidaseendoglycosidase cleaving internal glycosidic bonds.cleaving internal glycosidic bonds.

Dietary fibersDietary fibers bind bind toxic substances in the guttoxic substances in the gut and and decreases the transit timedecreases the transit time, so harmful , so harmful compounds such as carcinogens are removed from compounds such as carcinogens are removed from the body more quickly than would be the case with the body more quickly than would be the case with low-fiber diet.low-fiber diet.

The The sugar portions of the blood group sugar portions of the blood group glycoproteinsglycoproteins are the are the source of the antigenic source of the antigenic difference. difference.

Cross-linking Cross-linking can be expected to play a role in the can be expected to play a role in the structures of structures of cellulose and chitincellulose and chitin where mechanical where mechanical strength is afforded by strength is afforded by extensive hydrogen bondingextensive hydrogen bonding..

Converting a sugar to an epimerConverting a sugar to an epimer requires requires inversion inversion of configuration at a chiral centerof configuration at a chiral center. This can only be . This can only be done by done by breaking and reforming covalent bondsbreaking and reforming covalent bonds..

Vitamin CVitamin C is a is a lactone (a cyclic ester)lactone (a cyclic ester) with a with a double double bond between two of the ring carbonsbond between two of the ring carbons. The . The presence of a double bond makes it presence of a double bond makes it susceptible to susceptible to air oxidation.air oxidation.

The sequence of The sequence of monomers in a polysaccharidemonomers in a polysaccharide is is not genetically codednot genetically coded and in this sense does not and in this sense does not contain any information contain any information unlike the nucleotide unlike the nucleotide sequencesequence..

Glycosidic bondsGlycosidic bonds can be formed between the side can be formed between the side chain hydroxyls of serine or threonine residues chain hydroxyls of serine or threonine residues and the sugar hydroxylsand the sugar hydroxyls. In addition, there is a . In addition, there is a possibility of ester bonds forming between the possibility of ester bonds forming between the side side chain carboxyl groups of aspartate or glutamate chain carboxyl groups of aspartate or glutamate and the sugar hydroxylsand the sugar hydroxyls..

In In glycolysisglycolysis, reactions that , reactions that require ATPrequire ATP are: are:1. 1. phosphorylation of glucosephosphorylation of glucose ( (HK,GKHK,GK))2. 2. phosphorylation of fructose-6-phosphatephosphorylation of fructose-6-phosphate

((PFKPFK))Reactions that Reactions that produce ATPproduce ATP are: are:

1. 1. transfer of phosphate from 1,3-transfer of phosphate from 1,3-bisphosphoglycerate to ADPbisphosphoglycerate to ADP ( (PGKPGK))

2. 2. transfer of phosphate from PEP to ADPtransfer of phosphate from PEP to ADP ( (PKPK))

In In glycolysisglycolysis, reactions that , reactions that require NADHrequire NADH are: are:1. 1. reduction of pyruvate to lactatereduction of pyruvate to lactate ( (LDHLDH))2. 2. reduction of acetaldehyde to ethanolreduction of acetaldehyde to ethanol

((alcohol dehydrogenasealcohol dehydrogenase))Reactions that Reactions that require NADrequire NAD are: are:

1. 1. oxidation of G-3-P to give 1,3-DPGoxidation of G-3-P to give 1,3-DPG ( (G-3-PDG-3-PD))

NADH-linked dehydrogenasesNADH-linked dehydrogenases are are LDH, ADH & G-LDH, ADH & G-3-PD.3-PD.

The purpose of the The purpose of the step that produces lactatestep that produces lactate is to is to reduce pyruvatereduce pyruvate so so that NADH can be oxidized to that NADH can be oxidized to NAD+ needed for the step catalyzed by NAD+ needed for the step catalyzed by glyceraldehyde-3-phosphateglyceraldehyde-3-phosphate..

AldolaseAldolase catalyzes the catalyzes the reverse aldol condensation reverse aldol condensation of fructose-1,6-bisphosphate to glyceraldehyde-3-of fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate and DHAPphosphate and DHAP..

The The energy releasedenergy released by all the reactions of by all the reactions of glycolysisglycolysis is is 184.5 kJ mol glucose/mol184.5 kJ mol glucose/mol. The energy . The energy released by glycolysis released by glycolysis drives the phosphorylation of drives the phosphorylation of two ADP to ATP for each molecule of glucosetwo ADP to ATP for each molecule of glucose, , trapping 61.0 kJ mol/glucosetrapping 61.0 kJ mol/glucose. The estimate of . The estimate of 33% 33% efficiencyefficiency comes from the calculation (61.0/184.5) x comes from the calculation (61.0/184.5) x 100 = 33%.100 = 33%.

There is a There is a net gain of two ATP molecules per net gain of two ATP molecules per glucoseglucose molecule consumed in molecule consumed in glycolysisglycolysis. The . The gross yield of 4 ATPs per glucosegross yield of 4 ATPs per glucose molecule, but the molecule, but the reactions of glycolysis require two ATP per glucose.reactions of glycolysis require two ATP per glucose.

PyruvatePyruvate can be converted to can be converted to lactatelactate, , ethanolethanol or or acetylCoAacetylCoA..

The The free energy of hydrolysis of a substratefree energy of hydrolysis of a substrate is the is the energetic energetic driving force in substrate-level driving force in substrate-level phosphorylationphosphorylation. An example is the conversion of . An example is the conversion of glyceraldehyde-3-phosphate to 1,3-glyceraldehyde-3-phosphate to 1,3-bisphosphoglyceratebisphosphoglycerate..

Coupled reactions in glycolysisCoupled reactions in glycolysis are those reactions are those reactions catalyzed by catalyzed by hexokinase, phosphofructokinase, hexokinase, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerokinase, phosphoglycerokinase, andand pyruvate kinase. pyruvate kinase.

IsozymesIsozymes allow for allow for subtle control of the enzymesubtle control of the enzyme to to respond to different cellular needs. For example, in the respond to different cellular needs. For example, in the liver, liver, LDH is most often used to convert lactate to LDH is most often used to convert lactate to pyruvate, but the reaction is often reversed in the pyruvate, but the reaction is often reversed in the musclesmuscles. Having a . Having a different isozymedifferent isozyme in the liver and in the liver and the muscle allows for those the muscle allows for those reactions to be reactions to be optimizedoptimized..

Fructose-1,6-bisphosphate can only undergo the Fructose-1,6-bisphosphate can only undergo the reactions of glycolysisreactions of glycolysis. The components of the . The components of the pathway up to this point can have other metabolic pathway up to this point can have other metabolic fates.fates.

The The physiologically irreversible glycolytic stepsphysiologically irreversible glycolytic steps are those are those catalyzed by HK, PFK and PKcatalyzed by HK, PFK and PK. Thus, they . Thus, they are are controlling points in glycolysis.controlling points in glycolysis.

HexokinaseHexokinase is is inhibited by glucose-6-phosphateinhibited by glucose-6-phosphate. . PhosphofructokinasePhosphofructokinase is is inhibited by ATP and citrateinhibited by ATP and citrate. . Pyruvate kinasePyruvate kinase is is inhibited is inhibited by ATP, inhibited is inhibited by ATP,

acetylCoA and alanine. acetylCoA and alanine.

PhosphofructokinasePhosphofructokinase is is stimulated by AMP and stimulated by AMP and fructose-2,6-bisphosphatefructose-2,6-bisphosphate. .

Pyruvate kinasePyruvate kinase is is stimulated by AMP and fructose-stimulated by AMP and fructose-1,6-bisphosphate1,6-bisphosphate..

An An isomerase isomerase is a general term for an enzyme that is a general term for an enzyme that changes the form of a substrate without changing changes the form of a substrate without changing its empirical formulaits empirical formula..

A A mutasemutase is an enzyme that is an enzyme that moves a functional moves a functional group such as a phosphate to a new location in a group such as a phosphate to a new location in a substrate moleculesubstrate molecule..

The The glucokinase has a higher Km for glucose than glucokinase has a higher Km for glucose than hexokinasehexokinase. Thus, under conditions of . Thus, under conditions of low glucoselow glucose, , the the liver will not convert glucose to glucose-6-liver will not convert glucose to glucose-6-phosphatephosphate, using a substrate that is needed , using a substrate that is needed elsewhere. When the elsewhere. When the glucose concentration becomes glucose concentration becomes higherhigher, however, , however, glucokinase will function to help glucokinase will function to help phosphorylate glucose so that it can be stored as phosphorylate glucose so that it can be stored as glycogenglycogen..

The The net yield of ATPnet yield of ATP from glycolysis is the same, from glycolysis is the same, 2 2 ATPATP, when , when either fructose, mannose, and either fructose, mannose, and galactose is usedgalactose is used. The energetics of the conversion . The energetics of the conversion of hexoses to pyruvate are the same regardless of of hexoses to pyruvate are the same regardless of hexose type.hexose type.

The The net yield of ATPnet yield of ATP is 3 from is 3 from glucose derived from glucose derived from glycogenglycogen because the starting material is glucose-1- because the starting material is glucose-1-phosphate. One of the priming reactions is no longer phosphate. One of the priming reactions is no longer used.used.

A A reaction with a negative reaction with a negative ΔΔGGoo is is thermodynamically possiblethermodynamically possible under standard under standard conditions.conditions.

Individuals who Individuals who lack the gene that directs the lack the gene that directs the synthesis of the M form of the enzyme PFKsynthesis of the M form of the enzyme PFK can can carry on glycolysis in their livers but suffer muscle carry on glycolysis in their livers but suffer muscle weaknessweakness because they lack the enzyme in muscle. because they lack the enzyme in muscle.

The reaction of The reaction of 2-PG to PEP2-PG to PEP is a is a dehydrationdehydration (loss of (loss of water) rather than a redox reaction.water) rather than a redox reaction.

The The hexokinasehexokinase molecule molecule changes shape changes shape drastically on binding to substratedrastically on binding to substrate, consistent with , consistent with the the induced fit theoryinduced fit theory of an enzyme adapting itself to of an enzyme adapting itself to its substrate.its substrate.

ATPATP is an is an inhibitor of several steps of glycolysisinhibitor of several steps of glycolysis as as well as other catabolic pathways. The purpose of well as other catabolic pathways. The purpose of catabolic pathways is to produce energycatabolic pathways is to produce energy, and high , and high levels of ATP mean the cell already has sufficient levels of ATP mean the cell already has sufficient energy. energy. G-6-P inhibits HKG-6-P inhibits HK and is an example of and is an example of product inhibitionproduct inhibition. If G-6-P level is high, it may . If G-6-P level is high, it may indicate that sufficient glucose is available from indicate that sufficient glucose is available from glycogen breakdown or that the subsequent enzymatic glycogen breakdown or that the subsequent enzymatic steps of glycolysis are going slowly. Either way there steps of glycolysis are going slowly. Either way there is no reason to produce more G-6-P. is no reason to produce more G-6-P.

PhosphofructokinasePhosphofructokinase is is inhibited by a special inhibited by a special effector molecule, fructose-2,6-bisphosphateeffector molecule, fructose-2,6-bisphosphate, , whose levels are controlled by hormones. It is also whose levels are controlled by hormones. It is also inhibited by citrateinhibited by citrate, which indicates that there is , which indicates that there is sufficient energy from the TCA cycle probably from fat sufficient energy from the TCA cycle probably from fat or amino acid catabolism. or amino acid catabolism.

PKPK is also is also inhibited by inhibited by acetylCoAacetylCoA, the , the presence of presence of which indicates that fatty acids are being used to which indicates that fatty acids are being used to generate energygenerate energy for the citric acid cycle. for the citric acid cycle.

The The main function of glycolysismain function of glycolysis is to is to feed carbon feed carbon units to the TCA cycleunits to the TCA cycle. When these carbon . When these carbon skeletons can come from other sources, glycolysis is skeletons can come from other sources, glycolysis is inhibited to spare glucose for other purposes.inhibited to spare glucose for other purposes.

Thiamine pyrophosphate (TPP)Thiamine pyrophosphate (TPP) is a coenzyme in the is a coenzyme in the transfer of 2-carbon unitstransfer of 2-carbon units. It is required for . It is required for catalysis by catalysis by pyruvate decarboxylase in alcoholic fermentationpyruvate decarboxylase in alcoholic fermentation. The . The important part of TPP is the five-membered ring where important part of TPP is the five-membered ring where a C is found between an S and Na C is found between an S and N. This . This carbon forms a carbon forms a carbanion and is extremely reactive, making it able to carbanion and is extremely reactive, making it able to perform nucleophilic attack on carbonyl groupsperform nucleophilic attack on carbonyl groups leading leading to decarboxylation of several compounds in different to decarboxylation of several compounds in different pathways. pathways.

TPPTPP is a coenzyme is a coenzyme required in the reaction required in the reaction catalyzed by pyruvate carboxylasecatalyzed by pyruvate carboxylase. Because this . Because this reaction is a part of the reaction is a part of the metabolism of ethanolmetabolism of ethanol, less , less will be available to serve as a coenzyme in the will be available to serve as a coenzyme in the reactions of other enzymes that require it.reactions of other enzymes that require it.

Animals that have been run to deathAnimals that have been run to death have have accumulated large amounts of lactic acidaccumulated large amounts of lactic acid in their in their muscle tissue, accounting for the muscle tissue, accounting for the sour taste of their sour taste of their meat.meat.

Conversion of glucose to lactate rather than pyruvateConversion of glucose to lactate rather than pyruvate recycles NADHrecycles NADH..

The The formation of fructose-1,6-bisphosphateformation of fructose-1,6-bisphosphate is the is the committed step in glycolysiscommitted step in glycolysis. It is also one of the . It is also one of the energy-requiring steps of the said pathway.energy-requiring steps of the said pathway.

A A positive positive ΔΔGGo o does not necessarily meandoes not necessarily mean that the that the reaction has a positive reaction has a positive ΔΔGG. . Substrate concentrationsSubstrate concentrations can can make a make a negative negative ΔΔG out of a positive G out of a positive ΔΔGGoo. .

The The entire pathwayentire pathway can be looked at can be looked at as a as a large coupled reactionlarge coupled reaction. Thus, . Thus, if the overall if the overall pathway has a negative pathway has a negative ΔΔG, an individual step G, an individual step may be able to have a positive may be able to have a positive ΔΔG and the G and the pathway can still continue. pathway can still continue.

In In glycogen storageglycogen storage, the reactions that , the reactions that require ATPrequire ATP are: are:1. 1. formation of UDP-glucose from glucose-1-phosphate formation of UDP-glucose from glucose-1-phosphate

and UTP (indirect requirement since ATP is and UTP (indirect requirement since ATP is needed needed to regenerate UTP)to regenerate UTP) (UDP-glucose (UDP-glucose phosphorylase)phosphorylase)

2. 2. regeneration of UTPregeneration of UTP (nucleoside phosphate kinase)(nucleoside phosphate kinase)3. 3. carboxylation of pyruvate to oxaloacetatecarboxylation of pyruvate to oxaloacetate (pyruvate (pyruvate

carboxylase)carboxylase)Reactions that Reactions that produce ATPproduce ATP are are NONENONE..

Three differences Three differences between NADPH between NADPH andand NADHNADH1. 1. phosphate at 2’ position of ribosephosphate at 2’ position of ribose in NADPH in NADPH2. NADH is 2. NADH is produced in oxidative reactions that yield produced in oxidative reactions that yield

ATPATP while NADPH is a while NADPH is a reducing agentreducing agent in biosynthesis. in biosynthesis.3. 3. Different enzymes use NADH as a coenzymeDifferent enzymes use NADH as a coenzyme

compared compared to those that require NADPH.to those that require NADPH.

In In glycogen storageglycogen storage, there is , there is no reaction no reaction that requires acetylCoAthat requires acetylCoA but but biotin is biotin is required in the carboxylation of pyruvate required in the carboxylation of pyruvate to oxaloacetate.to oxaloacetate.

The The four fates of glucose-6-phosphatefour fates of glucose-6-phosphate are: are: Converted to glucose (gluconeogenesis)Converted to glucose (gluconeogenesis) Converted to glycogen (glycogenesis)Converted to glycogen (glycogenesis) Converted to pentose phosphatesConverted to pentose phosphates Hydrolyzed to pyruvate (glycolysis)Hydrolyzed to pyruvate (glycolysis)

In In making equal amounts of NADPH and pentose making equal amounts of NADPH and pentose phosphatesphosphates, it , it only involves oxidative reactionsonly involves oxidative reactions. In . In making making mostly or purely NADPHmostly or purely NADPH, the , the use of oxidative reactions, use of oxidative reactions, transketolase and transaldolase reactions, and transketolase and transaldolase reactions, and gluconeogenesisgluconeogenesis are required. In are required. In making mostly or only making mostly or only pentose phosphatespentose phosphates, needed reactions are , needed reactions are transketolase, transketolase, transaldolase, and glycolysis transaldolase, and glycolysis in reversein reverse..

Transketolase catalyzes the transfer of 2-carbon unitTransketolase catalyzes the transfer of 2-carbon unit, whereas , whereas transaldolase catalyzes the transfer of a 3-carbon unittransaldolase catalyzes the transfer of a 3-carbon unit..

It is essential that the It is essential that the mechanisms that activate glycogen mechanisms that activate glycogen synthesis also deactivate glycogen phosphorylasesynthesis also deactivate glycogen phosphorylase because because they both occur in the same cell compartment. they both occur in the same cell compartment. If both are on at If both are on at the same time, a futile ATP hydrolysis resultsthe same time, a futile ATP hydrolysis results. On/off . On/off mechanism is highly efficient in its control.mechanism is highly efficient in its control.

UDPGUDPG, in glycogen biosynthesis, , in glycogen biosynthesis, transfers glucose to transfers glucose to the growing glycogen moleculethe growing glycogen molecule..

Glycogen synthaseGlycogen synthase is is subject to covalent subject to covalent modification and to allosteric controlmodification and to allosteric control. The enzyme is . The enzyme is active in its phosphorylated form and inactive when active in its phosphorylated form and inactive when dephosphorylateddephosphorylated. .

AMPAMP is an is an allosteric inhibitor of glycogen synthaseallosteric inhibitor of glycogen synthase, , whereas whereas ATP and glucose-6-phosphateATP and glucose-6-phosphate are are allosteric activatorsallosteric activators..

In In gluconeogenesisgluconeogenesis, , biotin is the molecule to which biotin is the molecule to which carbon dioxide is attached to the process of being carbon dioxide is attached to the process of being transferred to pyruvatetransferred to pyruvate. The reaction . The reaction produces produces oxaloacetateoxaloacetate, which then undergoes further reactions , which then undergoes further reactions of gluconeogenesis. Biotin is of gluconeogenesis. Biotin is not used in not used in glycogenesis and PPP.glycogenesis and PPP.

In gluconeogenesis, glucose-6-phosphate is In gluconeogenesis, glucose-6-phosphate is dephosphorylated to glucose (last step); in glycolysis, dephosphorylated to glucose (last step); in glycolysis, G-6-P isomerizes to fructose-6-phosphate (early step).G-6-P isomerizes to fructose-6-phosphate (early step).

The The Cori cycleCori cycle is a pathway in which there is is a pathway in which there is cycling of cycling of glucose due to glycolysis in muscle and glucose due to glycolysis in muscle and gluconeogenesis in livergluconeogenesis in liver. The . The blood transports lactate blood transports lactate from muscle to liver and glucose from liver to musclefrom muscle to liver and glucose from liver to muscle. .

There is a There is a net gain of 3net gain of 3, rather than 2, , rather than 2, ATP when ATP when glycogenglycogen, not glucose, , not glucose, is the starting material of is the starting material of glycolysisglycolysis..

Control mechanisms are important in metabolism. Control mechanisms are important in metabolism. They are:They are: Allosteric control (takes place in msec)Allosteric control (takes place in msec) Covalent control (takes place from s to min)Covalent control (takes place from s to min) Genetic control ( longer time scale)Genetic control ( longer time scale)

Enzymes, like all catalysts, speed up the forward and Enzymes, like all catalysts, speed up the forward and reverse reaction to the same extent. Having different reverse reaction to the same extent. Having different catalysts is the only way to ensure independent catalysts is the only way to ensure independent control over the rates of the forward and the reverse control over the rates of the forward and the reverse process. process.

The glycogen synthase is an exergonic reaction The glycogen synthase is an exergonic reaction overall because it is coupled to phosphate ester overall because it is coupled to phosphate ester hydrolysis.hydrolysis.

Increasing the level of ATP is favorable to both Increasing the level of ATP is favorable to both gluconeogenesis and glycogen synthesis. gluconeogenesis and glycogen synthesis.

Decreasing the level of fructose-1,6-bisphosphate Decreasing the level of fructose-1,6-bisphosphate would tend to stimulate glycolysis, rather than would tend to stimulate glycolysis, rather than gluconeogenesis and glycogen synthesis. gluconeogenesis and glycogen synthesis.

If a cell needs NADPH, all the reactions of the PPP If a cell needs NADPH, all the reactions of the PPP take place. If a cell needs ribose-5-phosphate, the take place. If a cell needs ribose-5-phosphate, the oxidative portion of the pathway can be bypassed and oxidative portion of the pathway can be bypassed and only the nonoxidative reshuffling reactions take place. only the nonoxidative reshuffling reactions take place. The PPP does not have a significant effect on the ATP The PPP does not have a significant effect on the ATP supply of a cell.supply of a cell.

Glucose-6-phosphate is expectedly oxidized to a Glucose-6-phosphate is expectedly oxidized to a lactone rather than an open-chain ester because the lactone rather than an open-chain ester because the latter is easy to hydrolyze. latter is easy to hydrolyze.

In the PPP resshuffling reactions, without an In the PPP resshuffling reactions, without an isomerase, all the sugars involved are keto isomerase, all the sugars involved are keto sugars that are not substrates for sugars that are not substrates for transaldolase. transaldolase.

Sugar nucleotides (UDPG) have two Sugar nucleotides (UDPG) have two phosphates which when hydrolyzed drives phosphates which when hydrolyzed drives towards the polymerization of glycogen. Thus, towards the polymerization of glycogen. Thus, they are fit for glycogenesis. they are fit for glycogenesis.

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