Chapter 9Chapter 9

Energy in a Energy in a CellCell

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ATP

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9.1 – The Need for Energy 9.1 – The Need for Energy (p. (p. 221-224)221-224)

Energy is essential to life.Energy is essential to life. Organisms are Organisms are endergonicendergonic systems. systems. What do we need “E” for?What do we need “E” for?

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Active Transport Cell Division Transport Synthesis (proteins) others

ATP is the universal currency of ATP is the universal currency of energy exchange in biological systems.energy exchange in biological systems.

No matter what form of energy a cell uses No matter what form of energy a cell uses as its primary source, the energy is as its primary source, the energy is ultimately transformed and conserved as ultimately transformed and conserved as ATP.ATP.

•adenosine monophosphate (AMP) nucleotide

• two phosphate groups

•pyrophosphate bonds (~P).

•These two bonds are energy rich in the sense that their hydrolysis (breakage which releases water) yields a great deal more energy than a covalent bond of another molecule.

The ATP reaction is commonly written as:The ATP reaction is commonly written as:

ADP + Pi + energyADP + Pi + energy ATP ATP

The forming of ADP into ATP The forming of ADP into ATP requires energy (requires energy (endothermicendothermic) – 8 kcal/mole) – 8 kcal/mole is pH dependent.is pH dependent.

Note: Forming ADP is like making a bank Note: Forming ADP is like making a bank deposit or coiling a spring for each deposit or coiling a spring for each phosphate bond. (see figure 9.2 on p. 223)phosphate bond. (see figure 9.2 on p. 223)

The CalorieThe Calorie

KcalKcal – kilocalorie – kilocalorie equivalent to 1000 calories. equivalent to 1000 calories. When we say that a cup of milk has 120 When we say that a cup of milk has 120

calories we really mean 300 kilocalories calories we really mean 300 kilocalories or 300 000 calories.or 300 000 calories.

Even though we use the word calorie it Even though we use the word calorie it is, by definition, kilocalorie.is, by definition, kilocalorie.

The MoleThe Mole

ABOUT THE MOLE:Analogous to a dozen, it is a ”count” of molecules used in chemistry and biochemistry.

1 mol = 6.022 x 1023 molecules 0.5 mol = 3.011 x 10 23 molecules2.0 mol – 12.044 x 10 23 molecules or

1.2044 x 10 24 molecules

9.2 Photosynthesis: 9.2 Photosynthesis: Trapping the Sun’s Energy Trapping the Sun’s Energy

p. 225-230p. 225-230 We’ve seen in our past learning that We’ve seen in our past learning that

the cell uses energy during ACTIVE the cell uses energy during ACTIVE TRANSPORT. Where does this TRANSPORT. Where does this energy come from?energy come from?

RECALL FROM EARLIER GRADESRECALL FROM EARLIER GRADESAll animals are heterotrophs - All animals are heterotrophs - require food sources of energy.require food sources of energy. i.e. trophic levels in a food chaini.e. trophic levels in a food chain

We do not make our own food for energy like plants, We do not make our own food for energy like plants, algae and some bacteria (autotrophs). This is algae and some bacteria (autotrophs). This is summarized by the carbon-oxygen cycle below:summarized by the carbon-oxygen cycle below:

Photosynthesis: The Energy Photosynthesis: The Energy Maker Maker

Autotrophs under go Autotrophs under go PHOTOSYNTHESISPHOTOSYNTHESIS to produce sugars (starches made up of to produce sugars (starches made up of glucose molecules)—we say the sun’s glucose molecules)—we say the sun’s energy is stored in a energy is stored in a chemicalchemical bondbond. .

Recall:Recall:UV energy + COUV energy + CO22 + 6H + 6H22O O C C66HH1212OO66 + 6 O + 6 O22

In actuality, this reaction is elegant, In actuality, this reaction is elegant, but is not simple. but is not simple.

MANY reactions occur inside the MANY reactions occur inside the chloroplast’s chloroplast’s grana grana membrane.membrane.

The chlorophyll in chloroplasts is The chlorophyll in chloroplasts is one one pigmentpigment (a green one, there are (a green one, there are others) that absorbs sun energy (all others) that absorbs sun energy (all colours except green) which excite colours except green) which excite electrons and cause a phosphate to electrons and cause a phosphate to attach to ADP molecules. attach to ADP molecules.

LIGHT DEPENDENT-LIGHT DEPENDENT-REACTIONS REACTIONS

Energized electrons provide energy Energized electrons provide energy that:that: Forms ATP. Forms ATP. Releases oxygen molecules (from the Releases oxygen molecules (from the

splitting of Hsplitting of H22O)O)

See Fig. 9.5 p. 227See Fig. 9.5 p. 227

Fig. 9.6 p. 228Fig. 9.6 p. 228

LighLight Independent t Independent Reactions/Dark ReactionsReactions/Dark Reactions

At the same time (and more so at At the same time (and more so at night when there is no sun) the night when there is no sun) the Calvin cycle takes place in the Calvin cycle takes place in the stroma of the chloroplast.stroma of the chloroplast.

Powered by ATPPowered by ATP

from photosynthesisfrom photosynthesis

Carbon dioxide gas (COCarbon dioxide gas (CO22) is taken in ) is taken in and used to form sugars (CHand used to form sugars (CH22O is O is short hand to represent many short hand to represent many different types of different types of sugarsugar moleculesmolecules, , most importantly glucose). most importantly glucose).

These are stored as These are stored as starch starch granulesgranules in chloroplasts. in chloroplasts. They are also transported to other cells They are also transported to other cells

and accumulate in roots.and accumulate in roots. See Fig. 9.7 p. 229See Fig. 9.7 p. 229

The new summary of The new summary of photosynthesis:photosynthesis:

Light dependent reactions:Light dependent reactions:

12H12H22O + O + 12NADP + 18ADP12NADP + 18ADP → 6O → 6O22 + + 12NADPH12NADPH + + 18ATP18ATP

Light Independent reactions (*Calvin cycle)Light Independent reactions (*Calvin cycle)

6CO6CO22 + + 12NADPH + 18ATP12NADPH + 18ATP→C→C66HH1212OO66++12NADP12NADP++18ADP18ADP+6H+6H22OO

Can you see how we get the overall Can you see how we get the overall PsPs equation?equation?

The whole point of these reactions is to The whole point of these reactions is to make a safe, energy rich molecule, make a safe, energy rich molecule, glucose.glucose.

9.3 Getting Energy to 9.3 Getting Energy to Make ATPMake ATP

Cellular RespirationCellular Respiration When we consume the sugars from plants, When we consume the sugars from plants,

(producers) or animals that have eaten (producers) or animals that have eaten plants (primary consumers), energy from plants (primary consumers), energy from the sugar bonds is released. the sugar bonds is released.

The release of this energy is called The release of this energy is called respirationrespiration..

Recall:Recall:

CC66HH1212OO66 + 6 O + 6 O22 6 CO 6 CO22 + 6 H + 6 H22O + EnergyO + Energy (ATP)(ATP)

Again, the reaction is elegant but far from Again, the reaction is elegant but far from simple! simple!

When animals and plants consume energy When animals and plants consume energy molecules like starch and glucose, many molecules like starch and glucose, many reactions occur.reactions occur. Glycolysis (anaerobic)Glycolysis (anaerobic) Citric Acid Cycle (aerobic)Citric Acid Cycle (aerobic) Electron Transport Chain Electron Transport Chain

-also aerobic -also aerobic

The last two occur The last two occur

inside the mitochondrion.inside the mitochondrion.

GlycolysisGlycolysis

Glycolysis is the only metabolic Glycolysis is the only metabolic pathway shared by pathway shared by ALL organisms. ALL organisms.

Occurs in the Occurs in the cytoplasmcytoplasm.. i.e. not in an organellei.e. not in an organelle

Glycolysis (cont’d)Glycolysis (cont’d)

A process whereby glucose molecules are A process whereby glucose molecules are split in half (makes a 3-C compound called split in half (makes a 3-C compound called pyruvate) in a series of steps.pyruvate) in a series of steps.

Glycolysis releases a 2 – ATP molecules Glycolysis releases a 2 – ATP molecules per glucose molecule that are used to per glucose molecule that are used to drive other reactions AND drive other reactions AND

This process does not require OThis process does not require O22 AnerobicAnerobic

See Fig. 9.8 p. 232See Fig. 9.8 p. 232

Aerobic vs. AnaerobicAerobic vs. Anaerobic

From here, pathways diverge in different From here, pathways diverge in different organisms and in different situations—organisms and in different situations—oxygen poor (anaerobic) and oxygen rich oxygen poor (anaerobic) and oxygen rich (aerobic). (aerobic). More about that later.More about that later.

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BUT more ATP is made inside the BUT more ATP is made inside the mitochondrion in two separate pathways:mitochondrion in two separate pathways: The The Citric Acid Cycle, CAC (KREBS Citric Acid Cycle, CAC (KREBS

CYCLE, KC)CYCLE, KC) ELECTRON TRANSPORT CHAINELECTRON TRANSPORT CHAIN ( (ETCETC))

CAC releases 1 ATP moleculeCAC releases 1 ATP molecule ETC releases 30 ATP molecules!ETC releases 30 ATP molecules! These reactions drive far more chemical These reactions drive far more chemical

reactions in our tissues because of it.reactions in our tissues because of it.

Citric Acid Cycle (CAC)Citric Acid Cycle (CAC)

The The CACCAC occurs inside the occurs inside the mitochondrial matrix.mitochondrial matrix.

It is called a cycle, because one of its It is called a cycle, because one of its end-products is recycled in the end-products is recycled in the cycle. cycle.

Named because it forms citric acidNamed because it forms citric acid an important intermediate molecule. an important intermediate molecule.

Citric Acid Cycle (cont’d)Citric Acid Cycle (cont’d) The main outcome is the generation of a The main outcome is the generation of a

variety of energy intermediate molecules, variety of energy intermediate molecules, not just ATP. not just ATP. GTPGTP NADHNADH FADHFADH22. .

This cycle also This cycle also releases 3 COreleases 3 CO22 molecules molecules per pyruvate (3-C). per pyruvate (3-C).

See Fig. 9.10 p. 233See Fig. 9.10 p. 233

A diagram shows the numbers of A diagram shows the numbers of energy molecules generated:energy molecules generated:

animationanimation

The Electron Transport The Electron Transport Chain (ETC)Chain (ETC)

From the Krebs cycle (Citric Acid From the Krebs cycle (Citric Acid cycle) inside the mitochondrion, the cycle) inside the mitochondrion, the ETC occurs inside the ETC occurs inside the mitochondrial membranemitochondrial membrane..

It causes a It causes a cascadecascade of energy of energy release by using the other energy release by using the other energy molecules of NADH, FADH2 to cash molecules of NADH, FADH2 to cash in and make more ATP.in and make more ATP.

See Fig. 9.11 p. 234 See Fig. 9.11 p. 234

The specialized molecules that do this The specialized molecules that do this are called are called CYTOCHROMESCYTOCHROMES and they and they pass excited electrons from one pass excited electrons from one cytochrome to another stepwise—this cytochrome to another stepwise—this releases even more ATP—30 more ATP!releases even more ATP—30 more ATP!—in a controlled manner. —in a controlled manner.

This is where This is where oxygen is consumed, oxygen is consumed, and water formedand water formed..

TOTAL ATP from 1 glucose molecule:TOTAL ATP from 1 glucose molecule:

- 2 gly - 2 (Act T)+ 2 CAC + 30 ETC = 32 - 2 gly - 2 (Act T)+ 2 CAC + 30 ETC = 32 ATPATP

The schematic below shows how electrons The schematic below shows how electrons transferred from the NADH in Krebs are transferred from the NADH in Krebs are transferred in a cascade of reactions in transferred in a cascade of reactions in the ETC—note the need for flavin M (part the ETC—note the need for flavin M (part of the group of of the group of riboflavinsriboflavins, or B vitamins, or B vitamins—B2) and the role of iron ions (Fe). —B2) and the role of iron ions (Fe).

This releases a LOT of ATP molecules.This releases a LOT of ATP molecules.

Cellular Respiration Cellular Respiration SchematicSchematic

In summaryIn summary

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In summary:In summary: SO, back to our original reaction—the SO, back to our original reaction—the

important component is the ENERGY:important component is the ENERGY:

CC66HH1212OO66 + 6O2 + 6O2 6CO 6CO22 + 6H + 6H22O + O + 32ATP32ATP

We now know We now know

where oxygen is consumed, where oxygen is consumed, how COhow CO22 is generated, is generated, where the Hwhere the H22O comes fromO comes from and how many energy molecules are made.and how many energy molecules are made.

Anaerobic RespirationAnaerobic Respiration If no oxygen continues to be present or, in If no oxygen continues to be present or, in

some organisms like yeast, where it is not some organisms like yeast, where it is not used, used, fermentation fermentation occurs. occurs.

This is also known as This is also known as anaerobic anaerobic respiration. respiration.

uses the 3-C molecules (pyruvate) and uses the 3-C molecules (pyruvate) and makes makes lactic acid in our muscles or in lactic acid in our muscles or in yogurt) yogurt) or or ethanol (as in brewing)ethanol (as in brewing). .

Anaerobic Respiration Anaerobic Respiration (cont’d)(cont’d)

Only another Only another 2 ATP2 ATP molecules are molecules are mademade

This occurs with some fungi, and This occurs with some fungi, and with with Lactobacillus acidophilusLactobacillus acidophilus in in yogurt, and in yeasts. yogurt, and in yeasts.

This is the basis of cheese, yogurt, This is the basis of cheese, yogurt, buttermilk, root beer (real root buttermilk, root beer (real root beer), breads, wines, spirits.beer), breads, wines, spirits.

Anaerobic ExerciseAnaerobic Exercise

In vigorous exercise, In vigorous exercise, lactic acid lactic acid builds up in our muscles when we’ve builds up in our muscles when we’ve exhausted the oxygen supply in our exhausted the oxygen supply in our haemoglobinhaemoglobin i.e. We produce more lactic acid than i.e. We produce more lactic acid than

our cells can remove and they begin to our cells can remove and they begin to seize up creating pain.seize up creating pain.

Athletes can increase their tolerance Athletes can increase their tolerance for lactic acid.for lactic acid.

Aerobic RespirationAerobic Respiration

AEROBIC RESPIRATION AEROBIC RESPIRATION occurs in occurs in our mitochondriaour mitochondria these pathways occur when oxygen is these pathways occur when oxygen is

required (as in us) and is present in required (as in us) and is present in sufficient amounts.sufficient amounts. Longer duration of exercise Longer duration of exercise

For these cycles to occur, active For these cycles to occur, active transport of pyruvate from glycolysis is transport of pyruvate from glycolysis is needed – this uses up the 2 ATP that needed – this uses up the 2 ATP that were made. were made.

MetabolismMetabolism

METABOLISMMETABOLISM refers to two contrasting refers to two contrasting cellular activities:cellular activities: the total biochemical reactions required for energy the total biochemical reactions required for energy

making reactions called making reactions called CATABOLISM (CATABOLISM (includes includes breaking down foods to breaking down foods to store energystore energy – ATP - in our – ATP - in our tissues) tissues)

andand

the use of energy to synthesize cell material from the use of energy to synthesize cell material from small molecules in the environment, called small molecules in the environment, called ANABOLISMANABOLISM (energy consuming, using ATP to (energy consuming, using ATP to release energy). release energy).

Catabolic ReactionsCatabolic Reactions Produce energy in the chemical bonds of a Produce energy in the chemical bonds of a

molecule called molecule called ATP (adenosine ATP (adenosine triphosphate).triphosphate). glycolysisglycolysis CACCAC ETC ETC

lead to end products, which are "waste lead to end products, which are "waste products" like water and CO2products" like water and CO2

most important—they generate ATPmost important—they generate ATP which is later used in which is later used in anabolicanabolic reactions to reactions to build cell material from nutrients in the build cell material from nutrients in the environment, like muscle tissue. environment, like muscle tissue.

Anabolic PathwaysAnabolic Pathways

Lead to release of the energy to drive other Lead to release of the energy to drive other reactions.reactions.

These reactions make These reactions make important molecules important molecules like proteins for our muscles, hair, nails, like proteins for our muscles, hair, nails, lipids for our fatty tissues, and so onlipids for our fatty tissues, and so on..

When energy is required during anabolism, When energy is required during anabolism, it may be it may be spentspent as the breaking of a high as the breaking of a high energy bond of ATP which has a value of energy bond of ATP which has a value of about about 8 kcal/mol of ATP molecules8 kcal/mol of ATP molecules. . This This is like a withdrawal from your account.is like a withdrawal from your account.

Role of WaterRole of Water

Breaking the ATP to make ADP Breaking the ATP to make ADP releasesreleases 8 kcal/mol. The ATP 8 kcal/mol. The ATP reaction is commonly written as:reaction is commonly written as:

ATP ATP ADP + Pi + 8 kcal/mol ADP + Pi + 8 kcal/mol

The diagram showing the relationships The diagram showing the relationships between catabolism and anabolism is between catabolism and anabolism is not to be memorizednot to be memorized, but to help you , but to help you understand the connections:understand the connections:

IMP: During catabolism, energy is changed IMP: During catabolism, energy is changed from one form to another, but such energy from one form to another, but such energy transformations are never completely transformations are never completely efficient, i.e., some energy is lost in the form efficient, i.e., some energy is lost in the form of heat. This forms part of our body heat.of heat. This forms part of our body heat.

In both catabolism and anabolism, energy is In both catabolism and anabolism, energy is formed formed stepwisestepwise and broken down and broken down stepwisestepwise in a number of cycles. in a number of cycles.

This controls the amount of energy stored or This controls the amount of energy stored or released. released.

The energy is passed along in two The energy is passed along in two energy processes: energy processes: Exergonic Exergonic reactionsreactions and and Endergonic Endergonic reactionsreactions..