Chapter 9

Cellular Respiration

I CAN’S/YOU MUST KNOW

The difference between fermentation & cellular The difference between fermentation & cellular respirationrespiration

The role of glycolysis in oxidizing glucose to two The role of glycolysis in oxidizing glucose to two molecules of pyruvatemolecules of pyruvate

The process that brings pyruvate from the cytosol The process that brings pyruvate from the cytosol into the mitochondria & introduces it into the citric into the mitochondria & introduces it into the citric acid cycleacid cycle

How the process of chemiosmosis utilizes the How the process of chemiosmosis utilizes the electrons from NADH & FADHelectrons from NADH & FADH22 to produce ATP to produce ATP

9.1

Catabolic pathways release energy by Catabolic pathways release energy by oxidizing organic fuelsoxidizing organic fuels

Occur when molecules are broken downOccur when molecules are broken down

Releases the molecules’ energyReleases the molecules’ energy

2 types of catabolism2 types of catabolism

1) Fermentation1) Fermentation

Partial degradation of sugars that occurs without OPartial degradation of sugars that occurs without O22

2) Cellular Respiration2) Cellular Respiration

Most prevalent & efficient catabolic pathwayMost prevalent & efficient catabolic pathway

Uses OUses O22 as a reactant with the organic fuel as a reactant with the organic fuel

Known as AEROBIC RESPIRATIONKnown as AEROBIC RESPIRATION

CAN also use anaerobic respirationCAN also use anaerobic respiration

Carbs, Fats, & Proteins are all broken down in Carbs, Fats, & Proteins are all broken down in cellular respirationcellular respiration

Glucose is the primary nutrient molecule used:Glucose is the primary nutrient molecule used:

CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6H + 6H22O + O + ENERGY ENERGY

(ATP/heat)(ATP/heat)

The exergonic release of energy from glucose The exergonic release of energy from glucose is used to phosphorylate ADP to ATPis used to phosphorylate ADP to ATP

Life processes constantly consume ATPLife processes constantly consume ATP

Cellular respiration burns the organic fuels & Cellular respiration burns the organic fuels & uses the energy to regenerate ATPuses the energy to regenerate ATP

Redox Reactions

Electrons are transferred from one reactant to Electrons are transferred from one reactant to anotheranother

Reduction = substance gains electrons & Reduction = substance gains electrons & energy (reduced + charge)energy (reduced + charge)

Oxidation = substance loses electrons & Oxidation = substance loses electrons & energy (oxidized)energy (oxidized)

LEO GERLEO GER

The electron donor is called the The electron donor is called the reducing reducing agentagent

The electron receptor is called the The electron receptor is called the oxidizing oxidizing agentagent

Some redox reactions do not transfer Some redox reactions do not transfer electrons but change the electron sharing in electrons but change the electron sharing in covalent bondscovalent bonds

During cellular respiration, the fuel (such as During cellular respiration, the fuel (such as glucose) is oxidized, and Oglucose) is oxidized, and O22 is reduced: is reduced:

At key steps in cellular respiration:At key steps in cellular respiration:

Electrons are stripped from glucoseElectrons are stripped from glucose

Each electron travels with a proton (forms Each electron travels with a proton (forms hydrogen)hydrogen)

The hydrogen atoms are not transferred directly The hydrogen atoms are not transferred directly to oxygen (formula shows that) – they are to oxygen (formula shows that) – they are passed to an electron carrierpassed to an electron carrier

Electron Carrier:Electron Carrier:

Coenzyme NADCoenzyme NAD++

NADNAD++ accepts 2 electrons + the stabilizing accepts 2 electrons + the stabilizing hydrogen ion to form NADHhydrogen ion to form NADH

NADH has been reduced & has gained energyNADH has been reduced & has gained energy

Stored energy used later to make ATPStored energy used later to make ATP

More than: CMore than: C66HH1212OO66 + 6O + 6O66 6CO 6CO22 + 6H + 6H22O + O + ENERGY ENERGY

Cellular respiration has three stages:Cellular respiration has three stages:

Glycolysis Glycolysis (breaks down glucose into two molecules (breaks down glucose into two molecules of pyruvate)of pyruvate)

The The citric acid cycle citric acid cycle (completes the breakdown of (completes the breakdown of glucose)glucose)

Oxidative phosphorylation Oxidative phosphorylation (accounts for most of (accounts for most of the ATP synthesis)the ATP synthesis)

9.2Glycolysis

Occurs in cytosolOccurs in cytosol

The degradation of glucose begins as it is The degradation of glucose begins as it is broken down into two PYRUVATE moleculesbroken down into two PYRUVATE molecules

The 6-Carbon glucose molecule is split into The 6-Carbon glucose molecule is split into TWO 3-Carbon sugars through a long series of TWO 3-Carbon sugars through a long series of stepssteps

2 major phases:2 major phases:

Energy (ATP) consuming phaseEnergy (ATP) consuming phase

Energy (ATP) producing phaseEnergy (ATP) producing phase

Energy consumingEnergy consuming

2 ATP are used2 ATP are used

Destabilize glucose & makes it more reactiveDestabilize glucose & makes it more reactive

Energy producingEnergy producing

Later in glycolysis, 4 ATP are madeLater in glycolysis, 4 ATP are made

Results in net gain of 2 ATPResults in net gain of 2 ATP

– 2 NADH are also made – used later2 NADH are also made – used later

• NET gain of 2 ATP & 2 NADHNET gain of 2 ATP & 2 NADH

• Most potential energy is still in the 2 Most potential energy is still in the 2 pyruvatespyruvates

• Pyruvates will then move to step 2 – citric acid Pyruvates will then move to step 2 – citric acid cyclecycle

9.3Kreb’s (Citric Acid) Cycle

• When OWhen O22 is present, pyruvates enter the is present, pyruvates enter the mitochondriamitochondria

• Before Kreb’s begins, pyruvate is converted to Before Kreb’s begins, pyruvate is converted to acetyl CoA acetyl CoA

• 1) Pyruvate uses a transport protein to move 1) Pyruvate uses a transport protein to move into the matrix of the mitochondriainto the matrix of the mitochondria

• 2) When there, an enzyme complex removes a 2) When there, an enzyme complex removes a COCO22, strips away electrons to convert NAD+ to , strips away electrons to convert NAD+ to NADH, & adds coenzyme A to form acetyl CoANADH, & adds coenzyme A to form acetyl CoA

• 3) Two acetyl CoA’s are produced per glucose. 3) Two acetyl CoA’s are produced per glucose. It now enters the citric acid cycleIt now enters the citric acid cycle

Kreb’s (Citric Acid)

• 8 steps – each catalyzed by a specific enzyme8 steps – each catalyzed by a specific enzyme

• The job of breaking down glucose is The job of breaking down glucose is completed with COcompleted with CO22 released as waste released as waste

• Each turn of the cycle requires the input of Each turn of the cycle requires the input of one acetyl CoAone acetyl CoA

• Must make 2 turns before the glucose is Must make 2 turns before the glucose is completely oxidizedcompletely oxidized

• One turn produces:One turn produces:

– 2CO2CO22, 3NADH, 1FADH, 3NADH, 1FADH22 & 1 ATP & 1 ATP

• Thus 2 turns produce:Thus 2 turns produce:

– 4CO4CO22, 6NADH, 2FADH, 6NADH, 2FADH2 2 & 2 ATP & 2 ATP

• At the end of the Kreb’s cycle all 6 carbons At the end of the Kreb’s cycle all 6 carbons from glucose have been released as COfrom glucose have been released as CO22

• Only 2 ATP have been producedOnly 2 ATP have been produced

– The rest is held in the electrons in the NADH & The rest is held in the electrons in the NADH & FADHFADH22

– Utilized in the Electron Transport ChainUtilized in the Electron Transport Chain

9.4ETC

• The electron carriers will donate electrons to The electron carriers will donate electrons to power ATP synthesis through OXIDATIVE power ATP synthesis through OXIDATIVE PHOSPHORYLATION PHOSPHORYLATION

• In the cristae of the mitochondriaIn the cristae of the mitochondria

• The ETC itself produces no ATP (comes from The ETC itself produces no ATP (comes from the products of the ETC)the products of the ETC)

4 Step Process of ETC

• 1) ETC is embedded in the inner membrane of 1) ETC is embedded in the inner membrane of the mitochondriathe mitochondria

– Has 3 transmembrane proteins that act as Has 3 transmembrane proteins that act as hydrogen pumps hydrogen pumps

– 2 carrier molecules that move electrons 2 carrier molecules that move electrons between hydrogen pumpsbetween hydrogen pumps

• 2) ETC is powered by electrons from NADH & 2) ETC is powered by electrons from NADH & FADHFADH22

– As electrons flow, the loss of energy is used to As electrons flow, the loss of energy is used to pump protons across the inner membranepump protons across the inner membrane

– At the end of the ETC, the electrons combine At the end of the ETC, the electrons combine with 2 hydrogen ions & Oxygen to form waterwith 2 hydrogen ions & Oxygen to form water

– Oxygen is the final electron acceptor – if none is Oxygen is the final electron acceptor – if none is available, the ETC STOPS!!!available, the ETC STOPS!!!

• 3) Hydrogen ions flow down their gradient 3) Hydrogen ions flow down their gradient through ATP synthase (channel in protein)through ATP synthase (channel in protein)

– ATP synthase harnesses proton motive force (the ATP synthase harnesses proton motive force (the gradient of protons) to phosphorylate ADPgradient of protons) to phosphorylate ADP

– The proton motive force exists because inner The proton motive force exists because inner mit. Membrane is impermeable to hydrogen ionsmit. Membrane is impermeable to hydrogen ions

• 4) The movement of the proton motive force is 4) The movement of the proton motive force is called chemiosmosiscalled chemiosmosis

– Energy-coupling mechanism that uses energy Energy-coupling mechanism that uses energy from the proton gradient to drive cellular workfrom the proton gradient to drive cellular work

– The ETC & chemiosmosis compose OXIDATIVE The ETC & chemiosmosis compose OXIDATIVE PHOSPHORYLATIONPHOSPHORYLATION

• ATP yield per molecule of glucose is between ATP yield per molecule of glucose is between 36 & 38 ATP36 & 38 ATP

• 32-34 comes from oxidative phosphorylation 32-34 comes from oxidative phosphorylation

Process NADH ATP FADH2 TOTAL ATP

Glycolysis 2 (3 ATP each in

ETC)

4 (2 net) X 8

Pyruvic acid acetyl CoA

2 X X 6

Kreb’s Cycle 6 (3 ATP each in

ETC)

2 2 (2 ATP each in

ETC)

24

ATP Totals: 30 4 4 38

9.5

• Fermentation allows a cell to produce ATP Fermentation allows a cell to produce ATP without Oxygen (anaerobic)without Oxygen (anaerobic)

• Consists of glycolysis (2 net ATP) & reactions Consists of glycolysis (2 net ATP) & reactions that regenerate NAD+that regenerate NAD+

• Oxygen not required to accept electronsOxygen not required to accept electrons

Types of fermentation

• 1) Alcohol1) Alcohol

– Pyruvate is converted to ethanolPyruvate is converted to ethanol

– Releases COReleases CO22 & oxidizing NADH to create more & oxidizing NADH to create more NAD+NAD+

• 2) Lactic acid 2) Lactic acid

– Pyruvate is reduced by NADH (NAD+) formedPyruvate is reduced by NADH (NAD+) formed

– Lactate is a waste productLactate is a waste product

• Facultative anaerobesFacultative anaerobes

– Organisms that make ATP by aerobic respiration Organisms that make ATP by aerobic respiration if oxygen presentif oxygen present

– Can switch to fermentation in anaerobic Can switch to fermentation in anaerobic conditionsconditions

9.6

• Proteins & fats are used to generate ATP Proteins & fats are used to generate ATP through cellular respirationthrough cellular respiration

• Organic molecules are used in biosynthesis Organic molecules are used in biosynthesis (the building of macromolecules)(the building of macromolecules)

– Amino acids from the hydrolysis of proteins can Amino acids from the hydrolysis of proteins can be incorporated into the consumer’s own be incorporated into the consumer’s own proteinsproteins