Ch 9 Cellular Respiration and Fermentation

Formula of Cellular Respiration

Glucose (C6H12O6) + O2 → CO2 + H2O + ATP

(C6H12O6 + 6O2 → 6O2 + 6CO2 + energy [heat and 32 ATP])

Oxidation vs Reduction

oxidation:

• reaction in which a substance loses electrons

• becomes oxidized

reduction:

• reaction in which a substance gains electrons

• becomes reduced

• electrons travel with hydrogens

mnemonic OIL RIG (oxidation is loss of electrons, reduction is gain of electrons)

Reducing Agent & Oxidizing Agent

reducing agent: the electron donor in a redox reaction

oxidizing agent: the electron acceptor in a redox reaction

• oxygen is strong oxidizing agent

Redox During Cellular Respiration

glucose is oxidized (it loses electrons) and oxygen is reduced (it gains electrons)

glucose is the reducing agent; oxygen is the oxidizing agent

(remember how much electronegativity oxygen has)

NAD

nicotinamide adenine dinucleotide

a derivative of the vitamin niacin; can easily cycle between its oxidized form and its reduced form; essentially functions as an electron shuttle and sends electrons to electron transport chain (ETC)

NAD+ & NADH

NAD+: oxidized form of NAD

• a coenzyme that can accept electrons (to become NADH) that functions as oxidizing agent during respiration

• will accept one hydrogen (proton + electron) and one free electron

• NADH: the reduced form NAD

• temporarily stores electrons during cellular respiration

• NADH acts as electron donor to the electron transport chain

• carries 2 electrons to another molecule

Electron Transport Chain

series of electron carrier molecules (proteins) that shuttle electrons from NADH/FADH2 down a series of redox reactions that release energy used to make ATP

• transfer of electrons to increasingly electronegative proteins

• energy is released with each transfer (remember “hot potato” example)

• electrons rest when they land on O2 (aerobic respiration) or other inorganic molecule (anaerobic respiration)

3 Phases of Aerobic Cellular Respiration

1.) glycolysis

2.) Krebs cycle/citric acid cycle

3.) oxidative phosphorylatoin

Glycolysis

series of reactions that split glucose into pyruvate, serves as starting point to cellular respiration or fermentation; does not require oxygen

• location: in the cytoplasm

• reactant: glucose

• products:

  • 2 pyruvate

  • 2 ATP (via substrate-level phosphorylation)

  • 2 NADH (electron carrier)

Substrate-Level Phosphorylation

an enzyme is used to transfer a phosphate group from a substrate to ADP to make ATP; the enzyme-catalyzed formation of ATP

Pyruvate Modification

the steps that links glycolysis and the citric acid cycle; the transitional phase

1.) pyruvate is converted to acetyl coenzyme A (Acetyl CoA) by losing a molecule of CO2;

2.) remaining piece is oxidized

3.) coenzyme A (CoA) binds to 2-carbon intermediate and forms acetyl CoA

Krebs Cycle/Citric Acid Cycle

2nd chemical cycle in cellular respiration that completes breakdown of glucose molecules by oxidizing acetyl CoA to carbon dioxide

• location: inner mitochondrial membrane

• reactant: acetyl CoA

• products:

  • 4 carbon dioxide (CO2)

  • 6 NADH

  • 2 FADH2 (another electron carrier)

  • 2 ATP (via substrate-level phosphorylation)

Oxidative Phosphorylation

3rd step in cellular respiration; the production of ATP using energy derived from redox reactions of an electron transport chain (ETC)

• location: inner mitochondrial membrane

• reactants:

  • NADH

  • FADH2

  • O2

• products:

  • 28 ATP

  • H2O

Net Production During Each Phase

glycolysis:

• 2 ATP

• 2 NADH

• 2 pyruvate

citric acid cycle:

• 2 ATP

• 8 NADH

• 2 FADH

• 6 CO2

oxidative phosphorylation:

• 28 ATP

• H2O

Components of ETC

collection of molecules (mostly proteins) embedded in the inner membrane of the mitochondrion that alternate between oxidized and reduced states as they pass the electron down the chain

(hot potato example in lecture)

Multiprotein Complexes I-IV

multiple proteins with electron carriers

complexes I, III, & IV:

• function: energy from electron transfer is used to pump hydrogen ions out of the mitochondrial matrix into the inner membrane

complex II:

• accepts electrons from FADH2

Ubiquinone

nonprotein mobile electron carrier molecule that delivers to other complexes

Cytochromes c & a₃

iron-containing protein that is component of ETC

c: mobile electron carrier

a3: gives electron to oxygen (last phase in ETC)

ATP Synthase

complex of several membrane proteins that use the energy of a hydrogen ion (proton) concentration gradient that produce 28 ATP

how:

• hydrogen ion gradient (proton motive force)

• H+ ions flow back into the cell along their gradient through ATP synthase

• rotor spins (sort of like a water wheel)

• knob adds inorganic phosphate to ADP

Chemiosmosis

energy-coupling mechanism that uses energy from the hydrogen ion gradient across a membrane to drive ATP synthesis

Net Yield of ATP per Glucose Molecule

32 total ATP collected from

• glycolysis: 2 ATP

• citric acid cycle: 2 ATP

• oxidative phosphorylation (ATP synthase): 28 ATP

Fermentation

catabolic process that takes place in the absence of oxygen; makes a limited amount of ATP without an ETC

recycles NAD

generate NAD+ by transferring electrons from NADH

Fermentation & NADH

main purpose is to regenerate NAD+ from NADH

Alcohol Fermentation

glycolysis followed by the reduction of pyruvate to ethyl alcohol; regenerates NAD+ and releases CO2

1.) CO2 removed from pyruvate to make acetaldehyde

2.) acetaldehyde is reduced to ethyl alcohol by NADH

organisms that use alcohol fermentation: yeast; many bacteria under anaerobic conditions

Lactic Acid Fermentation

glycolysis followed by the reduction of pyruvate to lactate; regenerates NAD+ with no release of CO2

How Humans Use Fermentation

use yeast’s ability to ferment sugar to

• use the ethanol produced to make alcoholic beverages

• use the CO2 it releases to cause bread to rise

use bacteria’s ability to ferment sugar to:

• use lactic acid it produces that thickens the dairy

• lactic acid gives it its tangy flavor