Aerobic Respiration

Cellular respiration is a series of

oxidation and reduction reactions

Dehydrogenation

lost electrons are accompanied by protons / loss of a H atom

Redox reactions

electrons carrying energy from a molecule to another

Nicotinamide adenosine dinucleotide (NAD+)

a cofactor that carries electrons and protons, accepts 2 electrons and 1 proton to become NADH

Electron acceptors in aerobic respiration

oxygen

Electron acceptors in anaerobic respiration

an inorganic molecule that’s not oxygen

Electron acceptors in fermentation

an organic molecule

Equation for aerobic respiration

C6H12O6 + 6 (O2) = 6 (CO2) + 6 (H2O)

Free energy for glucose

-686 kcal / mol glucose

Soluble electron carriers

move electrons from one molecule to another

Membrane-bound electron carriers

form redox chain

Electrons in the C-H bonds of glucose are stripped off in stages in a series of enzyme catalyzed reactions with

glycolysis and krebs cycle (citric acid cycle)

Electrons released by oxidation reactions use

electron transport chain

Delta G for reaction of ATP to ADP

-7.3 kcal / mol (free energy of hydrolyzing terminal phosphate)

ATP synthesis is

endergonic

Substrate-level phosphorylation

happens during glycolysis / transfer phosphate group directly to ADP

Oxidative phosphorylation

ATP synthase uses energy from proton gradient

Oxidation of glucose occurs in stages

glycolysis, pyruvate oxidation, krebs cycle, electron transport chain, chemiosmosis (synthesis of ATP)

Steps of glycolysis (anaerobic)

converts 1 glucose (6 C) to 2 pyruvate (3 C) that requires an input of 2 ATP and uses a 10-step biochemical pathway, and 2 NADH are produced by the reduction of NAD+

Fate of pyruvate in aerobic respiration

pyruvate is oxidized to acetyl-CoA and enters krebs cycle

Fate of pyruvate in fermentation

pyruvate is reduced in order to oxidize NADH back to NAD+

Oxidation of pyruvate eq

2 (3 C) pyruvate = 2 (CO2) + 2 (2 C) acetyl-CoA

Multienzyme complex for oxidation of pyruvate

pyruvate dehydrogenase

Acetyl-CoA

acetyl coenzyme A

Krebs cycle location

mitochondrial matrix

What is krebs cycle

it’s a series of 9 reactions (citric acid cycle; TCA cycle) that completes the oxidation of glucose with a series of oxidation, decarboxylation, and rearrangement reactions beginning and ending with oxaloacetate (4 C)

Oxidation of acetyl-CoA (in krebs cycle) forms

CO2 molecules

2 (2 C) acetyl-CoA = 4 (CO2)

gives 2 ATP by substrate-level phosphorylation (1 per turn), 6 NADH (3 per turn), and 2 FADH2 (1 per turn)

In aerobic respiration, why is oxygen so important?

It is the final electron acceptor

Oxidation of pyruvate location

mitochondrial matrix

Phase 1 (accepting phase) of krebs cycle

oxaloacetate (4 C) + acetyl-CoA (2 C) = citric acid / citrate (6 C)

Phase 2 (oxidation) of krebs cycle

citric acid / citrate (6 C) → (5 C) + CO2 + NADH → (4 C) + CO2 + NADH

Phase 3 (rearrangement of 4 C compound at end of phase 2) of krebs cycle

the 4 C molecule at the end of phase 2 is rearranged back to oxaloacetate and ATP is created

When is FADH used in krebs cycle?

FADH2 is used to carry electrons when a 4 C molecule is being rearranged to oxaloacetate and energy is released

Output for krebs cycle per 1 glucose molecule

2 ATP, 6 NADH, 2 FADH2, and 4 CO2 that are released

10 NADH + 2 FADH2 (output from glycolysis and krebs cycle)

proceed to electron transport chain

Location of e- transport chain (aerobic)

inner mitochondrial membrane

Function of e- transport chain

e- transferr to a membrane carrier protein (NAHD dehydrogenase) and passed along a series of membrane proteins

Energy released from electron transfer of e- transport chain

is released as heat and some energy is used to pump H ions (protons) from the matrix to the intermembrane space

Outcome of e- transport chain

oxygen is the final electron acceptor and combines with H ions to produce water

CoA

coenzyme A brings acetyl to krebs cycle

Hydrogen ions that are being moved are being pumped to

the matrix from inner membrane

Chemiosmosis

diffusion of a chemical

Chemiosmosis in aerobic respiration

diffusion of H ions / uses energy from the many H ions trying to move back into the matrix to make ATP (ATP synthase pump)

NADH and FADH2 enter e- transport chain at different points

NADH enters right at the beginning, FADH2 enters at coenzyme Q

ATP produced from NADH and FADH2

NADH produces ATP per carrier, FAHD2 produces 2 ATP per carrier

ATP is transported out of the mitochondria using

facilitated diffusion

ATP synthase pump

allows ATP synthase to occur by using a rotary motor driven by the proton gradient

Total ATP produced from respiration

38 ATP (36 in eukaryotes)

Feedback inhibition in glycolysis

phosphofructokinase is allosterically inhibited by ATP or citrate

Feedback inhibition in pyruvate oxidation / krebs cycle

pyruvate dehydrogenase inhibited by high levels of NADH, and citrate synthetase inhibited by high levels of ATP

Respiration of 6-C fatty acid

yields 20% more energy than glucose by using beta oxidation (takes a fatty acid and converts it to many 2-C molecules)

Catabolism of prorteins

removes amino groups (deamination)

Deamination

removal of a nitrogen-containing side group (amino group) from each amino acid

Amino acid after deamination

converted to a molecule that enters glycolysis or krebs cycle

Alanine

converted to pyruvate

Aspartate

converted to oxaloacetate

Final e- acceptors in anaerobic respiration

sulfur, nitrate, carbon dioxide, metals

Fermentation in yeast

alcoholic fermentation

Fermentation in animals

lactic acid fermentation

Alcoholic fermentation

pyruvate is reduced to NAD+ / CO2, ethanol (alcohol), and NAD+ are produced

Lactic acid fermentation

electrons are transferred from NADH to pyruvate to produce lactic acid