aerobic respiration

what are the 4 stages of aerobic respiration?

1. glycolysis

2. link reaction

3. kreb’s cycle (citric acid cycle)

4. oxidative phosphorylation (E.T.C)

symbol equation for aerobic respiration

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 32ATP

what is respiration?

the process by which organisms release ATP

properties of ATP that make it a suitable energy source

- releases energy in small, manageable amounts
- single bond is broken to make energy available immediately
- can phosphorylate substances to make them more reactive
- can be regenerated

why do we need to synthesis so much ATP everyday?

- it cannot be stored
- it releases energy in small amounts

where does respiration take place?

in the mitochondria

site of glycolysis

cytoplasm of the cell (enzymes found here)

site of link reaction

matrix of the mitochondria

site of kreb’s cycle

matrix of the mitochondria

site of oxidative phosphorylation

inner mitochondrial membrane (membrane that forms the cristae)

is glycolysis an aerobic or anaerobic process?

anaerobic

glycolysis is a universal feature of every living organism. what does this mean?

it provides indirect evidence for evolution

net production of glycolysis

• 2x pyruvate

• 2x NADH

• 2x ATP

next destination of pyruvate after glycolysis

actively transported to matrix

next destination of NADH after glycolysis

electron transport chain

next destination of ATP after glycolysis

used for energy

why does glycolysis occur in the cytoplasm?

the glucose is too big

how many times does the link reaction occur for every glucose?

twice

the link reaction

pyruvate actively transported to matrix
- 1 carbon is lost in the form of CO2
- pyruvate donates H+ to NAD (pyruvate is oxidised)
- acetate formed
- coenzyme A binds to acetate to form Acetyl coenzyme A

net production of link reaction per pyruvate

• 1x CO2

• 1x NADH

• 1x Acetyl coenzyme A

net production of link reaction per glucose

• 2x CO2

• 2x NADH

• 2x Acetyl coenzyme A

next destination of CO2 after link reaction

released as a waste product

next destination of NADH after link reaction

electron transport chain

next destination of Acetyl coenzyme A after link reaction

Kreb’s cycle

how many times does the Kreb’s / citric acid cycle occur per pyruvate / acetyl CoA

once

how many times does the Kreb’s / citric acid cycle occur per glucose?

twice

Kreb’s / citric acid cycle

- Acetyl CoA → acetate + CoA (returns to link reaction)
- acetate + oxaloacetate (4C) → citric acid (6C)
- 2x CO2 removed
- 1x ATP produced
- 3x NAD reduced to form NADH
- 1x FAD reduced to form FADH2
- oxaloacetate regenerated

net production of Kreb’s / citric acid cycle

- 2x CO2
- 3x NADH
- 1x FADH2
- 1x ATP
- 1x oxaloacetate
- 1x CoA

next destination of CO2 after Kreb’s cycle

released as a waste product

next destination of NADH after Kreb’s cycle

electron transport chain

next destination of FADH2 after Kreb’s cycle

electron transport chain

next destination of ATP after Kreb’s cycle

used for energy

next destination of oxaloacetate after Kreb’s cycle

regenerated for next Kreb’s cycle

next destination of CoA after Kreb’s cycle

returns to the link reaction to pick up another acetate

about oxidative phosphorylation (ETC - electron transport chain)

- ETC performs oxidative phosphorylation to form large amounts of ATP
- ATP formed using energy from electrons
- substrate level phosphorylation = ATP formed by Pi added to ADP
- ETC is present in multiple copies in the inner mitochondrial membrane
- composed of protein complexes (I to IV), mobile electron carriers (coenzyme Q/ubiquinone and cytochrome C)

what does oxidative phosphorylation require?

- oxygen
- NADH and FADH
- electrons and their carriers (proteins in the inner mitochondrial membrane)

the steps of oxidative phosphorylation

1. H atoms are released from NADH and FADH. the coenzymes are oxidised to NAD and FAD 2. H atoms split into H+ and e- 3. electrons are accepted and released by protein carriers, releasing energy in a series of redox reactions 4. energy is used to pump H+ across the inner mitochondrial membrane, from the matrix into the intermembrane space 5. this forms an electrochemical gradient (conc gradient of ions) 6. H+ travel from the intermembrane space (high conc) to the matrix (low conc) via ATP synthase (facilitated diffusion). ADP + Pi → ATP (phosphorylation) 7. (in the matrix at the end of the ETC), H+ form reduced NAD/FAD, electrons and oxygen combine to form water. oxygen is the terminal electron acceptor.

how many ATP molecules does each NADH molecule produce during oxidative phosphorylation

3

how many ATP molecules does each FADH2 molecule produce during oxidative phosphorylation?

2

why is the total amount of ATP produced by NADH and FADH2 during oxidative phosphorylation not always the net amount of ATP made per respiration reaction?

- H+ can leak from the intermembrane space back into the matrix
- ATP produced may actively transport pyruvate into mitochondria
- NADH is made during glycolysis in the cytoplasm, ATP is used to move this into the mitochondria

cyanide

- acts as a competitive inhibitor to the enzyme cytochrome c oxidase
- this prevents the ETC (the last part of cellular respiration) from working, meaning that the cell can no longer produce ATP for energy

mitochondrial diseases

- smaller surface area of cristae
- so less oxidative phosphorylation
- so not enough ATP produced

substrate-level phosphorylation

formation of ATP by addition of Pi to ADP

describe the process of glycolysis

1. phosphorylation of glucose using ATP
2. oxidation of triose phosphate to pyruvate
3. net gain of ATP is 2 because 4 ATP produced and 2 used
4. NAD reduced

Malonate inhibits a reaction in the Krebs cycle. Explain why malonate would decrease the uptake of oxygen in a respiring cell.

1. oxidises reduced NAD to produce NAD
2. so glycolysis continues