respiration

4 stages aerobic respration and where do they occur

glycolysis → cytoplasm

link reaction → mitochondrial matrix

Krebs cycle → mitochondrial matrix

oxidative phosphorylation → mitochondrial inner membrane cristae

what stage happens in both aerobic and anaerobic respiration

glycolysis → bc doesn’t require oxygen

glycolysis steps

glucose phosphorylated to glucose phosphate → using 2 inorganic phosphates from 2 ATPs

glucose phosphate hydrolysed to 2 molecules triose phosphate

triose phosphate molecules oxidised to 2 pyruvate molecules → done by 2 ADP molecules → 2 ATP (2 for each triode phosphate so overall 4) and NAD → reduced NAD (NADH)

products of glycolysis

2 molecules pyruvate

2 reduced NAD (NADH)

net gain of 2 ATP

what happens after glycolysis

pyruvate actively transported from cytoplasm to mitochondrial matrix for link reaction

link reaction

pyruvate (3 C) oxidised to acetate (2 C)

NAD picks up H → produce reduced NAD (NADPH)

CO2 produced

acetate combines w coenzyme A → produce acetylcoenzyme A (enters Krebs cycle)

for every glucose molecule, there r 2 pyruvates created → link reaction occurs twice for every glucose molecule

what are the products of link reaction per glucose molecule

2x acetyle coeznyme A

2x CO2

2x reduced NAD

Krebs cycle

acetyl coenzyme A (2 C) reacts w 4 carbon molecule

→ releases coenzyme A

→ produces 6 carbon molecule that enters Krebs cycle

in a series of oxidation-reduction reactions (redox reactions) → 4C molecule regenerated

and :

• 2x CO2 lost

• ATP produced by substrate level phosphorylation

• 3 reduced coenzyme NAD (NADH)

• 1 reduced coenzyme FAD (FADH)

the products per Krebs cycle

• 2x CO2

• 1 ATP

• 3 reduced NAD coenzyme

• 1 reduced FAD coenzyme

the products of Krebs cycle per glucose ( 2 acetyl coenzyme A)

• 4x CO2

• 2x ATP

• 6x reduced NAD coenzyme

• 2x reduced FAD coenzyme

oxidative phosphorylation

reduced coenzymes NAD and FAD release H atoms (oxidised) → splits into protons (H+) and electrons (e-)

electrons transferred down electron transfer chain → releases energy

energy released by electrons used actively transport protons from mitochondria matrix to intermembrane space

creates electrochemical gradient → protons move by facillitated diffusion down electrohemical gradient (from intermembrane space to mitochondrial matrix) via ATP synthase (embedded into membrane)

ATP synthase phosphorylate ADP to ATP (produce ATP from ADP + Pi)

at the end of the electron transport chain, electrons are picked up by oxygen (oxygen is final electron acceptor) -> electrons cant pass along otherwise

oxygen also picks up protons

so oxygen, electrons and protons combine to form water

2H + 2e- + ½ O2 → H2O

what happens after glycolysis if respiration anaerobic (absence of oxygen)

pyruvate remains cytoplasm

pyruvate produced in glycolysis is reduced (gains hydrogen from reduced NAD)

→ form ethanol (+CO2) in plants and microbes

→ or form lactate in animals and some bacteria

oxidising reduced NAD (NADH) → NAD regenerated (2x)

so NAD can be reused in glycolysis (glycolysis can continue) → allowing production of ATP to be continued

lactic acid = acidic = can denture enzymes and other proteins → cant respire anaerobically bc build up of lactic acid will eventually denature enzymes involved in glycolysis

suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration

in anaerobic respiration → only glycolysis involved which produces little ATP (2 molecules)

→ there’s no oxidative phosphorylation (unlike aerobic respiration) → which forms majority of ATP (around 34 molecules)

Respiration produces more ATP per molecule of glucose in the presence of oxygen than it does when oxygen is absent. Explain why.

(2)

Oxygen is the final electron acceptor in the electron transport chain,

allowing oxidative phosphorylation to continue + produce large amounts of ATP.

In the absence of oxygen, the electron transport chain stops, so only glycolysis occurs and much less ATP is produced.

(Oxygen is final / terminal (electron) acceptor / oxygen combines with electrons and protons;

Oxidative phosphorylation / electron transport chain provides (most) ATP / only glycolysis occurs without oxygen / no Krebs / no link reaction)

no oxygen → no NAD regeneration → link + Krebs stop

what other respiratory substrates are there

breakdown of lipids and amino acids → enter Krebs cycle

fatty acids from hydrolysis of lipids → converted to acetyl coenzyme A

amino acids from hydrolysis of proteins → converted to intermediates in Krebs cycle

importance of Krebs cycle

Krebs cycle produces reduced NAD and reduced FAD

which pass electrons to electron transfer chain → allowing oxidative phosphorylation

process that occurs in anaerobic respiration but does not occur in aerobic respiration.

Reduction of pyruvate to lactate/ ethanol + CO2→ anaerobic respiration

oxidation of pyruvate to acetate→ aerobic respiration

Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration

Regenerates / produces NAD / oxidises reduced NAD;

(NAD used) in glycolysis.

In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this.

(Pyruvate used) in aerobic respiration / (lactate / lactic acid) is toxic / harmful / causes cramp / (muscle) fatigue.

Accept: (pyruvate) can enter link reaction Accept: reduces cramp / (muscle) fatigue

1. Less / no malonyl-CoA

2. (More) fatty acids transported / moved into mitochondria;

3. Respiration / oxidation of fatty acids provides ATP;

1. ‘Inhibition of malonyl-CoA’ on its own is not enough but accept production of malonyl-CoA is inhibited.

2. Accept: ‘transport of fatty acids into mitochondria is not inhibited’.

2. Ignore: method of entry.

3. Accept: for respiration any stage of aerobic respiration e.g. Krebs (cycle), link (reaction) etc.

3. Reject: production of energy, but accept production of energy in the form of ATP.

3. Accept: acetyl CoA can enter Krebs cycle / mitochondria to provide ATP.

Describe the advantage of the Bohr effect during intense exercise.

1. Increases dissociation of oxygen;

   Accept unloading/ release/reduced affinity for dissociation

   2. For aerobic respiration at the tissues/muscles/cells