4.3 carbohydrate metabolism

what are the 4 pathways in carbohydrate metabolism

in the cytosol:

1. glycolysis

• glucose → pyruvate → ATP at substrate level phosphorylation+ electrons carried via NADH to 4.

in the mitochondria

2. pyruvate oxidation

• pyruvate → acetyl CoA

3. then citric acid cycle (Kreb’s)

• produces electrons carried via NADH and FADH2 to 4) + ATP at the substrate level phosphorylation

4. oxidative phosphorylation:

• electron transport chain and chemiosmosis

• electrons from 1. and 3. are transported here

• ATP at the oxidative phosphorylation is produced

where does glycolysis occur (1st pathway: glycolysis)

cytosol

what is the substrate for glycolysis

glucose

what is the product of glycolysis

• 2 molecules of pyruvates

• energy released is transferred to activated carriers ATP and NADH

what is the net yield of the molecules of ATP and NADH from glycolysis

2 ATP, 2 NADH

how does pyruvate transfer into the mitochondrion

glucose → enters cell from cell membrane → undergoes glycolysis → produces pyruvate → enters via mitochondrial pyruvate carrier into mitochondrion

what is pyruvate oxidation (2nd pathway)

• 3 enzyme-catalysed steps → 1 carbon is lost in the form of CO₂

• energy is stored in the form of activated carriers NADH and acetyl-CoA

what is the net yield of ATP and NADH from pyruvate oxidation

0 ATP, 1 NADH

what is the citric acid cycle (3rd pathway)

• when acetyle-CoA → further oxidised → in mitochondrial matrix (TCA / Kreb’s cycle)

• 8 enzyme-catalyzed steps

• 2 remaining carbons → lost in the form of CO₂

• energy released → stores in ATP, NADH, FADH₂

what are the steps in the citric acid cycle

step 1: acetyle CoA → combines with → oxaloacetate to form → citrate

step 2 - 4: decarboxylation

step 5 - 8: regeneration of oxaloacetate

what is the net yield of molecules of ATP, NADH and FADH2 are produced from 1 molecule of acetyl CoA

1 ATP, 3NADH, 1FADH2

what is oxidative phosphorylation (4th pathway)

series of protein complexes in the inner mitochondrial membrane

what are the 2 steps in oxidative phosphorylation

1. electron transport chain (ETC):

• NADH/FADH2 transfers → electrons to protein complexes in ETC

• energy released → drives protons across inner membrane → create a gradient

2. chemiosmosis:

• energy released → from diffusion of H+ → back down an electrochemical + concentration gradient → via → enzyme ATP synthase powers ATP synthesis

what is the net yield of the molecules of ATP are produced from NADH and FADH2 in oxidative phosphorylation

• each NADH = 2.5 ATP

• each FADH2 = 1.5 ATP

glycolysis: 2ATP, 2NADH

pyruvate oxidation: 2NADH

citric acid cycle: 2ATP, 6NADH, 2FADH2

ATP yield from NADH and FADH2 → 10(2.5) + 2(1.5) = 28

what is the maximum yield per glucose molecule

30 - 32 ATP

what is the efficiency of cellular respiration

efficiency = actual / theoretical

efficiency = 34%

what is the structure and the processes within the structure of the mitochondria

• outer membrane → permeable to molecules >5000 daltons

• matrix → pyruvate oxidation, citric acid cycle

• inner membrane → site of electron transfer chain + ATP synthase for chemiosmosis

• intermembrane space → site of H+ accumulation: proton gradient

where does ATP synthesis occur

many sites simultaneously with about 10 million ATP molecules produced per second in each cell

what is the importance of the role of oxygen in cellular respiration

• glycolysis occurs independently of O2

• O2 acts as a final electron acceptor in ETC

• absence of O2 → pyruvate enters alternative pathway: fermentation

  • fermentation:

    • net yield of 2 ATP

    • regenerates NAD+ to be reused in glycolysis