CB16 Cellular Energy

Question 1

How is glucose broken down in animal cells to produce energy

Answer 1

Living cells use a series of tightly controlled reactions to stepwise oxidise glucose, paying out small amounts of energy to activated carrier molecules by means of coupled reactions

Why? So as much energy as possible is stored in high energy bonds (efficient)

Question 2

List the commonly used activated carrier molecules used by cells to temporarily store energy

Answer 2

• ATP - phosphate
• NADH, NADPH, FADH2 - electrons & hydrogens
• Acetyl CoA - acetyl group
  Carboxylated biotin - carboxyl group
  S-adenosylmethionine - methyl group
  Uridine diphosphate glucose - glucose

Question 3

Describe glycolysis

Answer 3

• Energy is invested (x2 ATP)
• energy allows glucose to be split into x2 three-carbon pyruvate
• this produces 4 ATP
• electron removed from carbon atoms by NAD+ → NADH (pumped into mitochondria where it donates é to electron transport chain)
• net gain: 2 ATP

Question 4

Describe the citric acid cycle

Answer 4

• First pyruvate is actively pumped from cytosol into mitochondrial matrix, where pyruvate dehydrogenase converts each pyruvate to acetyl CoA, CO2, NADH
• actetyl CoA combines with 4-carbon oxaloacetate → 6-carbon citric acid
• each turn of the citric acid cycle produces x3 NADH, x1 FADH2, x1 GTP

Net yield: x6 NADH, x2 FADH2 1 x2 GTP
(CO2 waste product)

Question 5

Describe the electron transport chain

Answer 5

• NADH & FADH2 transfer electrons to proteins in membrane
• provides energy for H+ ions to be pumped across inner membrane
• flow of H+ ions back across membrane synthesises ATP by ATP synthase
• O2 diffuses into mitochondria, combines with H+ ions to form H2O

Total ATP = ~ 30

Question 6

Describe where in the cell each of these sets of reactions occur

Answer 6

Glycolysis - cytosol

Citric acid cycle - matrix of the mitochondria

Electron transport chain - inner membrane of the mitochondria

Question 7

Explain the structure & function of mitochondria

Answer 7

• Mitochondria are the centre which all energy-yielding processes lead
• lots of membranes increase surface area (final stage of respiration)
• muscle cells require lots of energy = lots of mitochondria