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Biology ยท Unit 2

Bioenergetics: MDCAT Notes and MCQs

Glucose โ€” the reference fuel

  • Glycolysis (cytoplasm): glucose โ†’ 2 pyruvate, net 2 ATP + 2 NADH. Anaerobic; occurs in all cells.
  • Link reaction (mitochondrial matrix): pyruvate โ†’ acetyl CoA + CO2 + NADH.
  • Krebs cycle (matrix): per acetyl CoA โ†’ 2 CO2, 3 NADH, 1 FADH2, 1 ATP (GTP). Starts with oxaloacetate (4C) + acetyl CoA (2C) โ†’ citrate (6C).
  • Electron transport chain (inner membrane / cristae): NADH โ‰ˆ 3 ATP, FADH2 โ‰ˆ 2 ATP; final electron acceptor is O2 โ†’ water. Total โ‰ˆ 36โ€“38 ATP per glucose.

Respiration of fats

  • Lipase splits triglycerides โ†’ glycerol + fatty acids.
  • Glycerol โ†’ converted to PGAL (glyceraldehyde-3-phosphate) โ†’ enters glycolysis.
  • Fatty acids โ†’ ฮฒ-oxidation in mitochondria โ†’ many 2-carbon acetyl CoA units โ†’ Krebs cycle.
  • Fats are the richest energy source: โ‰ˆ 9 kcal/g (โ‰ˆ 38 kJ/g) vs โ‰ˆ 4 kcal/g for carbohydrates and proteins, because they are more reduced (more H, less O).

Respiration of proteins

  • Proteins โ†’ amino acids. Used for energy mainly during starvation.
  • Deamination (liver) removes โ€“NH2 as ammonia โ†’ converted to urea.
  • Remaining carbon skeletons enter as pyruvate, acetyl CoA or Krebs cycle intermediates (e.g. ฮฑ-ketoglutarate, oxaloacetate).
Respiratory quotient (RQ = CO2 released / O2 used): carbohydrate = 1.0 ยท protein โ‰ˆ 0.8โ€“0.9 ยท fat โ‰ˆ 0.7
PMDC learning outcomes for this unit
  • Respiration: 2.1 Outline the cellular respiration of proteins and fats and correlate these with that of glucose.

Bioenergetics MCQs with answers

Practise and track your score โ†’
Q1
During respiration of fats, glycerol enters the respiratory pathway as:
APyruvate
BOxaloacetate
CAcetyl CoA
DPGAL (glyceraldehyde-3-phosphate)
Show answer
Answer: D (PGAL (glyceraldehyde-3-phosphate)). Glycerol is phosphorylated and converted to PGAL, which joins glycolysis.
Q2
Fatty acids are broken into 2-carbon acetyl CoA units by:
ADeamination
Bฮฒ-oxidation
CGlycolysis
DDecarboxylation
Show answer
Answer: B (ฮฒ-oxidation). ฮฒ-oxidation in the mitochondrial matrix cleaves fatty acids two carbons at a time.
Q3
Removal of the amino group from amino acids is called:
ATransamination
BDeamination
CDecarboxylation
DHydrolysis
Show answer
Answer: B (Deamination). Deamination (mainly in the liver) removes โ€“NH2; the ammonia is converted to urea.
Q4
Which food yields the MOST energy per gram when respired?
AGlucose
BStarch
CFat
DProtein
Show answer
Answer: C (Fat). Fats yield โ‰ˆ 9 kcal/g, more than double carbohydrates or proteins (โ‰ˆ 4 kcal/g).
Q5
The respiratory quotient (RQ) of fat is approximately:
A1.3
B0.9
C1.0
D0.7
Show answer
Answer: D (0.7). Fats are highly reduced and need more O2 than the CO2 they release, so RQ โ‰ˆ 0.7.
Q6
Net ATP gain from glycolysis of one glucose molecule is:
A38
B36
C4
D2
Show answer
Answer: D (2). Glycolysis makes 4 ATP but uses 2, giving a net gain of 2 ATP (+2 NADH).
Q7
The final electron acceptor in the electron transport chain is:
ACytochrome c
BOxygen
CNAD+
DFAD
Show answer
Answer: B (Oxygen). Oxygen accepts electrons and protons to form water at the end of the chain.
โ† Acellular LifeBiological Molecules โ†’