Cellular Respiration
No description yet. This curated deck is ready for daily study.
Card preview (24)
What is the role of NAD in cell respiration?
NAD acts as a hydrogen carrier. It accepts hydrogen atoms (protons + high-energy electrons) during oxidation reactions, becoming NADH. It transports these electrons to the electron transport chain (ETC) for ATP production via oxidative phosphorylation.
What is oxidative phosphorylation?
The indirect synthesis of ATP using energy released from the oxidation of NADH/FADH2 via the electron transport chain and chemiosmosis. Requires oxygen.
What are the two main energy carriers in cells?
ATP (direct energy carrier) and reduced hydrogen carriers (NADH, FADH2 — transitional carriers that feed the ETC).
How does substrate-level phosphorylation differ from oxidative phosphorylation?
Substrate-level phosphorylation directly transfers a phosphate group from a phosphorylated intermediate to ADP using an enzyme; oxidative phosphorylation uses energy from electron transport and chemiosmosis.
Why is the ETC aerobic?
Because oxygen is the terminal electron acceptor; without O₂, electrons cannot be removed and the chain becomes blocked.
Define oxidation and reduction.
Oxidation = loss of electrons/hydrogen OR gain of oxygen. Reduction = gain of electrons/hydrogen OR loss of oxygen.
State two mnemonic devices for redox.
OIL RIG; LEO goes GER; ELMO (Electron Loss Means Oxidation).
What happens to NAD during oxidation reactions in respiration?
NAD is reduced to NADH (gains hydrogen/electrons).
Where does glycolysis occur?
Cytosol.
What is glycolysis?
The stepwise breakdown of glucose (6C) into two molecules of pyruvate (3C) with a net gain of 2 ATP and 2 NADH.
What are the four key steps of glycolysis?
Phosphorylation: 2 ATP used to form hexose bisphosphate. Lysis: 6C sugar splits into two 3C triose phosphates. Oxidation: Hydrogen removed → NADH ×2. ATP formation: 4 ATP produced (net +2).
Why is glucose phosphorylated at the start of glycolysis?
Makes it more reactive, raises energy level, prevents diffusion out of the cell.
Why is fermentation needed when there is no oxygen?
Without oxygen, NADH cannot be oxidised by the ETC, causing NAD depletion. Fermentation regenerates NAD so glycolysis can continue producing ATP.
What is the fermentation product in animals?
Lactate (lactic acid). The reaction is reversible.
Why can fermentation only sustain ATP production for a short time?
Only glycolysis produces ATP anaerobically, and the yield is very low (2 ATP/glucose).
What are fermentation products in plants/yeast?
Ethanol + CO₂. The reaction is irreversible.
Where does the link reaction occur?
Mitochondrial matrix (pyruvate is transported in first).
What happens during the link reaction?
Pyruvate is decarboxylated → CO₂. Remaining 2C fragment is oxidised → NADH. 2C acetyl group attaches to coenzyme A → acetyl CoA.
How many times does the link reaction occur per glucose?
Twice (once per pyruvate).
Products per glucose (link reaction)?
2 × acetyl CoA, 2 × NADH, 2 × CO₂.
Where does the Krebs cycle occur?
Mitochondrial matrix.
What enters the Krebs cycle, and what does it combine with?
Acetyl group (2C) from acetyl CoA combines with oxaloacetate (4C) to form citrate (6C).
What are the key outputs per cycle (per acetyl CoA)?
3 NADH 1 FADH₂ 1 ATP (substrate-level) 2 CO₂
What is produced per glucose?
2 ATP 6 NADH 2 FADH₂ 4 CO₂ (Cycle turns twice.)