8.2 Cell Respiration Detail (HL)

Question 1

What is oxidation?

Answer 1

• loss of electrons
• gain of oxygen
• loss of hydrogen (H carriers)

Question 2

What is reduction?

Answer 2

• gain of electrons
• loss of oxygen
• gain of hydrogen (H carriers give up H)

Question 3

Step 1 - Glycolysis

Answer 3

cytoplasm

• phosphorylation: a hexose sugar is phosphorylated by 2ATP to become hexose biphosphate (this process makes molecules less stable)
• lysis: hexose biphosphate splits into two triose phosphates (3C)
• oxidation: H is removes from triose phosphates and NAD is converted to NADH + H+
• ATP formation: 4ATP molecules are released as the triose phosphates are converted to pyruvate

summary: one molecule of glucose results in 2 pyruvate, 2 (NADH + H+) and 2 ATP

Question 4

Step 2: formation of acetyl co-enzyme A (link reaction)

Answer 4

matrix

• pyruvate (3C) enters matric where is loses a C as CO2 (it is decarboxylated and oxidised) and becomes 2C acetyl group
• this cannot exist by itself so is held by carrier co-enzyme A to become acetyl co-enzyme A

Question 5

Step 3: Krebs Cycle (citric acid cycle)

Answer 5

matrix

• series of oxidation reactions, acetyl group joins with oxaloacetate (4C) to form citrate (6C), this citrate is converted back to oxaloacetate in other reactions
• CO2 is released during this reaction (decarboxylation)
• many hydrogens are produced by oxidation reactions
• 2 ATP molecules are produced (phosphorylation)
• NAD carriers go onto ETC

Question 6

Step 4: Electron Transport Chain (respiratory chain)

Answer 6

cristae
- as electrons pass along the electron transport chain the energy generated pumps hydrogen across the membrane into intermembrane space
- hydrogen returns down the concentration gradient, ATP is produced as protons diffuse through ATP synthase
- this process is called chemiosmosis
- 34ATP produced
- at the end of the ETC, O2 accepts both the electrons and the hydrogens form water
(if O2 not available NADH cannot be converted to NAD and so link reaction and Krebs cycle stops)

Question 7

What is oxidative phosphorylation?

Answer 7

• describes the production of ATP from oxidised hydrogen carriers
• when electrons are donated to the ETC, they lose energy as they are passed between successive carrier molecules
• this energy is used to translocate H+ ions from the matrix to the intermembrane space against the concentration gradient
• the buildup of H+ ions creates an electrochemical gradient (proton motive force)
• the protons return to the matrix via ATP synthase (transmembrane enzyme)
• as they return they release energy used to produce ATP
• process called chemiosmosis and occurs in cristae
• the H+ ions and electrons are combined with oxygen to form water allowing process to be repeated
  overall 38 molecules of ATP are produced from aerobic respiration