Respiration

Question 1

What happens in glycolysis?

Answer 1

> Phosphorylating glucose to glucose phosphate using ATP ⇒ (2 molecules) - glucose phosphate is a highly reactive molecule.
Splits from c6 ⇒ c3 - The production of triose phosphate
Oxidation of triose Phosphate to produce pyruvate by the reduction of NAD+ to NADH on both molecules with a net gain of ATP and reduced NAD.
The products of glycolysis: 2 x pyruvate, net gain of 2 ATP, 2 x NADH

Question 2

What happens in glycolysis?

Answer 2

> Pyruvate transported into the mitochondria matrix
oxidised to acetate ⇒ carbon dioxide is formed
Acetate combines with coenzyme A to produce acetylocoenzyme

Question 3

What happens in the krebs cycle?

Answer 3

• Acetyl-CoA reacts with a 4-carbon molecule, releasing co-enzyme A and producing a 6-carbon molecule
• the 6-carbon citrate is decarboxylated - and loses CO2- to give a 5-carbon molecule
• Both the citrate and the 5-carbon formed from it are dehydrogenated (lose hydrogen) in the cycle to reduce the coenzymes NAD and FAD
• Overall, 3 reduced NAD and 1 reduced FAD are produced. These coenzymes carry the hydrogen to the electron transport chain.
• The 5-carbon compound is decarboxylated bringing you back to the 4-carbon molecule, and ATP and Co2 are released.
• Products PER glucose molecule: - 6 x reduced NAD, 2x reduced FAD, 2 x ATP, 4 x C02, 2 x CoA reused
  CoA is reused for the next reaction, and 4 carbon molecule is regenerated so it can be reused in the next Krebs cycle

Question 4

What happens in Oxidative phosphorylation?

Answer 4

• When the electrons are released from reduced NAD or FAD they pass along the carriers of the ETC
• each carrier is at the slightly lower energy level and energy from the electrons is released at each stage
• this energy is used to move protons into the intermembrane space is the mitochondrion
• As the protons move back through the membrane their energy is used to combine ADP with phosphate to produce ATP - ATP synthase catalyses this reaction
• Oxygen - can pick up the electrons and protons - to produce water and is the final electron accepter - if it didn’t accept then a gradient wouldn’t be formed

Question 5

Where does Krebs cycle take place?

Answer 5

Mitochondrial matrix

Question 6

How does aerobic respiration work without oxygen?

Answer 6

• Coenzymes in the cell that have been reduced (NADH and FADH₂) must be oxidised again, but this cannot happen if the electron transport chain stops.
• Glycolysis does not require oxygen, so can keep going as long as there is a supply of NAD. So NAD is regenerated by converting pyruvate (the end-product of glycolysis) to lactate.
• The enzyme (lactate dehydrogenase) that catalyses this reaction, can also catalyse the reverse reaction, so when oxygen becomes available again, lactate can be converted back to pyruvate.