Topic 14: Respiration

Question 1

Where does glycolysis occur?

Answer 1

cytoplasm

Question 2

What stage of respiration is glycolysis?

Answer 2

first stage of aerobic AND anaerobic respiration

Question 3

What are the four main stages of glycolysis?

Answer 3

1. phosphorylation of glucose - glucose is phosphorylated to** glucose phosphate **by 2x ATP (ATP hydrolysis supplies Pi) - lower activation energy for enzyme activity
2. Splitting of phosphorylated glucose - glucose phospate splits into 2x triose phosphase
3. Oxidation - two hydrogens removed from each triose phosphate and transfered to 2 NAD - forms 2x pyruvate - two molecule of ATP per pyruvate are regenerated from ADP
   **NET GAIN: 2 reduced NAD and 2 ATP **

Question 4

How does pyruvate from glycolysis enter the mitochondria?

Answer 4

active transport

Question 5

What are the two main stages of the link reaction?

Answer 5

1. Oxidation - 3C pyruvate is oxidised to 2C acetate - Pyruvate loses 1x CO2 and 2H - 2H are accepted by NAD to form reduced NAD and one H+
2. Acetate combines with coenzyme A to produce acetlycoenzyme A

Question 6

Summary equation for the link reaction

Answer 6

Pyruvate + NAD + CoA = Acetyl - CoA + reduced NAD + CO2

Question 7

What are the main stages of the Krebs cycle?

Answer 7

1. Acetyl portion of Acetyl-CoA combines with 4C oxalacetate to produce 6C citrate - CoA carrier is released
2. Series of further reactions - Citrate loses CO2 and hydrogen - results in a n**ew 4 carbon molecule and one molecule of ATP **(substrate level phosphorylation)

substrate level phosphorylation - Production of ATP from ADP via the transfer of a phosphate group from a short lived, highly reactive intermediate (different from oxidative as there is no electron transport chain)

Question 8

What is the electron transport chain

Answer 8

a series of carrier proteins embedded in the membrane of the CRISTAE in the mitochondria - produces ATP through oxidative phosphorylation via chemiosmosis (during aerobic respiration)

Question 9

What happens in the electron transport chain?

Answer 9

1. electrons released from REDUCED NAD and FAD are accepted by proton carriers in the ETC
2. electrons pass along the ETC - successive REDOX reactions
3. energy released maintains the proton gradient
4. oxygen acts as a final electron acceptor - protons, electrons and oxygen combine to form water

Question 10

Oxidative phosphorylation - How is a protein concentration gradient established during chemiosmosis?

Answer 10

energy released from ATP is coupled to the active transport of H+ ions from the mitochondrial matrix to the intermembrane space

Question 11

Oxidative phosphorylation - How does chemiosmosis result in ATP formation

Answer 11

H+ ions move DOWN their concentration gradient from the intermbrane space to the matrix via the channel protein ATP synthase
- This catalyses ADP + Pi = ATP

Question 12

Role of oxygen in aerobic respiration

Answer 12

final electron acceptor in the electron transfer chain - produces water as a byproduct

Question 13

Why is the electron tranfer chain preferable to a single reaction?

Answer 13

energy is released gradually and less energy is released as heat

Question 14

How can lipids act as alternative respiratory substrate?

Answer 14

lipids = glycerol + fatty acids
* phosphorylation of glycerol produces triose phosphate for glycolysis
* fatty acids can be converted into acetate which is converted into acetyl-coenzyme A

Question 15

How can amino acids act as an alternative respiratory substrate?

Answer 15

Deamination (amino group is removed)
* 3C carbon compounds are converted to pyruvate
* 4C and 5C carbon compounds to intermediates in the Krebs cycle

Question 16

What happens during anaerobic respiration in animals?

Answer 16

Pyruvate + reduced NAD = lactate and oxidised NAD (for further glycolysis)
- Each pyruvate takes up TWO hydrogen atoms to form lactate and prevent build up of reduced NAD

Question 17

What happens to the lactate produced in anaerobic respiration?

Answer 17

transported to the liver where it is oxidised to pyruvate - further oxidised (link reaction) to release energy or stored as glycogen - This only happens when oxygen is available again

Question 18

What happens during anaerobic respiration in plants and microoganisms?

Answer 18

Pyruvate + reduced NAD = ethanol, carbon dioxide and oxidised NAD

Question 19

Similarities and differences between aerobic and anaerobic respiration

Answer 19

similarities
* both involve glycolysis
* both need NAD
* both produce ATP
Differences
* anaerobic has substrate level phosphorylation only while aerobic has substrate level and oxidative
* aerobic produces MORE ATP (anaerobic can only produce ATP in glycolysis)
* aerobic DOES NOT produce ethanol and lactate

Substrate level (glycolysis and Krebs) - direct transfer of phosphate from a respiratory intermediate to ADP to produce ATP
oxidative (electron transport chain) - indirect linking of energy from phosphate to ADP to produce ATP - involving energy from hydrogen atoms