Respiration

Question 1

What are the steps of respiration?

Answer 1

• glycolysis
• Link reaction
• Kreb cycle
• Oxidative phosphorylation

Question 2

Describe glycolysis

Answer 2

• It is the initial stage of respiration in both anaerobic and aerobic respiration
• It occurs in the cytoplasm of all living cells and uses a hexose sugar, glucose which is converted to a 3 carbon pyruvate

Question 3

Draw a diagram of glycolysis

Question 4

What is step one of glycolysis?

Answer 4

1. Phosphorylation of glucose to glucose phosphate
   - Glucose is first made more reactive by the addition of two phosphate molecules which are generated by the hydrolysis of two ATP molecules to ADP
   - This provides energy to activate glucose and reduce the activation energy of enzyme reactions

Question 5

What is step two of glycolysis?

Answer 5

2. Phosphorylated glucose is split into 3 carbon molecules called triose phosphate

Question 6

What is step three of glycolysis?

Answer 6

3. Oxidation of triose phosphate. Hydrogen is removed from each molecule of triose phosphate.
   - these hydrogen molecules are used to reduce NAD to reduced NAD

Question 7

What is step four of glycolysis?

Answer 7

4. Triose phosphate is then converted to a 3 carbon molecule called pyruvate. This produces two molecules of ATP

Question 8

What are the products of glycolysis?

Answer 8

• 2 molecules of ATP
• 2 molecules of pyruvate
• 2 molecules of reduced NAD

Question 9

In aerobic respiration how does the link reaction start?

Answer 9

• pyruvate from glycolysis enters the mitochondrial matrix by active transport

Question 10

What are the steps of the link reaction?

Answer 10

Step 1 = pyruvate is oxidized to acetate which is a 2 carbon molecule. Pyruvate does so by loosing a co2 molecule and 2 hydrogens. These hydrogens are accepted by NAD to form reduced NAD
Step 2 = The 2 carbon acetate then combines with a molecule called coenzyme A which produces a compound called acetyl co- enzyme A

Question 11

Draw the process of the link reaction

Question 12

Describe the kreb cycle

Answer 12

• This is the third stage of respiration which occurs in the matrix of the mitochondria
• It involves a series of oxidation and reduction reactions

Question 13

Draw the kreb cycle

Question 14

Describe the process of the kreb cycle?

Answer 14

• The 2 carbon acetyl coenzyme A from the link reaction combines with a 4 carbon molecule to produce a 6 carbon molecule
• In a series of reactions, then 6 carbon molecule looses co2 and hydrogen which is used to reduce NAD and a single molecule of ATP
• This produces a 4 carbon molecule which can react with acetylcoenzyme A again

Question 15

Descibe oxidative phosphorylation

Answer 15

• This occurs in the inner folded membrane (cristae) and this process results in the generation of ATP
• in metabollically active cells, there is a high number of mitochondria to increase the surface area of mitochondrial membranes for enzymes in oxidative phosphorylation

Question 16

What is the process of oxidative phosphorylation.

Answer 16

1. hydrogen atoms produced during glycolysis and the kreb cycle combine with coenzymes NAD and FAD
2. The reduced NAD and FAD donates the electrons of the hydrogen atoms that they are carrying to the first molecule of the electron transfer chain
3. The electrons pass along a number of electron transfer molecules in a series of oxidation and reduction reactions. As they pass along the chain, they release energy which causes the active transport of protons in across the inner mitochondrial membrane
4. These protons accumulate in the inner membranal space before they diffuse back into the matrix through atp synthase channels which are embedded in the inner mitochondrial membrane which produces ATP
5. At the end of the chain, the electrons combine with these hydrogen protons and oxygen to form water. Therefore oxygen is the final electron acceptor

Question 17

Why is it important that oxygen is the final electron acceptor

Answer 17

• This ensures that hydrogen atoms do not accumulate and that there is a concentration gradient for respiration to continue

Question 18

What occurs to pyruvate in anaerobic respiration

Answer 18

• in anaerobic respiration, the pyruvate produced in glycolysis is converted to ethanol or lactate using reduced NAD

Question 19

What happens in alcoholic fermentation in plants and yeast?

Answer 19

• pyruvate is converted to ethanal, which uses a molecule of CO2
• ethanal is converted to ethanol. This converts reduced NAD to NAD

Question 20

What happens in lactate fermentation in animals

Answer 20

• pyruvate is converted to lactate
• this converts reduced NAD to NAD

Question 21

Why is the conversion of reduced NAD to NAD important?

Answer 21

• Anaerobic respiration regenerares NAD which means glycolyis can continue and ATP can be produced when there is insufficient oxygen present

Question 22

What alternative respiratory substances are there

Answer 22

• lipids
• proteins

Question 23

How are lipids used for respiration?

Answer 23

1. before being respired, lipids are first hydrolysed to glycerol and fatty acids
2. the glycerol is then phosphorylated to triose phosphate which then enters the glycolyis pathway
3. The fatty acid is broken into to 2C fragments which is converted to acetyl coenzyme A and enters the kreb cycle

Question 24

Why do lipids release more energy than glucose?

Answer 24

• lipids release x2 the energy as carbohydrates as when oxidised they release hydrogen atoms which can be used in oxidative phosphorylation to produce ATP

Question 25

How are proteins used in respiration?

Answer 25

• proteins are first hydrolysed to amino acids.
• They have their amine group removed before entering the respiratory pathway depending on how many carbons they contain
• 3C = pyruvate, enter the link reaction
• 4 & 5 = enter the kreb cycle as intermediates