Respiration

Question 1

Anabolic reactions

Answer 1

‘building up’ large molecules made from small molecules

Question 2

Catabolic reactions

Answer 2

‘breaking down’ hydrolysis of larger molecules to form smaller molecules

Question 3

3 main stages of glycolysis

Answer 3

1. Phosphorylation of glucose to hexose bisphosphate
2. Splitting hexose bisphosphate into two triose phosphate molecules
3. oxidation of triose phosphate to pyruvate

Question 4

Glycolysis - phosporylation

Answer 4

1. ATP is hydrolysed and the phosphoryl group is added to glucose making hexose monophosphate
2. Another molecule of ATP is hydrolysed and phosphoryl group added to make hexose-1,6-bisphosphate

Question 5

Glycolysis - oxidation of triose phosphate

Answer 5

1. Dehydrogenase enzymes and coenzyme NAD remove hydrogens from triose phosphate
2. 2 molecules of NAD become NADH
3. 2 molecules of NADH made for every glucose molecule. 4 molecules of ATP made for every 2 triose phosphates

Question 6

Products of glycolysis

Answer 6

2 ATP
2 NADH
2 pyruvate

Question 7

The matrix of mitochondria contains

Answer 7

• enzymes that catalyse link and Krebs
• NAD and FAD
• oxaloacetate that accepts the acetyl group from the link reaction
• mitochondrial DNA which codes for mitochondrial enzymes and proteins
• mitochondrial ribosomes

Question 8

Transporting pyruvate

Answer 8

Transported across the outer and inner mitochondrial membrane by a pyruvate-H+ symport. A symport is a transport protein that transports 2 ions or molecules in the same direction

Question 9

The equation for the link reaction

Answer 9

2 pyruvate + 2NAD + 2CoA –> 2CO2 + 2NADH + 2 acetyl CoA

Question 10

What happens to pyruvate in the link reaction?

Answer 10

It is decarboxylated and dehydrogenated by a large multi-enzyme complex to an acetyl group is produced. The acetyl group combines with coenzyme A to form acetyl CoA

Question 11

Where does Krebs take place?

Answer 11

In the mitochondrial matrix

Question 12

The stages of Krebs

Answer 12

1. Acetyl group, released from acetyl CoA combines with 4C oxaloacetate to form 6C citrate
2. Citrate is decarboxylated and dehydrogenated producing a 5C compound, CO2 and NADH
3. 5C compound is decarboxylated and dehydrogenated producing a 4C compound, CO2 and NADH
4. 4C compound combines temporarily with and is released from coenzyme A. Substrate level phosphorylation occurs releasing one molecule of ATP
5. 4C compound is dehydrogenated producing a different compound and FADH2
6. Isomerase enzyme rearranges the 4C compound and it is dehydrogenated regenerating oxaloacetate

Question 13

products of the link reaction

Answer 13

2 NADH
2 CO2
2 acetyl CoA

Question 14

Products of the Krebs cycle

Answer 14

6 NADH
2 FADH2
4 CO2
2 ATP

Question 15

How are electrons carried along the electron transport chain?

Answer 15

Each electron carrier protein carries a cofactor - a haem group that contains an iron ion. It becomes reduced (Fe2+) when gaining an electron and oxidised (Fe3+) when donating the electron to the next electron carrier.

Question 16

Steps of oxidative phosphorylation

Answer 16

1. NADH and FADH2 are reoxidised as they deliver their hydrogen atoms to the electron transport chain
2. The hydrogen atoms split into protons and electrons
3. The protons go into solution in the mitochondrial matrix
4. Electrons pass along chain of electron carriers
5. As electrons are passed, some of the energy is used to pump protons across into intermembrane space
6. Proton gradient forms generating a chemiosmotic potential known as a proton motive force which is a source of potential energy
7. Protons diffuse throgh ATP synthase and case a conformational change and ATP is produced
8. Oxygen combines with electrons coming off the electron transport chain and with protons diffusing down ATP synthase and forms water.

Question 17

Chemiosmosis

Answer 17

The flow of protons down their concentration gradient across a membrane, through a channel associated with ATP synthase

Question 18

Why is the theoretical yield of ATP rarely achieved?

Answer 18

• some ATP is used to transport pyruvate into the mitochondria
• some ATP transports NADH, made during glycolysis, into mitochondria
• some protons may leak out through the outer mitochondrial membrane

Question 19

How much NADH and FADH2 is made altogether after Krebs?

Answer 19

10 NADH

2 FADH2

Question 20

What would happen without oxygen?

Answer 20

• oxygen couldn’t act as the final electron acceptor at the end of OP. Water could not form
• Concentration of protons increases in the matrix and reduces proton gradient across inner mitochondrial membrane
• OP ceases
• NADH and FADH2 can’t unload hydrogens and can’t be reoxidised
• Krebs and link stops

Question 21

Which fermentation pathway do mammals use?

Answer 21

Lactate

Question 22

Which fermentation pathway do fungi and plants use?

Answer 22

Ethanol

Question 23

The ethanol fermentation pathway

Answer 23

1. Pyruvate decarboxylated to ethanal, catalysed by pyruvate decarboxylase, and CO2 is released
2. Ethanal accepts hydrogen atoms as NADH –> NAD, catalysed by ethanol dehydrogenase, ethanol is prodced
3. NAD is reoxidised and made available to accept more H from triose phosphate

Question 24

The lactate fermentation pathway

Answer 24

Pyruvate accepts hydrogens from NADH, catalysed by lactate dehydrogenase. Pyruvate is reduced to lactate.
Reoxidised NAD can accept more hydrogens from triose phosphates so glycolysis can continue

Question 25

What happens to the lactate?

Answer 25

It is carried away from the muscles, in the blood, to the liver. It is either converted to pyruvate so it can enter Krebs or it is recycled to glucose and glycogen.