Respiration

Question 1

Why do living organisms need to respire?

Answer 1

To synthesise ATP from ADP and an inorganic phosphate molecule, the ATP can then be hydrolysed to release energy for biological processes

Question 2

Name 3 reasons that organisms need energy

Answer 2

• Endo/exocytosis
• Active transport
• DNA replication and cell division

Question 3

When ATP is broken down what type of reaction is it?

Answer 3

Hydrolysis, water is added and heat is released

Question 4

What type of reaction is it when ATP is synthesised?

Answer 4

ATP is synthesised from ADP and an inorganic phosphate group when a water molecule is removed, it is a condensation reaction

Question 5

How much energy is released when ATP and ADP are hydrolysed?

Answer 5

30.5kJmol-1

Question 6

How much energy is released from the hydrolysis of AMP?

Answer 6

13.8kJmol-1, adenosine is produced (adenine and a pentose sugar)

Question 7

What is the enzyme associated with the synthesis and hydrolysis of ATP?

Answer 7

ATP synthase

Question 8

Describe the process of glycolysis

Answer 8

• Glucose (6C) is converted into hexose monophosphate (6C), hydrolysis of a molecule of ATP takes place to provide the phosphate group
• Hexose monophosphate (6C) is converted into hexose bisphosphate, another molecule of ATP is hydrolysed to provide another phosphate group
• The hydrolysis of the 2 ATP molecules and the addition of the phosphate molecules to the glucose molecule is referred to as substrate level phosphorylation
• The hexose bisphosphate molecule is split into 2 molecules of triose phosphate
• Dehydrogenase enzymes remove hydrogens from the triose phosphate molecules and 2 molecules of NAD accept the hydrogens as protons and electrons to form 2 molecules of NADH
• For every 2 molecules of triose phosphate that are oxidised, 4 molecules of ATP are produced

Question 9

What are the products of glycolysis?

Answer 9

• 2 molecules of pyruvate
• 2 molecules of NADH
• 2 molecules of ATP, 4 are made from the oxidation of triose phosphate molecules but 2 are used for to provide the phosphates for the phosphorylation of glucose

Question 10

Where does glycolysis take place?

Answer 10

In the cytoplasm

Question 11

What happens to the 2 molecules of pyruvate produced in glycolysis?

Answer 11

• Under aerobic conditions they’re transported to the mitochondria for the link reaction
• Under anaerobic conditions, they’re converted (in the cytoplasm) to lactate (in mammals) and ethanol (in fungi, such as yeast, and plants), this reoxidises NADH molecules meaning that glycolysis can continue

Question 12

What is the average length and diameter of the mitochondria?

Answer 12

The average length is around 2-5um but can be up to 10um and the average diameter is around 0.5-1um

Question 13

What does the inner membrane fold into?

Answer 13

Cristae

Question 14

What does the mitochondrial matrix contain?

Answer 14

• Mitochondrial ribosomes
• Looped mitochondrial DNA
• Enzymes and Coenzymes (NAD and FAD) for the link reaction and Krebs cycle
• Oxoloacetate

Question 15

What is ATP synthase?

Answer 15

An enzyme that synthesises ATP from ADP and an inorganic phosphate molecule, it has channel proteins associated with it that protons pass through to provide energy for the synthesis of ATP

Question 16

How is pyruvate transported to the the matrix?

Answer 16

Pyruvate is transported across the outer and inner mitochondrial matrix via pyruvate-H+ symport (a carrier protein that transport two ions or molecules in the same direction)

Question 17

Where does the link reaction occur?

Answer 17

In the matrix

Question 18

Describe the process of the link reaction

Answer 18

• Carboxyl group is removed from pyruvate and this is the origin of some of the carbon dioxide produced in respiration
• Decarboxylation along with dehydrogenation of pyruvate produces an acetyl group
• Acetyl group combines with CoA to produce acetyl CoA
• NAD becomes reduced to form NADH as it accepts the hydrogen when pyruvate is dehydrogenated

Question 19

Summarise the link reaction into an equation

Answer 19

One molecule of glucose: 2Pyruvate + 2NAD + 2COA → 2AcetylCoA + 2NADH + 2CO2

Question 20

Where does the Krebs cycle take place?

Answer 20

In the matrix

Question 21

Describe the process of the Krebs cycle

Answer 21

• Acetyl group is released from the Acetyl CoA and combines with oxolacetate (4C) to form citrate (6C)
• Citrate is decarboxylated and dehydrogenated to produce a 5C compound, one molecule of CO2, and one molecule of NADH
• 5C is further decarboxylated and dehydrogenated to produce 4C, one molecule of CO2 and one molecule of NADH
• 4C combines and is then released from CoA, substrate level phosphorylation takes place and one molecule of ATP is produced
• 4C is dehydrogenated producing a molecule of reduced FAD and a different 4C
• Rearrangement of atoms in the new 4C compound (catalysed by an isomerase enzyme) followed by further dehydrogenation regenerates a molecule of oxolacetate that can then combine with an acetyl group to restart the Krebs cycle

Question 22

For each molecule of glucose how many turns of the Krebs cycle are there?

Answer 22

2, as each molecule produces 2 molecules of pyruvate are produced for each molecule of glucose

Question 23

How many molecules of ATP are produced for each molecule of glucose in the link reaction and Krebs cycle combined?

Answer 23

2

Question 24

How many molecules of NADH are produced for each molecule of glucose in the link reaction and Krebs cycle combined?

Answer 24

8

Question 25

How many molecules of FADH2 are produced for each molecule of glucose in the link reaction and Krebs cycle combined?

Answer 25

2

Question 26

How many molecules of CO2 are produced for each molecule of glucose in the link reaction and Krebs cycle combined?

Answer 26

6

Question 27

How can other substrates besides glucose be respired aerobically?

Answer 27

- Fatty acids can be broken down into many molecules of acetate that enter the Krebs cycle via acetyl CoA - Glycerol can be converted to pyruvate that can enter the Krebs cycle via the the link reaction - Amino acids may be deaminated and the keto acid produced can enter the Krebs cycle

Question 28

Why can't the link reaction and Krebs cycle take place in the absence of oxygen?

Answer 28

If oxygen isn't present during oxidative phosphorylation then the protons and electrons released from NADH and FADH2 cant't combine with the oxygen meaning that the electron transport chain becomes backed up so the coenzymes can't release their hydrogens anymore meaning they can't become reoxidised for the link reaction or Krebs cycle. Glycolysis can still take place as in absence of oxygen pyruvate enters lactate or ethanol fermentation pathway which reoxidises NADH that can be used in glycolysis.