Aerobic Respiration

Question 1

Define aerobic respiration

Answer 1

The release of large quantities of ATP energy from glucose or another organic substrate in the presence of oxygen. Carbon dioxide is produced.

Question 2

Define anaerobic respiration

Answer 2

Takes place in the absence of oxygen and produced lactate in animal cells and carbon dioxide and ethanol in yeast cells, together with a small yield of ATP energy.

Question 3

What are 2 substrates that can be used to release energy in respiration?

Answer 3

Glucose and fatty acids

Question 4

Most of the energy released during respiration is used to synthesise ATP. How is the rest of the energy released?

Answer 4

Heat energy

Question 5

How does respiration release energy?

Answer 5

Respiration oxidises glucose in a series of small reactions to release energy in the form of ATP

Question 6

Why is ATP often called the ‘universal energy currency’?

Answer 6

Because ATP provides energy in all cells in all reactions in all organisms

Question 7

What is the role of ATP in protein synthesis?

Answer 7

ATP required for amino acid activation in the cytoplasm

Question 8

What is the role of ATP in active transport?

Answer 8

ATP changes the shape of transport proteins to move molecules against a concentration gradient

Question 9

What is the role of ATP in bulk transport?

Answer 9

Packaging and transport of secretory products, like enzymes in vesicles

Question 10

What is the role of ATP in nerve transmission?

Answer 10

Sodium/potassium pumps actively transport ions across the axon membrane

Question 11

What is the role of ATP in muscle contraction?

Answer 11

Energy is required for contraction of muscle fibres

Question 12

What is the role of ATP in DNA replication?

Answer 12

Synthesis of DNA from nucleotides during DNA replication at interphase

Question 13

Name 6 different processes ATP is required for

Answer 13

• Protein synthesis
• Active transport
• Bulk transport
• Nerve transmission
• Muscle contraction
• DNA replication

Question 14

Describe the formation of ATP

Answer 14

The enzyme ATP synthase combines ADP and Pi in a condensation reaction. This requires an input of energy (30.6kJmol) in an endergonic reaction. The addition of this phosphate to ADP is called phosphorylation.

Question 15

Describe the hydrolysis of ATP

Answer 15

The enzyme ATPase hydrolyses the terminal phosphate bond releasing a small packet of energy (30.6kJmol) in an exergonic reaction. This forms ADP and Pi

Question 16

How are the properties, structure and formation of ATP linked to its role in cells?

Answer 16

1. The hydrolysis of ATP to ADP releases immediate energy. The hydrolysis of glucose takes much longer and involves many intermediate reactions.
2. Only one enzyme is needed to release energy from ATP, whereas many are needed in the case of glucose.
3. ATP releases energy in small packets when and where it is needed.
4. ATP is the universal energy currency in many reactions in all living organisms
5. ATP is easily transported across membranes

Question 17

Name the 4 stages of respiration and state where they occur

Answer 17

1. Glycolysis: cytoplasm of cell
2. Link reaction: mitochondrial matrix
3. Krebs cycle: mitochondrial matrix
4. Electron transport chain: inner mitochondrial membrane

Question 18

State 2 examples of redox reactions in respiration

Answer 18

2 co-enzymes act as hydrogen carriers
- NAD+ is reduced to form reduced NAD
- FAD is reduced to form reduced FAD

Question 19

Describe the 5 stages of glycolysis

Answer 19

• Glucose (6C) is phosphorylated to form hexose phosphate (6C). This requires the addition of 2 ATP molecules
• Hexose phosphate (6C) splits into two triose phosphate molecules (3C)
• Each triose phosphate molecule is oxidised to pyruvate (3C). This means that hydrogen is removed by a dehydrogenase enzyme in a dehydrogenation reaction. The hydrogen is accepted by NAD forming reduced NAD
• The production of pyruvate from triose phosphate also results in phosphorylation of 2 ADP molecules to produce 2 ATP (substrate level phosphorylation)
• Overall in glycolysis 2 reduced NAD and 2 pyruvate are produced. There is also a net gain of 2 ATP molecules as 4 ATP molecules were produced but 2 were required in the first stage of the pathway to phosphorylate glucose

Question 20

Describe the link reaction

Answer 20

• Pyruvate (2C) is decarboxylated by a decarboxylase enzyme. Pyruvate is also oxidised to acetate. Dehydrogenase enzymes remove hydrogen which is accepted by NAD to form redNAD. Acetate (2C) is produced.
• Acetate (2C) combines with coenzyme A to form acetyl Coenzyme A which enyers the Krebs Cycle.
• Overall, 2 molecules of CO2, 2 molecules of reduced NAD and 2 molecules of acetyl coenzyme A are produced per glucose molecule

Question 21

Why is pyruvate provided as a respiratory substrate for mitochondria and not glucose?

Answer 21

Glucose can only be hydrolysed in the cytoplasm during glycolysis as there are no glucose specific carrier proteins. Pyruvate can enter the mitochondrion by facilitated diffusion for the link reaction.

Question 22

Describe the Krebs Cycle

Answer 22

• Krebs cycle liberates energy from carbon-carbon bonds to make ATP, redNAD and redFAD. CO2 released as a waste product.
• The acetate from acetyl coenzyme A combines with a 4C compound to form a 6C compound. Coenzyme A is regenerated and returns to the link reaction to collect another acetate
• A series of enzyme controlled reactions then take place. There are 2 decarboxylation reactions and 4 dehydrogenation reactions per turn of the cycle
• The acetate which enters the Krebs cycle is completely broken down to CO2 and water and the 4C compound is regenerated via 6C and 5C intermediates

Question 23

Define decarboxylation

Answer 23

Any chemical reaction in which a carboxyl group is split off from a compound as CO2. Catalysed by decarboxylase enzymes.

Question 24

Define dehydrogenation

Answer 24

A chemical reaction that involves the elimination of hydrogen. It is catalysed by dehydrogenase enzymes.

Question 25

Describe the electron transport chain

Answer 25

• redNAD and redFAD deliver their pairs of hydrogen atoms to the ETC at the inner mitochondrial membrane
• The hydrogen atoms split into protons and electrons
• The high energy electrons are transferred along carriers in the inner mitochondrial membrane along the ETC, moving from high energy level to lower energy levels
• The energy released during electron transport fuels the proton pumps
  -Protons are pumped through channel proteins from the matrix to the intermembrane space
• The build up of protons in the intermembrane space forms an electrochemical gradient
• Stalked particles lining the cristae contain the enzyme ATP synthase
• Protons flow down their concentration gradient through an ion channel in ATP synthase (only part of the membrane permeable to H+)
• The flow of protons releases enough energy for the synthesis of ATP from ADP and Pi
• Oxygen acts as the final electron acceptor. The electrons and protons combine with oxygen to form water.
• This method of producing ATP is called oxidative phosphorylation

Question 26

Define chemiosmosis

Answer 26

Production of an electrochemical gradient resulting in the diffusion of protons through a proton channel in ATP synthase, fuelling the synthesis of ATP from ADP and Pi

Question 27

Glucose catabolism is spread over many reactions. Suggest an advantage of this.

Answer 27

Energy is released in small packets rather than all at once which could release too much heat. Excessive increases in temperature could lead to the denaturing of proteins in cells