5.2 Respiration

Question 1

What is respiration?

Answer 1

The process by which the energy stored in a complex organic molecules (such as glucose) is used to produce ATP

Question 2

What are the three ways in which ATP can be produced?

Answer 2

1. Photophosphorylation (light dependent reaction)
2. Oxidative phosphorylation (respiration, in the mitochondria)
3. Substrate level phosphorylation (anaerobic respiration, no ATP synthase generating it, glycolysis)

Question 3

What is NAD?

Answer 3

Nicotinamide adenine dinucleotide (NAD)
NAD is an important co-enzyme (electron carrier) - involved in respiration. Its role is to accept hydrogen atoms from molecules that are being oxidised.

Question 4

What is aerobic respiration?

Answer 4

1. Requires oxygen and produces a lot of ATP
2. The waste products are carbon dioxide and water

Question 5

What is anaerobic respiration?

Answer 5

• Does not require oxygen, and produces a lot less ATP
  In humans the waste product is lactic acid
  In yeast the waste products are ethanol and carbon dioxide

Question 6

What are the four stages of aerobic respiration:

Answer 6

1. Glycolysis - ATP/ no O2 used, takes place in cytoplasm
2. Link reaction - matrix
3. Krebs Cycle - cristae
4. Oxidative Phosphorylation and the Electron Transport Chain - cristae

Question 7

In glycolysis, glucose molecules are oxidised to form what substance?

Answer 7

• Glucose molecules are oxidised to form pyruvate (stable 3 carbon molecule)

Question 8

Describe the process of glycolysis:

Answer 8

• Glucose molecule is phosphorylated - makes glucose more reactive. The energy comes from the hydrolysis of ATP providing a phosphate group
• Further phosphorylation occurs
• Splits into two molecules of phosphorylated triose sugar
• Four phosphate groups are transferred from the molecules of triose sugar to ADP, forming two molecules of ATP - substrate-level phosphorylation
• At the same time, triose sugars are oxidised. Two pairs of hydrogen atoms are released. Each pair of hydrogen atoms is transferred to a molecule of NAD forming reduced NAD
• The formation of pyruvate ions marks the completion of glycolysis

Question 9

What are the overall products per glucose molecule?

Answer 9

2x pyruvate
2x ATP
2x Reduced NAD

Question 10

What happens if there is no oxygen present after glycolysis?

Answer 10

Pyruvate converted to lactate or ethanol
Oxidising reduced NAD -> NAD regenerated
So glycolysis can continue which needs/uses NAD

Question 11

If oxygen is present after glycolysis…

Answer 11

The link reaction and the Krebs cycle will take place

Question 12

Where does the link reaction and Krebs cycle take place?

Answer 12

Matrix of the mitochondria

Question 13

Describe the link reaction:

Answer 13

• Pyruvate passes into a mitochondrion where it is oxidised by the removal of hydrogen atoms, which are transferred to NAD to produce reduced NAD
• A molecule of CO2 is also released
• As a result 3-carbon pyruvate is converted to a 2-carbon acetyl group
• The acetyl group formed combines with coenzyme A, producing acetyl coenzyme A

Question 14

Describe the Krebs cycle:

Answer 14

• Acetyl coenzyme A combined with 4 carbon molecules form a 6 carbon molecule
• This 6C molecule gets decarboxylated and loses carbon dioxide and hydrogen to give a 4-carbon molecule and a single molecule of ATP produced as a result of substrate-level phosphorylation
• The 4-carbon molecule can now combine with a new molecule of acetyl coenzyme to begin the cycle again
• Reduced coenzymes such as NAD and FAD. These have the potential to provide the energy to produce ATP molecules by oxidative phosphorylation and are therefore the important products of Krebs

Question 15

What are the overall products of the link reaction and the Krebs cycle:

Answer 15

4x reduced NAD
1x reduced FAD
1x ATP
3x CO2

Question 16

Where does the oxidative phosphorylation and the electron transport chain take place?

Answer 16

Inner membrane of the mitochondria (cristae)

Question 17

Describe the process of oxidative phosphorylation and the ETC:

Answer 17

• Takes place on the inner membrane of the membrane of the mitochondria (cristae)
• Reduced NAD/FAD oxidised to release H atoms -> split into protons (H+) and e-
• Electrons transferred down the ETC by redox reactions:

Energy released by electrons used in the production of ATP from ADP + Pi:
- Energy used by electron carriers to actively transport, protons from the matrix to the intermediate space
- Protons diffuse down a proton gradient, via ATP synthase back into the matrix
- Releasing energy to combine ADP + Pi -> ATP

In the matrix at the end of the ETC, oxygen is the final electron acceptor - protons, electrons and oxygen combine to form water

Question 18

What do other respiratory substrates include?

Answer 18

The breakdown products of lipids and amino acids, which enter the Krebs cycle
Eg/
- Fatty acids from the hydrolysis of lipids are converted to Acetyl Coenzyme A
- Amino acids from the hydrolysis of proteins are converted to intermediates in Krebs cycle