MODULE 5: Respiration !!

Question 1

Steps of aerobic respiration:

Answer 1

Glycolysis, link reaction, Krebs cycle, electron transport chain

Question 2

Steps of anaerobic respiration:

Answer 2

Glycolysis and fermentation (lactate/ethanol)

Question 3

Glycolysis:

Answer 3

1 - PHOSPHORYLATION
2 - LYSIS
3 - PHOSPHORYLATION
4 - DEHYDROGENATION AND FORMATION OF ATP

Question 4

Glycolysis in depth:

Answer 4

1 - 2 molecules of ATP release 2 molecules of phosphate to form hexose bisphosphate (6C) from glucose
2 - Hexose biphosphate is unstable, so splits into two molecules of triose phosphate (3C)
3 - Phosphate groups are added to each molecule of TP to form triose biphosphate (from free inorganic phosphate ions in the cytoplasm)
4 - Both molecules of triose biphosphate are oxidised by the removal of hydrogen molecules (dehydrogenation) to form pyruvate. The hydrogens reduce NAD to NADH. The phosphate groups are released to reform 2ATP per triose phosphate (4 ATP, so generally net gain of 2ATP)
- This takes place in the cytoplasm of a cell

Question 5

Substrate level phosphorylation:

Answer 5

Formation of ATP without the involvement of the electron transport chain (ETC)

Question 6

Link reaction depth:

Answer 6

• Pyruvate (3C) undergoes decarboxylation to form an acetyl group (2C) and is oxidised
• The released hydrogen forms NADH
• A coenzymes binds to the acetyl group to transport it into the mitochondria (acetylcoA)
• Therefore, this can be called oxidative decarboxylation

Question 7

Mitochondria structure:

Answer 7

Cristae, matrix, inner and outer mitochondrial membranes, intermembrane space

Question 8

Krebs cycle depth:

Answer 8

1 - Acteyl group combines with oxaloacetate (4C) to form citrate (6C)
2 - Citrate (6C) undergoes decarboxylation and dehydrogenation to form one NADH and CO2, 5C intermediate formed
3 - 5C intermediate undergoes further decarboxylation and dehydrogenation reactions to reform oxaloacetate (4C). This forms 1CO2, 2NADH and 1FADH2. ATP is also produced by substrate level phosphorylation
* Takes place in the mitochondrial matrix

Question 9

Coenzymes involved in respiration:

Answer 9

NAD, FAD, CoenzymeA

Question 10

Importance of coenzymes in respiration:

Answer 10

Coenzymes transfer protons, electrons and functional groups to ensure redox can take place

Question 11

Differences between NAD and FAD:

Answer 11

• NAD can take 1 hydrogen, FAD can take 2
• NAD is used in all stages of cellular respiration, but FAD is only used in the Krebs cycle
• NADH results in the release of 3 ATP but FADH2 results in the release of 2ATP

Question 12

Oxidative phosphorylation:

Answer 12

• Coenzymes FADH2 and NADH are delivered to the electron transport chain (ETC) in the inner membrane of of the cristae
• Hydrogens disociate from the coenzyme and split into electrons and H+
• The high energy of the electrons are used in synthesis of ATP by chemiosmosis (ATP synthase)
• At the end of the ETC, electrons combine with H+ and oxygen to form water, hence oxygen acts as the electron acceptor
• Thus, this makes respiration aerobic

Question 13

Alcoholic fermentation:

Answer 13

A form of anaerobic respiration that occurs in yeast and some plant root cells, and forms alcohol and carbon dioxide

Question 14

Alcohol fermentation depth:

Answer 14

• IRREVERSIBLE PROCESS
• Pyruvate converted to ethanal by decarboxylation, catalysed by pyruvate decarboxylase
• Ethanal is reduced to ethanol by accepting a hydrogen atom from NADH
• The reformed NAD can then continue to act as a coenzyme, and glycolysis can continue
• Can continue indefinitely in absence of oxygen, and since alcohol is a toxic waste product cells are unable to survive if ethanol accumulates up to 15%

Question 15

Lactate fermentation depth:

Answer 15

• Pyruvate is reduced by accepting a hydrogen from NADH, catalysed by lactate dehydrogenase
• This converts the pyruvate into lactate (lactic acid)
• This can be used to maintain a small ATP synthesis, to support muscles
• Lactic acid is converted into glucose in the liver but oxygen is need for the breakdown

Question 16

Why can’t lactate fermentation occur indefinitely?

Answer 16

• Reduced ATP production cannot sustain the vital processes for a long period of time
• Accumulation of lactic acid leads to a decrease in pH, causing proteins to denature. Respiratory enzymes and muscle filaments will cease function

Question 17

RQ:

Answer 17

respiratory quotient = CO2 produced/O2 produced

*can be measured with a respirometer

Question 18

Difference in relative energy values of
carbohydrates, lipids and proteins as respiratory
substrates:

Answer 18

Most to least:
- Lipids
- Carbohydrates
- Proteins
Lipids have twice as many C-H bonds as carbohydrates, so release a significantly higher amount of ATP. Proteins first need to be converted to amino acids, then deaminated before entering the respiratory pathway (reducing the net production of ATP.)

Question 19

Difference in RQ values of
carbohydrates, lipids and proteins as respiratory
substrates:

Answer 19

Most to least:

• Carbohydrates
• Proteins
• Lipids