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A-Level Biology > 18 Respiration > Flashcards

18 Respiration Flashcards

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1
Q

What are the four stages in aerobic respiration?

A

1) Glycolysis
2) The link reaction
3) The Krebs cycle
4) Oxidative Phosphorylation

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2
Q

Where does glycolysis occur?

A

Glycolysis occurs in the cytoplasm.

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3
Q

Why is glycolysis an anaerobic process?

A

Glycolysis is an anaerobic process as it does not require oxygen.

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4
Q

What are the main steps in glycolysis?

A

1) Phosphorylation
2) Lysis
3) Phosphorylation
4) Dehydrogenation and formation of ATP

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5
Q

Describe the process of glycolysis in detail.

A

1) Two phosphates released from the two ATP molecules are attached to a glucose molecule forming hexose biphosphate.
2) This destabilises the molecule causing it to split into triose phosphate.
3) Another phosphate group is added to each triose phosphate forming two triose biphosphate molecules. These phosphate groups come from the free inorganic phosphate ions present in the cytoplasm.
4) The two triose biphosphate molecules are then oxidised by the removal of hydrogen atoms (dehydrogenation) to form two pyruvate molecules. NAD coenzymes accept the removed hydrogens-they are reduced, forming two reduced NAD molecules.

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6
Q

What is the overall net ATP yield from glycolysis? How is this calculated?

A 
The overall net ATP yield from glycolysis is two molecules of ATP.
This is calculated because:
- Two ATP molecules used
- Four ATP molecules produced
4-2=2
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7
Q

State the subcellular structures of the mitochondria.

A
  • Outer mitochondrial membrane
  • Inner mitochondrial membrane
  • Cristae
  • Matrix
  • Intermembrane space
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8
Q

What is the role of the outer mitochondrial membrane?

A

Separates the contents of the mitochondrion from the rest of the cell, creating a cellular compartment with ideal conditions for aerobic respiration.

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9
Q

What is the role of the inner mitochondrial membrane?

A

Contains electron transport chains and ATP synthase

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10
Q

What are cristae?

A

Cristae are projections of the inner membrane which increase surface area available for oxidative phosphorylation

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11
Q

What is the role of the matrix?

A

The matrix contains enzymes for the Krebs cycle and link reaction. It also contains mitochondrial DNA.

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12
Q

What is the role of the intermembrane space?

A

Protons are pumped into this space by the electron transport chain. The space is small so the concentration builds up quickly.

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13
Q

What is the first step is aerobic respiration?

A

The first step in aerobic respiration is OXIDATIVE DECARBOXYLATION.

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14
Q

What is oxidative decarboxylation also known as? Why?

A

Oxidative decarboxylation is also known as the LINK REACTION because it links anaerobic glycolysis to the aerobic steps of respiration.

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15
Q

Where does oxidative decarboxylation (link reaction) occur?

A

In the mitochondrial matrix.

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16
Q

Describe the link reaction in detail.

A

1) Pyruvate enters the mitochondrial matrix by active transport via specific carrier proteins.
2) Pyruvate then undergoes oxidative decarboxylation- carbon dioxide is removed (decarboxylation) along with hydrogen (oxidation).
3) The hydrogen atoms removed are accepted by NAD.
4) NAD is reduced to form NADH.
5) The resulting two carbon acetyl group is bound to coenzyme A forming acetylcoenzyme A (acetyl CoA)

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17
Q

What is the purpose of the acetyl group binding to coenzyme A?

A

When bound together, Acetyl CoA delivers the acetyl group to the next stage of aerobic respiration- the Krebs cycle.

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18
Q

Where does the Krebs cycle take place?

A

The Krebs cycle takes place in the mitochondrial matrix.

19
Q

Describe the process of the Kreb’s cycle in detail.

A

1) Acetyl coA delivers an acetyl group to the Krebs cycle. The two carbon acetyl group combines with four carbon oxaloacetate to form six-carbon citrate. This is catalysed by citrate synthase.
2) The citrate molecule undergoes decarboxylation and dehydrogenation producing one reduced NAD and carbon dioxide. A five carbon compound is formed.
3) The 5 carbon molecule is converted to a 4 carbon molecule. Decarboxylation and dehydrogenation occur, producing one molecule of reduced FAD and two of reduced NAD. ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP. Citrate has now been converted into oxaloacetate.

20
Q

What are the differences between coenzymes NAD and FAD? (coenzymes)

A

1) NAD takes part in all stages of cellular respiration but FAD only accepts hydrogens in the Krebs cycle.
2) NAD accepts one hydrogen and FAD accepts two hydrogens.
3) Reduced NAD is oxidised at the start of the electron transport chain releasing protons and electrons while reduced FAD is oxidised further along the chain.
4) Reduced NAD results in the synthesis of 3 ATP molecules but reduced FAD results in the synthesis of only 2 ATP molecules.

21
Q

Where does oxidative phosphorylation take place?

A

Oxidative phosphorylation takes place in the inner mitochondrial membrane.

22
Q

What is oxidative phosphorylation?

A

Oxidative phosphorylation is the formation of ATP by adding a phosphate group to ADP, in the presence of oxygen, which is the final electron acceptor

23
Q

Describe the process of oxidative phosphorylation in detail.

A

1) Hydrogen atoms are released from reduced NAD and reduced FAD as they’re oxidised to NAD and FAD. The hydrogen atoms split into protons and electrons.
2) The electrons move along the electron transport chain, losing energy at each carrier. The electron transport chain is located in the inner mitochondrial membrane. This membrane is folded into cristae, which increases the membrane’s surface area to maximise respiration.
3) This energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space.
4) The concentration of protons is now higher in the intermembrane space than in mitochondrial matrix- this forms an electrochemical gradient,
5) Protons move down the electrochemical gradient, back into the mitochondrial matrix, via ATP synthase.
6) This movement drives the synthesis of ATP from ADP and inorganic phosphate. This process of ATP production driven by the movement of H+ ions across a membrane is called chemiosmosis.
7) In the mitochondrial matrix, at the end of the transport chain, the protons, electrons and oxygen combine to form water. Oxygen is the final electron acceptor.

24
Q

What is substrate level phosphorylation?

A

Substrate level phosphorylation is the direct formation of ATP without the involvement of an electron transport chain.
E.g the transfer of a phosphate group to ADP

25
Q

How many ATP molecules are formed in 1 glucose molecule? And how is this worked out?

A

38 ATP molecules
Glycolysis: 2 ATP & 2 Reduced NAD = 8 ATP
Link Reaction: 1 Reduced NAD= 3 ATP2= 6 ATP (Remember link reaction only for one pyruvate, and we have two)
Kreb’s cycle: 1 ATP, 3 Reduced NAD, 1 Reduced FAD = 12 ATP2= 24 ATP

24 + 6 + 8= 38 ATP (NET)

26
Q

How many ATP molecules can reduced NAD produce by oxidative phosphorylation?

A

3 ATP

27
Q

How many ATP molecules can reduced FAD produce by oxidative phosphorylation?

A

2 ATP

28
Q

What are obligate anaerobes?

A

Obligate anaerobes cannot survive in the presence of oxygen.

29
Q

What are facultative anaerobes?

A

Facultative anaerobes synthesise ATP by aerobic respiration is oxygen is present, but can switch to anaerobic respiration in the absence of oxygen e.g yeast

30
Q

What are obligate aerobes?

A

Obligate anaerobes can only synthesise ATP in the presence of oxygen e.g mammals.

31
Q

What is fermentation?

A

Fermentation is anaerobic respiration without the involvement of an electron transport chain.

32
Q

Where does alcoholic fermentation occur and what does it produce?

A
  • Alcoholic fermentation occurs in yeast and some plant root cells.
  • It produces ethanol and carbon dioxide.
33
Q

Where does lactate fermentation occur and what does it produce?

A
  • Lactate fermentation occurs in animal cells and produces lactate.
34
Q

How does lactate fermentation work?

A
  • Pyruvate acts as a hydrogen acceptor by taking the hydrogen from reduced NAD, catalysed by lactate dehydrogenase and is converted to lactate and NAD is regenerated.
  • This can be used to keep glycolysis going so a small quantity of ATP is still synthesised.
35
Q

How does alcoholic fermentation work?

A
  • Pyruvate loses carbon dioxide and is converted to ethanal, catalysed by the enzyme pyruvate decarboxylase.
  • Ethanal accepts a hydrogen atom from reduced NAD becoming ethanol.
  • NAD regenerated to keep glycolysis going.
36
Q

How do you calculate respiratory quotient? (RQ)

A

CO2 produced/O2 consumed

37
Q

Why do lipids produced much more ATP in respiration?

A

Lipids have a greater proportion of carbon-hydrogen bonds

38
Q

What is the RQ value of carbohydrates?

A

1.0

39
Q

What is the RQ value of proteins?

A

0.9

40
Q

What is the RQ value of lipids?

A

0.7

41
Q

decarboxylase enzyme

A

removes carbon dioxide

42
Q

dehydrogenase enzyme

A

removes hydrogen (forms reduced NAD/ NADH)

43
Q

where are the electron carriers for etc located ?

A

The electron transport chain is located in the inner mitochondrial membrane. This membrane is folded into cristae, which increases the membrane’s surface area to maximise respiration

44
Q

phosphocreatine

A

source of phosphate for the synthesis of ATP

- ADP + phosphocreatine -> ATP + creatine

A-Level Biology (41 decks)

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