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Biology A-Level > Aerobic Respiration, Energy and ATP (Chapter 12) > Flashcards

Aerobic Respiration, Energy and ATP (Chapter 12) Flashcards

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1
Q

What are the 4 stages of respiration?

A

Glycolysis
The link reaction
The Krebs cycle
Oxidative Phosphorylation (OP)

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2
Q

What is glycolysis?

A
  • The lysis (splitting) of glucose
  • It is a multi-step process in which a glucose molecule with 6 C atom is eventually split into 2 molecules of pyruvate, each with 3 C atoms
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3
Q

Where does glycolysis occur?

A

In the cytoplasm of the cell

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4
Q

What is the net gain of ATP molecules per molecule of glucose broken down during glycolysis?

A

2 (4 produced, 2 lost)

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5
Q

What is the first stage of glycolysis called?

A

Phosphorylation

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6
Q

What happens during phosphorylation?

A
  • Glucose is phosphorylated using 2 molecules of ATP, in order to make it more reactive
    1) glucose is first converted to fructose phosphate
    2) fructose phosphate is converted to fructose 1,6-biphosphate
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7
Q

What happens during the second stage of glycolysis?

A

1) fructose 1,6-biphosphate breaks down to produce 2 molecules of triose phosphate (TP)
2) hydrogen is removed from TP + transferred to the carrier molecule (coenzyme) NAD
3) 2 TP is converted to 2 glycerate-2-phosphate (GP)
4) 2 GP is converted to 2 pyruvate and 2 ATP

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8
Q

How many molecules of reduced NAD are produced for each molecule of glucose entering glycolysis?

A

2

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9
Q

What is the end-product of glycolysis?

A

Pyruvate (which still contains lots of chemical potential energy)

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10
Q

What happens during the link reaction?

A

1) Pyruvate is actively transported from the cytoplasm, through the outer and inner membranes of the mitochondria into the mitochondrial matrix
2) Here, it is decarboxylated and dehydrogenated and combined with coenzyme A (CoA) to produce acetyl CoA
3) The hydrogen removed is transferred to NAD

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11
Q

What are hydrogens carried by reduced energy used for?

A

They are transferred to other molecules and used in OP to generate ATP

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12
Q

What is the equation for the link reaction?

A

pyruvate + CoA + NAD <=> acetyl CoA + CO2 + reduced NAD

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13
Q

How many carbons does acetyl CoA have?

A

2C

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14
Q

When (and only when) does the link reaction happen?

A

When oxygen is present

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15
Q

When in respiration is CO2 first produced?

A

During the link reaction

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16
Q

What is the Krebs cycle?

A

A closed pathway of enzyme-controlled reaction

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17
Q

What happens during one turn of the Krebs cycle?

A

1) acetyl CoA combines with oxaloacetate (4C) to form citrate (6C)
2) citrate is decarboxylated and dehydrogenated in a series of steps, to yield CO2 (given off as a waste gas) and hydrogens (which are accepted by NAD and FAD)
3) citrate is then reconverted to oxaloacetate

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18
Q

For each turn of the Krebs cycle, how many molecules of CO2 are produced?

A

2

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19
Q

For each turn of the Krebs cycle, how many molecules of FAD/NAD are reduced?

A

1 FAD

3 NAD

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20
Q

For each turn of the Krebs cycle, how many molecules of ATP are generated?

A

1, via an intermediate compound

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21
Q

Really Fat Americans Can’t Run Normally?

A

1 reduced FAD
1 ATP
2 CO2
3 reduced NAD

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22
Q

What molecule to the reactions of the Krebs cycle make no use of?

A

Oxygen

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23
Q

What is the most important contribution of the Krebs cycle to the cell’s energetics?

A

The release of hydrogens which can be used in OP to provide energy to make ATP

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24
Q

Where does the link reaction take place?

A

The matrix of the mitochondrion

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25
Q

Where does the Krebs cycle take place?

A

The matrix of the mitochondrion

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26
Q

Where does oxidate phosphorylation take place?

A

In the inner mitochondrial membrane

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27
Q

Where does the energy for the phosphorylation of ADP and ATP come from in OP?

A

The activity of the electron transport chain

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28
Q

Describe the process of OP (up to the movement of H+)

A

1) reduced NAD and FAD are passed to the ETC
2) here, the hydrogens are removed from NAD and FAD that they gained in the Krebs cycle and each hydrogen is split into its constituent H+ and e-
3) the energetic e- is transferred to the first in a series of electron carriers, H+ remains in solution
4) as an electron moves from one carrier at a higher energy level to another one at a lower level, energy is released
5) some of this energy is used to move H+ from the matrix to the space between the inner and outer membranes of the mitochondrial envelope

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29
Q

Describe the process of OP (after the movement of H+)

A

6) this produces a higher [H+] in the intermembrane space than in the matrix, setting up a conc gradient
7) now H+ pass back into the matrix through protein channels in the inner membrane, moving down their conc gradient - associated with each channel is ATP synthase
8) as the H+ pass through the channel, their electrical potential energy is used to synthesise ATP via chemiosmosis
9) in the matrix and e- and a H+ are transferred to O2, reducing it to H2O

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30
Q

What role does oxygen have in OP?

A

It is the final electron acceptor

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31
Q

What kind of continuous supply of energy do living organisms need to stay alive?

A

1) absorption of light energy

2) chemical potential energy (energy stored in nutrient molecules)

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32
Q

What does photosynthesis supply living organisms with?

A

2 essential requirements: an energy supply and usable carbon compounds

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33
Q

Why do all living organisms need a source of carbon?

A

Bc all biological macromolecules contain carbon

34
Q

What are autotrophs?

A

Organisms that can use an inorganic carbon source in the form of CO2

35
Q

What are heterotrophs?

A

Organisms that need a ready-made organic supply of carbon

36
Q

For what processes is energy needed in living organisms?

What does ‘work’ in a living organism include?

A

1) anabolic reactions e.g. DNA replication and protein synthesis
2) active transport of substances against a diffusion gradient e.g. activity of the Na-K pumo
3) mechanical work (movement) e.g. muscular contraction, movement of cilia/flagella, movement of vesicles through cytoplasm
4) the maintenance of body temperature
5) cell division

37
Q

What are anabolic reactions?

A

The synthesis of complex substances from simpler ones

38
Q

What are ectotherms?

A

Animals for whom the thermal energy that warms them comes from outside their bodies

39
Q

What are endotherms?

A
  • Animals that use thermal energy (heat) released from metabolic reactions to maintain a constant body temperature (mammals and birds)
  • They release enough thermal energy within their bodies to maintain them above the temperature of their surroundings when necessary
  • They also maintain a constant body temperature through negative feedback loops
40
Q

What must energy requiring reactions be linked to for a living organism to do work?

A

Reactions that yield energy

41
Q

What is the equation for the complete oxidation of glucose in aerobic respiration?

A

C6H12O6 + 6O2 = 6H2O + 6CO2

42
Q

How is energy released in aerobic respiration and what does this allow?

A
  • The reactions take place in a series of small steps, each releasing a small quantity of the total available energy
  • This allows precise control via feedback mechanisms and the cell could not usefully harness the total available energy if all of it were made available at one instant
43
Q

Why does the oxidation of glucose not happen easily?

A

Bc glucose is quite stable due the activation energy that has to be added before an reaction takes place

44
Q

How is the activation energy of reactions involving glucose overcome in living organisms?

A

By lowering it using enzymes and by raising the energy level of the glucose by phosphorylation

45
Q

What are energy-yielding reactions in all organisms used to make?

A

An intermediary molecule, ATP (a phosphorylated nucleotide)

46
Q

What happens as the three phosphate groups are removed from ATP?

A

1) removal of the first phosphate group from ATP releases 30.5KJ/mol of energy and forms ADP
2) removal of the second phosphate group from ADP releases the same amount of energy and forms AMP
3) removal of the third and final phosphate group releases less energy (14.2) and forms adenosine
(all of these reactions are reversible)

47
Q

Where does the energy come from as phosphate groups are removed from ATP?

A

From changes in chemical potential energy of all parts of the system, not just from breaking the first two covalent bonds

48
Q

Which reaction of ATP is the most important for providing energy for the cell?

A
  • the interconversion of ATP and ADP:
    ATP (+H2O) <=> ADP + Pi(H3PO4)
  • the rate of interconversion (turnover) is enormous
49
Q

What are the cell’s energy yielding reactions linked to?

A

ATP synthesis - the ATP is then used by the cell in all forms of work

50
Q

What can ATP be referred to and why?

A

The ‘energy currency’ of the cell bc the cell ‘trades’ in ATP rather than making use of a number of different intermediates

51
Q

What is ATP a highly suitable molecule for its role as the cell’s ‘energy currency’?

A

1) it is readily hydrolysed to release energy

2) small and water soluble ∴ can be easily transported around the cell

52
Q

Why are energy transfers inefficient and what is done with this extra energy?

A
  • Bc some energy is converted to thermal energy whenever energy is transferred
  • At different stages in a multi-step reaction e.g. respiration, the energy made available may not perfectly correspond with the energy needed to synthesise ATP and many energy-required reactions in a cell use less energy that that released by the hydrolysis of ATP to ADP
  • Any of this extra energy is converted and released as thermal energy (which we do need ∴ not wasted)
53
Q

What is an energy currency molecule?

A

An immediate donor of energy

54
Q

What is an energy storage molecule?

A

A short or long term store of chemical potential energy

55
Q

How is energy for ATP synthesis made available through respiration?

A

In respiration, energy released by reorganising chemical bonds (chemical potential energy) during glycolysis and the Krebs cycle is used to make some ATP

56
Q

How is most ATP in cells generated through chemiosmosis (using electrical potential energy)?

A

1) electrical potential energy is stored as a difference in [H+] across phospholipid membranes in mitochondria and chloroplasts, which are essentially impermeable to protons
2) protons are then allowed to flow down their conc gradient (by facilitated diffusion) through a protein that spans the phospholipid bilayer - part of this protein acts as an enzyme that synthesises ATP (ATP synthase)
3) the transfer of 3 protons allows the production of one ATP molecule, provided that ADP + Pi are available inside the organelle

57
Q

Where does electrical potential energy come from?

A

The transfer of electrons by electron carriers in mitochondria and chloroplasts

58
Q

Where does chemiosmosis occur?

A

In mitochondria and chloroplasts

59
Q

Describe ATP synthase

A

1) it has 3 binding sites and a part of the molecule (gamma) that rotates as H+ ions pass
2) this produces structural changes in the binding sites and allows H+ ions to pass sequentially through 3 phases: binding to ADP+Pi, forming tightly bound ATP, releasing ATP

60
Q

Why is energy from ATP needed for active transport?

A

To counteract the tendency of these particles to move by diffusion down (against) the (concentration) gradient

61
Q

What is the Na-K pump?

A

A protein that spans the CSM

62
Q

Describe the Na-K pump

A
  • It has binding sites for Na+ and ATP on the inner side and for K+ on the outer side
  • The protein acts as an ATPase and catalyses the hydrolysis of ATP to ADP+Pi, releasing energy to drive the pump
  • Changes in the shape of the protein move Na+ + K+ across the membrane in the opposite direction
  • For each ATP used, 2 K+ are moved into the cell and 3 Na+ are moved out of the cell
63
Q

Explain how the Na-K pump generates a potential difference (p.d)

A

1) Bc only 2 K+ are added to the cell contents for every 3 Na+ removed, a p.d. is created across the membrane that is negative on the inside w.r.t the outside
2) Both Na+ and K+ leak back across the membrane, down their diffusion gradients - however, CSMs are much less permeable to Na+ than to K+ ∴ this diffusion increases the p.d. across the membrane

64
Q

What is respiration?

A
  • The release of energy
  • A process in which organic molecules (mainly glucose but also fatty acids, glycerol or amino acids) as a fuel
  • The organic molecules are broken down in a series of stages to release chemical potential energy, which is used to synthesise ATP
65
Q

What is coenzyme A?

A

A complex molecule composed of a nucleotide (adenine+ribose) with a vitamin and acts as a carrier of acetyl groups to the Krebs cycle

66
Q

How can fatty acids be used to produce acetyl CoA?

A
  • Fatty acids from fat metabolism may also be used to produce acetyl CoA
  • Fatty acids are broken down in the mitochondrion in a cycle of reactions in which each turn of the cycle shortens the fatty acid chain by a 2C acetyl unit which reacts with CoA to form acetyl CoA
67
Q

In OP, where does the energy for the phosphorylation of ADP and ATP come from?

A

The activity of the ETC

68
Q

What are most electron carriers associated with?

A

Membrane proteins (4 types)

69
Q

What is a respiratory complex?

A

A functional unit consisting of one of each of the 4 membrane proteins in electron carriers, arranged in such a way that electrons can be passed from one to another down an energy gradient

70
Q

How many ATP molecules can theoretically be produced from each reduced NAD?

A

3

71
Q

How many ATP molecules can theoretically be produced from each reduced FAD?

A

2

72
Q

Why can the full yield of ATP not be achieved?

A

1) ADP+Pi have to be inside the mitochondrion ∴ roughly 25% of the total energy yield of electron transfer is used to transport ADP into the mitochondrion and ATP into the cytoplasm
2) ∴ each reduced NAD molecule entering the chain produces on average 2.5 ATP and each reduced FAD produces 1.5 ATP

73
Q

Describe the structure of NAD?

A
  • Made of two linked nucleotides
  • One nucleotide contains adenine (nitrogenous base)
  • The other has a nicotinamide ring, which can accept a H+ and 2 electrons ∴ becoming reduced
74
Q

Describe the structure of FAD?

A

Made of one nucleotide containing ribose and adenine and one with an usual structure involving a linear molecule, ribitol, instead of ribose

75
Q

What is the function of NAD?

A

To act as a hydrogen/electron acceptor

76
Q

What is the final ATP yield of aerobic respiration?

A

32 ATP

77
Q

What are some similarities between respiration and photosynthesis?

A

1) electron carriers are used
2) the carriers are at decreasing energy levels
3) energy is released during electron transfer
4) involve reduction and oxidation reactions
5) phosphorylation of ADP to ATP

78
Q

What is decarboxylation?

A

The removal of CO2/a carboxyl group

79
Q

What is dehydrogenation?

A

The removal of hydrogen (H NOT H2)

80
Q

Describe the structure of ATP?

A

1) nitrogenous base (adenine)
2) ribose sugar
3) 3 phosphate groups

81
Q

Why is ATP needed at the start of glycolysis?

A

To provide the activation energy

Biology A-Level (44 decks)

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