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A Level Biology > C1- Respiration > Flashcards

C1- Respiration Flashcards

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1
Q

Define metabolism.

A

All the reactions of the organism.

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2
Q

What is a metabolic pathway?

A

A sequence of reactions controlled by enzymes.

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3
Q

Respiration is a catabolic reaction, what does this mean?

A

It breaks down energy rich macromolecules, such as glucose and fatty acids.

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4
Q

When ATP is hydrolysed what occurs?

A

Energy is released and available to use by the cell or lost as heat.

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5
Q

What are the three types of phosphorylation?

A
  • Oxidative phosphorylation
  • Photophosphorylation
  • Substrate-level phosphorylation
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6
Q

What is oxidative phosphorylation and where does it occur?

A
  • occurs in the inner membranes of the mitochondria in aerobic respiration
  • the energy for making ATP comes from the oxidation-reduction reactions and is released in the transfer of electrons along a chain of electron carrier molecules
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7
Q

What is Photophosphorylation and where does it occur?

A
  • occurs in the thylakoid membranes of the chloroplasts during the light dependent stage of photosynthesis
  • the energy for making the ATP comes from light and is released in the transfer of electrons along a chain of electron carrier molecules.
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8
Q

What is substrate level phosphorylation?

A

Occurs when phosphate groups are transferred from donor molecules e.g.
- glycerate-3-phosphate to make ADP to ATP in glycolysis

OR

When energy released for a reaction to bind inorganic phosphate to ADP e.g.
- the Krebs cycle

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9
Q

What are obligate anaerobes?

A

Respire without oxygen and cannot grow in its presence

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10
Q

What are obligate aerobes?

A

Break down substrates using oxygen, with the release of relatively large amounts of energy.

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11
Q

What are facultative anaerobes?

A

Respire aerobically, but can also respire without oxygen.

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12
Q

Define aerobic respiration.

A

The release of large amounts of energy made available as ATP, from the breakdown of molecules, with oxygen as the terminal electron acceptor.

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13
Q

Define anaerobic respiration.

A

The breakdown of molecules in the absence of oxygen, releasing relatively little energy, making a small amount of ATP by substrate level phosphorylation.

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14
Q

What four stages can aerobic respiration be divided into?

A
  • Glycolysis
  • The link reaction
  • The Krebs cycle
  • The electron transport chain
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15
Q

What does glycolysis generate?

A
  • pyruvate
  • ATP
  • reduced NAD
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16
Q

Where does glycolysis occur?

A

in solution in the cytoplasm

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17
Q

Where does the link reaction occur?

A

in solution in the matrix of the mitochondria

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18
Q

Extremely briefly explain what occurs during the link reaction.

A

Pyruvate is converted into acetyl coenzyme A

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19
Q

Where does the Krebs cycle occur?

A

in solution in the matrix of the mitochondria

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20
Q

What does the Krebs cycle generate?

A
  • carbon dioxide
  • reduced NAD
  • reduced FAD
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21
Q

Where is the electron transport chain located?

A

on the cristae of the inner mitochondrial membrane.

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22
Q

What is generated by the electrons and protons in the electron transport chain?

A

ATP is generated from ADP and inorganic phosphate Pi.

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23
Q

Why does glycolysis occur in the cytoplasm?

A
  • Glucose cannot pass through the mitochondria membranes.

- There are no enzymes present in the mitochondria, so it could not be metabolised there.

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24
Q

What is the initial stage of both anaerobic and aerobic respiration.

A

Glycolysis

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25
Q

Define dehydrogenation

A

The removal of one or more hydrogen atoms from a molecule

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26
Q

Describe the stages of glycolysis.

A
  • A glucose molecule (6C) is phosphorylated with two molecules of ATP to produce glucose diphosphate.
  • Glucose diphosphate splits into two molecules of triose phosphate- glyceraldehyde-3-phosphate
  • The triose phosphate molecules are dehydrogenated, oxidising them to pyruvate- the hydrogen then bonds with NAD (a hydrogen carrier molecule) to make two molecules of reduced NAD.
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27
Q

What is NAD?

A

a hydrogen carrier molecule

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28
Q

Describe two features of glucose diphosphate.

A
  • more reactive so less activation energy is required for the enzyme controlled reactions
  • polar and therefore less likely to diffuse out of the cell
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29
Q

What type of phosphorylation occurs during glycolysis and how many ATP molecules does it produce overall?

A
  • Four ATP molecules are formed by substrate level phosphorylation- the phosphate from the triose phosphate converts ADP to ATP without the electron transport chain producing pyruvate.
  • Of four ATP molecules produced, two were used to phosphorylate the glucose molecule so there is a net gain of two ATP per molecule of glucose.
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30
Q

Two molecules of NAD are synthesised during glycolysis, if oxygen is available how many more molecules of ATP might be produced?

A

Each has the potential to synthesise an additional three molecules of ATP, making six all together from the electron transport chain.

31
Q

During aerobic respiration which two stages is the link reaction between?

A

It links glycolysis with the Krebs cycle.

32
Q

Describe the stages of the link reaction.

A
  • Pyruvate diffuses from the cytoplasm into the mitochondria matrix.
  • The pyruvate is dehydrogenated- the hydrogen released binds to NAD forming reduced NAD
  • The pyruvate is decarboxylated- a molecule of CO2 is removed from it.
  • All that remains of the original glucose molecule is a acetate group (2C) which combines with coenzyme A (CoA), making acetyl coenzyme A (AcCoA).
  • AcCoA enters the Krebs cycle.
33
Q

Describe an equation to summaries the link reaction.

A

pyruvate + NAD + CoA → AcCoA + reduced NAD + CO2

34
Q

Define decarboxylation.

A

the removal of a carboxyl group from a molecule releasing carbon dioxide.

35
Q

what is the purpose of the Krebs cycle?

A
  • To liberate energy from C-C, C-H or C-OH bonds and produce ATP that contains the energy once held in those bonds.
  • It also produces reduced NAD and FAD which delivers hydrogen atoms to the electron transport chain.
36
Q

How many molecules of water are used in reactions in the Krebs cycle?

A

three molecules of water

37
Q

Describe the stages of the Krebs cycle.

A
  • AcCoA eneters he Krebs cycle by combining with a 4C acid to form a 6C compound- this regenerates CoA
  • The 6C acid is dehydrogenated to make reduced NAD and decarboxylated to make 5C acid and carbon dioxide
  • The 5C acid is dehydrogenated making reduced NAD and FAD, and decarboxylated to make (regenerate) 4C acid and carbon dioxide
  • Th 4C acid combines with more AcCoA and the cycle repeats.
38
Q

What two types of reaction occur during the Krebs cycle?

A
  • carboxylation

- hydrogenation

39
Q

How many times does decarboxylation occur during the Krebs cycle?

A

Twice- removes carbon dioxide from the COOH groups of Krebs cycle intermediates as…
6C acid → 5C acid → 4C acid

40
Q

How many times does hydrogenation occur during the Krebs cycle?

A

Four times- four hydrogen atoms are removed from Krebs cycle intermediates, which are then collected by hydrogen carriers creating three molecules of reduced NAD and one of reduced FAD.

41
Q

By the end of the Krebs cycle what is the acetate group broken down into?

A

carbon dioxide and water

42
Q

In summary what is produced for every turn of the Krebs cycle?

A
  • one ATP by substrate level phosphorylation
  • three molecules of reduced NAD
  • one molecule of reduced FAD
  • two molecules of carbon dioxide
43
Q

Define coenzyme

A

a molecule required by an enzyme in order to function

44
Q

What is the electron transport chain made up of?

A

A series of protein molecules that are carriers and pumps, which are sometimes called respiratory enzymes.

45
Q

name a type of carrier molecule in the electron transport chain.

A

cytochromes- proteins conjugated to iron or copper and the metal ions are oxidised and reduced by electron transport.

46
Q

What coenzymes carry hydrogen into the electron transport chain?

A

NAD and FAD

47
Q

Summaries reduced NAD and reduced FADs role in producing ATP.

A
  • NAD feeds electrons and protons into the electron transport chain at an earlier point than FAD does.
  • each pair of hydrogen atoms carried by reduced NAD provides enough energy for the synthesis of three molecules of ATP, using three proton pumps.
  • reduced FAD passes hydrogen atoms directly to the second proton pump, hence two molecules of ATP are produced for each pair of hydrogen atoms.
48
Q

Describe the passage of electron in the electron transport chain.

A
  • reduced NAD donates the electrons of the hydrogen atoms to the first of a series of electron carriers in the electron transport chain.
  • electrons from these atoms provide energy for the first proton pump and protons from the hydrogen atoms are pumped into the inter-membrane space
  • the electrons pass along the chain of carrier molecules providing energy for each of the three proton pumps in turn
  • at the end of the chain the electrons combine with protons and oxygen to form water
49
Q

What is the equation to represent the formation of water at the end of the electron transport chain?

A

2H^ + 2e^- + 1/2O2 → H2O

50
Q

Describe the passage of protons in the electron transport chain.

A
  • the inner membrane is impermeable to protons so protons accumulate in the inter membrane space
  • the concentration in the inter membrane space become higher than in the matrix- this creates a gradient in charge and concentration maintained by the proton pumps
  • Protons flow back into the mitochondrial matrix through protein complexes in the membrane.
  • The enzyme ATP synthetase is associated with each channel the protons flow back through- as they flow through their electrical potential energy produces ATP
  • at the end of the chain, the protons combine with electrons and oxygen to form water.

relevant equation:
ADP + Pi → ATP + H2O

51
Q

Why is oxygen referred to as the ‘final electron/ hydrogen acceptor’?

A

It removes the hydrogen and electrons once they’ve passed through the electron transport chain- it is reduced by their addition to make water.

52
Q

Explain how cyanide causes a cell to die.

A
  • it is a non-competitive inhibitor of the final carrier in the electron transport chain
  • it prevents electrons and protons being transferred to water
  • the accumulate destroying the proton gradient
  • ATP synthetase cannot operate and the cell dies quickly
53
Q

For each molecule of glucose entering the Krebs cycle the electron transport system receives…? That produces how many molecules of ATP?

A

10 reduced NAD- 30 ATP

2 reduced FAD- 4 ATP

54
Q

If no oxygen is present what cannot occur that would normally during respiration?

A
  • there is no oxygen to remove hydrogen atoms from reduced NAD and make water so the electron transport chain cannot function- subsequently there is no oxidative phosphorylation so no ATP is formed.
  • without oxygen NAD cannot be regenerated to pick up more hydrogen- subsequently the Krebs cycle and link reaction cannot take place, only glycolysis.
55
Q

How does glycolysis continue to occur despite a lack of oxygen?

A

The pyruvate and hydrogen is constantly removed and reduced NAD is regenerated by the pyruvate accepting the hydrogen from the reduced NAD.

56
Q

How is ATP produced during glycolysis when no oxygen is present?

A

by substrate level phosphorylation

57
Q

How many different anaerobic pathways are there to remove hydrogen from reduced NAD and where do these pathways occur?

A

There are two different pathways, both o which take place in the cytoplasm.

58
Q

Describe anaerobic respiration within animals and the conditions which must be met for this to occur.

A
  • muscle cells do not get sufficient oxygen during vigorous exercise
  • pyruvate becomes the hydrogen acceptor and is converted to lactate
  • if oxygen becomes available the lactate can be respired to carbon dioxide and water- releasing the energy it contained
59
Q

Describe anaerobic respiration within microorganisms such as yeast and plant cells in waterlogged conditions and the conditions which must be met for this to occur..

A
  • pyruvate is converted into carbon dioxide and to ethanal- a hydrogen acceptor by carboxylase
  • ethanal is reduced to ethanol and NAD is regenerated in alcoholic fermentation
  • the pathway is not reversible in the presence of oxygen- it can accumulate within the cells and rise to toxic levels
60
Q

Explain why cells are not a efficient in respiration as the theoretical total of ATP molecules would suggest?

A
  • ATP is used to move pyruvate
  • ADP is used to move reduced NAD and reduced FAD across the mitochondrial membrane
  • The proton gradient may be compromised by proton leakage across the inner mitochondrial membrane- rather than passing through ATP synthetase
  • molecules may also leak though the membrane
61
Q

Describe the theoretical yield of ATP.

A

Glycolysis:

  • 2 ATP- SLP
  • 6 ATP from 2x reduced NAD- OP

The link reaction:
- 6 ATP from 2x reduced NAD- OP

The Krebs cycle:

  • 2 ATP- SLP
  • 18 ATP from 6x reduced NAD
  • 4 ATP from 2x reduced FAD

SLP- substrate level phosphorylation
OP- oxidative phosphorylation

62
Q

On average how many ATP molecules are actually produced per molecule of glucose?

A

30- 32 molecules of ATP

63
Q

How do you calculate the efficiency of ATP production?

A

(energy made available through ATP/ energy released in combustion) x 100

64
Q

Why is the Krebs cycle referred to as the ‘metabolic hub’?

A
  • The metabolic pathways of carbohydrates, lipids and proteins can feed into it.
  • In some situations fats and proteins can be used as respiratory substrates.
65
Q

What links the metabolism of the three types of macromolecules?

A

Acetyl coenzyme A

66
Q

When is fat used as a respiratory substrate?

A

When carbohydrate in the body such as glycogen and blood glucose are low.

67
Q

Describe how lipids can be used to produce ATP.

A

Fat is hydrolysed into its constituent molecules- glycerol and fatty acids.

Glycerol:

  • glycerol is phosphorylated with ATP to produce glycerol-3-phosphate
  • glycerol-3-phosphate is dehydrogenated with reduced NAD and converted into a triose phosphate
  • triose phosphate then enters the glycolysis pathway

Fatty acids:

  • fatty acids split into two carbon fragments
  • they enter the Krebs cycle as AcCoA
  • hydrogen is released and picked up by NAD to be fed into the electron transport chain
  • this produces a large number of ATP molecules- the exact amount depends on the length of the hydrocarbon chain of the fatty acid
68
Q

What is the problem with respiring longer fatty acid chains?

A
  • more carbon atoms so more carbon dioxide is produced
  • muscles have a limited blood supply so if they respire fat rather than glucose they will produce more carbon dioxide than could be removed quickly enough
69
Q

Why do tissues with a large blood supply, such as the liver, respire fat?

A
  • fat has more hydrogen atoms so more reduced NAD is produced
  • this means a large amount of ATP can be produced and readily transported around the body
70
Q

Why do desert animals respire fat?

A
  • fat contains more hydrogen atoms so more water is produced

- metabolic water is very important for desert animals and explains why they respire fat

71
Q

When is protein used as a respiratory substrate?

A
  • When carbohydrates and fats are lacking in a diet protein is diverted from food supply energy
  • During prolonged starvation tissue protein is metabolised to supply energy
72
Q

During prolonged starvation which tissue protein is metabolised to supply energy first?

A
  • heart muscle

- kidney tissue

73
Q

Describe how protein enters the Krebs cycle.

A
  • it is hydrolysed into its constituent amino acids
  • they are then deaminated in the liver
  • the amino group is converted into urea and excreted
  • the residue is converted into acetyl CoA or pyruvate or another Krebs cycle intermediate
  • it is the oxidised

A Level Biology (10 decks)

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