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MPW biology > 5.2.2 Respiration > Flashcards

5.2.2 Respiration Flashcards

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1
Q

Draw a molecule of ATP, and label it

A
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2
Q

Draw a molecule of ATP with a Pi

A
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3
Q

How is ADP and Pi formed from an ATP molecule?

A

ATP is hydrolysed by ATPase enzyme

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4
Q

what are the 4 main properties of ATP which make is ideal as an energy currency molecule?

A

High water‐solubility - diffuses rapidly within cells

Hydrolysis releases a useful amount (‘packet’) of energy for a cellular process, but not so much energy that cellular components are damaged

Hydrolysis of ATP (to remove the terminal phosphate group) releases 30kJ mol‐1 of energy

The products of ATP hydrolysis, ADP and Pi, can be re‐used to make new ATP molecules via respiration, either by substrate‐level phosphorylation or by oxidative phosphorylation.

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5
Q

Where does Glycolysis occur?

A

cytoplasm

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6
Q

where does the link reaction occur?

A

Mitochondrial matrix

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7
Q

where does the krebs cycle occur?

A

mitochondrial matrix

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8
Q

where does chemiosmosis occur?

A

cristae (the folds of the inner mitochondrial membrane)

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9
Q

where does oxidative phosphorylation occur?

A

cristae (the folds of the inner mitochondrial membrane)

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10
Q

where does the re-oxidation of NADH in anareboic respiration occur?

A

cytoplasm

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11
Q

What is this? Label it

A

It is a mitochondion

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12
Q

what is the function of the inner and outer mitochondral matrix (mitochondrial envelope)?

A

partially permeable barrier - controlls what enters and leave the cell.

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13
Q

what is the function of the inter-membrane space of a mitochondria, and what is it?

A

the space in‐between the two mitochondrial membranes

The area where hydrogen ions (protons) accumulate - creates steep proton gradient between the mitochondrial matrix and the intermebrane space

inner mitochondrial membrane is not permeable to H+ ions means that the gradient is maintained

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14
Q

what are the cristae, and what is its function?

A

infolded regions of the inner mitochondrial membrane

It is the site of chemiosmosis and oxidative phosphorylation

cristae provide increased surface area for attachment of Electron Transfer Chain components and ATP synthase enzymes, increasing ATP production

ATP synthase enzyme is embedded in theinner mitochondrial membrane

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15
Q

what is the inner mitochondrial membrane and ATP synthase enzymes reffered as?

A

stalked particles as the ATP synthases are embedded in the inner mitochondrial membrane, but part of their structure projects out into the matrix

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16
Q

what is the mitochondiral matrix and what does it contain?

A

the fluid that fills the mitochondrion

Contains:

small circular DNA molecule (mitochnodrial DNA) - contains genes that encode some of the proteins needed in the mitochondrion

18nm (70S) ribosomes - synthesise new proteins

enzymes which are used in link reaction and krebs cycle

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17
Q

what is glycolysis?

A

A multi‐step metabolic pathway which oxidises glucose to pyruvate

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18
Q

What are the products of glycolysis?

A

4x ATP (net production of 2 ATP)

2x NADH

2x Pyruvate

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19
Q

What are the named steps of glycolysis?

A
  1. Phosphorylation
  2. Lysis
  3. Phosphorylation
  4. dehydrogenation/oxidation
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20
Q

Draw out the steps of glycolysis

A
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21
Q

Describe the 5 steps of glycolysis

A
  1. A glucose molecule (which contains six carbon atoms) is phosphorylated twice, to give hexose bisphosphate; this step involves the transfer of a phosphate group from each of two ATP molecules, i.e. ATP is actually being used, not generated, at the start of glycolysis
  2. Hexose bisphosphate is split (lysed) into two molecules of the three carbon sugar, triose phosphate
  3. Each triose phosphate combines with an inorganic phosphate ion from the cytoplasm, to form triose bisphosphate
  4. Both triose bisphosphate molecules are oxidised to pyruvate; this oxidation reaction requires the coenzyme oxidised NAD, which itself becomes reduced as a hydrogen atom is transferred to it; two reduced NAD molecules are generated in total (one per triose bisphosphate)
  5. During the oxidation of triose bisphosphate to pyruvate, each triose bisphosphate molecule can pass phosphate groups to two ADP molecules; this step therefore produces a total of four ATP molecules via substrate‐level phosphorylation (transfer of a phosphate group to ADP from a phosphorylated organic molecule).
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22
Q

how many ATP molecules are produced in glycolysis per glucose? therfore what is the total net yield for both glucose?

A

Per glucose molecule, two ATP molecules are used but then four are produced

OVERALL NET YIELD OF 2 ATP IN GLYCOLYSIS

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23
Q

in aerobic respiration, what happens to the NADH after glycolysis?

A

the reduced NAD generated by glycolysis enters the mitochondria and drives further ATP production by oxidative phosphorylation.

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24
Q

where does the pyruvate go after glycolysis in aerobic coonditions?

A

It enters the mitochondria (using specific carrier proteins to cross the outer and inner mitochondrial membranes) and then undergoes the Link Reaction in the mitochondrial matrix.

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25
Q

what is another name for the link reaction?

A

Oxidative decarboxylation

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26
Q

Draw out the steps of the link reaction

A
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27
Q

Describe the link reaction

A
  1. a) The decarboxylation involves one carbon atom and two oxygen atoms being removed from pyruvate, forming a carbon dioxide molecule (which diffuses out of the mitochondrion); this leaves a two carbon product, acetyl
  2. b) Oxidation happens simultaneously and involves the oxidised form of NAD accepting a hydrogen atom from pyruvate, meaning that the pyruvate is oxidised but the NAD becomes NADH (NAD is reduced to NADH)
  3. The acetyl immediately combines with Coenzyme A (CoA), forming acetyl‐CoA which will next deliver the acetate into the Krebs Cycle.
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28
Q

what happens to the NADH after the link reaction?

A

it enable a great deal of ATP to be generated via chemiosmosis and oxidative phosphorylation.

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29
Q

Draw out the krebs cycle

A
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30
Q

what is the krebs cycle?

A

Third stage in aerobic respiration

follows the Link Reaction

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31
Q

what is produced during one turn of the krebs cycle?

A

1x ATP

3x NADH

1x FADH

[2x CO2]

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32
Q

What is significant about the NADH and FADH produced during the krebs cycle?

A

These reduced coenzymes subsequently supply electrons into Electron Transfer Chains and lead to the production of much more ATP by chemiosmosis and oxidative phosphorylation.

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33
Q

what is the link reaction?

A

second stage of aerobic respiration

following glycolysis

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34
Q

what are the five steps of the krebs cycle?

A
  1. The four carbon acceptor molecule OAA (oxaloacetate) combines with a (two carbon) acetyl group supplied by acetyl‐CoA (from the Link Reaction), forming the six carbon product, citrate (or citric acid)
  2. The citrate is decarboxylated (meaning carbon dioxide is released in the reaction) and oxidised (or dehydrogenated) by NAD (which becomes reduced as it gains hydrogen) leaving a five carbon compound
  3. The five carbon compound is itself decarboxylated (releasing another carbon dioxide molecule) and oxidised (or dehydrogenated) by NAD (which becomes reduced) to give a four carbon compound
  4. Further oxidation (dehydrogenation) reactions follow in order to regenerate the acceptor molecule OAA, during which there is reduction of another NAD, plus reduction of one FAD coenzyme and synthesis of one ATP molecule by substrate‐level phosphorylation
  5. Since OAA has been regenerated, the Cycle can continue as OAA will again combine with an acetyl group supplied by acetyl‐CoA, forming citrate.
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35
Q

what is regenerated in the krebs cycle?

A

OAA (oxaloacetate)

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36
Q

What is the NADH and FADH use for?

A

These reduced coenzymes now supply electrons into Electron Transfer Chains,

37
Q

where is NADH and FADH use in the electron tranpsort chain?

A

NADH supplies electrons at the beginning of the ETC

FADH supplies electons to a component later in the ETC.

38
Q

What happens to the electron carriers in the ETC?

A

The electrons from reduced NAD or FAD are passed along a chain of electron carriers, each of which is reduced and then oxidised in turn as it accepts and then loses an electron.

As the reduced NAD/FAD molecules give electrons into the ETC, they also release H+ ions into the mitochondrial matrix

39
Q

Draw the electron transport chain

A
40
Q

Describe the movement of H+ ions in the etc

A

Some of the electron carriers in the ETC act as proton pumps and, using the energy released as the electrons pass from carrier to carrier, they actively transport the H+ ions against their concentration gradient across the inner mitochondrial membrane, from the matrix into the inter‐membrane space.

In this way, a steep proton gradient (i.e. steep concentration gradient of H+ ions or Proton Motive Force) is set up, meaning there is a strong tendency of H+ ions to move back across the inner mitochondrial membrane into the matrix – but this membrane is itself not very permeable to H+ ions.

There are however many ATP synthase proteins embedded in the inner mitochondrial membrane, which have a pore that allows H+ ions to pass through, down their concentrationgradient back into the matrix. This flow of H+ ions down their concentration gradient is called chemiosmosis.

‘Chemiosmotic theory’ is the idea that the flow of H+ ions down their concentration gradient drives (i.e. causes, provides the energy) for ATP synthesis.

The proposed mechanism is that the flow of H+ ions releases energy which causes turning movements in part of the ATP synthase protein, and these movements are crucial in the catalytic mechanism by which ATP is synthesised in a condensation reaction between ADP and Pi on the innermost surface of the inner mitochondrial membrane.

The synthesis of ATP (i.e. phosphorylation of ADP) by this mechanism depends ultimately on the series of oxidation‐reduction reactions that the electron carriers in the ETC undergo following receipt of electrons from reduced NAD or FAD; hence the mechanism is also referred to as oxidative phosphorylation.

41
Q

how the proton gradient set up by the ETC is used to drive ATP synthesis by oxidative phosphorylation carry on forever?

A

the last carrier in the ETC needs to be able to pass electrons on (such that it is re‐oxidised) to a final electron acceptor (which will be reduced): this final electron acceptor (or hydrogen acceptor) in aerobic respiration is oxygen. One oxygen atom (from an O2 molecule) combines with two electrons from the ETC plus two H+ ions from the matrix), forming a water molecule.

42
Q

What is the net yield of ATP in the whole of aerobic respiration?

A

32 ATP molecules

43
Q

why may the actual yield of ATP be lower than 32 molecules of ATP?

A

oxidative phosphorylation can be inefficient, for example some H+ ions leak back across the inner mitochondrial membrane from the intermembrane space into the mitochondrial matrix. This dissipates the proton gradient (and releases heat), but without the occurrence of chemiosmosis. The consequence is that less ATP is synthesised by ATP synthase, since oxidative phosphorylation depends on chemiosmosis.

44
Q

WHAT PART OF RESPIRATION IS THE ETC IN?

A

OXIDATIVE PHOSPHORYLATION

45
Q

What is the net yeild of ATP in anaerobic repsiration?

A

2 ATP molecules from glycolysis

46
Q

what is a coenzyme?

A

an organic molecule that associates reversibly with an enzyme and is vital in catalysis of a reaction

47
Q

what are the main coenzymes required for respiration?

A

NAD, FAD, Coenzyme A, [ADP and ATP]

48
Q

Why is NAD an important coenzyme?

A

This is a hydrogen carrier (or a carrier of electrons and H+ ions), capable of oxidising another compound (becoming reduced itself) and then reducing another compound (becoming re‐oxidised itself), i.e. NAD participates in redox reactions

The oxidised form of NAD is required in glycolysis, the Link Reaction and the Krebs Cycle; during these processes, NAD becomes reduced

Reduced NAD then supplies electrons into the beginning of the Electron Transfer Chain, leading to ATP synthesis by chemiosmosis and oxidative phosphorylation

Approximately 2.5‐3 ATP molecules are made via oxidative phosphorylation for each reduced NAD that supplies electrons into an ETC.

In anaerobic respiration (see below), reduced NAD donates a hydrogen atom to reduce pyruvate to lactate (in lactate fermentation), or to reduce ethanal to ethanol in alcoholic fermentation: this re‐oxidises the NAD so that it is once more available for use in glycolysis, keeping glycolysis running in order to make ATP by substrate‐level
phosphorylation.

49
Q

why is FAD an important coenzyme?

A

This is also a hydrogen carrier (or a carrier of electrons and H+ ions), capable of oxidising another compound (becoming reduced itself) and then reducing another compound (becoming re‐oxidised itself), i.e. FAD participates in redox reactions

The oxidised form of FAD is only required the Krebs Cycle (not in glycolysis or the Link Reaction); during the Krebs Cycle, FAD becomes reduced

Reduced FAD then supplies electrons into the middle (not the beginning) of the Electron Transfer Chain, leading to ATP synthesis by chemiosmosis and oxidative phosphorylation

Approximately 1.5‐2 ATP molecules are made via oxidative phosphorylation for each reduced FAD that supplies electrons into an ETC.

50
Q

what is the short hand for Coenzyme A?

A

CoA

51
Q

why is Coenzyme A an important coenzyme?

A

Unlike NAD and FAD, CoA does not participate in redox reactions

CoA is used in the Link Reaction: CoA combines with acetate (formed by oxidation and decarboxylation of pyruvate), and forms acetyl‐CoA

Acetyl‐CoA is used to transfer acetyl groups into the Krebs Cycle: the acetyl‐CoA undergoes a reaction with the acceptor molecule OAA (oxaloacetate), forming citrate and regenerated CoA (which is reusable and can now participate in another Link Reaction)

52
Q

why is ADP/ATP an important coenzyme?

A

ADP can accept a phosphate group from another molecule (dephosphorylating it), whereas ATP can donate a phosphate group to another molecule (phosphorylating it): ADP and ATP are therefore acting as coenzyme that transfer phosphate groups in enzyme‐catalysed reactions

Two ATP molecules are used to phosphorylate glucose (twice) to produce hexose‐1,6‐ bisphosphate at the start of glycolysis: this activates the glucose

Later in glycolysis, ADP accepts phosphate from triose phosphate: this generates ATP by substrate‐level phosphorylation, to be used as an immediate energy source

In the Krebs cycle, ADP accepts phosphate from an intermediate during the regeneration of OAA from citrate: this generates ATP by substrate‐level phosphorylation

In oxidative phosphorylation, ADP combines with a phosphate group from the matrix in a reaction catalysed by ATP synthase: this captures the energy released by chemiosmosis.

53
Q

what is anaerobic repsiration?

A

Anaerobic respiration (also called fermentation) is the incomplete breakdown of glucose molecules (or other respiratory substrates) in the absence of oxygen, releasing a limited amount of energy for ATP production.

54
Q

what is an Obligate aerobe?

A

e.g. mammals: can only survive if they can aerobically respire (although certain individual cells, e.g. in muscles, may temporarily use anaerobicrespiration to supplement aerobic respiration and generate additional ATP during exercise);

55
Q

what is an Facultative anaerobe?

A

e.g. yeast: will aerobically respire if oxygen is available but can survive (albeit with lower metabolic rate and cell division rate) in the absence of oxygen by anaerobically respiring;

56
Q

what is an Obligate anaerobe?

A

e.g. some prokaryotes (including Clostridium difficile): can only survive in the absence of oxygen and can only respire anaerobically – in fact oxygen is toxic to them.

57
Q

what is the efficiency of anaerobic repiration like?

A

Not very efficient.

aerobic respiration, in which glucose is completely oxidised and broken down in the presence of oxygen, is much more efficient in producing ATP than anaerobic respiration.

58
Q

what are the two main advantages of anaerobic respiration?

A
  1. Allows some ATP to be made (only by substrate level phosphorylation in glycolysis), even when oxygen is not available as a final electron (or hydrogen) acceptor: for example, enabling a high rate of muscle contraction to be sustained in a mammal escaping from a predator
  2. Allows the regeneration of the oxidised form of NAD: this is critical in allowing glycolysis to continue (and thus continued ATP production by substrate‐level phosphorylation). Glycolysis requires oxidised NAD but involves its reduction to reduced NAD; the total availability of NAD is fixed and limited in the cell so glycolysis will stop if reduced NAD cannot be re‐oxidised for reuse.
59
Q

why does anaerobic respiration produces a much lower yield of ATP per glucose respired than aerobic respiration?

A

In anaerobic respiration, the only step which produces ATP is glycolysis: there is a net yield of 2 ATP (per glucose) formed by substrate‐level phosphorylation

There is no Krebs cycle in anaerobic respiration (since pyruvate does not enter the mitochondria and does not undergo the Link Reaction), so no further opportunity for substrate‐level phosphorylation after glycolysis

Most significantly, there is no net production of reduced NAD (because that produced in glycolysis is immediately re‐oxidised and there is no Link Reaction and no Krebs Cycle occuring) and no reduced FAD production (due to absence of Krebs cycle)

This means there are no reduced coenzymes supplying electrons to the Electron Transfer Chains in the inner mitochondrial membrane, hence no establishment of a proton gradient, no chemiosmosis and no production of ATP by oxidative phosphorylation.

60
Q

what is most of the ATP in aerobic repsiration made by?

A

Oxidative phosphorylation (ETC)

61
Q

Draw out lactate fermentation

A
62
Q

Describe lactate fermentation

A

Glycolysis occurs first, resulting in the breakdown and oxidation of each glucose molecule into two molecules of pyruvate; there is a net yield of two ATP molecules by substrate‐level phosphorylation

During glycolysis, oxidised NAD is reduced to form reduced NAD, however the total amount of NAD in a cell is limited. This means that glycolysis (and hence ATP production) will stop unless the reduced NAD can be re‐oxidised and reused, since the oxidised form is required in glycolysis

To achieve re‐oxidation of reduced NAD, pyruvate itself acts as a hydrogen acceptor, becoming reduced to lactate in a reaction catalysed by lactate dehydrogenase enzyme, found in the cytoplasm.

63
Q

what is lactate also known as?

A

lactic acid

64
Q

what does lactic acid do?

A

H+ ions from the acid lower the pH in muscle fibres if it accumulates, potentially disrupting the tertiary structures of proteins in the myofibrils, causing the contraction mechanism to work less efficiently.

65
Q

what happens to the lactic acid from lactate fermentation?

A

Lactate passes out of muscle fibres into the blood and is taken to the liver. In the liver, the lactate can be converted (oxidised) back into pyruvate, which is then respired aerobically if oxygen is present (i.e. enters mitochondria and undergoes the Link Reaction and Krebs cycle), with the final products being carbon dioxide and water

66
Q

what is oxygen debt, and what causes it?

A

what: the additional oxygen needed after exercise for the liver tobreakdown lactate produced by anaerobic respiration

cause: breakdown of lactate produced by anaerobic respiration in muscles actually requires increased oxygen consumption by liver cells

67
Q

Draw a diagram for Alcoholic fermentation in yeast

A
68
Q

How is ethanol produced by yeast?

A

glucose respired anaerobically

Glycolysis occurs first, resulting in the breakdown and oxidation of each glucose molecule into two molecules of pyruvate; there is a net yield of two ATP molecules by substrate‐level phosphorylation

During glycolysis, oxidised NAD is reduced to form reduced NAD, however the total amount of NAD in a cell is limited. This means that glycolysis (and hence ATP production) will stop unless the reduced NAD can be re‐oxidised and reused, since the oxidised form is required in glycolysis

To achieve re‐oxidation of reduced NAD so that glycolysis can continue:
o Pyruvate is first decarboxylated to ethanal, in a reaction catalysed by pyruvate decarboxylase enzyme (that releases carbon dioxide);o It is this ethanal which acts as the final hydrogen acceptor, converting reduced
NAD to oxidised NAD as the ethanal itself is reduced to ethanol; this reaction is catalysed by alcohol/ethanol dehydrogenase, in the cytoplasm.

69
Q

what is substrate level phosphorylation?

A

The formation of ATP without the use of the electron transfer chain. ie in krebs cycle and glycolysis

ADP + Pi -> ATP

70
Q

Is alcohol fermentation reversible?

A

No, due to the decarboxylation step (CO2 produced), i.e. the ethanol cannot be converted back to pyruvate

71
Q

at what % ethanol does is the yeast killed? and why is it killed?

A

15%

Killed due to disruption to the phospholipid bilayer

72
Q

which respiratory substrate releases the most energy per gram?

A

Lipids release the most energy per gram when respired (about double the amount compared to respiration of carbohydrates or proteins)

73
Q

why do lipids release the most energy per gram when respired?

A

The higher energy value of lipids is due to their higher proportion of hydrogen: thisleads to more production of reduced NAD when they are oxidised and so more ATP production via chemiosmosis and oxidative phosphorylation

To respire triglycerides (which are stored in the body as subcutaneous and visceral fat), they are first hydrolysed to glycerol and fatty acids (by lipase enzymes)

Glycerol can be converted to pyruvate, which enters mitochondria and undergoes the Link Reaction to form acetyl‐CoA which enters the Krebs Cycle

Meanwhile, fatty acids undergo process called beta‐oxidation, in which they are broken down by removing two carbon sections at a time, which form many acetyl‐CoA molecules to fuel many turns of the Krebs Cycle; each turn generates one ATP by substrate level phosphorylation plus 3 reduced NAD and 1 reduced FAD to drive much more ATP production by oxidative phosphorylation.

74
Q

what amount of energy do proteins release per gram?

A

Proteins release around the same amount of energy per gram as carbohydrates when respired

75
Q

why do proteins release around the same amount of energy per gram as carbohydrates when respired?

A

To respire proteins, they are first hydrolysed to amino acids (by protease enzymes), in a step which consumes some ATP and thus reduces the net yield of ATP produced;

Amino acids undergo deamination (removal of amine group) and can then be converted to pyruvate, which enters mitochondria and undergoes the Link Reaction to form acetyl‐CoA which enters the Krebs Cycle

76
Q

what is the Respiratory quotient?

A

Volume of CO2 produced
Volume of O2 consumed

77
Q

what is the RQ of carbohydrates?

A

1.0

suggesting rates of oxygen consumption and carbon dioxide production are equal;

78
Q

what is the RQ for proteins?

A

0.9

relatively more oxygen is needed to respire proteins than carbohydrates; this is due to the lower proportion of oxygen found in protein molecules, meaning that more oxygen is needed to oxidise them in respiration

79
Q

what is the RQ for lipids?

A

0.7

even more oxygen is needed to respire lipids than proteins or carbohydrates; this is due to the even lower proportion of oxygen found in lipid molecules, meaning that even more oxygen is needed to oxidise them in respiration

80
Q

what is happeneing if the respiratory quotient is greater than 1?

A

Some Anaerobic respiration is occuring since more CO2 is being released than O2 being used up.

81
Q

what piece of apparatus do we use to measure the rate of respiration?

A

Respirometer

82
Q

how do we measure the rate of aerobic respiration?

A

rate of oxygen consumption.

83
Q

draw a diagram of a aerobic respiration investigation

A
84
Q

what control can we use in aerobic respiration?

A

Dead woodlice

85
Q

how do we measure the rate of anaerobic respiration?

A

rate of carbon dioxide production or time taken (t) to achieve a certain degree of cloudiness could be measured, from which the anaerobic respiration rate could be calculated as 1/t.

86
Q

Draw the diagrams for an anerobic repsiration investigation

A
87
Q

what needs to be controlled when investigating respiration?

A

Temperature

pH

Different types of respiratory substrate (glucose, sucrose, lactose etc)

Concentration of respiratory substrate.

88
Q

Validity of respiration investigation.

A

If the changes in gas volume occurring are very small, this means large percentage errors on the measurements – it is generally better to find the change in gas volume over a longer time period or to include more organisms, so that the changes are biggerand the percentage errors lower;

If any gas leaks out of the apparatus, the changes in volume recorded are smaller than they should be, giving an underestimation of the respiration rate – all joins in the respirometer must be sealed carefully before readings are taken

If judging the position of the meniscus of a fluid droplet, the subjectivity of this judgement will mean poor accuracy and poor repeatability in the data – where possible, use digital apparatus to make measurements in order to remove subjectivity

Taking readings only infrequently means the trend over time will not be very accurate, since we do not have information about what happens to the rate between the data points – take readings more often so that more detail of the change over time is obtained

Consider whether the respirometer is measuring the rate of aerobic or anaerobic respiration, or could there be a mixture of both happening and/or photosynthesis in addition to respiration (!) – if a change in gas volume is being measured, there will be a serious concern about validity if we are not certain what is causing the change.

89
Q

adaptations to low o2 environments

A

MPW biology (26 decks)

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