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A-Level Biology - OCR A > 5.2.2 Respiration > Flashcards

5.2.2 Respiration Flashcards

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1
Q

What is respiration?

A

The release of energy stored within organic molecules - predominantly Glucose

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2
Q

What is respiration not?

A

The Production/Creation/Making of Energy.

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3
Q

What is the energy from respiration used for?

A

Synthesis of ATP from ADP and inorganic phosphate (Pi)

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4
Q

What is ATP used for?

A

Active transport.

Endocytosis.

Exocytosis.

Protein Synthesis.

DNA replication.

Spindle action in cell division.

Movement - e.g. Flagella, motor proteins.

Active loading.

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5
Q

What is the general word equation for respiration?

A

Glucose + Oxygen -> Carbon Dioxide + Water (+ Energy)

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6
Q

What is the balanced symbol equation for respiration?

A

C6H12O6 + 6O2 -> 6CO2 + 6H2O

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7
Q

What does ATP stand for?

A

adenosine triphosphate

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8
Q

What is ATP known as?

A

The universal energy carrier

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9
Q

Why is ATP known as the Universsal Energy Carrier?

A

It acts as a standard intermediary between energy-releasing and energy-consuming reactions within a cell.

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10
Q

What is the structure of an ATP molecule?

A
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11
Q

How does ATP release energy?

A

As ATP is relatively stable it does not readily break down.
However, it can be hydrolysed by the enzyme ATPase to release energy.

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12
Q

What does ATPase do?

A

Catalyses the reaction that removes a phosphate group from the ATP molecule to form ADP. This releases energy.

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13
Q

How much energy does the hydrolisation of ATP produce?

A

30.5 kj/mol for the first 2 bonds.
13.8 kj/mol for the last bond

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14
Q

What are the stages of Aerobic Respiration?

A

Glycolysis.

Link Reaction.

Krebs Cycle.

Oxidative Phosphorylation.

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15
Q

Where does Glycolysis take place?

A

The cytoplasm of cells of all living organisms that respire.

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16
Q

What is the function of Glycolysis?

A

To turn glucose into two molecules of pyruvate

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17
Q

What are the two parts of glycolysis?

A

Energy Investment Phase.
Energy Payback Stage.

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18
Q

Why is it called the energy investment stage?

A

As two molecules of ATP are needed to carry out this stage - so energy is invested into it.

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19
Q

What happens during the energy investment stage?

A

Glucose is phosphorylated by ATP to form glucose-6-phosphate.
The shape of the molecule is then changed by the isomerase enzyme to form fructose-6-phosphate.
The molecule is then phosphorylated again by ATP to form hexose-1,6-bisphosphate.
Hexose-1,6-bisphosphate then splits into two 3-carbon molecules of Triosephosphate (TP).

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20
Q

What happens in the energy payback stage?

A

An ADP molecule is phosphorylated to form ATP (substrate-level phosphorylation) and one hydrogen is lost to reduce NAD to form NADH. This forms an intermediate 3-carbon compound.
Another ADP molecule is phosphorylated to form an ATP molecule - Substrate-level phosphorylation. This produces a molecule of Pyruvate

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21
Q

How many Pyruvate molecules are produced at the end of glycolysis?

A

Two.
During the splitting of the hexose, two TP molecules are produced. Both of these go through the energy payback stage to produce one Pyruvate molecule each.

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22
Q

What is the mitochondria?

A

An organelle present in all types of eukaryotic cells.

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23
Q

What is the general structure of the mitochondria?

A

Has an inner and outer phospholipid membrane which makes up the envelope.
The outer membrane is smooth and the inner is folded into cristae - giving it a large surface area.
The inner membrane encapsulates the matrix.
The space between the inner and outer mitochondrial membranes is called the intermembrane space.

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24
Q

What is the structure of the mitochondrial matrix?

A

It is enclosed by the inner membrane. It’s a semi-rigid, gel-like structure.
The matrix contains; enzymes that catalyse stages of the link reaction and Krebs cycle, molecules of coenzymes (e.g. A NAD and FAD), oxaloacetate for the Krebs cycle, mitochondrial DNA which codes for mitochondrial enzymes and ribosomes, and mitochondrial ribosomes where proteins are assembled.

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25
Q

What is the structure of the outer mitochondrial membrane?

A

Has a similar structure to most other membranes with a few proteins that act as channels for molecules such as pyruvate.

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26
Q

What is the structure of the inner mitochondrial membrane?

A

The inner membrane is less permeable to small ions such as hydrogen than the outer. The folded cristae give it a large surface area for carriers and ATP synthase molecules.

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27
Q

What is the intermembrane space?

A

Between the inner and outer mitochondrial membranes and is involved with oxidative phosphorylation. It is in close contact with the matrix to allow NADH and FADH to deliver hydrogens through the electron transfer chain.

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28
Q

Where does the Link reaction take place?

A

The matrix of the Mitochondria

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29
Q

What is the need for the link reaction?

A

Pyruvate (produced at the end of glycolysis) is too large to pass through the outer and inner mitochondrial membranes and into the matrix.

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30
Q

What happens in the Link Reaction?

A

Pyruvate is decarboxylated to form a 2-carbon molecule of acetate.

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31
Q

How does the link reaction take place?

A

CO2 is released as pyruvate is decarboxylated - catalysed by pyruvate decarboxylase.
NAD is reduced to NADH to remove the hydrogen - catalysed by pyruvate dehydrogenase.
This produces an acetate molecule.

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32
Q

What happens to the Acetate produced during the link reaction?

A

It combines with coenzyme A (CoA) to form Acetyl CoA

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33
Q

What does the Acetyl CoA do?

A

Can enter the mitochondrial matrix through the inner and outer mitochondrial membrane to enter the Krebs cycle.

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34
Q

What is the overall equasion for the link reaction?

A

2Pyruvate + 2NAD + 2CoA -> 2CO2 + 2NADH + 2Acetyl CoA
Each is doubled as the link reaction takes place twice for each glucose molecule

35
Q

What is the Krebs Cycle?

A

A series of enzyme-catalysed reactions that oxidise Acetate.

36
Q

Where does the Krebs Cycle take place?

A

The mitochondrial matrix

37
Q

Where does Acetate come from for the kreb cycle?

A

Most from glycolysis of glucose and then the link reaction. However, it can come from fatty acids and amino acids.

38
Q

What does the Krebs cycle look like?

A
39
Q

What happens in the krebs cycle?

A

The acetyl group is released from acetyl CoA and combines with the 4-carbon compound oxaloacetate to form a 6-carbon compound, citrate. The CoA leaves to be used again in the link reaction.
Citrate is decarboxylated and dehydrogenated to produce succinate (5-carbon), CO2 and NADH.
Succinate is further decarboxylated and dehydrogenated to produce a 4-carbon molecule and a molecule of CO2 and NADH.
Substrate-level phosphorylation then takes place to produce a molecule of ATP.
It gets dehydrogenated to form FADH from FAD.
More dehydrogenation to turn NAD into NADH.
Changes back into oxaloacetate

40
Q

What are the key bits of the krebs cycle?

A

Oxaloacetate.
Citrate.
CO2, NADH.
Succinate.
CO2, NADH.
ATP.
FADH.
NADH.
Oxaloacetate.

41
Q

How many times does the krebs cycle take place?

A

Twice per glucose molecule - as two tp produced during glycolysis.

42
Q

What is oxidative phosphorylation?

A

The final stage of aerobic respiration which produces the most ATP in the presence of oxygen.

43
Q

Where does oxidative phosphorylation occur?

A

The inner mitochondrial membrane and intermembrane space

44
Q

What does oxidative phosphorylation involve?

A

Proteins that make up the electron transfer chain within the inner mitochondrial membrane and chemiosmosis within the intermembrane space.

45
Q

What happens to NADH and FADH in oxidative phosphorolation?

A

They are oxidised as they deliver hydrogen to the electron transfer chain. The hydrogen released is split into protons(H+) and electrons e-

46
Q

What happens to the hydrogen ions and electrons released from the H from NADH?

A

e- moves into the protein cytochrome I. The protein uses the energy to turn it into a pump in order to pump protons (H+) through the membrane.

47
Q

What happens to the hydrogen ions and electrons released from the H from FADH?

A

e- moves into the protein cytochrome II.
Cytochrome II is an extrinsic protein so the protons remain in the matrix and move to other cytochromes within the membrane.

48
Q

What happens to the electrons in the cytochromes?

A

They pass down the chain of cytochromes (2, 3 and 4), by a series of redox reactions, and provide energy to pump hydrogen.
They stop at cytochrome IV.

49
Q

What happens to the hydrogens after being pumped?

A

A high number of hydrogen ions (protons) build up in the intermembrane space and create an electrochemical gradient with a high concentration by the cytochromes.

50
Q

How do the protons move to counteract the electrochemical gradient?

A

By chemiosmosis from the high to low concentration by the ATP synthase molecules.

51
Q

What happens at the ATP synthase molecules?

A

Protons enter ATP synthase from the intermembrane space and diffuse through back into the matrix.

52
Q

Why can hydrogen pass through ATP synthase?

A

ATP synthase is permeable to Hydrogen. As it is the only place on the inner membrane lots of hydrogen passes through the molecules.

53
Q

What happens to the ATP synthase as the protons pass through?

A

Creates the proton motor force which rotates the ATP synthase molecule.

54
Q

What effect does the rotating ATP Synthase molecule have?

A

Combines an ADP molecule with an inorganic phosphate group (Pi) in the matrix to form a molecule of ATP.

55
Q

What is the role of oxygen in oxidative phosphorylation?

A

Acts as the final electron acceptor.
it combines with electrons and hydrogen to form water.

56
Q

What is the equation for the formation of water at the end of oxidative phosphorylation?

A

4H+ + 4e- +O2 -> 2H2O
or
2H+ + 2e- + 1/2 O2 -> H2O

57
Q

What does anaerobic mean?

A

without oxygen

58
Q

What happens to aerobic respiration if no oxygen is present?

A

Oxygen can’t act as the final electron acceptor in oxidative phosphorylation so no water is formed.
This means that a high concentration of protons builds up in the matrix, reducing concentration across the membrane so protons don’t move through the ATP synthase molecule - oxidative phosphorylation stops.
NADH and FADH are unable to offload hydrogen atoms so they can’t be oxidised so the Link reaction and Krebs cycle stops.

59
Q

Why is anaerobic respiration not preffereable?

A

It is unsustainable and inefficient as only small amounts of ATP are produced

60
Q

How does anaerobic respiration produce ATP?

A

Through glycolysis, as no oxygen is needed for this stage.
Only small quantities are produced.

61
Q

What method do fungi and plants use to oxidise NADH to NAD?

A

The Ethanol Fermentation Pathway

62
Q

What method do mammels use to oxidise NADH to NAD?

A

The Lactate Fermentation Pathway

63
Q

Where do the ethanol and lactate fermentation pathways take place?

A

Cytoplasm

64
Q

What happens in the ethanol fermentation pathway?

A

Pyruvate from glycolysis is decarboxylated by pyruvate decarboxylase to produce ethanal.
Ethanal accepts hydrogen from NADH to form ethanol. NAD returns to glycolysis.

65
Q

Where is the ethanol fermentation pathway sustainable?

A

Yeast

66
Q

What happens in the lactate fermentation pathway?

A

Pyruvate produced in glycolysis accepts hydrogen from NADH in a reaction catalysed by lactate dehydrogenase.
This causes pyruvate to be reduced to lactate.
And NADH to be oxidised to NAD which returns to glycolysis.

67
Q

What happens to the produced lactate?

A

Builds up in the muscles and liver and forms lactic acid. This is felt as a stitch.

68
Q

What happens when oxygen becomes avaliable again?

A

The reverse reaction takes place to convert lactate to pyruvate which can then enter the link reaction and continue aerobic respiration.
Or it can be recycled to glucose or glycogen for storage.

69
Q

Why does the lactate pathway cause an oxygen debt?

A

Oxygen is required to turn lactate into pyruvate, so we are in oxygen debt as more oxygen is needed to reverse the effect of anaerobic respiration.

70
Q

What molecules can be used as respiratory substrates?

A

Carbohydrates.
Lipids.
Proteins.

71
Q

What is a respiratory substrate?

A

Something that can be oxidised to produce ATP, Carbon Dioxide and water in respiration.

72
Q

How are carbohydrates used as a respiratory substrate?

A

Glucose is the main respiratory substrate and some cells can only use glucose.
Disaccharides can be digested into monosaccharides to be used in respiration.
Monosaccharides like fructose and galactose can be changed by the isomerase enzyme to make glucose.

73
Q

How can lipids be used as a respiratory substrate?

A

Triglycerides are hydrolysed by lipase to glycerol and fatty acids.

74
Q

How is glycerol used as a respiratory substrate?

A

Glycerol can be converted to triosephosphate and respired.

75
Q

How are fatty acids used as a respiratory substrate?

A

Fatty acids contain lots of hydrogen which acts as a major source of protons for oxidative phosphorylation.
Fatty acids can be combined with CoA - using ATP - which enters the mitochondrial matrix where it’s broken down into 2-carbon molecules of acetyl where it enters the Krebs cycle.

76
Q

How are proteins used as a respiratory substrate?

A

Amino acids get deaminated within the liver to produce a keto acid which enters the respiratory pathway as pyruvate, Acetyl CoA or a kreb cycle acid (e.g. oxaloacetate)

77
Q

When are proteins used a lot as a respiratory substrate?

A

During fasting, starvation or prolonged excersise.

78
Q

What does RQ Stand for?

A

Respiratory Quotient

79
Q

What is the formula for RQ?

A

RQ = CO2 produced / O2 consumed
values are in moles produced

80
Q

What does an RQ of 1 show?

A

Carbohydrates are being respired

81
Q

What does an RQ of 0.8-0.9 show?

A

amino acids are being respired

82
Q

What does an RQ of approximately 0.7 mean?

A

Fatty acids are being respired

83
Q

What does an RQ of over 1 mean?

A

Some anaerobic respiration is taking place.
There is more CO2 being produced than O2 being consumed

A-Level Biology - OCR A (16 decks)

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