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5- Energy transfer in and between organisms > Respiration > Flashcards

Respiration Flashcards

1
Q

What are the four stages of aerobic respiration

A

1) Glycolyis
2) Link reaction
3) Krebs cycle
4) Oxidative phosphorylation

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2
Q

What are the two forms of cellular respiration

A
  1. Aerobic respiration which requires oxygen and produces carbon dioxide, water and much ATP
  2. Anaerobic respiration which takes place in the absence of oxygen and produces lactate (in animals) or ethanol and carbon dioxide (in plants and fungi) but only a little ATP in both cases.
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3
Q

Summarise what happens during the first stage of aerobic respiration- glycolysis

A

Glucose, which is a 6-carbon molecule is split into two 3-carbon pyruvate molecules.

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4
Q

Summarise what happens during the second stage of aerobic respiration- the link reaction

A

The 3-carbon pyruvate molecules enter into a series of reactions which lead to the formation of acetylcoenzyme A, a 2-carbon molecule

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5
Q

Summarise what happens during the third stage of aerobic respiration- Krebs cycle

A

The introduction of acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of reduced NAD and FAD.

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6
Q

Summarise what happens during the fourth stage of aerobic respiration- oxidative phosphorylation

A

The use of electrons, associated with reduced NAD and FAD, released from the Krebs cycle to synthesise ATP with water produced as a by-product.

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7
Q

What is glycolysis

A

-The initial stage in both aerobic and anaerobic respiration.
- The 6-carbon glucose molecule is split into two 3-carbon pyruvate molecules.

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8
Q

Name the four stages in glycolysis

A

1) Phosphorylation of glucose to glucose phosphate
2) Splitting of the phosphorylated glucose
3) Oxidation of triose phosphate
4) The production of ATP

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9
Q

Describe the first stage of glycolysis

A
  1. Phosphorylation of glucose to glucose phosphate:
    - Before it can be split into two,glucose must first be made more reactive by the addition of two phosphate molecules.
    - The phosphate molecules come from the hydrolysis of two ATP molecules to ADP.
    - This provides the energy to activate glucose and lowers the activation energy for the enzyme-controlled reactions that follow.
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10
Q

Describe the second stage of glycolysis

A
  1. Splitting of phosphorylated glucose:
    - Each glucose molecule is split into two 3-carbon molecules known as triose phosphate.
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11
Q

Describe the third stage of glycolysis

A
  1. The oxidation of triose phosphate:
    - Hydrogen is removed from each of the two triose phosphate molecules and transferred to a hydrogen-carrier molecule known as NAD to form reduced NAD
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12
Q

Describe the fourth stage of glycolysis

A
  1. The production of ATP:
    - Enzyme-controlled reactions convert each triose phosphate into another 3-carbon molecule called pyruvate.
    - In the process,four molecules of ATP are regenerated from ADP.
    - Across all of glycolysis, a there is a net production of two ATP molecules.
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13
Q

How many stages of glycolysis are there

A

Four

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14
Q

Describe the overall yield from glycolysis

A
  • Two molecules of ATP (four molecules of ATP are produced, but two were used in the initial phosphorylation of glucose and so the net increase is two molecules).
  • Two molecules of reduced NAD
  • Two molecules of pyruvate
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15
Q

Why does glycolysis provide indirect evidence for evolution

A

It is a universal feature of every living organism

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16
Q

What does glycolysis need to occur

A
  • The enzymes for the glycolytic pathway are found in the cytoplasm of cells and so glycolysis does not require any organelle or membrane to take place.
  • Glycolysis does not require oxygen and therefore can take place in the absence of oxygen.
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17
Q

What stage of respiration is glycolysis

A

The first stage

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18
Q

What stage of aerobic respiration is the link reaction

A

The second

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19
Q

What stage of aerobic respiration is the Krebs cycle

A

The third

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20
Q

What stage of aerobic respiration is oxidative phosphorylation

A

The fourth (final)

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21
Q

Describe the link reaction

A
  • The pyruvate molecules produced in the cytoplasm during glycolysis are actively transported into the matrix of mitochondria.
  • The pyruvate is then oxidised to acetate. In this reaction, the 3-carbon pyruvate loses a carbon dioxide molecule and two hydrogens.
  • These hydrogens are accepted by NAD to form reduced NAD (NADH), which is later used to produce ATP.
  • The 2-carbon acetate combines with a molecule called coenzyme A (CoA) to produce a compound called acetylcoenzyme A.
  • The overall equation can be summarised as: pyruvate+ NAD + CoA —> acetyl CoA + reduced NAD + CO2
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22
Q

What is the overall equation for the link reaction of aerobic respiration

A

Pyruvate+NAD+CoA—> acetyl CoA+ reduced NAD+CO2

23
Q

Describe what happens during the Krebs cycle

A
  • The 2-carbon acetylcoenzyme A from the link reaction combines with a four carbon molecule to produce a 6-carbon molecule.
  • In a series of reactions this 6-carbon molecule loses carbon dioxide and hydrogen to give a 4-carbon molecule and a single molecule of ATP produced as a result of substrate-level phosphorylation.
  • The 4-carbon molecule can now combine with a new molecule of acetylcoenzyme A to begin the cycle again.
24
Q

For each molecule of pyruvate, what do the link reaction and Krebs cycle produce

A
  • Reduced coenzymes such as NAD and FAD. These have the potential to provide energy to produce ATP molecules by oxidative phosphorylation and are therefore important products of the Krebs cycle.
  • One molecule of ATP (per pyruvate)
  • Three molecules of carbon dioxide.
25
Q

Per each glucose molecule at the start of aerobic respiration, what does the link reaction and Krebs cycle produce

A
  • Reduced coenzymes such as NAD and FAD. These have the potential to provide energy to produce ATP molecule by oxidative phosphorylation and are therefore the important products of the Krebs cycle.
  • Two molecules of ATP
  • Six molecules of carbon dioxide.
26
Q

Define coenzyme

A

An organic molecule that binds to the active site of certain enzymes to assist in the catalysis of a reaction.

27
Q

What key role do coenzymes play in photosynthesis and respiration

A

They carry hydrogen atoms from one molecule to another

28
Q

What are the coenzymes that are needed in photosynthesis and respiration

A
  • NAD, which is important throughout respiration.
  • FAD, which is important in the Krebs cycle
  • NADP, which is important in photosynthesis.
29
Q

Which is the most important coenzyme in respiration

A
  • In respiration, NAD is the most important carrier.
  • It works with dehydrogenase enzymes that catalyse the removal of hydrogen atoms from substrates and transfer them to other molecules involved in oxidative phosphorylation.
30
Q

Explain the four reasons why the Krebs cycle performs an important role in the cells of organisms

A

1) It breaks down macromolecules into smaller ones- pyruvate is broken down into carbon dioxide.
2) It produces hydrogen atoms that are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation. This leads to the production of ATP that provides metabolic energy for the cell.
3) It regenerates the 4-carbon molecule that combines with acetylcoenzyme A, which would otherwise accumulate
4) It is a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, amino acids and chlorophyll.

31
Q

Summarise what oxidative phosphorylation is

A

The mechanism by which some of the energy of the electrons within the hydrogen atoms is conserved in the formation of adenosine triphosphate (ATP)

32
Q

Where does oxidative phosphorylation take place

A

The mitochondria

33
Q

Describe the structure of a mitochondrion

A
  • Each mitochondrion is bound by a smooth outer membrane and an inner one that is folded into extensions called cristae.
  • The inner space (matrix) of the mitochondrion contains proteins, lipids and traces of DNA.
  • Within the inner folded membrane (cristae) are the enzymes and other proteins involved in oxidative phosphorylation and hence ATP synthesis.
34
Q

What types of cell have a lot of mitochondria

A

Metabolically active cells such as muscle, liver and epithelial cells.

35
Q

Summarise the way in which ATP is synthesised is oxidative phosphorylation

A

The synthesis of ATP by oxidative phosphorylation involves the transfer of electrons down a series of electron carrier molecules which together form the electron transfer chain.

36
Q

Describe the process of oxidative phosphorylation (chemiosmotic theory of oxidative phosphorylation)

A
  • The hydrogen atoms produced during glycolysis and the Krebs cycle combine with the coenzymes NAD and FAD.
  • The reduced NAD and FAD donate the electrons of the hydrogen atoms they are carrying to the first molecule in the electron transfer chain.
  • The electrons pass along a chain of electron transfer carrier molecules in a series of oxidation-reduction reactions.
  • As the electrons flow along the chain, the energy they release causes the active transport of protons across the inner mitochondrial membrane and into the inter-membranal space.
  • The protons accumulate in the inter-membranes space before they diffuse back into the mitochondrial matrix through ATP synthase channels embedded in the inner mitochondrial membrane.
37
Q

Explain the importance of oxygen in respiration

A
  • Oxygen acts as the final acceptor of the hydrogen atoms produced in glycolysis and the Krebs cycle.
  • Without its role in removing hydrogen atoms at the end of the chain, the hydrogen ions (protons) and electrons would ‘back up’ along the chain and the process of respiration would come to a halt.
38
Q

Explain how the energy from the electrons carried by NAD and FAD is released and why

A
  • When lots of energy is released in a single step, the more of it is released as heat and the less there is available for useful purposes.
  • When energy is released a little at a time, more of it can be harvested for the benefit of the organism.
  • For this reason, the electrons carried by NAD and FAD are not transferred in one step.
  • Instead they are passed along a series of electron transfer carrier molecules, each of which is at a slightly lower energy level.
  • The electrons therefore move down an energy gradient.
  • The transfer of electrons down this gradient allows their energy to be released gradually and therefore more usefully.
39
Q

What are two types of molecule that can be used as respiratory substrates under certain circumstances without being first converted to a carbohydrate

A

Proteins and lipids

40
Q

Describe the respiration of lipids

A
  • Before being respired, lipids are first hydrolysed to glycerol and fatty acids.
  • The glycerol is then phosphorylated and converted to triose phosphate which enters the glycolysis pathway and subsequently the Krebs cycle.
  • The fatty acid component is broken down into 2-carbon fragments which are converted to acetyl coenzyme A which enters the Krebs cycle.
  • The oxidation of lipids produced 2-carbon fragments of carbohydrate and many hydrogen atoms.
  • The hydrogen atoms are used to produce ATP during oxidative phosphorylation.
  • For this reason lipids release more than double the energy of the same mass of carbohydrate.
41
Q

Describe the respiration of proteins

A
  • Proteins are first hydrolysed to amino acids.
  • These have their amino group removed (deamination) before entering the respiratory pathway at different points depending on the number of carbon atoms they contain.
  • 3-carbon compounds are converted to pyruvate, while 4-carbon and 5-carbon compounds are converted to intermediates in the Krebs cycle.
42
Q

Why can normal aerobic respiration not happen in the absence of oxygen

A

In the absence of oxygen, neither the Krebs cycle nor electron transfer chain can continue

43
Q

Why can neither the Krebs cycle nor the electron transfer chain occur in the absence of oxygen

A
  • They cannot continue because after a short time, the FAD and NAD will all be reduced.
  • Without oxygen acting as the final electron acceptor, there will be no FAD or NAD to take up the H+ produced during the Krebs cycle and so the enzymes stop working.
  • This only leaves the anaerobic process of glycolysis as a potential source of ATP.
44
Q

What must happen in order for glycolysis to continue as a source of energy when there is a limited supply of oxygen

A
  • For glycolysis to continue to be a source of energy when there is a limited supply of oxygen, it’s products of pyruvate and hydrogen must be removed.
  • The hydrogen must be released from the reduced NAD in order to regenerate NAD.
  • Without this, the already tiny supply of NAD in cells will be entirely converted to reduced NAD, leaving no NAD to take up the hydrogen newly produced from glycolysis.
  • Glycolysis will then grind to a halt.
  • The replenishment of NAD is achieved by the pyruvate molecule from glycolysis accepting the hydrogen from reduced NAD.
  • The oxidised NAD produced can then be used further in glycolysis.
45
Q

What are the two types of anaerobic respiration that occur in eukaryotic cells

A
  • In plants and microorganisms such as yeast, the pyruvate is converted to ethanol and carbon dioxide.
  • In animals, the pyruvate is converted to lactate.
46
Q

Describe the fermentation stage of anaerobic respiration in plants and some microorganisms

A
  • The pyruvate molecule formed at the end of glycolysis loses a molecule of carbon dioxide and accepts hydrogen from reduced NAD to produce ethanol.
  • The equation is: pyruvate + reduced NAD —> ethanol + carbon dioxide + oxidised NAD
47
Q

When may plants and microorganisms undertake anaerobic respiration

A
  • Bacteria and fungi produced ethanol when they respire anaerobically.
  • Some cells of plants may report anaerobically such as root cells under waterlogged conditions.
48
Q

Give some examples of times when animals may respire anaerobically

A
  • A baby animal will respire anaerobically in the period immediately after birth.
  • An animal living in water where oxygen levels are low.
  • During exercise
49
Q

What is the equation for a anaerobic respiration in animals

A

Pyruvate + reduced NAD —> lactate + oxidised NAD

50
Q

What happens after a period of anaerobic respiration in animals

A
  • At some point the lactate produced is oxidised back to pyruvate.
  • This can then be either further oxidised to release energy or converted into glycogen.
  • This happens when oxygen is available again.
51
Q

Why is it important that the lactate produced by anaerobic respiration is oxidised back to pyruvate

A
  • Lactate is toxic and causes cramp and muscle fatigue if it is allowed to accumulate in muscle tissue.
  • As lactate is an acid, it also causes PH changes which affects enzymes.
52
Q

What removes lactate from muscle tissue to be converted to glycogen in the liver

A

The blood

53
Q

What are the two ways that energy is derived from cellular respiration

A
  • substrate-level phosphorylation in glycolysis and the Krebs cycle. This is the direct transfer of phosphate from a respiratory intermediate to ADP to produce ATP.
  • Oxidative phosphorylation in the electron transfer chain. This is the indirect linking of energy from phosphate to ADO to produce ATP involving energy from the hydrogen atoms that are carried on NAD and FAD. Cells produce most of their ATP in this way.

5- Energy transfer in and between organisms (5 decks)

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