C1: Aerobic respiration

Question 1

What are the four stages of aerobic respiration

Answer 1

Glycolysis
Link reaction
Krebs cycle
Electron transport chain

Question 2

What type of organisms carry out respiration

Answer 2

All living organisms

Question 3

Why do all living organisms carry out respiration

Answer 3

To provide energy for the cells

Question 4

Define aerobic respiration

Answer 4

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

Question 4

Describe respiration

Answer 4

It is a catabolic process involving a series of enzyme-controlled reactions
Energy rich respiratory substrates (glucose or fatty acids) are broken down their high energy bonds (C-C, C-H and C-OH) are broken, and lower energy bonds are formed. The excess energy released is used to phosphorylate ADP to ATP or is lost as heat energy.

Question 5

Where does glycolysis take place

Answer 5

Cytoplasm

Question 6

Describe Glycolysis

Answer 6

Glucose is phosphorylated using 2ATP into hexose phosphate.
The hexose phosphate splits into two triose phosphates.
The oxidation of these triose phosphates yields 2ATP by substrate level phosphorylation. Dehydrogenation releases 2 Hydrogens, these hydrogens reduce NAD. The resulting 2x 3C pyruvates diffuse into the mitochondria.

Question 7

What are the products of glycolysis
Include an equation

overall per glucose molecule

Answer 7

2 ATP
2 reduced NAD
2 Pyruvate

Glucose + 2 ATP + 2 NAD —-> 2 Pyruvate + 4 ATP + 2 reduced NAD

Question 8

Define substrate level phosphorylation

Answer 8

When a phosphate group is transferred from a donor molecule to ADP which produces ATP.(glycolyis)
OR
When enough energy is released from a reaction to bind ADP to Pi (Krebs)

Question 9

Define dehydrogenation

Answer 9

the removal of one or more hydrogen atoms from a molecule

Question 10

Where does the link reaction take place

Answer 10

The mitochondrial matrix

Question 11

Describe the link reaction

Answer 11

Decarboxylation of pyruvate catalysed by decarboxylase releases carbon dioxide.
Dehydrogenation catalysed by dehydrogenase releases 2 hydrogen atoms converting NAD to reduced NAD.
This forms acetate.
The addition of coenzyme A to acetate forms acetyl CoA (2C) which enters the Krebs cycle

Question 12

What are the products of the link reaction
Include an equation

Answer 12

Actetyl Coenzyme A
CO2
reduced NAD

Pyruvate + CoA —> AcCoA + CO2 + reduced NAD

Question 13

Define decarboxylation

Answer 13

The removal of a carboxyl group from a molecule releasing CO2

Question 14

Where does the Krebs cycle take place

Answer 14

The mitochondrial matrix

Question 15

Describe the Krebs cycle

Answer 15

AcCoA is added into the cycle at a 4C acid to form a 6C acid (Citric) which is decarboxylated and dehydrogenated to a 5C acid which undergoes dehydrogenation and decarboxylation again to form a 4C acid which with the addition of 2 waters is ddehydrogenated again which forms a 4C acid which is dehydrigenate again to form anothther 4C acid which has water added onto it and the cycle repeats

AcCoA combines with a 4C compound to form a 6C compound.
Decarboxylation forms a 5C compound and dehydrogenation occurs reducing NAD.
Decarboxylation forms a 4C compound and dehydrogenation to reduce NAD. There is also substrate level phosphorylation forming 1 ATP.
Dehydrogenation of this 4C compound forms reduced FAD.
Dehydrogenation again of a 4C coompound forms reduced NAD.

Question 16

What are the products from one Krebs cycle

how many waters are added

Answer 16

2 CO2
3 Reduced NAD
reduced FAD
ATP by substrate level phosphorylation

+ 4 H2O

Question 17

Where does the Electron transport chain take place

Answer 17

The Inner mitochondrial membrane

Question 18

Define oxidative phosphorylation

Answer 18

The energy for making ATP comes from redox reactons and is released in the transfer of electrons along a chain of electron carrier molecules.

Question 19

Describe the passage of electrons in the electron transport chain

Answer 19

High energy electrons from H atoms are provided by NAD and FAD to a series of electron carriers in the ETC.
The energy from the electrons are used by proton pumps.
The electrons pass along the chain of carrier molecules providing energy for each of these proton pumps.
At the end of the chain these electrons combine with H+ and oxygen to form water.

Question 20

Describe the passage of protons in the electron transport chain

Answer 20

Protons accumulate in the inter mitochondrial space so the concentration of protons is higher than in the matrix. so this forms an electrochemical gradient which is maintained by the proton pumps. Protons diffuse back into the mitochondrial matrix via the enzyme ATP synthetase and their electrical potential energy provides suffiecient energy to phosphorylate ADP to ATP

At the end of the chain protons combine with H+ and oxygen to form water.

Question 21

Describe the difference between reduced NAD and reduced FAD

Answer 21

reduced NAD utilises 3 proton pumps
whereas reduced FAD utilises 2 proton pumps

so eventually 3 ATP are formed per reduced NAD
and 2 ATP are produced per reduced FAD

Question 22

Name alternative respiratory substrates other than glucose

Answer 22

Lipids:
Glycerol can be converted into triose phosphate for use in glycolysis

Fatty acids are split into 2C acetate fragments which feed into the krebs cycle as AcCoA

Proteins:
Amino acids are deaminated in the liver into urea and different acids, one of which is pyruvate that is used in the link reaction the others are fed into the krebs cycle as different stages.

Question 23

Use equations to describe the phosphorylation of glycerol

Answer 23

Glycerol + ATP –> glycerol-3-phosphate + ADP + Pi

Glycerol-3-phosphate + NAD —–> reduced NAD + triose phosphate

Question 24

Why do Organisms respire Fat

Answer 24

More C atoms so more CO2 produced. Muscles have a limited blood supply therefore eventually more CO2 will be produved than can be removed. So they respire glucose

Longer chain lipids have more H atoms, so more NAD and FAD are reduced resulting in moe ATP being produced by oxidative phosphorylation.

More H produced so more metabollic water formed = good for desert animals so they respire fat

Question 25

What tissues respire fat

Answer 25

Tissues with a rich blood supply Eg: The liver respires fat

Question 26

When are lipids and proteins used as repsiratory substrates ?

Answer 26

Lipids: when carbohydrate levels within the body are low ( glycogen and blood glucose)

proteins: when carbohydrate and fat are lacking in the diet tissue protein is broken down

Question 27

In aerobic respiration what is the theoretical maximium yield for ATP

per glucose

Answer 27

Total: 38 ATP per glucose

Net 2 ATPs in glycolysis (substrate-level phosphorylation)

2 ATPs in the Krebs cycle (substrate-level phosphorylation)

34 ATPs from oxidative phosphorylation as 10 reduced NAD (2 from glycolysis, two from the link reaction, six from the Krebs cycle) forms 30 ATP and 2 reduced FAD (Krebs cycle) forms 4 ATP

Question 28

Why is the maximum yield never quite reached

Answer 28

proton leakage across the inner ‘impermeable’ membrane ( It doesnt pass through ATP synthestase)

ATP is used to move pyruvate, reduced NAD, reduced FAD and ADP into the matrix

Molecules may leak through membranes