8.2 Cell respiration
Understanding:
Cell respiration involves the oxidation and reduction of compounds
Phosphorylation of molecules makes them lesson stable
In glycolysis, glucose is converted to pyruvate
Glycolysis gives a small net gain of ATP with out the use of oxygen
In aerobic cell respiration pyruvate is concerted into acetyl coenzyme A
In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers
Energy released by oxidation reactions is carried to the cristae of the mitochondria
Transfer of electrons between carriers in the electron transport chain is couple to proton pumping
N chemiosmosis protons diffuse through ATP synthase to generate ATP
Oxygen is needed to bind with the free protons to form water to maintain the hydrogen gradient
The structure of the mitochondria is adapted to the function it performs.
Applications:
Electron tomography used to produce images of active mitochondria
Skills:
Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur
Annotation of a diagram to indicate the adaptations of a mitochondrion to its function
Nature of science:
- Paradigm shifts: the chemiosmotic theory led to a paradigm shift in the field of bioenergetics

Inner membrane
Outer membrane
Cristae
Matrix
Inter membrane space

Inner membrane
Outer membrane
Cristae
Matrix
Inter membrane space
What is the role of each part?

Inner membrane – Electron transport chain and ATP synthase
Outer membrane – Creates a cellular compartment with ideal conditions for aerobic respiration
Cristae – projections of inner membrane which increase surface area for oxidative phosphorylation
Matrix – Contains enzymes for Krebs cycle and link reaction
Inter membrane space - Protons pumped into space by electron transport chain. Small space means concentration builds up quickly

Always occur together
Involve transferring electrons from one thing to another
Oxidation = loss of electrons
Reduction = gain of electrons
For something to gain an electron, something has to lose one
Electron carriers accept or give up electrons as required – linking oxidations and reductions in cells.

Main electron carrier in respiration
(Nicotinamide adenine dinucleotide)
Initially has a positive charge and exists normally as NAD+

1. Two hydrogen atoms removed from substance being reduced
2. One hydrogen is split into a proton and an electron
3. NAD+ accepts the electron, and the proton (H+) is released
4. NAD accepts the proton and electron of the other hydrogen atom
NAD+ + 2H  NADH + H+
Oxidation can be achieved by losing these Hydrogen atoms again

Oxidation and reduction – describe what is happening below:

Addition of a phosphate molecule
Make a molecule less stable – so more likely to react
Reduces the activation energy required for reactions that follow – more likely to occur

Substrate level:
ATP produced via transport of phosphate group from an intermediate group directly to ADP
Oxidative:
ATP produced by reduction/oxidation reactions in an electron transport chain

1. Glycolysis
2. Link Reaction
3. Krebs cycle
4. Electron transport chain
5. Chemiosmosis

Gives a small yield of ATP without the use of oxygen (ANAEROBIC)
Converts glucose into pyruvate
In the cytoplasm of the cell (outside of mitochondrion)
Not a single step process – example of a metabolic pathway
1 glucose = 2 pyruvate
Reduced NAD made (has gained electrons)
Substrate phosphorylation – ATP produced

1. ATP used up to phosphorylate glucose
2. Fructose biphosphate split to form two molecules of triose phosphate
3. Each is then oxidised to glycerate-3-phosphate
(removes H atoms)
4. Hydrogen is accepted by NAD+ to make NADH + H+
5. Phosphate group transferred to ADP to produce more ATP and pyruvate

Two molecules of pyruvate produced in glycolysis per molecule of glucose.
If oxygen is present (AEROBIC) – pyruvate absorbed into mitochondria where it is oxidised (lose electrons) and
decarboxylated to form an acetyl group.
NADH is formed
(Decarboxylated = take away carboxyl group and forms CO
2
)
Acetyl group then joined to coenzyme A to make acetyl coenzyme A
Another metabolic pathway

Link
reaction as it links glycolysis with the cycle of reactions that follow

1. Acetyl CoA from link reaction combines with a 4 carbon compound, making a 6 carbon compound.
2. This is oxidised to form a 5 carbon compound. Carbon is released and combines with oxygen to form carbon dioxide. NAD+ is reduced to NADH

3. The 5 carbon compound is oxidized and decarboxylated to form a 4 carbon compound. This forms carbon dioxide and another NADH
4. The 4 carbon compound undergoes various changes resulting in more products:
- FAD reduced to FADH
- NAD reduced to NADH
- ADP reduced to form ATP

Must spin twice for each glucose molecule as two pyruvates are formed in glycolysis.
Every 1 glucose molecule (2 spins) produces:
- 6 NADH (oxidation)
- 4 CO
2
(decarboxylation)
- 2 FADH (oxidation)
- 2 ATP (reduced)
Substrate phosphorylation – ATP produced
Energy passed on to the final part of respiration: oxidative phosphorylation (electron transport chain)

By the end of the Krebs cycle, only 4 ATPs have been gained.
- 4 from glycolysis (but 2 used up in the process)
- 2 from Krebs cycle
All substrate level phosphorylation
Total of 36 ATPs gained overall from 1 glucose molecule.
(32 produced in the Electron transport chain and chemiosmosis)

Series of small steps, carried out by a chain of electron carriers.
Electrons passed from carrier to carrier, energy is used to transfer protons from matrix to inter membrane space.

Happens in inner mitochondrion membrane
H+ moves across a membrane down a concentration gradient
ATP synthase uses the energy to create ATP
(oxidative phosphorylation)

1.
Reduced NAD supplies H atoms to first carrier in the chain
2.
H atoms split and release 2 electrons, which pass from carrier to carrier
3.
ATP released as electrons pass down
4.
More electrons supplied from reduced FAD
5.
ATP used to transfer protons (H+) across inner mitochondrial membrane
6.
Concentration gradient of protons (H+) builds up
7.
Creates a store of energy
8.
Protons pass back from the inter membrane space to the matrix through ATP synthase
9.
ATP synthase makes ATP
This is oxidative phosphorylation (use of electron transport chain)

At the end of the electron transport chain oxygen is the final electron acceptor
Oxygen molecule is reduced (gains electrons)
Accepts electrons and forms a covalent bond with hydrogen to make water – diffuses out of cell as waste
(urine/perspiration/water vapour in breath)
By using up hydrogen the proton gradient across the inner membrane is maintained
Chemiosmosis can continue

Use a piece of A3/A4 paper
Create a respiration diagram – go step by step from the start.
Include:
Glycolysis
Link reaction
Krebs cycle
Oxidative phosphorylation
Electron transport chain
Chemiosmosis
Where do they happen
Is reduced NAD/FAD produced
Is ATP produced
What is made from that process
What happens here
Is it substrate level phosphorylation or oxidative phosphorylation

Allows 3D image of mitochondria to be made
Dr Carmen Mannella:
- Cristae are not just infoldings but are defining micro-compartments in the organelle
- Cristae are flexible and dynamic – change depending on the metabolism and other stimuli
- Specific proteins/lipids that actively regulate the inner membrane

Changes in internal organization of mitochondria associated with cell death and disease:
(A) Normal, isolated liver mitochondrion
(B) Liver mitochondrion treated with a protein that induces programmed cell death
(C) Mitochondrion from a patient with a mitochondrial myopathy (causes muscle weakness)