6A: Aerobic Cellular Respiration

Question 1

Cellular Respiration

Answer 1

`the process by which cells create useable energy in the form of ATP from a series of biochemical reactions involving the breakdown of glucose

As glucose carries a lot of energy, it must be broken down into smaller ATP packages

Question 2

Types of pathways to break down Glucose

Answer 2

1. Aerobic Cellular Respiration: cellular respiration that occurs in the presence of O2 involving glucose and O2 being converted into ATP and CO2 and water

C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + 30-32 ATP

Stages of Aerobic Cellular Respiration:
- Glycolysis
- The Krebs Cycle
- The electron transport chain

2. Anaerobic Fermentation: a metabolic pathway involving glycolysis followed by further reactions converting pyruvate into lactic acid in animals or ethanol and CO2 in yeast

• Occurs in the absence of oxygen

Animals: C6H12O6 -> 2 C3H6O3(lactic acid) + 2 ATP

Plants and yeasts: C6H12O6 -> 2 C2H5OH(ethanol) + 2 CO2 + 2 ATP

Question 3

Mitochondrion

Answer 3

a double membrane bound organelle that is the site of the second and third stage of Aerobic cellular respiration

Question 4

Structures of the Mitochondrion related to Aerobic Cellular Respiration

Answer 4

Cytosol: the aqueous fluid that surrounds the cells organelles inside the plasma membrane
- site of glycolysis

Mitochondrial matrix: the space inside the inner membrane of a mitochondrion
- the site of the Krebs cycle

Crista: the folds of the inner membrane of a mitochondrion
- Site of the electron transport chain

Question 5

Stage 1 of Aerobic Cellular Respiration: Glycolysis

Answer 5

the first stage of Aerobic cellular respiration in which the 6 carbon glucose is converted to two 3 carbon pyruvate molecules via a sequence of ten enzyme reactions

        - Located in the cytosol 

Inputs:
- 1 glucose
- 2 ADP + 2 Pi
- 2 NAD+ + 2 H+

Outputs:
- 2 pyruvates
- 2 ATP
- 2 NADH

Question 6

Stage 2 of Aerobic Cellular Respiration: Krebs Cycle

Answer 6

the second stage of Aerobic cellular respiration where multiple reactions occur to create ATP, NADH, FADH2 and CO2.

- Located in the mitochondrial matrix
    - Via a series of eight reactions, energy is extracted from acetyl(2 carbons), breaking it down to allow coenzyme A to be recycled back for use in the link reaction

Inputs:
- 2 Acetyl-CoA(derived from 2 pyruvate)
- 2 ADP + 2 Pi
- 6 NAD+ + 6 H+
- 2 FAD + 4 H+

Outputs:
- 4 CO2
- 2 ATP
- 6 NADH
- 2 FADH2

Question 7

Krebs Cycle: results from this key metabolic stage

Answer 7

Results from this Key metabolic Stages:
- By breaking down Acetyl-CoA, protons and high energy electrons are released which are loaded to create NADH and FADH2

- The Krebs cycle produces two CO2 molecules to produce from each of the two pyruvates meaning a total of 4xCO2 are produced for every glucose molecule

    - Produces only two ATP molecules(one per Acetyl-CoA molecule)

Question 8

Link Reaction

Answer 8

• A reaction that links glycolysis and the Krebs cycle by transporting pyruvate to the mitochondria matrix where a CO2 is removed and a coenzyme is added to form Acetyl CoA

    - This reaction produces 1 CO2 as a waste product and NADH

Question 9

Coenzyme A

Answer 9

a large organic non-protein molecule that plays a key role in the modification of pyruvate to allow it to enter the Krebs cycle

          - Known as CoA

Question 10

Stage 3 of Aerobic Cellular Respiration: Electron Transport Chain

Answer 10

the third stage of aerobic cellular respiration where energy from the electrons unloaded by NADH and FADH2 generates a proton gradient, driving significant ATP production

- Located in the cristae(inner membrane)

- Produces the greatest amount of ATP, 34-36

    - Continually recycles the high energy enzymes NAD+ and FAD back into NADH and FADH2 to be able to use them again in glycolysis and the Krebs cycle

Inputs:
- 6 O2
- 12 H+
- 26-28 ADP + 26-28 Pi
- 10 NADH
- 2 FADH2

Outputs:
- 6 H2O
- 26-28 ATP
- 10 NAD+ + 10 H+
- 2 FAD + 4 H+

Question 11

Steps in the Electron Transport Chain

Answer 11

1. NADH and FADH2 molecules unload protons and electrons at the first and second protein complexes through the reactions:
   
   • NADH -> NAD+ + H+ + 2 e-
   • FADH2 -> FAD + 2 H+ + 2 e-
   2. The excited released electrons are transferred through a number of different protein complexes powering the active transport of H+ from the mitochondrial matrix into the narrow intermembrane space
   3. This leads to a build up of H+ in the intermembrane space creating a high concentration and in turn creating a steep concentration gradient across the inner mitochondrial matrix
   4. In order to move down the gradient, protons must travel through ATP synthase, specialised protein channels. As they move through, they cause the enzyme to spin creating kinetic energy which produces the reaction
      - ADP + Pi -> ATP
      Creating 26-28 ATP per glucose molecule
      5. This process can lead to lots of free protons and electrons building up in the matrix which if remaining unbound, can cause problems for cells in large concentrations. They can damage DNA, interfere with enzyme reactions and create dysfunctional proteins. This is prevented by O2 binding to the free electrons and protons to form harmless water

Question 12

End Product Inhibition

Answer 12

the final product in a series of biochemical reactions prevent enzymatic catalysis of an earlier step in the sequences

   - Means the cell will only make more of this enzyme if there is a deficit of the product

Question 13

Coenzymes in Cellular Respiration

Answer 13

Coenzymes in Cellular Respiration:
Loaded:
- ATP
- NADH
- FADH2

Unloaded:
- ADP
- NAD+
- FAD+