Biology- Respiration

Question 1

What are the 4 stages of aerobic respiration?

Answer 1

• Glycolysis
• Link Reaction
• Krebs Cycle
• Electron transport chain

Question 2

Where does Glycolysis happen and why?

Answer 2

Happens in the cytoplasm of a mitochondrion

- Since glucose is too big a molecule to move into the mitochondrial matrix

Question 3

What is Glycolysis?

Answer 3

The splitting of the 6 carbon glucose molecule into two 3 carbon pyruvate molecules.

Question 4

What are the steps in Glycolysis?

Answer 4

1) Glucose is made more reactive by the addition of two phosphate molecules (from the hydrolysis of ATP to ADP + Pi)
2) Each glucose molecule is split into two 3 carbon molecules known as triose phosphate.
3) Hydrogen is removed from each of the triose phosphate molecules and transferred to NAD to form reduced NADH.
4) Enzyme controlled reactions convert each triose phosphate into 2 molecules of Pyruvate. Two molecules of ATP are regenerated from ADP.

Question 5

Where does the Link Reaction take place?

Answer 5

In the matrix of the mitochondria.

Question 6

Where does Krebs cycle take place?

Answer 6

In the matrix of the mitochondria.

Question 7

How does Pyruvate pass into the matrix from the cytoplasm of a mitochondria?

Answer 7

People are unsure- Evidence suggest through active transport.
We know pyruvate is small enough to move across the double membranes and get into the matrix (unlike glucose which is too big).

Question 8

What is substrate level phosphorylation?

Answer 8

ATP is produced during a metabolic reaction as ADP gets phosphorylated as a result of a metabolic reaction.

Question 9

What happens during the link reaction?

Answer 9

Pyruvate molecules from Glycolysis are actively transported into the matrix of the mitochondria.

1) The pyruvate is oxidised to acetate. In this reaction the 3 carbon molecule loses a CO2 molecule and two hydrogens (which get accepted by NAD)
2) The 2 carbon acetate combines with a molecule called coenzyme A (CoA) to produce a compound called acetylcoenzyme A.

Question 10

What is the overall equation for the link reaction?

Answer 10

Pyruvate _ NAD + CoA —> AcetylCoA + reduced NADH + CO2

Question 11

What is Coenzyme A?

Answer 11

Not an enzyme or even a protein.

These are needed for enzymes to function properly.

Question 12

What are the products of the link reaction?

Answer 12

2x AcetylCoA
2x NADH
2x CO2 —-> Waste Product.

Question 13

What happens during Krebs Cycle?

Answer 13

1) The 2 carbon AcetylCoA combines with a 4 carbon molecule to produce a 6 carbon molecule (citrate)
2) 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.
3) The 4 carbon molecule (oxaloacetate) can now combine with a new molecule of AcetylCoA to begin the cycle again.

Question 14

What are the products in each of the stages of Respiration?

Answer 14

Glycolysis:                                
2x NADH
2x ATP
Link Reaction:
2x CO2
2x NADH
Krebs Cycle
4x CO2
6x NADH
2x FADH2
2x ATP
Electron Transport Chain:
32x ATP
Overall:
6x CO2
10x NADH
2x FADH2
36x ATP

Question 15

Where does the electron transport chain take place?

Answer 15

Inner membrane of the mitochondria

Question 16

Where do electrons come from to be accepted by electron acceptors?

Answer 16

Reduced NADH and FADH2 become oxidised
NADH—-> H+ + e-
FADH2—-> 2H+ + e-

Question 17

What are the steps in the electron transport chain?

Answer 17

1) Electron hungry acceptor (oxidised state) accepts electrons from NADH/FADH2 (reduces it)
2) The next electron acceptor (eg. cytochrome) is oxidised so accepts previous acceptors e-.
3) Electron travels down the electron transport chain through redox reactions.
4) Final acceptor has the electron removed by O2 to form water.
5) Energy from redox reactions means the proton pump can can pump H+ ions into intermembranal space.
6) A chemiosmotic gradient forms so H+ ions move back into the matrix via ATPsynthases which catalyse the reaction for ADP + Pi to form ATP (lots of it)

Question 18

How much NAD and FAD is produced during respiration and how much ATP is produced from each?

Answer 18

10x NAD and 2x FAD
- NAD each produces 3x ATP
- FAD each produces 2x ATP
Therefore the net ATP produced
= (10x3) + (2x2) + 2ATP from Krebs cycle
=36 ATP molecules.

Question 19

How much ATP is produced from Anaerobic respiration?

Answer 19

2x ATP

Question 20

In animals and plants what are the Pyruvate molecules (from Glycolysis) converted to in anaerobic respiration?

Answer 20

Animals:
- Lactate
Plants and Yeast:
- Ethanol
- CO2

Question 21

What does anaerobic respiration often cause?

Answer 21

Causes Fatigue.