Metabolic Pathways

Question 1

Oxidation is loss or gain of electrons?

Answer 1

Loss

Question 2

Reduction is loss or gain of electrons?

Answer 2

Gain

Question 3

Redox reactions occur in couples, what does this mean?

Answer 3

Electrons are never lost, if one molecule is oxidised, another must be reduced.

Question 4

Loss of hydrogen =

Answer 4

Loss of electrons -> Oxidation.

Question 5

Addition of hydrogen =

Answer 5

Addition of electrons -> Reduction.

Question 6

What is the 1st Law of Thermodynamics?

Answer 6

The total amount of energy in the universe is constant, it just gets converted to different forms.

Question 7

What is the 2nd Law of Thermodynamics?

Answer 7

Entropy (level of disorder) increases over time. Things never spontaneously become more ordered.
= Loss of free available energy.

Question 8

Biochemical pathways occur in the direction of what? Refer to energy.

Answer 8

Pathways can only occur in the direction that leads to an overall loss of free energy.
= increased entropy.

Question 9

Gibbs Free Energy (G) measures what?

Answer 9

Level of disorder (entropy).

Question 10

System move spontaneously how? Refer to entropy.

Answer 10

Low -> High entropy

Question 11

A negative change in G is known as a what reaction?

Answer 11

Exergonic - is energetically favourable.

Energy of reactants > energy of products.

Question 12

A positive change in G is known as a what reaction?

Answer 12

Endergonic - is energetically unfavourable.

Energy of reactants < energy of products.

E.g. Making a protein.

Question 13

Positive or Negative change in G?

1. ATP -> ADP + Pi
2. Glycolytic bond between sugars
3. Glucose Oxidation

Answer 13

1. • (catabolic)
2. • (anabolic)
3. • (catabolic)

Question 14

What is the role of activated carriers?

Answer 14

Activated carriers store energy as either a transferrable chemical group or electrons.

Question 15

Why do coupled reactions use activated carriers?

Answer 15

Energy from exergonic reactions can be used to fuel endergonic, non-spontaneous, energetically unfavourable reactions.

Question 16

NADPH is known as a what carrier molecule?

Answer 16

Activated carrier molecule.

Question 17

NAD+ in words is…

Answer 17

Nicotinamide Adenine Dinucleotide

Question 18

NADP+ in words is…

Answer 18

Nicotinamide Adenine Dinucleotide Phosphate

Question 19

Define Metabolism.

Answer 19

All the catabolic and anabolic reactions that occur within a cell.

Question 20

What is the starting molecule of glycolysis?

Answer 20

Glucose.

Question 21

What are the products of glycolysis?

Answer 21

2 Pyruvate molecules.
2 ATP molecules.
2 NADH.

Question 22

What are the 3 phases that occur during glycolysis?

Answer 22

1. Energy investment phase.
2. Coupling of the reaction.
3. Energy generation phase.

Question 23

What happens in the ‘energy investment phase’ of glycolysis?

Answer 23

2 ATP molcules are hydrolysed to produce 2 ADP and 2 Pi.
2 Pi molecules phosphorylate glucose.
Forms fructose 1,6-bisphosphate.

Question 24

Why is a reaction coupled?

Answer 24

It make the reaction more energetically favourable, the energy output in one reaction can be put into the next sequence of reactions.

Question 25

What happens in the ‘energy generation phase’ of glycolysis?

Answer 25

4 ATP molecules generated -> Net yield of 2 ATP.
Substrate level phosphorylation
2 NAD are reduced to 2 NADH (electron transfer carriers).

Question 26

In step 7 of glycolysis, the oxidation of an aldehyde to a carboxylic acid produces what?

Answer 26

Energy in the form of ATP.

NAD is reduced to NADH.

Question 27

During anaerobic respiration, how is lactate produced?

Answer 27

1. NADH passes its electrons (H) to pyruvate to form lactate and NAD+.
2. NAD+ is then recycled back into glycolysis and more ATP can be produced to sustain short-term exercise.

Lactate can produce muscle fatigue and cramping before it is removed with the presence of oxygen.

Question 28

What happens in the pyruvate dehydrogenase complex reaction (link reaction)?

Answer 28

1. Pyruvate moves into the mitochondria from the cytosol.
2. Pyruvate is decaboxylated to form acetyl coA.
3. Acetyl coA can enter the Krebs Cycle.

Question 29

What are the products for the pyruvate dehydrogenase complex reaction (per glucose molecule)?

Answer 29

2 CO2
2 NADH2
2 Acetyl CoA

Question 30

What molecule does beta-oxidation turn into acetyl CoA?

Answer 30

Fatty acid.

Question 31

What happens in beta-oxidation?

Answer 31

1. FAs are converted to fatty acyl-CoA and transported to mitochondria.
2. Series of 4 enzymatic reactions which reduce the number of carbons on the fatty acyl-CoA (reduces by 2 carbons each cycle).

Question 32

What products are formed in beta-oxidation?

Answer 32

Per cycle:
Acetyl CoA
NADH
FADH2

Question 33

Palmitic acid (a FA) has 16 carbons.
How many cycles of beta oxidation will be needed for the FA to be totally degraded?
How many NADH and FADH2 molecules will be generated?
How many Acetyl CoA molecules will be generated?

Answer 33

1. Cycles = 7
2. NADH = 7
3. FADH2 = 7
4. Acetyl CoA = 8

Question 34

Where does the Krebs Cycle occur in a cell?

Answer 34

The mitochondrial matrix.

Question 35

What is the first step of the Krebs Cycle?

Answer 35

Acetyl CoA is combined with 4C Oxaloacetate to form 6C tricarboxylic acid/citric acid.

Question 36

What type of reactions are completed in Krebs Cycle to regenerate oxaloacetate from citric acid?

Answer 36

Oxidation (this reduces the electron transporters such as NAD and FAD).

Question 37

What are the products in the Krebs Cycle from one acetyl CoA (one pyruvate molecule)?

Answer 37

3 NADH
1 FADH2
1 GTP
2 CO2