Intro to cellular metabolism

Question 1

What are the three important Co-enzymes?

Answer 1

• co- enzyme is a substance that works with an enzyme to initiate or aid the function of the enzyme (also known as an energy carrier)
• Acetyl CoA (Acetyl Coenzyme A) - fats, lipids
• NAD+/NADH
• FAD+/FADH2

Question 2

How can enzymes regulate metabolic processes?

Answer 2

> sequential, multistep processes of enzymes are often regulated by the end product binding to the first enzymes site and inhibiting it. (first enzyme often the regulatory enzyme)
allosteric enzymes:
- binding of a modulator can cause a conformational change to increase the affinity/binding site availiability to the substrate to increase activity and vice versa

Question 3

what are the key enzymes in glycolysis?

Answer 3

key enzymes involved in control and regulation:
> hexokinase
- is regulated by insulin
- uses ATP to add phosphate to glucose, so it stays in cell
> phosphofructokinase:
- central role in control of glycolysis
- uses ATP to add phosphate to fructose 6 phosphate
- its activity is enhanced allosterically by several substances including ATP
- therefore, when ATP is high, there is a low metabolic demand and the enzyme is inhibited slowing the flux through the pathway.
- controlled by hormones as well
> Pyruvate kinase:
- takes the phosphate from phosphophenolpyruvate and adds it to ADP to create ATP and Pyruvate

Question 4

Describe the simplified pathway of glycolysis

Answer 4

occurs in cytoplasm of cell
1) Glucose –> glucose 6-phosphate (hexokinase)

equilibrium reactions

2) fructose 6-phosphate -> fructose 1,6, biphosphate (phosphofructokinase)

Equilibrium reactions

3) 2 x Phosphophoenolpyruvate –> 2 x pyruvate ( pyruvate kinase)

Question 5

What are the reactants and products used/ made in glycolysis?

Answer 5

Used:
one glucose molecule, 2 x ATP, 2 x NAD+, 4 X ADP

Made: 2 x ADP, 2 x NADH, 4 x ATP

Question 6

How is glycolysis controlled?

Answer 6

> high glucose conc -> fructose 6-P activates flux through the pathway
high ATP or NADH, there is low demand, therefore flux is slowed via inhibition of phosphofructokinase

Question 7

What is the transition process between glycolysis and citric acid cycle?

Answer 7

> pyruvate is oxidised to acetyl-CoA and CO2 by the Pyruvate dehydrogenase (PDH) complex
this is not reversible.

Question 8

What are the important molecules in the Citric acid cycle?

Answer 8

> Alpha - ketoglutarate
oxaloacetate
acetyl CoA

Question 9

what are the molecules used and made in the citric acid cycle, what regulates it and why is it important?

Answer 9

Used:
Acetyl CoA, 
GDP, 
FAD+, 
3 NAD+, 
inorganic phosphate, 
2 H2O 
O2

made:
2 CO2
1 GTP
3 NADH
FADH2
CoA

regulation:
- high ATP, citrate,NADH or FADH2, there is low metabolic demand, flux through the pathway is slowed

Importance:

• energy produced in form of electrons is captured by electron transfer to NADH and FADH2
• generates GTP - which can be converted into atp
• feeds oxaloacetate back into the cycle (combines with Acetyl CoA to make citrate)

Question 10

Give an overview of the Electron transport chain

Answer 10

• hydrogens are delivered to the ETC via NADH and FADH
• in the ETC, they are split into electrons and protons (H+).
• electrons are transported down the electron transport chain and the energy is extracted from them in a stepwise fashion
• this energy is used by transport proteins in the ETC to pump the protons out of the matrix, generating a proton gradient
• the gradient drives the activity of the ATP synthase enzyme, because the protons can only move down their conc. gradient by going through the enzyme, thus driving the ATP synthesis reaction