Carbohydrate Pathways Other Than Those Involved In Glucose Homeostasis

Question 0

Amino acid metabolism and protein turnover.

Why are amino acids important?

Answer 0

-amino acids are building blocks of protein
-protein consist of 20 diff amino acids linked by peptidyl bonds
-all protein aa are a-carbon (bonded through carbon 2) and have L-configuration.
Primary function: protein structure
Secondary function: energy source
-aa important source of carbon for synthesis of glucose in carnivores or starving animals

Question 1

What are the 2 main functions of the pentose phosphate pathway.
And what is the li action that it occurs?

Answer 1

1) an oxidative pathway (gain of Oxygen) that produces NADPH for synthesis of fatty acids and steroid hormone through reduction.
2) a non-oxidative pathways that produces ribose 5-phosphate for synthesis of nucleotides
Any unused intermediates are returned to glycolysis at fructose-6P or glyceraldehyde 3P.
Location: require NADH and most cells require ribose 5P for nucleotide synthesis. Therefor pathway happens in cytosol of cells

Question 2

What is an amino acid?

Answer 2

An amino acid is composed of carbon, hydrogen, oxygen and most characteristically nitrogen.
Nitrogen is essential for protein synthesis
-nitrogen can’t be used for energy and must be removes before it can transfer its energy to ATP.

Question 3

Do we have to know the pathways and all different amino acids?

Answer 3

?

Question 4

What is protein degredation?

What are the chemical signals for degredation of proteins? (4)

Answer 4

Proteins being broken down
Chemical signals
1) ubiquination: ATP dependant reaction of ubiquitin with lysine
2) oxidation of amino acid residues (oxygen added)
3) PEST sequences: short lived proteins contain one or more regions rich in proline, glutamate, serene and threonine
4) N-terminal residue:
- Phe, Leu, Asp, Lys, or Arg unstable
- Met, Ser, Ala, Thr, Val, Gly more stable
There are 2 major processes for degredation.
1) non regulated pathways which is ubiquitin dependant and requires ATP
2) regulated pathway occurring via lysosomes, and thus pathway is independent of ATP

Question 5

What are the roles for NADPH?

What regulates NADPH?

Answer 5

Detoxification:

• it reduces the oxidised glutathione (handles free radicals of toxins) -you reduced glutathione to become very good antioxidant in liver. Need NADP to reduce
• cytochrome

Reductive synthesis:

• fatty acid synthesis
• cholesterol synthesis
• neurotransmitters synthesis
• nucleotide synthesis

All need NADPH!
Regulation:
NADPH allosteric inhibitor is glucose6- phosphate dehydrogenase. Which is the first enzyme in its pathway!

Question 6

Tissue specificity.

What are the tissues that require reducing power?

Answer 6

Liver, adipose tissue, adrenal cortex, thyroid, erythrocytes, testis and lactating mammary gland.
All require the first stage of pentose phosphate pathway because they need the goods. NADPH!

Question 7

Some tissue don’t need alot of reducing power ie don’t make a lot of fat etc. so they don’t need to express the oxidative phase of the pentose phosphate pathways.
However what do all tissues express?

Answer 7

Ribose! Why? Because they all need RNA and DNA

Question 8

Summary of the pentose phosphate pathway.
Oxidative phase
Non oxidative phase

Answer 8

Oxidative phase:

• irreversible
• dehydrogenations

No oxidative phase:

• reversible
• avenue for producing ribose