Nitrogen Sources and Disposal

Question 1

Ubiquitin Dependent Pathway

Answer 1

1. In Cytoplasm, ubiquitin is attached (energy dependent) to lysine residues, targeting for degradation
2. Polyubiquinated protein is unfolded and degraded in protease core into smaller peptides
3. Non-specific proteases cleave peptides into amino acids

This is not the digestive tract.

Question 2

Authophagy

Answer 2

No insulin–>decreased protein synthesis and increased autophagy.

Cellular protiens/organelles are enclosed in membrane bound structures and delivered to lysosome

Starvation initiates this cup-like double membrane structure that picks up cytosolic elements

Pathway influenced by ATG genes

Question 3

mTORC Complex

Answer 3

Senses nutrient availability, regulates autophagy pathway

mTORC1 is activated by insulin and inactivates ULK complex which decreases autophagy.

Glucagon and low energy inhibits mTORC which leaves ULK active and increases autophagy

Question 4

Regulation of Protein Synthesis at Translation Initiation

Answer 4

Eukaryotic initiation factor (eIF), eIF2 is phosphorylated and inhibits translation

When insulin activates mTORC, eIF4 binding factor is phosphorylated and translation initiation is increased

mTORC can therefore modulate both synthesis and degradation

Question 5

What happens to excess amino acids?

Answer 5

Can get converted into fat

Make glucose (gluconeogenisis)

Can be combusted to make energy, or generate citrate

Question 6

Aminotransferases

Answer 6

Donates amino group from amino acid to alpha-keto acid to make glumate or vice versa to make alpha-ketoglutarate, reversible

remember alanine and aspartate aminotransferase

alanine + alphaKG makes pyruvate and gluamate

aspartate + alphaKG makes oxaloacetate and glutamate

Question 7

Pyridoxal Phosphate (PLP)

Answer 7

• Derived from vitamin B6 and required for aminotransferases
• donate amino group to plp, carries phosphate covalently
• PLP transfers amino group from aspartate to glutamate

Question 8

First step in amino acid catabolism

Answer 8

amino transfering (transamination)

-all amino acids can be catabolized by such a pathway

Question 9

Glutamate dehydrogenase reaction

Answer 9

Takes amino group off of glutamate to make alpha ketoglutarate, but reaction can go both ways

-can attach free amonia to AKG

Question 10

Oxidative deamination

Answer 10

Takes place inside mitochondria, important in making urea

Question 11

Urea

Answer 11

Gets rid of excess amino groups, produced during oxidative deamination

Question 12

Urea Synthesis

Answer 12

Ammonium + Aspartate + ATP + water need

Reverse reaction unfavorable bc of PPi production

Question 13

Urea cycle

Answer 13

-Ammonia generated in mitochondrial matrix
-CPS1 generates carbonyl phosphate from ammonia
Step 3 (arginosuccinate) is non-reversible

-aspartate and glumate shuttle amino groups back and forth in this cycle