Biochem- Turnover Of Proteins

Question 1

What is the Ubiquitin/Proteasome System (UPS)?

Answer 1

— the major pathway for protein degradation.
— uses ubiquitin as the marker to target cystolic and nuclear proteins in proteolysis
— ATP is required.

Question 2

Describe the events of UPS.

Answer 2

1) Ub activation- a thioester is formed between the carboxyl terminal of glycine residue of UB and cysteine residue of E2.
2) Conjugation of E2 - activated Ub is transferred to E2.
3) Binding of Ub to E3.

Question 3

List some characteristics of Proteasome.

Answer 3

— responsible of the degradation of intercellular proteins w/ ubiquitin chains
— made up of two sub-complexes — a catalytic particle and 19s regulatory particle and serves as a activator.

Question 4

Describe the 26S proteasome.

Answer 4

— it is a 2.5 -MDa multicatalytic degradation that contains a 20S CP and 19S RP.
— the 19S RP is responsible for the detecting the ubiquitylated client protein and unfold and translocates them into the interior of the 20S CP.

Question 5

What role does autophagy play in the UPS system?

Answer 5

— It mediates protein turnover
— degrades proteins and organelles en masse.

Question 6

List the three types of proteins in cells degraded by autophagy.

Answer 6

Misfold proteins
Insoluble misfold proteins
Cytoplasmic proteins

Question 7

Describe Chaperone- mediated Autophagy (CMA)

Answer 7

— Degrades soluble or unfoldable protein in a molecule to molecule basis
— Main Components- Heat shock protein 70 and Lysosome membrane protein type 2A.
— Criteria— must have presence of a peptide sequence that is biochemically related to KFERQ motif

Question 8

List the factors that affect protein synthesis and degradation.

Answer 8

HOT HAFEA
Hydration state
Oxygen availability
Tissue perfusion
Hormone secretin
Acid base balance
Free fatty acid pattern
Energy protein intake
Activation of systemic inflammatory response.

Question 9

State the significance of a positive NB and anabolic state.

Answer 9

Nitrogen intake exceeds nitrogen output.

Question 10

What happens when nitrogen excretion is greater than nitrogen intake?

Answer 10

A negative NB or catabolic state exist.

Question 11

State the calculation for NB.

Answer 11

(Protein intake/6.25) — (24hour UUN+4)

Question 12

List the factors that affect NB.

Answer 12

1. Dietary intake
2. Dietary content of carbohydrates and fats
3. Pregnancy
4. Growth
5. Illness/ trauma

Question 13

State the clinical significance of NB.

Answer 13

1. Protein enzyme malnutrion
2. Marasmus - caused by inadequate intake of protein and energy
3. Kwashiorkor - caused by inadequate intake of protein with adequate energy.