Samuelson BCH lec 8/15

Question 1

Protein Biochemistry

Answer 1

Translation, Processing, Trafficking, Function, Degradation

Question 2

There are over ~25,000 genes in the human genome that contain protein coding information for

Answer 2

~100,000 protein sequences

Question 3

Proteins have highly specialized

Answer 3

functions

Question 4

Signal Sequence of N-Terminal Amino Acids

Answer 4

?

Question 5

SRP: Signal Recognition Particle

Answer 5

a universally conserved ribonucleoprotein that recognizes the ER signal peptide

Question 6

Protein Glycosylation

Answer 6

adding carbohydrates to proteins

Question 7

Mitochondrial Localization Signal

Answer 7

1. Amino or N terminal amino acid sequence
2. Binds to chaperone
3. Protein/chaperone inserted into mitochondria
   through a transport complex
4. Signal sequence is cleaved in mitochondria

Question 8

Nuclear Localization Signal/Sequence (NLS)

Answer 8

1. Binds to importin subunit
2. Protein/importin passed through nuclear
   pore. (energy dependent)
3. NLS NOT removed

Question 9

Proteolytic Processing of Preproteins - Insulin

Answer 9

Pteproinsulin, proteases cleave, proinsulin, keep cleaving, insulin.

C chain is packaged in the secretory vessicle and is secreted along with active insulin

Question 10

Protein Phosphorylation is the most abundant

Answer 10

protein

Question 11

Protein Post-Translational Modification (PTM) Phosphorylation

Answer 11

Kinase enzymes add phosphate (PO4) groups. Over 500 exist

Reversible: Phosphatase enzymes remove phosphate groups. Over 100 exist

A dynamic mechanism that regulates multiple
types of protein functions

PO4 results in conformational change and has effects on protein interactions

Question 12

Reasons for protein degradation

Answer 12

Metabolic needs

removal of abnormal proteins, unnecessary proteins, and regulatory proteins

Question 13

Protein stability: proteins are degraded at different rates

Answer 13

One dependent factor is the N-terminal amino acid

Question 14

PEST Proteins are

Answer 14

rapidly degraded

Pro (P), Glu (E), Ser (S), Thr (T)

These proteins often contain phosphorylation sites that target them for ubiquitination

Ubiquitination = post-translational modifications

Question 15

Protein Degradation - Lysosomes

Answer 15

Lysosomes degrade many proteins
* ~50 hydrolytic enzymes
* Multiple proteases called cathepsins

• Internal pH ~5 (lysosomal enzymes are mostly
  inactive at cytosolic pH)

Question 16

Post-translational Modification - Poly-Ubiquitination

Answer 16

a PTM of a linked chain of
Ubiquitin that marks a protein for degradation

Question 17

Ubiquitin

Answer 17

76-residue monomeric protein

Ubiquitous and Abundant

Highly conserved eukaryotic
protein

Polyubiquitination marks proteins for degradation

Question 18

Poly-Ubiquitination

Answer 18

a repeated 3 step process that leads to protein degradation

Question 19

Poly-Ubiquitination - E3

Answer 19

E3 transfers activated Ub from E2 to a Lys (K) on the protein to be marked for degradation (Substrate) or the previous Ub

Question 20

Proteasome - Polyubiquitinated proteins are

Answer 20

unfolded and proteolytically degraded in a 26S proteasome

Multiprotein complex

ATP dependent

20S proteasome: a hollow
cylindrical core

19S cap