lec 12

Question 1

membrane insertion can be

Answer 1

1. co-translational
   - occurs when proteins are translated on bound ribosome on the ER
   > ribosomes docks near translocator
2. post-translational
   - peptide is fully translated and released before insertion into the target

Question 2

co-translational translocation

Answer 2

1. in the ER lumen
2. occurs in rough ER

Question 3

post-translational translocation

Answer 3

in free ribosomes in cytosol

Question 4

covalent mods

Answer 4

1. glycosylation by cell-specific enzymes can change func of shared protein
2. different kinases in different cells can lead to the phosphorylation of proteins at different sites
3. isomerization of disulfide linkages in different cells can produce different func
4. variability in methylase/acetylase proteins can dramatically alter cell phenotype and func

Question 5

covalent protein mods

Answer 5

1. glycosylation: addition of sugar group
2. phosphorylation: addition of phosphate group
   - kinase puts on the phosphate group

Question 6

proteolytic mods

Answer 6

1. occur when protein must be proteolytically processed (cleaved) to be functional
2. irreversible
3. polypeptide hormone insulin = synthesized as a large protein that is cleaved by proteolytic enzyme after protein chain has folded into a specific shape

Question 7

allostery

Answer 7

change protein’s activity at 1 site caused by the binding of regulatory ligands at different sites on the protein
- ligand binding alters protein form
> change protein’s activity

Question 8

allosteric regulation

Answer 8

always involve 2 different binding sites on the protein being regulated
1. positive: caused by positive conformational coupling between 2 distinct binding sites on the allosteric protein
-&raquo_space; affinity
2. negative: caused by negative conformational coupling between 2 distinct binding sites on the allosteric protein
- &laquo_space;affinity

Question 9

ex of positive allostery

Answer 9

hemoglobin
- binding of O2 causes a conformational change in other subunits
>&raquo_space; affinity of other subunits to bind to O2

Question 10

affecting polymerization

Answer 10

cells can start and stop a protein’s activity
- regulates processes that make active polymers from inactive subunits

Question 11

affecting scaffolding complex components

Answer 11

cells can start and stop a protein’s activity
- regulate the interactions of proteins within the scaffold complex
scaffolding proteins
- bridge and stabilize the protein’s interactions to bring proteins in proper proximity to each other
- manipulating just 1 of the proteins in the scaffolding complex will alter the func of the complex

Question 12

ex of scaffolding complex

Answer 12

ubiquitin ligase complex
- if any one protein is prevented from associating with the complex
> cannot func properly