PMT's and protein sorting mitochondria

Question 1

what do cells use to regulate the intrinsic activity of a protein

Answer 1

covalent modifications

Question 2

covalent modifications in a cell

Answer 2

can occur in various cellular locations
can increase or decrease proteins activity
can change conformation, charge and or ability to bind other molecules

Question 3

what are the three main modifications in the ER

Answer 3

addition of oligosaccharides
disulfide bonds
prolyl isoform modification via ER enzymes

Question 4

what do ER chaperons and lecitins do

Answer 4

ensure proper folding or transport misfolded proteins to cytosol for degradation

Question 5

what are o linked oligosachardies

Answer 5

added to hydroxyl group
sugar residues added in a linear chain

Question 6

N linked oligosacharides

Answer 6

start with a premade, oligosacharide precursor
added to many different proteins in the ER

Question 7

importance of addition of oligosacharides

Answer 7

proper protein folding, protection of mature proteins from proteolysis, adhesion, communication, etc

Question 8

dolichol phosphate

Answer 8

very hydrophobic lipid anchor in membrane

Question 9

amide derivatives and sugar groups added in the biosynthesis of oligosaccharide precursor

Answer 9

-2 N-acetylglucosamine (GlcNAc)
-5 mannose groups
-added via high energy pyrophosphate linkages

Question 10

biosynthesis of the oligosaccharide precuror in the ER steps

Answer 10

-dolichol phosphate anchor
-amide derivatives and sugar groups added
-the intermediate is flipped to the luminal face
-additional sugars are added- mannose and glucose

Question 11

details of additional sugars added to the flipped intermediate- mannose and glucose

Answer 11

transferrred from a nucleotide precursor to a carrier dolichol phosphate and flipped to the luminal face
-glucose resudues act as a signal of completion

Question 12

transfer to nascent protein steps

Answer 12

precursor is transferred to asparagine (Asn) residues on a nascent protein

glucose residues and one mannose removed
-readdition of one glucose residue can play a role in correct folding of many proteins

Question 13

what adds disulfide bonds

Answer 13

protein disulfide isomerase (PDI)

Question 14

active site of PDI

Answer 14

two cysteines

Question 15

what does PDI do

Answer 15

forms/ rearranges protein cysteine disulfide bonds

easily interconverted between the reduced dithiol form and the oxized disulfide form

Question 16

formation of a disulfide bond steps

Answer 16

cysteine thiol -s- on protein reacts with the disulfide s-s bond in oxidized PDI forming an intermediate

second thiol reacts with intermediate forming disulfide bond with protein

PDI disulfide bond reformed facilitated by electron transfer from another protein

Question 17

rearrangement of disulfide bonds

Answer 17

disulfide bonds commonly misform when a protein has a sequential cysteines in the sequence

reduced PDI forms transient disulfide bonds to break improper disulfides and on rlease allows proper bonds to form

Question 18

PTM examples

Answer 18

hemagglutin

Question 19

hemagglutinin assembly in infected cell

Answer 19

chaperones bind nascent proteins to prevent premature folding

lectins also binds to prevent premature folding

PDI catalyzes formation of disulfide bonds

protein subunits interact for final folding

Question 20

how are some mitochondrial proteins encoded

Answer 20

by nuclear genes as opposed to mitochondrial DNA

these nuclear genes are synthesized on cytosolic ribosomes
and maintained in an unfolded state by chaperons (Hsp70)

Question 21

Mitochondrial proteins encoded by nuclear genes

Answer 21

contain an N terminal targetting sequence that can also contain targeting sequences to direct the protein tot he inner membrane or the matrix

Question 22

HSP70 chaperons function

Answer 22

prevenet premature folding

Question 23

what does the receptor tom20/22 do

Answer 23

its on the outer membrane and binds MTS

Question 24

what does the bound receptor do

Answer 24

move to tranlocon tom40 in the outer membrane

Question 25

what happnes after the bound receptor moves to translocon tom 40 in the outer membrane

Answer 25

translocon tom40 aligns with inner membrane translocon tim23/17

Question 26

TIM proteins

Answer 26

translocation of the inner membrane

Question 27

what happnes after translocon tom40 aligns with inner membrane translocon tim23/17

Answer 27

4. passive transport- unfolded proteins goes through channel
5. protein bound in matrix by hsp70 chaperone
   -hydrolyzes ATP to pull protein through
6. signal sequence cleaved
7. protein refolded by mitochondrial chaperonins

Question 28

what does specific mitochondrial targetting involve

Answer 28

various internal targeting sequences
-targeting to matrix, outer membrane, inner membrane, or inner membrane space

Question 29

3 pathways to inner membrane

Answer 29

1. stop anchor stops transfer throug tim translocon for release into inner membrane
2. internal hydrophobic domains are recognized by inner membrane protein and inserted in membrane
3. no N-terminal matrix targetting- internal sequences recognized by alternate tom receptors in outer membrane, and tim translocon incorporates them into the inner membrane