protein targeting

Question 1

what are the four levels of protein structure?

Answer 1

primary
secondary
tertiary
quaternary

Question 2

which pathway are sulfide bonds found in?

Answer 2

secretory

Question 3

what is the definition of native structure?

Answer 3

the folded, active form of a protein

Question 4

what is the definition of random coil?

Answer 4

the unfolded structure with no secondary structure

Question 5

what is the definition of conformation?

Answer 5

a change in the 3D structure through rotation of bonds

Question 6

what is the definition of denaturation?

Answer 6

destruction of native structure by a change of conformation

can return to active conformation

Question 7

what is the definition of degradation?

Answer 7

breaking of covalent bonds to from smaller molecules

Question 8

what is protein homeostasis?

Answer 8

ensuring there is the correct amount of functional protein at all times

Question 9

what is protein homeostasis governed by?

Answer 9

production
folding
trafficking
degradation

Question 10

what are possible destinations for proteins?

Answer 10

stay in the cytosol
mitochondria or nucleus (post translational trafficking)
secretory pathway (co translational trafficking)

Question 11

what is the basic secretory pathway?

Answer 11

ER
cis golgi 
golgi 
trans golgi 
secretory vesicle 
plasma membrane

Question 12

what are common features of ER sorted protein signal sequences?

Answer 12

have between 13-36 amino acids leading the protein
contain 10-15 hydrophobic amino acid sequences
a short polar sequence at the carboxyl terminus

Question 13

what is the role of chaperones during translation?

Answer 13

Hsp70
stabilise unfolded protein
associate with hydrophobic residues to prevent misfolding or aggregation

Question 14

what is the role of chaperonin?

Answer 14

provides an isolated environment in which correct folding can occur
shields the polypeptide from the cytosol and prevents aggregation
used for proteins which are difficult to fold

Question 15

what is the role of cytosolic chaperones during post translational trafficking?

Answer 15

transport partially folded polypeptides from cytosol to mitochondria
stabilises unfolded polypeptide

Question 16

what is the role of mitochondrial chaperones?

Answer 16

facilitate transport and folding of polypeptide within the organelle

Question 17

how are proteins targeted to the ER?

Answer 17

signal recognition particle (SRP) recognises signal sequence and binds to N terminal of translated protein as it emerges from the ribosome
translation is halted
SRP escorts the complex to the ER where it binds to a SRP receptor
SRP is released, the ribosome binds to the translocon and the signal sequence is inserted
translation resumes
signal sequence is cleaved
growing polypeptide chain is translocated across the membrane and released into the ER lumen when completed

Question 18

what cleaves the signal sequences in the ER?

Answer 18

signal peptidase

Question 19

what mediates protein folding in the ER?

Answer 19

BiP

Question 20

what is sulphide bonding mediated by and what is it promoted by?

Answer 20

mediated by protein disulphide isomerase

promoted by oxidising environment in ER lumen

Question 21

what is N-linked glycosylation?

Answer 21

the addition of N-acetylglucosamine to asparagine

Question 22

what is O-linked glycosylation?

Answer 22

the addition of N-acetylgalactosamine to serine

Question 23

what happens during glycosylation in the ER?

Answer 23

a 14 sugar oligosaccharide is first synthesised on dolichol in the ER membrane
then transferred to the consensus sequence on an asparagine residue
3 glucose residues are removed

Question 24

how many enzymes does the golgi apparatus contain and what do they catalyse?

Answer 24

over 250 enzymes

catalyse addition of sugars to proteins

Question 25

where are proteins which contain mannose-6-phosphate transported to?

Answer 25

endosomes

Question 26

what happens in post golgi transport?

Answer 26

proteins in the trans-Golgi network are sorted into vesicles and then transported to final destination also sorted into secretory granules secretory granules store their contents until specific signals direct their fusion with the plasma membrane

Question 27

how many proteins does the mitochondrial genome encode for?

Answer 27

13

Question 28

why does the protein need to be in a partially unfolded when being transported to the mitochondria?

Answer 28

mitochondrial translocons are quite small

Question 29

what is the TOM complex?

Answer 29

translocase of the outer membrane

Question 30

what is the TIM complex?

Answer 30

translocase of the inner membrane

Question 31

how are mitochondrial proteins with presequences imported into the mitochondria?

Answer 31

N-terminal presequences target the protein to the TOM complex after translocation through TOM the presequence binds to TIM complex Hsp70-containing import motor complex in the matrix drives translocation across the inner membrane proteins with internal transmembrane domains exit TIM laterally proteins destined for the matrix associate with chaperones and presequences are cleaved by mitochondrial matrix processing peptidase

Question 32

how are proteins targeted to the mitochondrial inner membrane?

Answer 32

inner membrane protein with transmembrane domains have internal signal sequences after translocation through TOM the polypeptide associates with TIM9-TIM10 chaperones in the intramembrane space which transfer the protein to the TIM complex internal membrane sequence halts translocation and the protein exits the translocon laterally into the inner membrane

Question 33

what are proteins which are encoded by the mitochondrial ribosomes translocated via?

Answer 33

Oxa1 translocase

Question 34

what are alpha helical transmembrane domain proteins which are destined for the outer mitochondrial membrane inserted by?

Answer 34

Mim1 | mitochondrial insertase

Question 35

how are beta barrel precursors inserted into the outer mitochondrial membrane?

Answer 35

transferred through TOM and carried to SAM by TIM chaperones and is inserted into the outer membrane

Question 36

what are NLS and what are they recognised by?

Answer 36

nuclear localisation signals | recognised by importins

Question 37

what are NES and what are they recognised by?

Answer 37

nuclear export signals | recognised by exportins

Question 38

are nuclear localisation signals cleaved?

Answer 38

no

Question 39

what is the directionality of transport across the nuclear pore determined by?

Answer 39

Ran | a GTP-binding protein

Question 40

how are proteins transported into the nucleus?

Answer 40

transport begins when NLS is recognised by an importin cargo/importin complex binds to nuclear pore protein and is transported through the pore in the nucleus, Ran/GTP binds importin and the cargo protein is released importin-Ran/GTP is re-exported through the pore Ran-GDP associates with NTF2 and Ran-GEF exchanges GDP for GTP