Joint 5 - Getting to Cell Surface

Question 1

what proteins are exported and which are incorporated into membrane?

Answer 1

exp - hormones/enzymes

inc - channels/transporters/receptors

Question 2

pathway of a protein to be secreted>

Answer 2

cross ER membrane

cross plasma membrane

Question 3

what are signal peptides/sequences?

Answer 3

found on the N-TERMINAL [single pass] of a protein

- 15/20 aa

Question 4

term for movement across a membrane?

Answer 4

translocation

Question 5

key players involved in translocation?

Answer 5

ribosome
- in cytoplasm and synethesises the protein

SRP - recognise the signal peptide

SRP Receptor - SRP-Ribosome complex binds to it

Question 6

steps of a protein moving across a membrane?

Answer 6

• SRP recognises and binds to signal peptide
• stops translation
• the protein is still attached to the ribosome
• SRP- ribosome complex binds to SRP receptor in membrane [now localised to translocator in membrane]
• signal peptide inserted into translocator and transaltion continues
• growing peptide threaded through [translocation]
• SRP and SRP receptor dissociate from ribosome
• signal peptide cleaved [left in membrane]
• protein released

Question 7

what main processes occur in the ER membrane?

Answer 7

• signal peptide cleaved
• proteins get glycosylated
• proteins folded [disulphide bridges form]

Question 8

process of glycosylation?

Answer 8

• in membrane oligosachride is removed from Dolichol [lipid]
• put onto proteins s they get translocated
• enzyme - Oligosaccharyl Transferase

Question 9

how does the protein leave the ER and to where?

Answer 9

vesicle bud from ER and travel to cis face of Golgi

Question 10

faces of Golgi?

Answer 10

cis face - CGN
transface - TGN

Exported proteins arrive at CGN
leave through TGN

Question 11

how is the protein further glycosylated [modified] in Golgi?

Answer 11

complex oligosachrides
- the N-linked oligos is trimmed and sugars added [original has 14 sugars trimmed to 5]

high mannose oligosaccharides
- original n linked oligos trimmed and mannose sugars added

Question 12

what is O-Glycosylation?

Answer 12

in N-glycos the sugars are adde on ASAPARAGINE on the protein

iin O-linked sugars add to the Threonine or Serine

Question 13

what are proteoglycans?

Answer 13

• contain GAGS chains [unbranched] (glycoproteins are branched)
• where link tetrasacchride added to serine
• synthesised by glycosyl transferase

Question 14

what does the consitutitive secretory pathway and regulated secretory pathway consist of?

Answer 14

Constitutive

• continuous
• supplies membrane proteins
• proteins that are soluble are secreted in this path
• lipids are secreted this was

Regulated

• proteins to be put in secretory granules [hormones] @ TGN
• stored till required [extrac.signal causes it to be released]
• fuse with PM and released

Question 15

purpose of glycosylation?

Answer 15

• promote folding of protein as it makes it more soluble