The endoplasmic reticulum and secretory pathway

Question 1

Function of the endoplamsic reticulum

Answer 1

Protein synthesis
glycosylation
folding and assembly of multi protein complexes
lipid synthesis
Ca2+ sequestration (storage of Ca2+)
Detoxification by cytochrome P450 enzymes

Question 2

Endoplasmic reticulum protein synthesis and modification

Answer 2

AUG is the first codon of which an mRNA is translated

Ribosome begins translation to synthesise the nascent protein 

The amino terminus (first part of the nascent polypeptide) contains a signal sequence 

An SRP (signal recognition particle) recognizes the signal sequence and binds to the signal sequence and binds to the signal sequences as well as the ribosome resulting in protein synthesis in halting 

SRP binds to GTP, which halts elongation of the polypeptide chain 

The GTP-bound SRA directs the ribosome to the GTP-bound SRA receptors and the nascent polypeptide is delivered to a peptide translocation complex which directly interacts with the ribosome 

SRP dissociates from the ribosome accompanied with the hydrolysis of GTP in both SRP and SRP receptors 

The ribosome binds to sec61 translocation channel and the signal sequence is threaded into the channel 

Elongation of the polypeptide resumes until the complete protein has been synthesized. The signal sequence is removed by peptidase and the ribosome dissociates and recycled

Question 3

structure of golgi apparatus

Answer 3

cis face is where the proteins enter from

trans face is where the modified proteins proteins leave

Question 4

protein export from the endoplasmic reticulum

Answer 4

Protein first packaged into COPII - coated transport vesicles
these vesicles bud from regions called ER exit sites which have no ribosomes

Question 5

what are the roles of the golgi apparatus in protein modification?

Answer 5

glycosidase - hydolysis of glycosidic bond
O-linked glycosylation
sulfatases - hydrolysis of sulfate esters
proteases - hydrolysis of peptide bonds

Question 6

which lipids are synthesised?

Answer 6

sphingomyelin

glycosyleramide

Question 7

protein and lipid sorting to:

Answer 7

Secretory granules

Plasma membrane 

Basolateral versus apical membrane 

Apical is the portion of cell exposed to the lumen 

Basolateral is the rest of the cell 

Endosomes 

Lysosomes