Membrane Cytoskeleton

Question 1

How can you see if a protein is peripheral/integral using SDS page

Answer 1

Add salt wash after separated
Those that are removed with salt wash have to be peripheral
Those that remain are integral

Question 2

Erythrocyte cytoskeleton

Answer 2

Spectrin forms lattice
Adhered to membrane via attachment proteins
Ankyrin binds spectrin to band 3
Actin and band 4.1 binds Spectrin to glycophorin

Integral - band 3 and glycophorin
Attachment (but also peripheral) - ankyrin, band 4.1, actin
Peripheral - Spectrin

Question 3

Hereditary Spherocytosis

Answer 3

Spectrin depleted (40-50%, 1 allele damaged)
Round erythrocytes
Cleared by spleen
More likely to burst in water environment (not flexible)

Question 4

Hereditary Eliptocytosis

Answer 4

Defect in spectrin
Unable to form heterotetramers
Fragile elliptoid cells

Question 5

Secreted protein biosynthesis

Answer 5

Transcription occurs
Translation occurs reading 5’ —> 3’
SRP binds to signal peptide and ribosome
SRP goes to docking protein on ER and pulls sequence with it
Signal sequence binds to receptor/protein trans locator complex on ER surface - ribosome sits on top
Signal peptidase cleaves off signal sequence and peptide enters ER

Question 6

Problem with N terminal signal sequence in secretory protein synthesis

Answer 6

Contains positively charged residues - organise themselves to cytoplasmic side of membrane (BY FOLDING LIKE HAIR PIN)
Signal peptidase cleaves off
Allows polypeptide to go into lumen

Question 7

How are membrane proteins synthesised

Answer 7

Same way - but hydrophobic stop transfer sequence is synthesised which locks the peptide in place over the membrane
Ribosome detaches from ER and completes synthesis in cytoplasm

Question 8

Integral proteins of RBC

Answer 8

Band 3, Glycophorin A

Question 9

Peripheral proteins RBC

Answer 9

Ankyrin, Band 4.1, Spectrin (actin)

ABS