Protein transport 1

Question 1

Overview

Answer 1

• Bacteria = single compartment surrounded by plasma membrane
• Eukaryotic cells = compartment
• Proteins = crucial in compartmentalisation, produced in cytosol
• Autoradiography + electron microscopy

Question 2

Rough ER

Answer 2

• ER removes transmembrane + H20-soluble proteins from cytosol as made
• In mammals, import = co-translational
• Membrane-bound ribosomes are attached to cytosolic side, help
• Common pool of ribosomes used to make both proteins in cytosol + ER

Question 3

Signal peptide hypothesis

Answer 3

• Secretory + membrane proteins have stretches of aa that are specific to receptors of the ER
• Signal sequence = targeting sequence
• Signal peptide = cleaved signal sequence
• Signal peptidase = E that removes signal peptide
• Membranes need to stay impermeable
• Experiment = microsomal

Question 4

Experiments

Answer 4

• Systems purified from cell homogenates w/ differential or density-gradient centrifugation
• Inverted bacterial cytoplasmic membrane vesicles can be produced using French pressure cell
• In vitro protein assay

Question 5

Structure of secretary peptide for secretory systems

Answer 5

• N terminals = highly charged, polar, unstructured
• CTD = -ve charged, polar, not helical
• Hydrophobic area = natural charge, non polar, helical property