DONE Membrane Proteins

Question 1

What are the 3 modes of protein mobility?

Answer 1

Conformational change
Rotational
Lateral diffusion

Question 2

Peripheral membrane proteins

Answer 2

Bound to mem. surface

Removed by changes in pH/ionic strength

Question 3

Integral membrane proteins

Answer 3

Hydrophobic domains of membrane

Remove with detergents/organic solvents

Question 4

Secreted protein synthesis

Answer 4

• Signal sequence on N-terminus of polypeptide
• Signal recognition particle (SRP) binds to polypeptide
• Arrests synthesis (so ribosome doesn’t make protein from RNA in cyto.)
• SRP recognised by SRP receptor/docking protein on ER, SRP released, translation not arrested
• Signal sequence interacts with signal sequence receptor (SSR) within protein translocator complex in ER mem.
• Ribosome attaches + polypeptide chain extruded into ER lumen

Question 5

Membrane protein synthesis

Answer 5

Same as secreted protein BUT stop transfer signal of 20 hydrophobic AA’s arrests passage of protein thru mem. = forms transmembrane region of protein (N-terminus in ER lumen, C-terminus in cyto.)

Question 6

Membrane protein orientation

Answer 6

Signal peptidase cleavage of signal sequence in cytoplasm