Protein Transport

Question 1

Briefly describe the function of nucleus

Answer 1

DNA transcribed to mRNA

Question 2

Briefly describe the function of ribosomes

Answer 2

Translates RNA to protein

Question 3

Briefly describe the function of ER

Answer 3

Ensures correct folding of proteins, adds carb residues

Question 4

Briefly describe the function of RER

Answer 4

Ribosomes, site of protein synthesis, post translational modifications of proteins, disulfide

Question 5

Briefly describe the function of SER

Answer 5

Synthesis of lipids, cell membrane, secreted lipid eg steroids, metabolises carbs, detoxifies drugs

Question 6

Briefly describe the function of golgi apparatus

Answer 6

Modifies proteins, organises proteins, synthesises molecules for secretion

Question 7

Further describe the function of ribosomes within the endomembrane system

Answer 7

Read mRNA, bind tRNA to synthesise polypeptides/proteins, free in the cytosol or bound to ER

Question 8

What are the 2 major parts of a ribosome and their functions?

Answer 8

Small subunit - Reads RNA

Large subunit - Joins A.A, form polypeptide chain

Question 9

What is co-translation?

Give an example

Answer 9

Translated while transported eg ribosomes on ER translating proteins

Question 10

What is post-translation?

Give an example

Answer 10

Translated after transported eg free ribosomes in cytosol translating proteins

Question 11

Describe co-translational translocation

Answer 11

Signal peptide - Directs new translated proteins into RER via co-translational import
Signal recognition particle binds to receptor on ER tunnel next to receptor protein via lumen

Question 12

What are chaperones?

Answer 12

Proteins that help covalent folding/assembly of other macromolecules

Question 13

Further describe the golgi apparatus within the endomembrane system

Answer 13

Receiving end = Cis face
Opposite end = Trans face
Transport vesicles formed from ER travel to cis face, fuse with it, empty contents into lumen

Question 14

What are golgi vesciles coated in?

Answer 14

Clathrin

Question 15

Describe endosomes

Answer 15

Part of the endocytic pathway, has 3 stages:

Early, Late, Recycling

Question 16

Summarise the routes from RER

Answer 16

RER > Golgi > Lysosomes or Constitutive/Regulation secretion > Plasma membrane

Question 17

What is nuclear import?

Answer 17

To import large molecules which cannot pass freely through the nuclear pores complex

Question 18

Describe the process of nuclear import

Answer 18

Macromolecule has nuclear localisation signal NLS, it binds to importin which binds to nuclearporins (binding site receptor), moves across. Ran-GTP binds to importin, causes conformational change releasing cargo into nucleus. Ran-GTP bound importin moves back to cytosol, Ran-GTP hydrolysed to Ran-GDP + Pi (Ran acts as GTPase) so dissociates from importin

Question 19

Describe the process of nuclear export

Answer 19

Exportin binds to nuclearporin enters nucleus, binds to Ran-GTP, promotes binding to cargo, binds to nuclearporins and exported out to cytosol

Question 20

Describe mitochondrial proteins

Answer 20

Own DNA/ribosomes, manufacture some of their own proteins
Most come from cell nucleus
Synthesised on cytoplasmic ribosomes, imported into mitochondrion post-translationally