FLC Fate of newly synthesised proteins

Question 1

How many nuclear pore complexes are there per mammalian cell?

Answer 1

3000 to 4000 NPCs per mammalian cell

Question 2

What sized molecules require active transport, and not free diffusion?

Answer 2

Molecules of ≥ ~60 kDa require active transport

Question 3

Steps involved in nuclear import

Answer 3

1. Protein associated with nuclear localisation signal
   2.Crosses from cytosol into nucleus where protein is delivered to nucleus.
2. Ran-GTP binds to receptor and moves out of nucleus back into cytosol
   4.Ran-GDP dissociates from receptors

Question 4

What are the roles of mitochondria?

Answer 4

Respiration
ATP synthesis
Heat generation (in brown fat)
Fatty acid metabolism
Intermediary metabolism (synthesis &
breakdown of biomolecules)

Question 5

What are the sites of protein synthesis?

Answer 5

1. Cytosol
2. Mitochondria

Question 6

What are the protein destinations in mitochondria?

Answer 6

1.outer membrane
2.inner membrane
3.intermembrane space
4.Matrix

Question 7

Steps involved in protein import into the matrix of mitochondria

Answer 7

1. Precursor protein with the signal sequence binds to import receptor in the TOM complex
2. Then there’s insertion of the precursor protein into the mitochondria by TOM complex
3. Precursor protein translocates into the matrix
4. Then there’s cleavage by signal peptidase

Question 8

What does HSP70 do to proteins and what does it do to ATP?

Answer 8

HSP70 keeps protein unfolded in the cytosol which can hydrolyse ATP in protein translocation

Question 9

What does energy from electrochemical gradient help?

Answer 9

Electrochemical gradients help import of protein through the inner membrane to the matrix

Question 10

Roles of the endoplasmic reticulum

Answer 10

• Protein synthesis, folding, glycosylation & disulfide bond formation
• Protein quality control (if protein can’t fold properly – then degraded e.g. cystic fibrosis)
• Lipid synthesis
• Ca2+ storage
• Intermediary metabolism

Question 11

Roles of the golgi apparatus

Answer 11

-Post-translational protein modifications (glycosylation, sulfation, proteolysis)
- Lipid synthesis
- Protein & lipid sorting (secretory granules, plasma membrane, endosomes, lysosomes)

Question 12

Why is it called contranslational protein?

Answer 12

• Co-translational: because you have initiation of translation in cytosol and then translation occurs in the ER

Question 13

Steps involved in co-translational protein targetting to the ER

Answer 13

• You have signal protein at the N-terminus (where the protein translation usually starts in cytosol)
• When this signal protein is detected, translation stops and SRP (signal recognition particle) binds to the ribosome complex
• this SRP then binds with the SRP receptor on the ER membrane which allows the ribosome complex to dock onto another protein called Protein translocator (translocon)
• this is a type of channel
• Once this docking occurs, translation resumes and threads through to the ER where signal peptide is cleaved off
• Again with transmembrane proteins, they have the hydrophobic transmembrane domains to allow diffusion into the intermembrane space for insertion into the inner membrane

Question 14

What happens in the rough endoplasmic reticulum?

Answer 14

Rough – where ribosomes sit, where proteins are made and exported

Question 15

How does vesicular transport work?

Answer 15

There are proteins within the ER such as translocon but otherwise they are all transported
- proteins need to go from ER to golgi this occurs through vesicles
- donor compartment -> budding -> fusion -> Target compartment
(- often guided by cytoskeleton, or organelles, nerves etc)

Question 16

What are the different types of vesicle coats?

Answer 16

• clathrin
• COPI
• COPII

Question 17

What is vesicle formation and budding off mediated by?

Answer 17

• vesicle formation and budding off is mediated by these coats proteins