11 - Cell compartmentalisation & Protein sorting

Question 1

What type of transport happens between the nucleus and the cytoplsam?

Answer 1

Gated transport

Question 2

What type of transport takes proteins and other organelles into the ER?

Answer 2

Transmembrane Transport

Question 3

What type of transport takes materials into the extracellular portion?

Answer 3

Vesicular transport.

Question 4

What is the nuclear pore made out of?

Answer 4

Each complex appears to be made of 8 subunits with a central plug.

Question 5

What do the nuclear pore complexes do?

Answer 5

They are involved in moving substances across the nuclear envelope.

Question 6

What is the role of histone molecules in DNA synthesis?

Answer 6

They are needed to package the new DNA, that will be transported from the cytoplasm.

Question 7

What molecule is needed for protein production to occur?

Answer 7

Ribosomes, which are formed in the nucleolus.

Question 8

What are the 2 processes in which transport can occur?

Answer 8

• By diffusion
• By active transport

Question 9

How does the molecular weight of a substance affect diffusion?

Answer 9

As the ,olecular weight increases the longer it takes to diffuse through the membrane.

Question 10

What are signals linked to for active transport of proteins?

Answer 10

A peptide sequence, nuclear transport recognition sites rich in Pro, Lys and Arg

Question 11

What happens to the T-Antigen SV40 virus in the presence of the protein sequence Pro-Lys-Arg?

Answer 11

The T-Antigen can be localised in the nucleus, when the sequence is disrupted the traslocation stops.

Question 12

How are new proteins transported into organelles?

Answer 12

Either co or post- translationally.

Question 13

What is co-traslational translocation?

Answer 13

As the protein is being made its being transported into the lumen of the ER (coupling method).

Question 14

What is post-translational translocation?

Answer 14

When proteins are completely made in the cytoplasm and after they are completely formed they are post-translationally translocated into the ER.

Question 15

What is the signal hypothesis?

Answer 15

The idea that translocation into the ER requires a signal.

Question 16

In the signal hypothesis what needs to happen for there to be a signal?

Answer 16

The mRNA on the ribosome needs to be due to be translated.

Question 17

How are proteins translocated through the membrane of the ER?

Answer 17

Through the translocator SEC61 of the protein on the membrane which is closed till the signal is recieved, then opens allowing the protein through.

Question 18

How is the signal stopped?

Answer 18

By the closing of the pore and the removal of the signal by the signal peptidase.

Question 19

What molecules help the protein to fold?

Answer 19

Chaperones. (Bip)

Question 20

How are membrane proteins inserted into the ER?

Answer 20

• The protein moves through the translocator apparatus like before but encounters a stop transfer sequence.
• The siganl peptisade then stops the translocation.

Question 21

What is gycosylation?

Answer 21

the post-translational addition of sugar

Question 22

What is the role of glycosylation in protein insertion?

Answer 22

It ensures the quality control of the folding of the protein in the membrane.

Question 23

What happens if folding doesnt occur properly?

Answer 23

The process happens in reverse.

Question 24

What is an example of a muation casued by defects in protein folding?

Answer 24

CTFRdelta508 - The misfolded protein stimulate the unfolded protein response.

Question 25

What is the unflolded protein response (UPR)?

Answer 25

A transcriptional programme thats upregulates the sysnthesis of chaperones and also closes down translation to help cells recover.

Question 26

What happens when there are too many proteins present?

Answer 26

The apoptotic response is stimulated.

Question 27

How do proteins get into the mitochondrial matrix?

Answer 27

• Proteins are translocated in the cytosol and associated with chaperones.
• The N-Terminal sequence is recognised by the TOM and TIM23 complexes.
• The protein is then translocated through the TOM complex on the outer membrane and the TIM complex on the innner membrane to enter the matrix.
• The signal is then cleared off.