Cell Compartmentalisation

Question 1

The nuclear pore is made up of ____ nuclear porins.

Answer 1

~30

Question 2

How are molecules transported through pores?

Answer 2

• Diffusion
• Active transport

Question 3

What are the times of diffusion for different molecular masses?

Answer 3

• Up to 5,000 = freely diffusible
• 17,000 = 2 mins
• 44,000 = 30 mins
• 60,000 = cannot enter

Question 4

What evidence is there that active transport occurs in cells?

Answer 4

During the transport of mRNA out of the nucleus, ATP is hydrolysed and used.

Question 5

What evidence is there that active transport occurs in vitro?

Answer 5

Insertion of proteins into the nucleus.
Without ATP, proteins accumulate outside the nucleus.

Question 6

What do chaperones do?

Answer 6

Assist folding, ensure proper folding.

Question 7

What is an example of a chaperone protein?

Answer 7

BiP. Used in antibody production.

Question 8

What defects cause cystic fibrosis?

Answer 8

CFTRdelta508. The misfolded protein gets stuck in the ER membrane.

Question 9

What are the two ways proteins can be translocated?

Answer 9

• Co-translatory translocation: whilst protein synthesis is still occurring.
• Post-translatory translocation: after protein has been fully synthesised.

Question 10

When is co-translatory translocation used?

Answer 10

In the ER

Question 11

When is post-translatory translocation used?

Answer 11

In chloroplast and mitochondria.

Question 12

Outline translocation into the ER.

Answer 12

(Co-translatory translocation)
Signal protein recognised by Sec61.
Protein enters ER
Cleaved by signal peptidase

Question 13

Outline translocation of membrane proteins into the ER membrane.

Answer 13

Sec 61 recognises the signal
Protein enters the ER
Transmembrane domain anchors the protein into the membrane
Signal Peptidase cuts signal off

Question 14

Outline translocation of proteins into mitochondria.

Answer 14

(post-translatory translocation)
Signal binds to receptors
Protein enters TOM complex, enters intermembrane space.
Protein enters TIM23 complex, exits intermembrane space.
Signal is cleaved by signal peptidase.

Question 15

Outline the translocation of proteins into the outer membrane of bacteria. FROM THE CYTOSOL.

Answer 15

Protein enters TOM complex into inner membrane space.
Supported by chaperones, it enters SAM complex.
Fully folded protein inserted into outermembrane.

Question 16

Outline the translocation of proteins into the outer membrane of bacteria. FROM MATRIX.

Answer 16

Protein enters SEC complex into inner membrane space.
Supported by chaperones, is enters BAM complex.
Fully folded protein inserted into outer membrane.

Question 17

Outline translocation of proteins into the chloroplast.

Answer 17

Protein enters through TOC complex into inner membrane space.
Protein enters TIC complex into matrix.
Signal is cleaved off