Eukaryotic Structure 2

Question 1

Describe the nuclear envelope

Answer 1

It is a double membrane.
Outer nuclear membrane, peri nuclear space then the inner nuclear membrane

Question 2

What are nuclear pores ?

Answer 2

Protein lined channels on the nucleus that are gated by a nuclear pore complex (NPC) made of 30 different proteins

Question 3

Describe transport through the nuclear pore

Answer 3

1. Small molecules can diffuse through the nuclear pore via passive diffusion
2. Proteins created in the cytosol can be transported through the nuclear pore if they have a Nuclear localisation signal (NLS)

Question 4

Describe how the NLS works

Answer 4

1. The NLS on the protein is recognised by an importin protein
2. The importin complex binds to nucleoporins and enter the NPC
3. Ran GTP-ase binds to importin causing the complex to disassemble and release the protein

Question 5

What is nuclear export

Answer 5

The process of actively transporting proteins from the nucleus into the cytoplasm.
1. The nuclear export signal (NES) on the protein is recognised by a receptor called exportin and bind to it in the presence of Ran-GTP
2. Exportin then carries the protein through the NPC and releases it into the cytoplasm when Ran-GTP is hydrolysed into Ran-GDP

Question 6

What is the nuclear lamina ?

Answer 6

The tough fibrous mesh underneath the inner nuclear membrane.
It is made of lamins, which are intermediate filament proteins.
It helps maintain the shape of the nucleus.

Question 7

What is the nucleolus ?

Answer 7

Membrane-less compartment
It is the centre of ribosomal RNA production

Question 8

What is the endoplamic reticulum ?

Answer 8

It is connected to the outer nuclear membrane.
It is organised into interconnected tubes and flattened sacs.

Question 9

Describe the rough ER

Answer 9

The membrane is covered with ribosomes.
Involved in protein synthesis- the ribosomes on the ER surface synthesise proteins, then they are folded and undergo initial modifications within the lumen of the rough ER

Question 10

Describe the smooth ER

Answer 10

Involved in the synthesis of lipids.
Contains an enzyme for drug detoxification.
The SR in muscles is important for storing calcium ions.

Question 11

What is the transitional ER ?

Answer 11

It functions as a bridge between the rough and smooth ER.
Plays a role in transporting proteins from the rough ER to other parts of the cell.

Question 12

What is the Golgi apparatus ?

Answer 12

A collection of flattened, membrane-enclosed sacs known as cisternae.
Consists of:
Cis-complex which is adjacent to the ER. Receives proteins from the ER
Trans-complex which is towards the plasma membrane

Question 13

What is the function of the GA ?

Answer 13

Protein modification and sorting for traffic within the cell

Question 14

What are the 2 models that explain vesicle trafficking through the GA ?

Answer 14

1. Vesicular transport model
   Proposes that the cisternae are stationary and that transport between them occurs via small vesicles. Resident enzymes stay in the same cisternae.
2. Cisternae maturation model
   Proposes that the cisternae mature as they move from the cis to the trans face. Resident enzymes move between cisternae.

Question 15

Describe coated transport vesicles

Answer 15

1. Cathrin-coated= from Golgi, endosome, plasma membrane
2. COPI-coated= from Golgi
3. COPII-coated= from ER
4. Retromer-coated= endosome retrieval to Golgi