Le Noyau

Question 1

What is the difference between poly nucleated, enoucleated and syncytium cells?

Answer 1

poly nucleated -> 2 nuclei or more (osteoclasts)
syncytium -> many many nuclei (striated muscle cells)
enoucleated -> no nucleus (RBC)

Question 2

Describe the nuclear membrane?

Answer 2

It is a double membrane
En continuité avec le réticulum endoplasmique rugueux (RER)
Contains Nuclear Pores
Filled With Ribosomes

Question 3

Why can you say that the nuclear membrane is a a key area of protein synthesis?

Answer 3

Becasue it is covered in ribosomes

Question 4

When is the double membrane present in the cell?

Answer 4

All the time in interphase until separation of cell:
Prophase starting to degrade
Metaphase none is left (Mitose; metaphase and prophase)

Question 5

True or False, other than the outer membrane there are no internal vessicles in the nucleus.

Answer 5

True
Very Well organized in the inside as domains without using a membrane:

Question 6

What is the role of nuclear pores in the nucleus?

Answer 6

Important for exportation and Importation from the nucleus

Question 7

What is an NLS

Answer 7

signal de localisation nucléaire (NLS):

Question 8

What is an importine?

Answer 8

NLS is a signaling sequence that is recognized by Importine:
Together they are recognized by the pores and imported inside the nucleus.

Question 9

What is the main controller of the import and describe its role

Answer 9

In the nucleoplasm we have the main controller of the import: RAN-GTP:

The activity of RAN-GTP is controlled by Ran GEF(inside) and Ran GAP (outside)

RAN-GTP binds importin and releases the cargo

RAN-GTP bound to importin leaves the pore where RAN-GTP is hydrolyzed, and importin is released for recycling.

Question 10

Explain the key difference between inport and export (nucleus)

Answer 10

nstead of Importins here we have exportines

Instead of NLS here we have signaux d’exclusion nucléaire (NES)

Also depends on RAN-GTP

Question 11

What makes up lamine nucleaire?

Answer 11

Filament intermediate

Question 12

What is chromatine?

Answer 12

Combination of ADN+ proteins (+histones, transcription factors etc.)

Question 13

What are the two forms of chromatin? What does each mean?

Answer 13

Euchromatin: Lache
90% of chromatine is in this non-dense form

This is what is usually the genes that are transcribed

Heterochromatin: Dense
10% of chromatin is in this dense form

These are the genes that are silenced

Question 14

What is a nucleosome?

Answer 14

L’ADN n’est pas nue, mais est enroulée autour d’octamères de
histones

Question 15

Usually Histone acetyltransferase will lead to what?

Answer 15

More Acetyl -> Euchromatin → activated transcription

Question 16

What is the role of a Histone méthyl-transferase?

Answer 16

Transfer Histone on DNA -> Hétérochromatine (silencieuse)

Question 17

What is a nucleole?

Answer 17

Principal nuclear domain
Site of ARNr (ARN ribosomale) synthesis
Main site of ribosome activity

The size of the nucleole thus is an indicator of ribosome activity

Question 18

What is a Speckle?

Answer 18

Site of Facteur d’epissage: (splicing factors)

sites de processing des pré-ARN messagers (ARNm) pour éliminer les introns

Elimination des introns des pré-ARNm pour former les ARNm matures

Exons are the sequences that will become the proteins, introns will not become proteins