The cell Nucleus

Question 1

What are the main components of the nucleus?

Answer 1

Chromatin, nucleolus, and the nuclear envelope.

Question 2

What is chromatin composed of?

Answer 2

DNA, histones, non-histone proteins.

Question 3

What are two different types of chromatin and what are their differences?

Answer 3

Euchromatin (Pale, loose, transcriptionally active)
Heterochromatin (Dark, condensed, transcriptionally inactive)

Heterochromatin can be constitutive (noncoding or permanently inactive) or facultative (temporarily inactive)

Question 4

What is a nucleosome made up of?

Answer 4

A nucleosome has a core that is made up of histones. These histones are arranged as an octamer, built of: 
2 x H2A
2 x H2B
2 x H3
2 x H4

The nucleosome does also contain DNA (147 basepairs)

Question 5

What is the structure of chromatin.

Answer 5

DNA wraps around nucleosomes about 1.7 times or 147 base pairs. Between each nucleosome is about 10-90 base pairs (DNA linkers) + histone H1.

The chromatin packs tightly together into a fiber at about 30nm. This folds into a series of loops (300nm). These loops then spiralize into heterochromatin (700 nm) and then into what will be the chromosome (1400 nm)

Question 6

What does the nucleolus produce?

Answer 6

1. Pale fibrillar centers - rDNA (transcriptionally inactive)
2. Dense fibrillar centers - freshly transcribed rRNA
3. Granular components - Ribosomal subunits (mainly large)

Question 7

What are nucleolar organizers (NORs)? And where do you find their regions?

Answer 7

NORs are chromosomal regions that are important for the formation of the nucleolus. Found on the chromosomes 13, 14, 15, 21, 22.

Question 8

What is the space between the outer and inner membrane of the nuclear envelope called?

Answer 8

The perinuclear space.

Question 9

What is the family of proteins that are the building blocks of the nuclear pore complex (NPC) called?

Answer 9

Nucleoporins.

Question 10

What are the components of the NPC?

Answer 10

1. Basket
2. Columns
3. Nuclear ring
4. Central area
5. Cytoplasmic ring.

Question 11

What is transported out and in of the NPC?

Answer 11

Out: mRNA, tRNA, ribosomal subunits.
In: All nuclear proteins.

Question 12

How are molecules passed through the NPC?

Answer 12

1. Small molecules pass freely
2. Large bind to receptors. Only molecules complexed with receptors are allowed to pass. They are transported by nucleoporin chains in the central area.

Question 13

What is the nuclear lamina?

Answer 13

The nuclear lamina is a fibrillar network inside the nucleus of most cells. Its filaments are built of lamins.