The Nucleus

Question 1

What is the first organelle to be discovered?

Answer 1

Nucleus

Question 2

What is the nucleus?

Answer 2

Priciple defining charactersistic of eukaryotic cells.

Question 3

Why have a nucleus?

Answer 3

The nuclues seperates the process of transcription and translation, enables alternative splicing and associated complexity.

Question 4

What does alnernative splicing mean?

Answer 4

splicing of introns and combinations of extrons.

Question 5

Where did the nucleas come from evolutionarily? Give both the hypothesis.

Answer 5

Hypothesis 1 - Invagination of membrane around DNA.
Hypothesis 2 - Endosymbiosis.

Question 6

What is endosymbiosis?

Answer 6

Endosymbiosis is a theory suggesting that some organelles were free living bacteria which were enguled by a cell becoming combined with the cell.

Question 7

Which of the hypothesis have implications for topology?

Answer 7

Both

Question 8

How are DNA in the nucleus packaged?

Answer 8

They are packaged into chromosomes and are wrapped around histones for effecient packaging.

Question 9

How are DNA packed in non - dividing cells?

Answer 9

Loosely packed forming a tangle of strands called chromatin.

Question 10

How are chromatin organizations revealed?

Answer 10

EM staining techniques.

Question 11

Whate are the stages of chromatin organization?

Answer 11

1. Heterochromatin
2. Euchromatin
3. Nucleolus

Question 12

What is heterochromatin?

Answer 12

Dense staining of interphase DNA.

Question 13

What is Euchromatin?

Answer 13

Less - dense staining interphase DNA

Question 14

What is Nucleolus chromatin staining organization?

Answer 14

Highly dense staining of RNA.

Question 15

How are nucleus stained in colour?

Answer 15

Fluorescent in Situ hybridisation.

Question 16

Is the nucleus compatmentalised?

Answer 16

Yes - chromosomes occupy territories withim the nucleus through inheritance but can change after disease or differentiation.

Question 17

How does the location of a gene change?

Answer 17

Depending on its transcriptional status.

Question 18

How are the genes CD4 and centromeric heterochromatin identified?

Answer 18

Red stain for centromeric heterochromatin
Green stain for CD4.

Question 19

What is CD4?

Answer 19

HIV receptor.

Question 20

What has gene tagging proved?

Answer 20

Gene “tagging” together with improvements in microscopy have revealed the existence and
function of multiple sub-nuclear organelles in inter-chromatin space.

Question 21

What are the adaptations of Nucleolus?

Answer 21

1. Not membrane bound unlike other organelles
2. It is a collection of macromolecules - rDNA genes, precursor rRNA, mature rRNA and more.

Question 22

Give a function of nucleolus?

Answer 22

Site for processing ribosomal RNA to produce ribosomes.

Question 23

Sub nuclear organelles(Finish)

Question 24

What is lamina?

Answer 24

It is a fibrous meshwork supporting the nuclear envelopes which is adouble unit membrane perfortaed with pores.

Question 25

What does lamina do in part?

Answer 25

The lamina is responsible for ensuring the asymmetric nature of the double unit membrane.