L18 - The nucleus

Question 1

What is the role of the nucleus?

Answer 1

The nucleus separates the process of transcription & translation:
Transcription (DNA> RNA)
Translation (RNA> protein)
It enables alternative splicing; & associated complexity.

Question 2

Where (evolutionarily) did the nucleus come from?

Answer 2

There are 2 hypotheses:

1: Invagination of membrane around DNA - Formation of primitive nucleus
2: Endosymbiosis - A symbiotic relationship where one organism lives inside the other

Question 3

What is the significance of packaging in the nucleus?

Answer 3

DNA in the nucleus is packaged into chromosomes and DNA is wrapped around histones for effective packaging.

In non-dividing cells, DNA is loosely packed forming chromatin. Just before cell division, packaging tightens up and chromosomes become visible.

Question 4

EM staining technique reveals additional chromatin organisation.

What is heterochromatin, Euchromatin and the nucleolus?

Answer 4

Heterochromatin:
Dense staining of interphase DNA

Euchromatin:
Less-dense staining interphase DNA

Nucleolus: site for ribosome synthesis
Highly dense staining of RNA

Question 5

What is the nucleolus?

Answer 5

The nucleolus = site for ribosome synthesis

Question 6

What is the nuclear envelope?

Answer 6

Nuclear envelope is a double unit membrane perforated with pores
and supported by a fibrous meshwork called the lamina.

Question 7

What is the role of the lamina?

Answer 7

The lamina is responsible, in part, for ensuring the asymmetric nature
of the double unit membrane - plays a global role in gene regulation
as well as structural rigidity