The Cell Nucleus

Question 1

What are the functions of the nucleus?

Answer 1

• to store and maintain a cell’s DNA
• DNA replication
• transcription
• ribosomal biogenesis
• controls communication between the nucleoplasm and the cytoplasm

Question 2

What 3 key features to scientists use to identify chromosomes?

Answer 2

• SIZE
• BANDING PATTERN
• CENTROMERE POSITION

Question 3

List some differences between Heterochromatin and Euchromatin.

Answer 3

HETEROCHROMATIN:

• gene poor
• found near centromeres and telomeres
• highly condensed, usually resistant to gene expression
• often associated with the nuclear envelope

EUCHROMATIN:

• location for active genes
• less condensed that heterochromatin
• majority of the genome is euchromatin

Question 4

What is the difference in the spatial location of gene-rich vs. gene-poor chromosomes?

Answer 4

The gene-poor chromosomes are at the periphery of the nucleus, while the gene-rich are in the interior.

Question 5

What are nuclear compartments?

Answer 5

They are subnuclear compartments that exist within the nucleus , despite the absence of internal membranes.

Question 6

List 6 nuclear compartments and their functions.

Answer 6

• CHROMOSOME TERRITORIES: they store DNA and control access to it
• REPLICATION FACTORIES: nascent DNA (lagging strand) production
• TRANSCRIPTION FACTORIES: nascent RNA (lagging strand) production
• SPLICEOSOME: irregular domains containing splicing factors
• NUCLEOLI: ribosome biogenesis
• PML NUCLEAR BODIES: possible nuclear depot

Question 7

What are 3 functions of the nucleolus?

Answer 7

• transcription of rRNA genes to produce a large 45S precursor
• cleavage/modification of rRNA into 18S, 5.8S and 28S rRNA
• assembly of ribosomal subunits (18S, 5.8S, 5S and 28S)

Question 8

What are the three distinct zones in a nucleolus that you can identify under an electron microscope, and what are their functions?

Answer 8

• Fibrillar Centre (FC): ribosomal RNA genes
• Dense Fibrillar Component (DFC): rRNA transcripts
• Granular Component (GC): processing and assembly

Question 9

Describe the nuclear pores and movement through them.

Answer 9

The nuclear envelope contains nuclear pores, which is how communication between the nucleoplasm and the cytoplasm occurs.
Movement through the nuclear pores is strictly controlled and only small water soluble molecules can diffuse freely through the pore.

NUCLEAR EXPORT:
ribosomal subunits and mRNA proteins require a nuclear export signal

NUCLEAR IMPORT:
histones, DNA/RNA polymerase and other nuclear proteins - proteins require a nuclear localisation sequence