The nucleus

Question 1

What is the principle defining characteristic of eukaryotic cells?

Answer 1

The nucleus

Question 2

What is the key function of the nucleus and what does this enable?

Answer 2

it separates transcription & translation
→ enables for alternative splicing
= specialised cells = more complex organisms

Question 3

What are 2 hypotheses about the evolutionary origin of the nucleus?

Answer 3

1. Ancient prokaryotic cell → Invagination of membrane around DNA formed primitive nucleus
2. Emdosymbosis → where one form of prokaryote engulfed another

Question 4

Describe euchromatin

Answer 4

less compact around histones = more transcription can occur)

Question 5

Describe heterochromatin

Answer 5

more compact around histones = less transcription

Question 6

What is FISH?

Answer 6

Fluorescent In Situ Hybridization
→ Specific chromosome staining (painting) in interphase and mitosis = additional evidence for eu/hetero-chromatin distinction

Question 7

Describe how the nucleus is dynamic

Answer 7

• The location of the gene within the nucleus changes depending on its transcriptional status
• Sub-nuclear organelles can be dynamic and move in non-random ways in an ATP-dependent manner

Question 8

What is the function of the nucleolus?

Answer 8

ribosome synthesis

Question 9

What is the function of speckles in the nucleus?

Answer 9

pre-mRNA processing

Question 10

What is the function of Cajal bodies?

Answer 10

Splicing

Question 11

What is the function of PML bodies?

Answer 11

Appear to be storage depots

Question 12

Describe the nucleolus

Answer 12

• Not membrane bound (therefore probably a condensate)
• Site for processing ribosomal RNA to produce ribosomes
• Collection of macromolecules e.g mature rRNA, ribosomal protein subunits
• Processes other types of RNA: mRNA, tRNA

Question 13

Describe the nuclear envelope

Answer 13

Double unit membrane
Perforated with pores
Supported by a fibrous meshwork called the lamina

Question 14

Describe the lamina of the nuclear envelope and its function

Answer 14

• Made up of proteins called lamins (vvv insoluble)
• Help retain the structure of the nucleus
• Responsible, in part, for ensuring the asymmetric nature of the double unit membrane:
• Protein content of the inner/outer envelope are different because the lamina acts as an anchoring device

Question 15

Describe the nuclear pore

Answer 15

Access is controlled in a size-dependent manner
Particles MW>50,000 cannot enter the nucleus by simple diffusion
But can by active signal-dependent transport
On signal, pore can open up to 26 nm in diameter