Cell Nucleus

Question 1

What are centromeres and what is the purpose of centromeres?

Answer 1

• Megabases of repetitive DNA
• In humans: main component are α satellite DNA
• Lock sister chromatids together after S and G phase
• Acts as the attachment site for chromosomes to the mitotic spindle via kinetochore

Question 2

What are telomeres?

Answer 2

They are tandem repeats (TTAGGG)

Question 3

Where are telomeres located?

Answer 3

At the end of chromosomes

Question 4

What is the telomere end replication problem (TERP)?

Answer 4

After every round of replication, there is a loss of a part of the telomere

Question 5

What is TERP a basis of?

Answer 5

• The hayflick limit
• Tandems are lost after every replicatioN
• Limited number of times a cell can divide

Question 6

How does a cell ‘fix’ TERP?

Answer 6

• Telomerase (a type of RNA dependent polymerase) adds telomeric DNA
• RNA sequence is complementary to TTAGGG sequence and binds to tandem
• Tandem acts as a template and adds to telomeric sequence as 3’ end

Question 7

What do nucleoli do?

Answer 7

Manufacture subunits that make up the ribosome

Question 8

What is the granular material in the nucleolus?

Answer 8

Ribosomal subunits that have already been formed

Question 9

What us the space between the outer and inner membranes of the nuclear envelope called

Answer 9

Perinuclear space

Question 10

What signals are used to transport RNA and ribosomal subunits to cytoplasm

Answer 10

Nuclear export signals

Question 11

How big are chromosome territories?

Answer 11

2um

Question 12

What are the criteria for identifying chromosomes?

Answer 12

1) Size: being the largest, 23 smallest
2) Banding pattern
3) Centromere position: metacentric (equal length), submetacentric (closer to either arm), Acrocentric (ni genetic material in P arm)

Question 13

What is the technique used to visualise decondensed chromosomes?

Answer 13

FISH

Fluorescent in situ hybridisation

Question 14

Identify the 6 nuclear compartments and describe their functions

Answer 14

• Chromosome territories: store DNA and control access to DNA
• Replication factories: nascent DNA production (lagging strand)
• Transcription factories: nascent RNA production (lagging strand)
• Spliceosome: irregular domains containing splicing factories
• Nucleoli: ribosom biogenesis
• PML nuclear bodies: possible nuclear depot

Question 15

What are chromosome territories?

Answer 15

Chromosomes form non-overlapping domains in the interphase nucleus

Question 16

What is the nucleolus?

Answer 16

• Largest substructure of the nucleus

- Self organising nucleus compartment

Question 17

What are the 3 functions of the nucleolus?

Answer 17

• Transcription of rRNA 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 18

What are the 3 distinct zones of the nucleolus?

Answer 18

• fibrillar centre: ribosomal RNA genes
• dense fibrillar component: rRNA transcripts
• granular componentL processing and assembling

Question 19

What can move via nuclear pore complexes?

Answer 19

• nuclear export: ribosomal subunits and mRNA, proteins require a nuclear export signals
• nuclear import: histones, DNA/RNA pol and other nuclear proteins