Cell Nucleus

Question 1

List the main functions of the cell nucleus?

Answer 1

• stores and maintains DNA
• DNA replication
• Transcription
• Ribosomal biogenesis
• Nucleoplasm and cytoplasm communication control

Question 2

How is DNA stored in the nucleus?

Answer 2

As chromosomes

Question 3

How many chromosomes are present in humans?

Answer 3

23 pairs / 46 chromosomes

Question 4

How many base pairs do diploid cells contain?

Answer 4

6x10⁹ base pairs of DNA

Question 5

How is DNA in chromosomes so compact?

Answer 5

DNA has a negative charge
Histone proteins are positively charged
- DNA wraps around histones

Question 6

What is a nucleosome?

Answer 6

A length of DNA coiled around a core of histones

- the building blocks of chromatin

Question 7

How are nucleosomes even more compact?

Answer 7

Wrap themselves into 30nm fibres

Question 8

Describe the structural features of a chromosome

Answer 8

• single DNA molecule
• Linear in eukaryotes
• contains genes
• contains, Telomeres, Centromeres, and replication
  origins

Question 9

What is the significance of Centromeres?

Answer 9

Required during cell division

Question 10

What is the role of the telomeres?

Answer 10

Protect the chromosome ends

Question 11

Is number of chromosomes an organsim has significant?

Answer 11

Different organisms have different chromosome no.’s

Chromosome no. doesn’t affect the complexity of organisms

Question 12

How can chromosomes be identified?

Answer 12

Using idiography and idiograms

Question 13

How do idiograms work?

Answer 13

Chromosomes are patially digested and stained wit Giesma

- show chromosome banding patterns

Question 14

What factors do we measure to identify which chromosome it is?

Answer 14

We can use the

• length
• centromere position
• banding pattern

Question 15

How do we differentiate between the two chromosome arms?

Answer 15

p - short arm

q - long arm

Question 16

What is Heterochromatin?

Answer 16

Heterochromatin is a tightly packed form of DNA

Question 17

List the distinguishing features of heterochromatin

Answer 17

• Gene poor
• Dark
• In periphery of nucleus: found near centromeres &
  telomeres
• Highly condensed (resistant to gene expression)
• 10% of genome

Question 18

What is Euchromatin?

Answer 18

Euchromatin is a lightly packed form of chromatin that is enriched in genes

Question 19

List some features of euchromatin

Answer 19

• Gene rich
• Light
• Located centrally in nucleus
• Less condensed (expressed genes)
• Majority of genome

Question 20

How can chromosomal abnormalitites be observed?

Answer 20

Spectralkaryotyping

Question 21

What are chromosome territories?

Answer 21

Regions of the nucleus preferentially occupied by particular chromosomes

Question 22

What is the role of Chromomosome territories?

Answer 22

Store and control access to DNA

Question 23

What occurs at the replication Factories in the nucleus?

Answer 23

Nascent DNA production

Question 24

Explain what is meant by Nascent DNA?

Answer 24

DNA of the lagging strand

Question 25

What is produced at Transcription factories?

Answer 25

Nascent RNA

Question 26

What are spliceosomes?

Answer 26

Irregular domains containing splicing factors

Question 27

Which process occurs at the nucleoli?

Answer 27

Ribosome biogenesis

Question 28

What is the significance of DNA replication factories?

Answer 28

Contain all the enzymes and factors required for semi conservative replication

Question 29

What factors do RNA transcription factories contain?

Answer 29

- RNA Polymerase II - Template DNA Strand - Newly synthesised mRNA

Question 30

How does ribosome biogenesis occur at the nucleolus?

Answer 30

1. transcription of rRNA genes 2. producing large 45S rRNA precursor 3. Cleavage of RNA into 18s, 5.8s and 28s 4. assembly of rRNA subunits

Question 31

What are the final ribosomal subunit sizes?

Answer 31

Small ribosomal subunit: 18s | Large ribosomal subunit: 5.8s, 28s (5s)

Question 32

How are chromosomes arranged in the interphase nucleus?

Answer 32

They form non overlapping domains | Homologous pairs dont' lie adjacent to one another

Question 33

How many rRNA genes are copied per haploid genome?

Answer 33

~ 200

Question 34

Where are rRNA genes located?

Answer 34

In tandem copies on the accrocentric chromosomes

Question 35

Why are rRNA genes needed in such abundances?

Answer 35

- single mRNA can be translated many times - amplifies final product - rRNA molecules are the final products

Question 36

Describe the structure of the nucleur envelope?

Answer 36

2 lipid bilayers

Question 37

How many nuclear pores in a mammalian cell nucleus?

Answer 37

Approx. 3000-4000 nucleur pores

Question 38

What is the function of the nucleur pores?

Answer 38

Nuclear export - rRNA, mRNA, proteins (require nucleur export signal) Nucleur Import - Histones, DNA, RNA (require nucleur localisation sequence)