The Cell Nucleus

Question 1

The function of the nucleus

Answer 1

• Store and maintain the cell’s DNA
• DNA replication
• Transcription
• Ribosomal biogenesis
• Controls communication between nucleoplasm and cytoplasm

Question 2

How is DNA stored as in the nucleus

Answer 2

Stored as chromosomes

Question 3

How many pairs of chromosomes in the human nucleus?

Answer 3

23

Question 4

How do you go from DNA to chromosomes ?

Answer 4

• DNA has a negative charge and wraps around the positive charge histone proteins.

Question 5

How are nucleosomes made more compact?

Answer 5

Nucleosome made more compact by wrapping into 30nm fibre

Question 6

What is the highest level of compaction of chromosomes?

Answer 6

Metaphase chromosome

Question 7

Structure of chromosomes

Answer 7

Single molecule of DNA
Telomeres: protect chromosome ends
Centromere: needed during cell division
Origins of replication

Question 8

How are chromosomes identified?

Answer 8

Size
Banding pattern
Centromere position
G banding:chromosomes partially digested and stained with giemsa
G dark: gene poor, heterochromosome rich
G light: gene rich, euchromatin rich

Question 9

Euchromatin

Answer 9

• Location for active genes
• Less condensed

Majority of genome is made up of euchromatin

Question 10

Heterochromatin

Answer 10

• Gene poor
• Found near centromeres and telomeres
• Highly condensed- resistant to gene expression
• Associated with the nuclear envelope

About 10% of the genome is heterochromatin

Question 11

Nuclear compartments(Chromosome territory)

Answer 11

DNA and control access to DNA

Question 12

Nuclear compartments(Replication factories)

Answer 12

nascent DNA production

Question 13

Nuclear compartments(Transcription factors)

Answer 13

nascent RNA production

Question 14

Nuclear compartments(spliceosome)

Answer 14

irregular domains containing splicing factors

Question 15

Nuclear compartments(Nucleoli)

Answer 15

ribosome biogenesis

Question 16

Nuclear compartments(PML nuclear bodies)

Answer 16

possible nuclear depot

Question 17

What occurs at DNA replication factories and what do the factories contain?

Answer 17

DNA replication takes place here

Factories contain all the enzymes and other factors required to produce two new DNA strands.

Question 18

What does RNA transcription factories contain?

Answer 18

RNA polymerase II
Template DNA strand
Newly synthesised mRNA

Question 19

What does the nucleolus transcribe?

Answer 19

Transcription of rRNA to produce large 45S rRNA precursor

Question 20

What does the nucleolus modify rRNA into?

Answer 20

Modification of rRNA into 18S, 5.8S and 28S rRNA

Question 21

Assembly of ribosomal subunits

Answer 21

18S rRNA and 33 proteins-small ribosomal unit

5.8S, 28S and 5S rRNA and 49 proteins- Large ribosomal subunit.,

Question 22

How many rRNA genes are copied per haploid gene?

Answer 22

200

Question 23

Where are the rRNA genes located?

Answer 23

The genes are located in tandem copies on the acrocentric chromosomes

Question 24

Why does the cell need so many copies of rRNA?

Answer 24

A single mRNA can be translated so many times to give amplification of the final protein product

The ribosomal RNA molecule is not translated into protein, the ribosomal RNA molecule is the final product and the cell requires many ribosomes

Question 25

What is the nuclear envelope made up of?

Answer 25

Two lipid bilayer

Question 26

What type of molecules can diffuse through nuclear pores?

Answer 26

Movement strictly controlled and only small water soluble molecules can diffuse through the pore

Exports from the nucleus include ribosomal subunits and mRNA

Imports include histones, proteins etc.

Large molecules must be exported actively