Cell Nucleus

Question 1

What is function of nucleus?

Answer 1

Store + maintain cell’s DNA 
DNA replication 
Transcription
Ribosomal biogenesis
Controls communication between nucleoplasm + cytoplasm

Question 2

How is DNA stored?

Answer 2

Is stored as chromosomes

Human cells have 23 pairs of chromosomes containing 6 x 10^9 base pairs of DNA

Question 3

Describe the structure of chromosome?

Answer 3

Single molecule of DNA 
Linear in eukaryotes 
Contains genes 
Telomere= protects ends of chromosome 
Centromere= needed during cell division 
Origins of replication= required to replicate DNA of chromosomes within reasonable time frame

Question 4

Chromosomes + cell cycle

Answer 4

In G1 phase, there are 2 homologs, parental + maternal homolog
During s phase, there is firing of replication origins to get duplication of each of these chromosomes
In G2, cells is tetraploid=> 4 cops of chromosomes
As cell enters M phase, there is change in chromosomes as they become highly condensed

Question 5

What technique can be used to identify chromosomes?

What does it tell us?

Answer 5

G banding
Chromosomes are partially digested + stained with Giemsa
G dark= gene poor so heterochromatin rich
G light= gene rich so euchromatin rich

Question 6

What are 2 arms of chromosomes called?

Answer 6

P arm + q arm
P arm is slightly shorter
Q arm is slightly longer

Question 7

What is meaning of metacentric chromosomes?

Answer 7

Some chromosomes, arms looks relatively similar

Question 8

What is meaning of submetacentric chromosomes?

Answer 8

In some chromosomes, centromere is towards on end

Question 9

What is meaning of Acrocentric chromosomes?

Answer 9

P arm is very short which contains repetitive RNA + ribosomal RNA genes

Question 10

What is Karyotyping used for in human cell?

Answer 10

To identify chromosomal abnormalities

Question 11

What is heterochromatin?

Answer 11

Gene poor
Found near centromeres + telomeres
Highly condensed so usually resistant to gene expression
Often associated with nuclear envelope
In typical cell, 10% of genome is heterochromatin

Question 12

What is euchromatin ?

Answer 12

Gene rich
Location for active gene
Les condensed
Majority of genome is made up of euchromatin

Question 13

What is spectral karyotyping?

Answer 13

Fluorescent in situ hybridisation
Fluorescent markers used
In situ->cells on slide + add probe. You do hybridisation step between probe + DNA. Wherever the DNA happens to be on chromosome or within the nucleus, it will bind + give you a fluorescent signal

Question 14

How are chromosomes organised in metaphase nucleus?

Answer 14

Metaphase chromosomes, DNA is tightly packed (condensed)

Question 15

How is chromosome organised in interphase nucleus?

Answer 15

Interphase chromosomes, DNA is more relaxed (decondensed)

Question 16

What are chromosome territories?

Answer 16

Chromosomes arms + bands are distinct + mutually exclusive

These pattern of chromosome take within cell nucleus is called chromosome territories

Question 17

Where are gene poor chromosomes located?

Answer 17

Located in periphery of nucleus

Question 18

Where are gene rich chromosomes located?

Answer 18

Located in interior of nucleus

Question 19

Functional compartmentalisation of nucleus

Answer 19

Subnuclear compartment exist despite absence of internal membranes

Question 20

What are DNA replication factories?

Answer 20

Is where DNA replication takes place

Contains all enzymes + other required to produce 2 new DNA strands

Question 21

What are RNA transcription factories?

Answer 21

Contain RNA polymerase II, template DNA strand + newly synthesised mRNA
Each of these factories will contain general transcription factors that are required to open up DNA + in order to let RNA polymerase to come in + bind

Question 22

What is nucleolus?

Answer 22

Largest substructure in nucleus

Question 23

What are 3 distinct zones of nucleolus by electron microscopy?

Answer 23

FC (fibrillar center) - where ribosomal RNA genes are located
DFC( dense fibrillar component)- where rRNA transcripts being made from DNA containing ribosomal genes are
GC (granular component)- processing + assembly

Question 24

Why does cell need so many copies of ribosomal RNA genes?

Answer 24

Compare to single copy gene- single mRNA molecule can be translated many times to give amplification of final protein product
Ribosomal RNA molecule is not translated into protein, ribosomal RNA molecule transcribed is final product + cell requires many ribosomes

Question 25

Describe the structure of nuclear envelope?

Answer 25

2 lipid bilayer-> inner nuclear membrane + outer nuclear membrane

Question 26

Describe the function of nuclear pore?

Answer 26

Movement through this is strictly controlled + only small H2O soluble molecule can diffuse freely through pore
Has cytosolic side + nuclear side
Has nuclear basket which has particular amino acids that let certain molecules + proteins to be able to move for inside of nucleus of cytoplasm or reverse direction
Large molecules must be actively transported through the nuclear pore

Question 27

What is exported into the nucleus through the nuclear pore?

What do they require in order to be exported?

Answer 27

Ribosomal subunit + mRNA

Proteins require nuclear export signal to leave

Question 28

What is imported into the nucleus through the nuclear pore?

What do they require in order to be imported?

Answer 28

Histones, DNA/RNA polymerase + other nuclear proteins

Proteins require nuclear localisation sequence to be imported