Cell nucleus

Question 1

What are the functions of the cell nucleus?

Answer 1

store and maintain cell's DNA
DNA replication
Transcription
Ribosomal biogenesis
controls communication between the nucleoplasm and the cytoplasm

Question 2

How is DNA stored as and how many pairs are there in the human nucleus?

Answer 2

chromosomes

23 pairs

Question 3

How does DNA form chromosomes?

Answer 3

DNA has a negative charge so wraps around the positive charge histone proteins

Question 4

How are nucleosomes made more compact?

Answer 4

by wrapping into 30nm fibre

Question 5

what is the highest level of compaction of chromosomes?

Answer 5

metaphase chromosome

Question 6

What is the structure of chromosomes?

Answer 6

single molecule of DNA
linear
contains genes
telomeres
centromeres
origins of replication

Question 7

How are chromosomes identified?

Answer 7

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

Question 8

heterochromatin

Answer 8

Gene poor
Found near centromeres and telomeres
highly condensed - resistant to gene expression
associated with nuclear envelope
About 10% of the genome is heterochromatin

Question 9

Euchromatin

Answer 9

location of active genes
less condensed
majority of the genome is made up of euchromatin

Question 10

Nuclear compartments (chromosome territory)

Answer 10

store DNA and control access to DNA

Question 11

Nuclear compartments (replication factories)

Answer 11

nascent DNA production

Question 12

Nuclear compartments (transcription factories)

Answer 12

nascent RNA production

Question 13

Nuclear compartments (spliceosome)

Answer 13

irregular domains containing splicing factrors

Question 14

Nuclear compartments (nucleoli)

Answer 14

ribosome biogenesis

Question 15

Nuclear compartments (PML nuclear bodies)

Answer 15

possible nuclear depot

Question 16

what occurs at DNA replication factories and what do they contain?

Answer 16

DNA replication takes place here

They contain all the enzymes and other factors required to produce two new strands

Question 17

what do RNA transcription factories contain?

Answer 17

RNA polymerase II
Template DNA strand
Newly synthesised messenger RNA

Question 18

What occurs in the nucleolus?

Answer 18

Transcription of rRNA genes to produce large 45s rRNA precursor
cleavage/ modification of rRNA into 18s, 5.8s and 28s rRNA
assembly of ribosomal subunits: 18s (small subunit) and 5.8s,28s and 5s (large ribsomal subunit)

Question 19

How many rRNA genes are copied per haploid gene and where are they located?

Answer 19

200

the genes are located in tandem copies on the acrocentric chromosomes

Question 20

Why does the cell need so many copies of rRNA chromosomes?

Answer 20

a single mRNA can be translated so many times to give amplification of the final protein product
the ribosomal RNA molecules is not translated into protein, the rRNA molecule transcribed is the final product and the cell requires many ribosomes

Question 21

What does the nuclear envelope consist of?

Answer 21

2 lipid bilayer

Question 22

what types of molecules can diffuse through nulear pore?

Answer 22

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 histoness, proteinss, etc
large molecules must be exported actively