Week 9 - Nucleus

Question 1

What 5 things are inside the nucleus

Answer 1

Histone
Nucleosome
Chromatin
Chromosome
Sister chromatids

Question 2

Describe the nucleus

Answer 2

Largest single organelle, containing all genetic material packaged as chromatin
Site of RNA synthesis and contains nucleolus

Question 3

Describe the nuclear pore complex

Answer 3

Large protein structure, an aqueous channel connecting nucleoplasm to cytosol

Question 4

Molecule sizes and how it relates to transport through nuclear pore complex

Answer 4

<5KDa freely diffuses
>5 - <60KDa takes longer but diffuses
>60KDa requires mechanism and energy

Question 5

What is the role of nuclear localisation signals

Answer 5

Tell a protein to go into the nucleus
Proteins synthesised on a cytosilic ribosome containing a NLS

Question 6

What are NLS recognised by

Answer 6

Nuclear Import receptors

Question 7

How do NIRs work

Answer 7

They bind to FG repeats on nucleoporins in the cytosolic domain of the NPC

Question 8

What is GTP

Answer 8

Guanosine triphosphate

Question 9

What is a GTP binding protein

Answer 9

Protein that binds to GTP and acts as GTPase (GTP->GDP)

Question 10

What is GAP

Answer 10

GTPase activating protein. Binds to GTP binding protein and induces GTP hydrolysis

Question 11

What is GEF

Answer 11

Guanine nucleotide exchange factor, binds to GTP binding protein and causes release of GDP

Question 12

Describe nuclear import

Answer 12

NIR binds to protein which has nuclear localisation signal, enters nucleus and Ran-GTP takes place of protein, releasing the protein from the NIR, then after leaving nucleus Ran-GDP dissociates from NIR and cycle can repeat

Question 13

Describe nuclear export

Answer 13

NER enters nucleus, binds to Ran-GTP which allows protein with nuclear export signal to bind to NER, protein leaves and Ran-GDP dissociates and protein leaves into cytosol leaving NER to repeat cycle

Question 14

What are the two forms of chromatin in the nucleolus

Answer 14

Heterochromatin and euchromatin

Question 15

What is heterochromatin

Answer 15

Transcriptionally inactive and densely packed chromatin

Question 16

What is euchromatin

Answer 16

Transcriptionally active and loosely packed

Question 17

What is the role of the nucleolus

Answer 17

Ribosomal biogenesis (where ribosomes are synthesised)

Question 18

Describe rRNA

Answer 18

Encoded by 200rRNA genes, clustered together on DNA sequence (tandem repeats)

Question 19

What is the benefit of tandem repeats

Answer 19

Speed up rRNA transcription