nuclear structure and function

Question 1

nuclear envelope structure

Answer 1

• double membrane with 300-400 pores
• lamina on inside, ER on outside
• outer membrane has ribosomes

Question 2

nuclear lamina structure

Answer 2

• meshwork of lamin proteins A, B, C

- for support, organizes chromatin and regulates nuclear breakdown during mitosis (lamins get phosphorylated)

Question 3

nucleocytoplasmis transport

Answer 3

• nuclear pores are made of 100 proteins in 8x symmetry
• solutes and small proteins pass through
• larger proteins need signal and facilitation
• Ran GTPase hydrolyzes with help of Ran Gap to move cargo into nucleus
• carrier proteins (importin) bind substrate and move through pores
• Ran gets new GTP from GEF and moves back to cytosol with importin, leaves cargo
• Ran GEF recharges Ran with new GTP
• cargo +exportin +Ran GTP move out through pores into cytosol
• Ran hydrolyzes again into GDP and releases phosphate and cargo

Question 4

nucleolus

Answer 4

no membrane
3 parts:
1. fibrillar - DNA not being transcribed
2. dense fibrillar - rRNA being made
3. granular - rRNA precursors

first transcribe genes for 45s subunit in nucleolus
5s subunit comes in with 80 other proteins for transcription
–nucleases break up 45s into 18, 28, 5.8
-then they assemble into small and large subunit. do quality control to remove bad RNA

Question 5

chromosome structure

Answer 5

• carry genetic info on 2x DNA polymer

- gene = segment of DNA that codes for RNA

Question 6

chromatin

Answer 6

chromatin - chromosomal DNA, histones, and proteins
tight = heterochromatin (during mitosis)
loose = euchromatin. during interphase and not being expressed
-nucleosome - has histone core of 2x H2a, H2b, H3, H4
146 bp of DNA wraps around, plus a 30nm fiber of H1 histone

Question 7

Nuclear disease

Answer 7

1. Systemic Lupus Erythematosus - antibodies to self antigen in the nucleus like pore proteins, splicing factors, DNA. autoimmune and causes inflammation of skin
2. acute promyelocyte leukemia - PML needed to make compartment in nucleus. mutation –> severe bleeding
3. Spinal Muscular Atrophy - mutation in RNA splicing protein called SMN