Interphase Nucleus 8.21

Question 1

Describe the double membrane structure of the nuclear envelope

Answer 1

outer membrane - continuous with the ER - studded with ribosomes inner membrane - covered by the nuclear lamina with marginal heterochromatin anchored along its surface perinuclear space is between the outer and inner membrane nuclear pore complexes 10 nm deep span the inner and outer membrane

Question 2

describe the structure of nuclear pore complexes

Answer 2

3 stacked octameric nucleoporin rings

Question 3

describe the two types of nuclear import

Answer 3

only proteins are imported into the nucleus proteins smaller than 45kD diffuse passively into the nucleus proteins larger than 45kD are actively imported Proteins must carry a nuclear localization sequence (NLS) - sequence heavy in Lysine and Arginine (basic) Protein binds to the alpha subunit of importin a/b B subunit binds to a nucleoporin and the complex passes through into the nucleus Ran-GTP binds to the complex causing the cargo protein to release

Question 4

describe nuclear export

Answer 4

proteins and RNA are exported from the nucleus exported proteins must carry a nuclear export sequence (NES) enriched in Leucine (hydrophobic) cargo binds to exportin and Ran-GTP and is exported into the cytoplasm - dissociation of Ran-GTP from the complex causes the cargo to dissociate as well

Question 5

What fuels nuclear import and export

Answer 5

Ran-GTP gradient (high in the nucleus, low in the cytoplasm)

Question 6

why are drugs difficult to import into the nucleus

Answer 6

must be protein based and carry a NLS

Question 7

how and when does the nucleus change during the cell cycle

Answer 7

intact during interphase hyperphosphorylation will cause lamina to dissociate during mitosis - Lamin B remains bound to LBR on fragments of the nuclear envelope (Lamin A and C dissolve into solution) Lamin B’s associate with the nuclear membrane aids in reannealing after mitosis

Question 8

which genes code for which lamins

Answer 8

Muscular dystrophy, cadiomyopathy, and Premature aging resulting from mutations in the LMNA gene - nucleus has issues reforming during mitosis caused by rapid development of progerin (defective Lamin A)

Question 9

Describe the nuclear lamina

Answer 9

interweaved system of 10nm intermediate filaments provide anchor points for marginal heterochromatin

Lamin-B receptors on the inner membrane - attachment point for Lamin A, B and C