Lecture 7

Question 1

Components of the nucleus

Answer 1

Membrane
Nuclear Lamina
Chromosomes / chromatins
Nuclear pores

Question 2

Nuclear Membrane

Answer 2

1% of the cells total membrane

Composed of phospholipid bilayer

Question 3

Nuclear Lamina

Answer 3

Mesh of fibrous proteins

Underline the inner membrane of the nuclear envelope

Question 4

Chromosomes / Chromatin

Answer 4

-Within the cell
- condensed chromatin structures
- Cell not undergoing replication= chromatin uncoils and is a loss ball floating
Chromatin= DNA + proteins of interphase chromosome
—

Question 5

Chromatin types

Answer 5

Euchromatin
Heterochromatin
Nucleolus

Question 6

Euchromatin

Answer 6

Uncoiled

• Synthesis of mRNA and tRNA occur
• bulk of the chromatins in the nucleus

Question 7

Heterochromatin

Answer 7

Centromere region
— not needed during interphase
—tightly coiled
— outskirts of the nucleus

Question 8

Nucleolus

Answer 8

rRNA synthesis and ribosomal assembly

— round area in the middle of the nucleus

Question 9

Nuclear Pores

Answer 9

Comprised of hundreds of different proteins

• pore about 120nm in diameter
• about 3000 per mammalian nucleus

Question 10

Molecules move into nucleus

Answer 10

— nucleotides
— RNA and DNA polymerase 
— spliceosomes 
— transcription factors 
— histones
— Cdk/cyclin proteisn

Question 11

Molecules move out of nucleus

Answer 11

mRNA
—tRNA
— Ribosomes

Question 12

Purpose of Active transport

Answer 12

When larger molecules cannot diffuse passively

Question 13

Nuclear localization signal (NLS)

Answer 13

Series of amino acids that signals proteins to import a specific proteins into the nucleus

Kalderon er al 1984

Question 14

Missense Mutation Codon (lys) 128

Answer 14

How does the T-Antigen protein get into the nucleus?
— imports normally into nucleus
— if there is a mutation on codon 128 — no importation from cytosol to nucleus

Question 15

Test of Necessity

Answer 15

Remove something = does it still occur?

Kalderon et al 1984 removed sections of the T-antigen protein and noted whether or not it functioned properly

Question 16

Test of Sufficiency

Answer 16

Add something

— adding the short sequence of eukaryotic DNA to an E. Coil protein causes the beta- GAL to enter the nucleus

Question 17

Importins Proteins

Answer 17

Associated with both NLS and nuclear pore
Import cargo into the nucleus
-high affinity for cargo in the cytosol
- low affinity for cargo in nucleus

Question 18

Nuclear Export and Exportin Proteins

Answer 18

• Nuclear export signal and exporting proteins are necessary

Exportin proteins = high affinity for cargo in the nucleus; low affinity in cytosol

Question 19

RAN

Answer 19

Driving nuclear transport

—catalyze the nuclear import and export = protein RAN

Question 20

RAN- GTP and RAN-GDP

Answer 20

Ran binds both to importins and exportins
— slightly changing the shape of proteisn
RAN-GTP = it’s active form = found in nucleus
RAN-GDP= inactive form = found in cytosol

Question 21

RAN Mechanism

Answer 21

RAN enters nucleus -> GDP replaced with GTP(Guanine exchange factor protein)

RAN leaves nucleus -> enters the cytosol -> GTP is hydrolysis to GDP (Cytosolic GTPase activating protein)

Question 22

RAN and nuclear import

Answer 22

RAN- GTP binds to importins in the nucleus -> importins releases the cargo -> importin binds to nuclear pore -> can leave nucleus -> enter the nucleus -> GDP is removed -> RAN GTP is added

Question 23

RAN and Nuclear export

Answer 23

RAN-GTP binds to exportin in nucleus -> exportin binds to the cargo -> delivered to cytosol -> RAN-GTP converted to RAN-GDP -> importins has lower affinity for cargo in cytosol -> exportin protein going back into the nucleus -> RAN loads exportins in the nucleus