SFP: nucleus

Question 1

what are the components of the nuclear envelope?

Answer 1

• inner and outer membrane
• nuclear lamina
• nuclear pores

Question 2

what are the components of the nuclear matrix

Answer 2

• intermediate filaments
• nuclear matrix proteins

Question 3

describe the components of the nuclear membrane

Answer 3

• outer membrane: continuous with the ER
• inner: closely associated with the nuclear lamina
  -perinuclear space: continuous with the lumen of the ER

Question 4

what proteins are associated with the structure of the membrane?

Answer 4

lamins that underlie the membrane; they get farnesylated into the membrane

Lamin A: produced by alternative splicing of a single gene

Lamin B: products of separate genes

Question 5

Lamins bind to ____ to connect the nuclear envelope to chromatin

Answer 5

histones 2A and 2B

Question 6

describe the role of lamins in the breaking and forming of the nuclear envelope in mitosis

Answer 6

they can facilitate these processes by being phosphorylated or dephosphorylated

Question 7

what are the main components of a nuclear pore

Answer 7

cytoplasmic ring, spoke-ring, nuclear ring, and transporter

Question 8

describe the cytoplasmic ring

Answer 8

element of the nuclear pore that binds to spoke proteins and attach to the outer membrane. they anchor cytoplasmic filaments that couple the pore to the cytoskeleton

Question 9

describe the nuclear ring

Answer 9

binds to spoke proteins and attached to the inner membrane. they form a nuclear basket

Question 10

describe the spoke ring

Answer 10

form a central channel that connect the nuclear and cytoplasmic rings

Question 11

describe the transporter

Answer 11

subunits that are freely permeable to ions and small proteins, but nothing large

Question 12

what processes are associated with selective transport in the nucleus

Answer 12

import of proteins, export of proteins, export of RNA

Question 13

what is the nuclear association sequence

Answer 13

a sequence in the amino acid of a target protein that functions as a binding site for transport proteins

Question 14

which amino acids re common in nuclear localization sequences

Answer 14

lysine and arginine

Question 15

describe the main steps of importing proteins into the nucleus

Answer 15

1. importin binds to a cargo protein containing an NLS
2. importin-cargo protien binds to filaments in the nuclear pore
3. importin-cargo protein traverses the pore
4. importin-cargo protein binds to Ran GTP in the nucleus, releasing the cargo protein
5. importin-RanGTP is exported to the cytoplasm
6. GTP is hydrolyzed to GDP by GAP

Question 16

describe the main steps in exporting proteins from the nucleus

Answer 16

1. exportin binds to cargo proteins with an NLS
2. RanGTP binds to the exportin-cargo protein
3. exportin-cargo protein-RanGTP traverses the nuclear pore
4. GTP is hydrolyzed to GDP by ran GAP, releasing the cargo protein and exportin
5. exportin is transported back into the nucleus
6. ranGDP is transported back into the nucleus

Question 17

what is NTF2

Answer 17

it is an import receptor specific to RanGDP; when RanGTP in the cytoplasm is hydrolyzed to RanGDP, NTF2 brings it right back into the nucleus to be re-activated and reused

Question 18

what are the export receptors of mRNA and tRNA

Answer 18

mRNA: Crm1

tRNA: exportin-t

Question 19

all mRNAs are exported as ___

Answer 19

mRNP

Question 20

what is NXF1

Answer 20

they bind to mRNP to bring it out of the cell; this is used instead of ranGTP

Question 21

where are rRNAs transcribed

Answer 21

the nucleolus

Question 22

where do ribosomes assemble

Answer 22

the nucleolus

Question 23

does the nucleolus have a membrane?

Answer 23

no

Question 24

what are nucleolar organizing regions

Question 25

rRNA is processed by ___ after being transcribed

Answer 25

snoRNPs

Question 26

what are the structural correlates of ribosome production

Answer 26

• fibrillar centers: site of rRNA transcription. contain euchromatin. show up as light centers
• dense fibrillar component: site of processing into mature rRNA. very dark stained regions
• granular component: site of ribosome assembly. look grainy/dotted