Lecture 4- Nucleus

Question 1

Histones

Answer 1

Positively charged proteins that form the core of the nucleosome complex (DNA wraps around them)

Question 2

Nonhistones

Answer 2

Negatively charged proteins that regulate transcription, repair and replicate DNA, and convert chromatin structure

Question 3

Heterochromatin

Answer 3

Condensed chromatin

Not transcriptionally active

Question 4

Constitutive Heterochromatin

Answer 4

Contains DNA that is not transcribed

Question 5

Facultative Heterochromatin

Answer 5

DNA is not transcribed in particular cell being examined but may be transcribed in other cells

Question 6

Barr Body/Drumstick

Answer 6

Inactivated X chromosome

Question 7

Euchromatin

Answer 7

Transcriptionally active

Not condensed

Question 8

Nuclear Lamina

Answer 8

Support inner membrane
During cell division-phosphorylated to dissociate membrane
Post cell division-dephosphorylated to reassemble membrane

Question 9

How are chromosomes organized in the nucleus?

Answer 9

Each one occupies a discrete region and is anchored by lamina

Question 10

Replication Factories

Answer 10

Functional bodies where replication takes place inside the nucleus

Question 11

Nuclear Speckles

Answer 11

Concentrations of mRNA splicing machinery

Question 12

PML Bodies

Answer 12

Accumulation of transcription factors and chromatin-modifying proteins

Question 13

Cajal Bodies

Answer 13

Contain coilin protein

Question 14

What is the Nuclear Pore Complex?

Answer 14

A passageway for macromolecules to go between nucleoplasm and cytoplasm
It requires ATP and GTP

Question 15

What are the proteins called that transport macromolecules into and out of the nucleus?

Answer 15

Karyopherins (Importin alpha/beta & Exportin)

Question 16

What is the structure of the Nuclear Pore Complex?

Answer 16

8-fold symmetry around a central canal
8 spokes connect rings to nuclear and cytoplasmic surfaces
Basketlike structure on the nuclear side

Question 17

How does import through the Nuclear Pore Complex occur?

Answer 17

Importin alpha recognizes NLS
Ran-GDP binds to importin beta and moves through pore
Importin beta separates and is released from Ran-GDP
RCC1 generates Ran-GTP

Question 18

How does export through the Nuclear Pore Complex occur?

Answer 18

Exportins bind to Ran-GTP and protein and moves through pore
Ran-GTP is separated from exportin and protein
Ran-GAP converts Ran-GTP to Ran-GDP for import

Question 19

What are the Functional sequences of a Chromosome?

Answer 19

Telomeric Sequence-Located at ends of chromosome and insure integrity
Centromeric Sequence-Involved in separation during Mitosis and Meiosis
Replication Sequence-Start sites for DNA replication

Question 20

What is the Nucleolus?

Answer 20

A region inside the nucleus where rRNA is transcribed

A nucleus may have more than one nucleolus

Question 21

What are the regions of a Nucleolus?

Answer 21

Fibrillar Center-Tightly coiled non-transcribed DNA
Dense Fibrils-Active transcription of RNA (contains ribonucleoproteins)
Granules-Contains maturing ribosomes