Lecture 3 - Nuclear Architecture & Chromatin

Question 1

Nuclear envelope (general structure)

Answer 1

2 membranes, an underlying lamina, and nuclear pore complexes

Question 2

Lamina

Answer 2

• made up of lamins

- has high affinity for chromatin

Question 3

Nuclear pores

Answer 3

• the only channels in and out of the nucleus

Transport by:

• passive diffusion (small molecules)
• energy-dependent transport (RNA & proteins)

Question 4

Nuclear localization signals

Answer 4

specific aa’s recognized by transport receptors

nls are on protein to be transported

Question 5

Areas of high Ran GDP/Ran GTP concentration

Answer 5

Ran GDP is higher in cytoplasm

Ran GTP is higher in nucleus

Question 6

RNA transport

Answer 6

most RNAs are exported

RNAs are transported by RNPs (ribonucleoproteins)

Question 7

Nucleolus and RNA processing

Answer 7

Nucleolus is associated with chromosomal regions that contain genes for 5.8S, 18S, and 28S rRNAs.
- all cells contain multiple copies of these genes to meet the need for transcription of many rRNA molecules

Processing of rRNA looks like processing of pre-mRNA with removal of non-coding regions, but there is no splicing of the remaining parts. After this, rRNA is methylated.

Question 8

snRNA and snoRNA

Answer 8

snRNA and snoRNA fxn in processing of pre-rRNA

snoRNA is involved in base modification of pre-rRNA (such as methylation)

Question 9

Histones

Answer 9

• an octomer consisting of 2 each of H2A, H2B, H3, and H4
• H1 histone is a linker histone that holds nucleosome together
• Histones contain higher proportion of basic aa’s (arginine and lysine) which facilitates binding with neg. charged DNA

Question 10

Nucleosome

Answer 10

• subunit of chromatin consisting of aprox. 200 bp

- nucleosome core particle conatins aprox. 145 bp wrapped around histone octomer

Question 11

Heterochromatin v. Euchromatin

Answer 11

Hetero - condensed and transcriptionally inactive

Eu - decondensed, transcriptionally active interphase chromatin, distributed throughout nucleus

Question 12

Centromere

Answer 12

a specialized region of the chromosome that plays a critical role in ensuring the correct distribution of duplicated chromosomes to daughter cells during mitosis

Question 13

Kinetochore

Answer 13

a specific DNA sequence to which a number of centromere-associated proteins bind