Nucleus, Chromosomes & Chromatin

Question 1

Nuclear envelope

Answer 1

double membrane enclosing DNA

Question 2

Outer nuclear membrane

Answer 2

continuous with ER

Question 3

Inner nuclear membrane

Answer 3

carries nuclear specific protein

Question 4

Nuclear lamina

Answer 4

fibrous network that provides structural support to the nucleus

Question 5

Nuclear pore complexes

Answer 5

• channels through which polar molecules and macromolecules pass through the nuclear envelope
• large multi-protein complexes with 8-fold symmetry around central channel

Question 6

Nuclear localisation signal (NLS)

Answer 6

• tag for nuclear protein

- 1 or 2 short sequences with positively charged Lys residues

Question 7

Nuclear transport receptors

Answer 7

Importins - into nucleus

Exportins - out of nucleus

Question 8

What energy drives nuclear transport?

Answer 8

GTP hydrolysis - Ran GTP

Question 9

Ran-GEF

Answer 9

in nucleus

Question 10

Ran-GAP

Answer 10

in cytoplasm

Question 11

Nucleolus is site of and is a:

Answer 11

• site of ribosome biogenesis

- is an aggregation of rRNA gene clusters

Question 12

Ribosome structure:

Answer 12

• 2/3 RNA, 1/3 protein

- 1 small & 1 large subunit

Question 13

rRNA gene organisation

Answer 13

tandem arrays

Question 14

5.8S, 18S and 28S rRNAs transcribed as single:

Answer 14

pre-rRNA which is then cleaved to give rise to 3 mature rRNAs

Question 15

5S rRNA

Answer 15

encoded by separate gene

Question 16

Where are ribosomes assembled and exported to

Answer 16

assembled in nucleus and exported into cytoplasm

Question 17

pre-ribosomal particles

Answer 17

exported from nucleus via nuclear pores to yield active ribosomal subunits

Question 18

Compartmentalisation

Answer 18

• transcription in nucleus

- translation in cytoplasm

Question 19

Where do ribosomal proteins assemble

Answer 19

on pre-rRNAs in nucleolus

Question 20

Prokaryotic chromosome structure

Answer 20

circular with 1 origin of replication

Question 21

E.coli chromosome

Answer 21

~ 4.6 million bases encoding 4300 different proteins

Question 22

Eukaryotic genes contain:

Answer 22

introns and exons

Question 23

Is there correlation between genome size and evolution?

Answer 23

No

Question 24

Eukaryotic chromosome structure

Answer 24

linear

Question 25

Interphase nuclei chromosomes

Answer 25

distributed throughout nucleoplasm

Question 26

At mitosis chromosomes…

Answer 26

condense and can be individually seen with a light microscope

Question 27

3 sequence elements of a functional chromosome

Answer 27

1. telomere
2. centromere
3. replication origins

Question 28

DNA replication

Answer 28

semi-conservative

Question 29

Telomere function

Answer 29

stabilises ends of chromosomes with t-loops

Question 30

Centromere function

Answer 30

segregates sister chromatids

Question 31

Rabl configuration

Answer 31

centromeres clustered at one end and telomeres at other end of nuclear envelope

Question 32

chromosome organisation in interphase nucleus

Answer 32

individual chromosomes occupy a particular region of the nucleus to minimise tangles and help with segregation during mitosis

Question 33

Fundamental unit of chromatin

Answer 33

nucleosome

Question 34

Nucleosome core particle

Answer 34

• 147 base pairs of DNA wound around protein core

- protein core made out of histones

Question 35

Octomeric histone core

Answer 35

2 molecules of each:

• H2A
• H2B
• H3
• H4

Question 36

Histone H1

Answer 36

linker histone arranges nucleosomes into 30nm fibre

Question 37

2 types of chromatin

Answer 37

• euchromatic

- heterochromatin

Question 38

Euchromatin

Answer 38

de-condensed, open and transcriptionally active

Question 39

Heterochromatin

Answer 39

condensed, closed and transcriptionally inactive

Question 40

Heterochromatic chromosome regions

Answer 40

telomeres & centromeres

Question 41

Histone modification

Answer 41

methylation and acylation

Question 42

Epigenetic marks

Answer 42

• genes moved near telomeres can be silences

- X chromosome inactivation