Lecture 4

Question 1

The nucleus

Answer 1

-discovered by Robert Brown
-contains most of DNA in a eukaryotic cell

Question 2

functions of the nucleus (7)

Answer 2

-separate DNA from cytosol
-separate transcription from translation
-store genes on chromosomes
-organise genes into chromosomes to allow cell division
-organise the unwilling of DNA to replicate products via nuclear pores
-produce mRNA that coded for proteins
-produce ribosomal RNA in nucleus

Question 3

Nucleus structures

Answer 3

-nucleolus
-chromatin
-nuclear envelope
-inner membrane
-outer membrane
-nuclear pore

Question 4

The nuclear envelope

Answer 4

made up of inner membrane, outer membrane and nuclear pore

Question 5

Nuclear envelope components

Answer 5

-pores regulate the entry and exit of molecules from the nucleus such as proteins
-the inside surface is lined by nuclear lamina
-this is composed of protein filaments to maintain its shape and structure
-inside the nucleus, the nuclear matrix consists of a framework of fibres

Question 6

lamina

Answer 6

-internal scaffold and support for nucleus made from intermediate filaments (IF)

a network of intermediate filaments that extend over inner surface of nuclear envelope

Question 7

Defects in the nuclear lamina

Answer 7

the gene that codes for lamina is LMNA, mutations in this gene have been found to be the cause of a rare premature aging disorder called progeria
- mutations result in major shape changes to the cell nuclei
- these changes get worse with age and affect cell division

Question 8

Nuclear matrix

Answer 8

1. non-chromatin/DNA structures in the nuclei
2. nuclear matrix appears as fibres attached to granular material
3. 10nm fibre nuclear matrix is composed of internal nuclear matrix and nuclear lamina

Question 9

Nucleoplasm

Answer 9

the non-staining liquid substance of the interphase nucleus which fills the nuclear space around the chromosomes and the nucleoli

Question 10

Composition of nucleoplasm

Answer 10

primarily water, dissolved ions and a complex mixture of molecules

Question 11

Nucleoplasm function

Answer 11

-to act as a suspension medium for the organelle of the nucleus
-to maintain nuclear shape and structure
-to transport ions molecules and other substances important to cell metabolism

Question 12

Nuclear pore complex (NPC)

Answer 12

-pores regulate the entry and exist of molecules from the nucleus, such as proteins and RNAs
-small proteins and ions can diffuse through pores
-larger proteins must be actively transported through the NPC with the help of transporter molecules
-these bind to the large proteins and interact with nucleoporins as they pass through

Question 13

NPC structure

Answer 13

-octagonal shape made up of membrane-embedded proteins
-on the cytoplasmic surface proteins called nucleoporins extend out into the cytoplasm
-on the nuclear surface protein filaments extend inwards into the nucleus forming a nuclear basket arrangement

Question 14

Nucleolus

Answer 14

a region in the nucleus where ribosomal RNA is transcribed and processed
0.1-1 micrometers

Question 15

Nucleolus compartments

Answer 15

fibrillar centre
dense fibrillar component
granular component

Question 16

What happens in the nucleolus?

Answer 16

-protein and DNA complexes are found in the FC
-ribosomal subunits are made in the DFC
-ribosomes are assembled in GR

Question 17

Discovery of chromatin

Answer 17

by Walther Fleming
identified a structure within the cell that strongly absorbed basophilic dyes

Question 18

Chromatin

Answer 18

a complex of DNA and protein and if found in the nucleus or eukaryotic cells
-uncondensed

Question 19

Histones

Answer 19

proteins that are responsible for the first level of DNA packing in chromatin
-contain a lot of positively charged amino acids such as arginine and lysine so they can easily bind to the negatively charged DNA

Question 20

Chromatin composition

Answer 20

50% DNA
50% proteins (mainly histones)

Question 21

Chromatin and chromosomes

Answer 21

chromatin is condensed during mitosis to become chromosomes which allows a lot of DNA to fit in a much smaller space

Question 22

Chromosomes

Answer 22

a discrete unit of the genome carrying many genes
-composed of highly compacted chromatin
-chromsomes form during cell division to ensure all DNA is divided correctly and completely

Question 23

Karyotype

Answer 23

a complete set of chromosomes

Question 24

Chromatin remodelling factors

Answer 24

convert chromatin from active into inactive and back by addition/removal of acetyl/methyl groups

Question 25

Histone modifications

Answer 25

-in histone acetylation, larger acetyl groups are attached to positively charged lysines in histone tails
-this loosens chromatin structure thereby promoting the initiation of transcription
-the addition of smaller methyl groups can condense chromatin (found in inactive heterochromatin)

Question 26

Euchromatin

Answer 26

active chromatin
-less condensed
-lightly packed
-transcriptionally active
-histones in euchromatin have specific modifications
-characteristic for interphase chromosomes

Question 27

Heterochromatin

Answer 27

inactive chromatin
-highly condensed tightly packed and darkly stained
-so transcriptionally inert
-histones in heterochromatin have specific modifications