Unit 1: Genes, chromatin and chromosomes

Question 1

What is chromatin ?

Answer 1

A complex of DNA and associated proteins that is involved with the organisation of DNA in a cell

Question 2

What are the 3 functions of chromatin ?

Answer 2

1) Package and condense DNA
2) Prevent DNA damage
3) Control gene expression

Question 3

What is a nucleosome ?

Answer 3

A basic unit of chromatin

Question 4

What is a nucleosome comprised of ?

Answer 4

• The core is comprised of an octamer of histone proteins ( 8 Histones)
• 146bp of DNA wrapped 1.7 times around a core
• Core particles separated by 10-50bp of linker DNA

Question 5

What is the ‘bead of a string’ structure ?

Answer 5

The arrangement of linear arrays of nucleosomes

Question 6

What’s the job of a histone H1 protein (3) ?

Answer 6

• Involved in packing
• Brings nucleosomes together in rings to allow stacking
• Interactions condense chromatin further

Question 7

Multiple stacked rings form….?

Answer 7

30nm solenoid fibres

Question 8

30mn Solenoid fibres are further coiled to form what ?

Answer 8

Chromosmes

Question 9

What is euchromatin ?

Answer 9

Gene rich areas of the genome

Question 10

How are nucleosomes packed in euchromatin and how does this affect transcription ?

Answer 10

• Nucleosomes are loosely packed
• This allows DNA to be accessed by DNA binding proteins
• Better accessibility for transcription

Question 11

How does Euchromatin stain with Giemsa stain ?

Answer 11

It stains lightly due to looser packing and higher % of G-C

Question 12

What is Heterochromatin ?

Answer 12

Gene poor areas of the genome

Question 13

How are nucleosomes packed in heterochromatin and how does this affect transcription ?

Answer 13

• Nucleosomes tightly packed
• Accessibility to DNA binding proteins is more limited
• Less accessibility
• Less likely to be expressed

Question 14

What are the two types of heterochromatin ?

Answer 14

• Constitutive heterochromatin
• Facultative heterochromatin

Question 15

How can histone tails be modified to regulate chromatin structure ?

Answer 15

• Methylation
• Acetylation
• Phosphorylation

Question 16

What is a chromosome ?

Answer 16

A linear, highly compacted and organised DNA molecule with associated proteins, which encodes genetic information

Question 17

What is a telomere ?

Answer 17

Repetitive DNA sequences at the ends of chromosomes which act to preserve the integrity of the chromosome

Question 18

What is a centromere ?

Answer 18

The region of a chromosome which links sister chromatids

Question 19

What is a replication origin ?

Answer 19

DNA sequences from which DNA replication is initiated during cell division

Question 20

What is a gene ?

Answer 20

• The basic unit of heredity
• A sequence of DNA nucleotides, the order of which encodes determine the sequence of AAs in a polypeptide
• A stretch of DNA which is transcribed and encodes a functional product

Question 21

What are the components of a eukaryotic gene (5) ?

Answer 21

• Promoter
• Transcription start site
• Exon
• Intron
• Termination sequence

Question 22

What is a promoter ?

Answer 22

DNA sequence at which the machinery for transcription is assembled

Question 23

What is the transcription start site ?

Answer 23

The first nucleotide in the gene which is transcribed into RNA during transcription

Question 24

What is an Exon ?

Answer 24

DNA sequences in the gene that are included in the mature messenger (mRNA)

Question 25

What is an Intron ?

Answer 25

DNA sequences which are transcribed, but not included in the mature mRNA

Question 26

What is the termination sequence ?

Answer 26

DNA sequences which indicate the point at which to end transcription