Gene to Genome: DNA

Question 1

Define Gene

Answer 1

A segment of DNA that contains coding information for proteins

Question 2

Define Genomics

Answer 2

The study of genomes, the complete set of DNA in an organism, including all of its genes

Question 3

Define epigenetics

Answer 3

the study of changes in the DNA that don’t involve changes to the DNA sequence (eg methylation and histone modification)

Question 4

What contributes to gene regulation

Answer 4

promotors, enhancers, and transcription factors

Question 5

Name the purines and pyrimidines

Answer 5

• Purines
- Adenine
- Guanine

• Pyrimidines
- Cytosine
- Thymine (DNA only)
- Uracil (RNA only)

Question 6

What is the Watson Crick base pairing?

Answer 6

Adenine and Uracil or Thymine

Guanine and Cytosine

Question 7

How are chromosomes packed?

Answer 7

• DNA coils on to nucleosomes which are composed of octameric histone proteins
• Nucleosomes coil into a solenoid structure fixed in place using histone H1
• Solenoid forms loops which attach to a structural central scaffold
• The scaffold and solenoid loops arrange into a giant supercoil to form metaphase chromosomes

Question 8

Why do chromosomes need to be packaged?

Answer 8

• Otherwise they’d be too big to fit in the nucleus
• Protects them from damage
• helps control gene expression

Question 9

What are the packing requirements of chromosomes?

Answer 9

• Very long DNA molecules need protecting and maintaining through replication and cell division
• The DNA in human chromosome 1 is 0.1m long
• This is packaged down to 0.00001m in the nucleus

Question 10

How do chromosomes control gene expression?

Answer 10

• Chromosome organisation allows the mechanism for gene expression to be controlled
• Chromosomes are not homogeneous but have localised structure that affects gene expression

Question 11

How are chromosomes formed?

Answer 11

1) Dna wrapped around proteins called histones (nucleosomes) are chromatin
2) Nucleosomes coil unto a solenoid structure fixed in place using histone H1
3) solenoid forms loops which attach to a structural central scaffold
4) The scaffold and solenoid loops arrange into a giant supercoil to form metaphase chromosomes

Question 12

What are the chromatin found in chromosomes?

Answer 12

• Euchromatin: where most genes are found (active)

• Heterochromatin: contains simple, repetitive DNA sequences (silent)

Question 13

What is DNA replication

Answer 13

Each DNA strand acts as a template for the production of a new strand

Question 14

What are the rules of DNA replication?

Answer 14

• The new strands are synthesised by DNA polymerase following the baee pairing rules
• Replication is semi conservative, in that the template strands remain intact
• New DNA is only synthesised in the 5’->3’ direction

Question 15

What happens in transcription?

Answer 15

• Uracil replaces Thymine in RNA
• RNA polymerase binds to promoter site on DNA
• Double stranded DNA separates to allow transcription
• RNA polymerase reads in 3’->5’ direction on DNA template strand, synthesising RNA in 5’->3’ direction

Question 16

Which is the correct mRNA for the DNA sequence:

5’- GAATCTC-3’

Answer 16

5’- GAGAUUC-3’

(read backwards 3->5 and convert)

Question 17

What are mutations and how are they helpful?

Answer 17

• Replication is not perfect and changes (mutations) can occur that alter phenotypes
• Mutations are the raw material for evolution (subject to a variety of forced that shape both past and current diversity)

Question 18

Describe DNA replication

Answer 18

Semi conservative and high fidelity (Watson crick base pairing)