Genetics and Epigenetics: Gene expression and regulation

Question 1

What are the classes of histones?

Answer 1

• H1
• H2A
• H2B
• H3
• H4

Question 2

Describe chromosomal mutations

Answer 2

May occur during DNA Replication Affect larger portions of the genome

e.g.

• Deletions
• Duplications
• Inversions
• Translocations

Question 3

What are epigenetic mechanisms?

Answer 3

Modifications of DNA that switch specific gene expression on/off

Question 4

What are promoters?

Answer 4

• Are DNA sequences upstream (in front) of the coding sequence
• They ‘tell’ RNA polymerase where to start transcription and which DNA strand to transcribe
• Promoter binds proteins called transcription factors
• these proteins specifically recognise the DNA sequence

Question 5

What are transcription factors?

Answer 5

• DNA-binding proteins
  Contain two functional domains:
  1) DNA-Binding domain
  2) Transcriptional activation domain

Question 6

Describe RNA interference RNAi

Answer 6

Short singled-stranded RNA molecules which bind by base-pairing to other RNAs. If the target is mRNA, translation may be inhibited or the mRNA degraded

Question 7

Details of Pre-mRNA processing (specifically 2) RNA Splicing)

Answer 7

• A multistep process catalysed by a ribonucleoprotein complex called the spliceosome
• This involves a number of proteins and snRNA (small nuclear RNA) which bind at the exon/intron boundaries
• Splicing removes introns and joins exons to form mature mRNA

Question 8

Details of Pre-mRNA processing (specifically 3) Alternative Splicing)

Answer 8

Involves removing different regions from the pre-mRNA, therefore different exons are spliced together - insertion or deletion of coding regions, eventually resulting in different proteins being encoded

Question 9

Describe missense mutation

Answer 9

• Results in a change of amino acid primary sequence
• Can change protein function, e.g. altered haemoglobin in sickle cell anaemia

Question 10

Describe nonsense mutation

Answer 10

• Creates a new STOP codon
• Changes the length of the protein due to premature stop of translation

Question 11

Describe silent mutation

Answer 11

• No change in amino acid sequence
• Due to degeneracy of the genetic code (each amino acid has more than 1 codon)
• No effect on protein function

Question 12

Describe frameshift mutation

Answer 12

• Insertion or deletion of a single base (or two)
• Changes reading frame of translation into protein, can cause premature stop of translation