gene mutation and expression

Question 1

What does ‘mutation’ mean? [2]

Answer 1

• Any change in the quantity / structure of DNA in an organism
• It can affect a nucleotide or a whole chromosome

Question 2

What is a ‘gene mutation’?

Answer 2

An alteration to one or more nucleotide bases within a gene

Question 3

Substitution [3]

Answer 3

• Causes issues if affects the stop codon
• May change the amino acid coded for but not always
  (degenerate genetic code)
• If the amino acid changes it may not cause a problem
  (e.g. in the active site vs on the rest of the enzyme structure)

Why did you let the cat out, you cad ?!
Why did you let the can out, you cad ?!

Question 4

Deletion [2]

Answer 4

• Is a Frame shift mutation (causes the reading frame to alter)
• Effect varies depending on where the mutation occurs

Why did you let the cat out you cad ?!
Whd idy oul ett hec ato uty ouc ad ?!

Question 5

Addition

Answer 5

• Frame shift mutation
• Effect varies depending on where the mutation occurs
• Similar effects as deletion

Why did you let the cat out you cad ?!
Why cdi dyo ule tth eca tou tyo uca d ?!

Question 6

Duplication

Answer 6

• One or more bases are repeated
• Similar effect as addition

Why did you let the cat out you cad ?!
Why did you uuu uuu let the cat out you cad ?!

Question 7

Inversion

Answer 7

• Bases separate
• Rejoin but in a reverse order

Why did you let the cat out, you cad ?!
Why did you let the cat out, dac uoy?!

Question 8

What is Translocation?

Answer 8

A section of one chromosome separates and rejoins a different chromosome

Question 9

Mutagenic Agents

Answer 9

• Natural mutation rates are about 1/100,000 genes per generation
• Certain factors will increase the rate of mutation

Question 10

Mutagens

Answer 10

Chemical mutagens - benzopyrene (tobacco), nitrous acid
Ionising radiation - UV rays, α-, β- particles

Question 11

Pros + Cons of Mutations

Answer 11

• Provides genetic diversity (natural selection and evolution)
• Usually harmful (cancer)

Question 12

How does a mutation affect protein structure? [3]

Answer 12

• Alters primary structure (amino acid chain)
• Alters hydrogen/ionic/disulphide bonds
• Alters tertiary structure

Question 13

Transcription Factors [3]

Answer 13

• The first stage of gene expression can be controlled using transcription factors
• Transcription factors are found in the cytoplasm of the cell, then move into the nucleus when expression is to start
• Transcription factors are proteins that help turn specific genes “on” or “off” by binding to nearby DNA

Question 14

Promoter Regions [2]

Answer 14

• Located near the gene it usually controls
• When a transcription factor binds to the promoter region it enables RNA polymerase to attach to the start of the gene and begin transcription

Question 15

Oestrogen and Gene Transcription [4]

Answer 15

• Oestrogen is a hormone that diffuses across the cell membrane
• Oestrogen binds to a receptor on the transcriptional factor, altering its shape
• The transcriptional factor can now bind to the DNA, activating it
• The gene can now be transcribed

Question 16

Small, Interfering RNA (siRNA) [8]

Answer 16

• First discovered naturally in plants
• Investigations focus on therapeutic uses (e.g. cancer treatment and nervous system disorders|)
• In unhealthy cells, such as those invaded by viruses or damaged, dsRNA forms
• This is cut into small sections, forming siRNA
• The siRNA binds to a enzyme called RISC (RNA induced silencing complex)
• This splits the siRNA strands, taking the ‘guide’ strand to the mRNA
• It complementary base pairs to the mRNA and the enzyme cuts the mRNA
• This stops expression of the gene, and therefore production of the protein