Mutations and Variations

Question 1

Define a mutation

Answer 1

A change in a DNA base sequence caused by mutagens

Question 2

What are the 3 types of point mutation?

Answer 2

Substitution, insertion and deletion

Question 3

What type of mutation are insertion and deletion, and what does this mean?

Answer 3

Frameshift
- Changes every codon after the mutation , so likely to affect the tertiary structure

Question 4

What is a codon?

Answer 4

Sequence of 3 bases that codes for an amino acid

Question 5

Why might a substitution have no effect, and what is the name for this no effect?

Answer 5

The genetic code is degenerate, meaning some amino acids have multiple codons that code for them
- Neutral/silent

Question 6

What are two possible effects of a mutation?

Answer 6

Beneficial - Enhanced function of protein, can lead to natural selection
Damaging - Malfunctioning protein made

Question 7

What is a nonsense and a missense mutation?

Answer 7

Nonsense - Premature ‘stop’ codon
Missense - Substitution results in different amino acid being coded for

Question 8

What are chromosomal mutations and what are types of it?

Answer 8

Mutations where large sections of chromosomes are altered
Deletion - deleting part of a chromosome
Duplication - section of DNA doubled
Inversion - section of a chromosome turns upside down/inverts
Translocation - Section of a chromosome moves from one chromosome to another

Question 9

What are the 4 levels of control in transcriptional control of gene expression?

Answer 9

Transcriptional - Turning genes on/off
Post transcriptional - Editing mRNA
Translational - Turning translation on/off
Post translational - Editing protein

Question 10

Explain the transcriptional stage in eukaryotes when transcription can’t happen

Answer 10

Histone modification for chromatin remodelling
Heterochromatin is tightly wound DNA around histones in cell division
This means the gene is inaccessible to the RNA polymerase so transcription can’t happen

Question 11

Explain the transcriptional stage where transcription can occur

Answer 11

Heterochromatin is changed to euchromatin, where the DNA is loosely wrapped around histones in interphase, when protein synthesis can happen
Gene is accessible to RNA polymerase

Question 12

How does heterochromatin change to euchromatin?

Answer 12

Acetylation-Phosphorylation - adding an acetyl or phosphate group
This decreases the positive charge of histones
DNA is negatively charged, so they will attract less to histones if the histones are less positive

Question 13

How does euchromatin change to heterochromatin?

Answer 13

Methylation - adding a methyl group
This increases the hydrophobic nature of histones so they bind more tightly to each other

Question 14

What is the transcriptional level of control in prokaryotes and why is it called this?

Answer 14

Lac(tose) operon
Because prokaryotes would usually, and prefer to use glucose in respiration, but if there is a lack of glucose, prokaryotes can activate lac operon to break down lactose instead

Question 15

What is an operon?

Answer 15

A group of genes controlled by the same regulatory mechanism and expressed at the same time

Question 16

What are structural genes and what are they in lac operon?

Answer 16

Proteins not involved in DNA regulation
laz Z, Y and A in lac operon, which code for B galactose, lactose permease and lactose transacteylase, which are all enzymes that metabolise lactose

Question 17

What are regulatory genes and in lac operon?

Answer 17

Proteins that are involved in DNA regulation
lacI in lac operon codes for the repressor protein, which stops/represses the transcription of the structural genes in the absence of lactose

Question 18

What are the two other sections of the lac operon?

Answer 18

Operator - DNA sequence where repressor binds to
Promoter - DNA sequence where RNA polymerase binds to

Question 19

Explain what happens at the stages at lac operon when glucose is present (no lactose)

Answer 19

• LacI is expressed to make the repressor protein which binds to the operator
• Due to do it’s size and shape, it blocks the RNA polymerase binding site on the promoter, so transcription of the structural genes cannot occur

Question 20

Explain what happens at the stages at lac operon when lactose is present (no glucose)

Answer 20

• Lactose binds to the repressor protein causing a change in it’s shape, so it can’t bind to the operator anymore and is released
• This unblocks the binding site on the promoter, so RNA polymerase can bind to it to transcribe the three structural genes

Question 21

How can transcription be made more efficient?

Answer 21

• cAMP receptor protein (CRP) binds with cyclic AMP (cAMP) and upregulates the activity of RNA polymerase
• this upregulated RNA polymerase then goes on to transcribe the structural genes to make B-galactosidase, lactose permease and lactose transacetylase
• These free enzymes metabolise lactose to release energy

Question 22

What are introns and exons?

Answer 22

Introns - DNA sequences that do not code for proteins
Exons - DNA sequences that do code for proteins

Question 23

What is RNA splicing?

Answer 23

• First step of post transcriptional control
• Removes introns from pre-mRNA

Question 24

What happens after RNA splicing to protect the exons from damage during transportation?

Answer 24

• Add cap (modified nucleotide) to 5 prime end
• Add tail of adenine to 3 prime end
• This stabilises mRNA and prevents degradation
• Mature mRNA for the ribosome

Question 25

What is the point of mRNA editing after mRNA is protected?

Answer 25

Different versions of mRNA to make different proteins of different functions

Question 26

What is a homeobox gene? Give feature

Answer 26

• Regulatory genes (180 base pairs)
• Code for homeodomain (part of a protein)
• Control body development
• Highly conserved
• Regulate mitosis

Question 27

What are Hox genes?

Answer 27

The homeobox genes found in animals