6.1.1 Cellular control Flashcards
What is a mutation?
A change in the sequence of base pairs in a DNA molecule.
When do mutations occur?
They can occur spontaneously but the probability of a mutation can increase with the presence of mutagens.
Give some examples of mutagens.
- Ionising radiation
- Deaminating chemicals
Give three main ways that harmful mutations are caused.
- Insertion of one or more nucleotides
- Deletion of one or more nucleotides
- Substitution of one or more nucleotides.
Explain how the insertion of a nucleotide can lead to a mutation.
This will change the amino acid that would have been coded for by the original base triplet. An insertion mutation has a knock-on effect by changing the triplets further on in the DNA sequence and this can sometimes dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function.
What is the insertion or deletion of nucleotides also often called?
Frameshift mutation.
Explain how deletion of nucleotides can lead to mutations.
A mutation can occur when a nucleotide is randomly deleted from the base sequence as this changes the amino acid that would have been coded for. This has a knock-on effect.
This can dramatically change the amino acid sequence produced from the gene.
Explain how the substitution of nucleotides can lead to a mutation.
This will only change the amino acid for the triplet in which the mutation occurs and will not have a knock on effect
What is a silent mutation.
The mutation does not alter the amino acid sequence (because the genetic code is degenerate so certain codons may code for the original amino acid).
What is a missense mutation?
The mutation alters a single amino acid in the polypeptide chain.
Example of a disease caused by a missense mutation.
Sickle cell anaemia.
What is a nonsense mutation?
A mutation which creates a premature stop codon (signals for the cell to stop translation of the mRNA molecule into an amino acid which causes the polypeptide chain to be incomplete).
Example of a disease caused by a nonsense mutation.
Cystic fibrosis.
Give an example of a beneficial mutation.
The pigment melanin.
Early humans living in Africa had dark skin as they produced high concentrations of the pigment melanin.
This provided protection from harmful UV radiation from the sun as well as synthesis vitamin D (from the high sunlight intensity) At lower sunlight intensities, pale skin synthesises vitamin D more easily so as humans moved to cooler climates, certain mutations occurred leading to a decrease in melanin production. Those paler skinned individuals had a selective advantage in cooler climates as they could synthesise more vitamin D.
Give an example of harmful mutations.
Many genetic diseases are caused by harmful mutations e.g haemophilia and sickle cell anaemia.
Give an example of neutral mutations.
The ability to taste a bitter chemical that is found in brussel sprouts.
Why do neutral mutations occur?
A mutation does not alter the polypeptide
a mutation only alters the polypeptide slightly so its function and structure are not changed
a mutation alters the structure and function of the polypeptide but the resulting characteristic provides no particular advantage or disadvantage
Three types of regulatory mechanisms in gene control.
Transcriptional level
Post-transcription level
Post-translation level
What are regulatory mechanisms?
Mechanisms that exist within cells to make sure the correct genes are expressed in the correct cell at the correct time (switching genes on or off)
What does it mean if gene control is occurring at the transcriptional level?
If the structural genes being controlled are in any way involved in the process of transcription.
What are transcriptional factors?
Proteins that bind to DNA and switch genes off or on by increasing or decreasing the rate of transcription.
What are factors that increase the rate of transcription called?
Activators.
