Mutations Flashcards
What is the definition of a mutation?
A random spontaneous change in the base sequence of the DNA which can result in a new allele occurring
What is a substitution mutation?
Where one (or more) bases are swapped for another
e.g ATGCCT becomes ATTCCT
What are the 3 different types of substitution mutations?
- Silence
- Missense
- Nonsense
Explain what a silence substitution mutation is and if there are any consequences for this.
-When the altered base sequence still codes for the same amino acid
-This would have no consequence for the final protein made
Explain what a missense substitution mutation is and if there are any consequences for this.
-When the substituted base does code for a different amino acid in the primary protein structure, causing the final protein structure to be altered in some way
-This MAY or MAY NOT have an effect on the proteins structure as it depends on where on the protein the amino acid changed (if on active site would have an effect compared to on a different part) and it depends on how similar the changed amino acid is to the original one as well
Explain what a nonsense substitution mutation is and if there are any consequences for this.
-When the base sequence is altered in such a way that the triplet code changes from an amino acid to a ‘STOP’ codon.
-this will result in a shorter then supposed to be protein which will not function properly and so will be broken down in the cell
What is a deletion mutation?
Where one (or more) nucleotides are removed from the DNA sequence
E.g ATGCCT becomes ATG^CT
What is an insertion mutation?
Where one (or more) nucleotides are added to the DNA sequence
E.g ATGCCT becomes ATG A CCT
What are the consequences for both insertion and deletion mutations?
-They would both alter the whole triplet code from the point of the mutation onwards
-This is called a FRAMESHIFT
-This usually alters most of the amino acids coded for by the base sequence
-This therefore means that the protein would not function due to having a completely different shape and structure to normal
What are the 3 types of effects that mutations can have on organisms?
- Neutral = When it is neither harmful or beneficial to the organism they occur in, so does not alter survival chances
- Beneficial = Increases the chances of survival and can help drive evolution through natural selection
- Harmful = Reduces the chances of survival for an organism
How do you know that a mutation is neutral? Give an example for this type of mutation
-It occurs in the non-coding sections of DNA (introns)
-It is a silent substitution mutation so still codes for the same amino acid
-It is a missesne substitution mutation: but the changed amino acid is so chemically similar to original amino acid that it makes no difference to final protein
-It is a missense substitution mutation resulting in a completely different amino acid, but it is not in a crucial part of the protein so has no effect
-It may result in a different final protein, but this does not affect the survival chances of an organism
E.g the ability to roll the tongue in humans
How do you know if a mutation is beneficial? Give an example for this type of mutation
- It has advantageous effects on the organism, and increases the chances of survival
E.g some bacteria have mutations that enable them to resist the effects of antibiotics
E.g humans in some parts of the world can digest lactose due to a mutation
How do you know id a mutation is harmful? Give an example for this type of mutation
-it has a disadvantage effect on an organism, and reduces its chance of survival
E.g Cystic Fibrosis is caused by the deletion of 3 bases in a gene which codes for a membrane transport protein in cells of the airways. It causes excessive mucus production, reduced lung function and reduced life expectancy
Give an example of how some mutations could be beneficial or harmful in different circumstances
Eye colour
-blue eyes mean less pigmentation in the iris, more light can get through to the back of the retina so have better vision, useful in parts of the world where there is lower light intensity
-however this would be harmful in parts of the world where light intensity is very high
-in these regions it is advantageous to have brown eyes as more pigmentation in the iris, so more light absorbed before it reaches the retina reducing the risk of damage
Explain what the causes of mutations are
-often occur spontaneously during DNA replication, but the rate of the mutation is increased by “mutagens”. These are chemical, physical and biological agents which actually cause mutations
