20.1 - Gene Mutations Flashcards
Define mutation
Mutations are changes to the base sequence in the DNA. Mutations can be caused by addition, deletion and substitution of bases.
Define gene mutations
A gene mutation is a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide. Mutations occur continuously and spontaneously
What part of the cell cycle are mutations most likely to occur
Interphase
What happens normally during interphase
- DNA is unwound as chromatin so the genes are accessible for transcription
- Cell growth and DNA replication take place
- this takes up around 90% of the cell cycle
Describe how a mutation occurs during interphase
- DNA is proofread by specialist proteins to stop mistakes being made during the cell cycle when the DNA is replicated (S phase)
- if this doesn’t work and change happens, then we call this a mutation
Why might not all mutations that make it past interphase continue to exist
- during S phase, before DNA replication the amount of DNA doubles
- and the DNA is once again checked for errors (mutations)
How can changes to DNA triplets affect a protein
- change in DNA effects change in amino acid sequence for polypeptide coded
- this change in primary structure of a protein will affect the tertiary structure
- this is because it affects the bonding of r-groups in the tertiary structure which determines the shape and therefore functionality of the protein
Why might a mutation have no effect on the amino acid sequence?
Due to the degeneracy of the genetic code, some amino acids are coded by more than one codon.
What is a substitution mutation
One or more nucleotides in a DNA molecule are replaced by another nucleotide with a different base
What are the three potential outcomes of substitution mutations?
1) Formation of a stop codon, prematurely terminating the polypeptide.
2) Substitution of a codon for a different amino acid, possibly altering the protein’s function.
3) Substitution of a codon for the same amino acid (no effect due to the genetic code’s degeneracy)
Give an example of a condition caused by substitution mutation
Sickle cell anaemia
What is a deletion mutation
One or more nucleotides are lost from the DNA sequence
What major change might a deletion mutation cause
Frame shift - altering to the reading of all subsequent triplets after the mutation
Why is the position of the deleted base important?
A deletion near the start of a sequence impacts all subsequent triplets, while one near the end has less severe effects.
What is an addition/insertion mutation?
An extra one or more nucleotides are inserted into the DNA sequence
—> just like deletion, might cause a frame shift