19.1 Mutations & Variations Flashcards
What’s a mutation
a change in the sequence of bases in DNA.
What is the type of point mutation
substitution
Why is it called a point mutation
because only one nucleotide will be affected
What’s a substitution mutation
when one nucleotide is changed which alters a codon; if the new codon codes for a different amino acid, it will change the primary structure of the final protein.
What’s a missense mutation, as a result of substitution
when the new sequence still makes some sense but likely won’t code for the same amino acid.
What’s a nonsense mutation, as a result of substitution
when the new sequence makes no sense whatsoever and codes for a stop codon
what’s a silent mutation, as a result of substitution
when the sequence still makes sense, can code for the same amino acid, but sometimes code for others.
Why is DNA degenerate
because if there is a change to a codon or amino acid, the final amino acid it codes for may be the same, no change will occur
What’s a frameshift mutation
when the order of the base sequence is completely changed because of a nucleotide being inserted or deleted.
What’s insertion in mutations
When an extra nucleotide is inserted into the base sequence, changing the sequence of the codons after the insertion, therefore, changing the amino acid produced
What’s deletion in mutations
When a nucleotide is deleted from the base sequence, messing up the order after the deletion because all nucleotides will be brought back a space, creating different triplet code codons.
What are the effects of mutations
- no effect - no effect on the phenotype because normally functioning proteins are still synthesised
- damaging - phenotype of organism is negatively affected; can interfere with essential processes, cause cancers etc.
- beneficial - very rarely are they completely beneficial; for example, some are immune to infection from HIV.
What causes mutations
Can occur spontaneously; rate of mutations occurring is increased by MUTAGENS.
What is a mutagen
a physical, chemical, biological agent that causes mutations
What’s depurination and depyramidination
loss of a purine base and pyrimidine base, respectively
What are examples of physical mutagens and how do they work
examples include ionising radiations (x-rays)
break one or both DNA strands, some breaks can be repaired but mutations can occur in the process
what are chemical mutagens
example include deaminating agents
chemically alter bases in DNA such as converting cytosine to uracil in DNA, changing base sequence
What are biological agents
examples include viruses - viral DNA may insert itself into a genome, changing the sequence;
base analogs - incorporated into DNA in place of the usual bases during replication, changing the base sequence;
alkylating agents - methyl or ethyl groups are attached to bases resulting in the incorrect pairing of bases during replication.
What causes genetic disorders
Some mutations can affect whether a protein is actually produced.
If a mutation occurs at the start of a gene, the RNA polymerase can’t bind to it and begin transcription so the code can’t be made.