Chapter 19 Flashcards
Define Mutation
A mutation is a change to the sequence of the bases in DNA which may affect the phenotype of the organism
What causes mutations
- Mutations can happen randomly, with no external cause but the rate of mutation is increases by the presence of mutagens (EG: ionising radiations)
- Another mutagen: Free radicals can affect structures of nucleotides and also disrupt base pairing , increasing the likelihood of mutation
What are the terms to describe the 3 types of gene mutation
1- Substitution
2- Deletion
3- Insertion
What does is substitution?
A gene mutation where one or more bases are swapped for another
What is Deletion?
A gene mutation where one or more bases are removed
What is Insertion?
A gene mutation where one or more bases are added
Why are deletion and insertion called “frameshift mutations”?
Insertion or deletion leads to a frameshift mutation which would change every successive
codon read from the point of mutation (since the genetic code is triplet and
non-overlapping), so the amino acids would change.
What is a frameshift mutation?
A frameshift mutation in a gene refers to the insertion or deletion of nucleotide bases in numbers that are not multiples of three
When are insertion or deletion not
frameshift mutations?
If the number of added or deleted nucleotides is a multiple of 3, the reading frame is not
actually changed, so the protein would be changed but would still form.
What might the possible effects of a gene
mutation of a protein be?
1- Beneficial
2- Damaging
3- Neutral/silent
4- Nonsense mutations
5- Missense mutations
Why is an effect of a gene mutation beneficial?
New and useful characterists develops in the phenotype; this is the basis of evolution by natural selection and is rare)
Why is an effect of a gene mutation Damaging?
(proteins are no longer synthesised or are non-functional, which can interfere with
essential processes)
Why is an effect of a gene mutation Neutral/silent?
(mutant triplet codes for same amino acid or mutant triplet changes amino acid but
there is no effect on the function of the protein or mutation occurs in non-coding part of DNA)
Why is an effect of a gene mutation nonsense mutations ?
(codon becomes a stop codon, resulting in a shortened protein which is
likely unfunctional)
Why is an effect of a gene mutation missense mutation?
(changes an amino acid in the primary structure; the new amino acid may
have similar properties to the original (conservative mutation) or vastly different properties to the
original (non-conservative mutation))
What are the types of chromosome mutations?
Sections of chromosomes may :
- break off (deletion);
- be duplicated;
- break off and join another non-homologous chromosome (translocation);
- or break off, be reversed and rejoin the same chromosome (inversion)
(b) Lac operon: Define ‘operon’ and describe
how they are expressed.
An operon is a sequence of DNA containing a cluster of genes under the control of a single promoter and operator.
Hence, genes within an operon will always be expressed together or not at all (their
expression patterns are linked).
(b) Lac operon: Why are operons
advantageous in prokaryotes?
In general, an operon will contain genes that function in the same process. For instance, a
well-studied operon called the lac operon contains genes that encode proteins involved in
uptake and metabolism of a particular sugar, lactose.
Operons allow the cell to efficiently express sets of genes whose products are needed
at the same time.
Lac operon: Define “promoter region”
Upstream sequence to which RNA polymerase binds.
Lac operon: Define “operator region”
Segment of DNA to which a repressor protein binds (inhibits transcription by obstructing
RNA polymerase).
Lac operon: Define “structural gene” and give the 3 in Lac operon
Genes that code for structural proteins or enzymes not involved in DNA regulation.
In lac operon:
lacZ (codes for β-galactosidase),
lacY (codes for lactose permease)
and lacA (codes for transacetylase).
Lac operon: Give the roles of the proteins coded for lacZ , lacY and lacA
lacZ codes for β-galactosidase: Enzyme which catalyses hydrolysis of lactose into
glucose and galactose.
lacY codes for lactose permease: Protein which transports lactose into the cell.
lacA codes for transacetylase: Relevance in lactose metabolism is not entirely clear
Lac operon: Define “regulatory gene” and give the 1 in Lac operon
A gene that codes for proteins involved with DNA regulation (activator or repressor).
In lac operon:
LacI (codes for repressor protein which prevents transcription of the structural genes in
absence of lactose).
Is Lac operon an inducible or repressible operon?
inducible, meaning that it can be turned on by the presence of a particular small molecule.
