19 - Genetics of living systems Flashcards
What is a mutation?
Change in the base sequence of DNA
What are the 3 types of mutation?
- Substitution 2. Deletion 3. Insertion
What is a substitution mutation?
Replacement of one or more DNA bases with others
What is a deletion mutation?
When one or more nucleotides are removed (i.e., deleted) from the DNA sequence
What is an insertion mutation?
Where one or more bases are added to the DNA sequence
What is it called when a mutation only affects one nucleotide?
Point mutation
When might a mutation affect a protein’s primary structure?
When it creates a new codon which codes for a different amino acid
What are the 3 different types of mutation effects?
- No effect 2. Damaging 3. Beneficial
When would a frameshift mutation occur?
When a deletion or addition mutation occurred in a number of bases that is not a multiple of 3
What would a frameshift mutation cause?
Every successive codon from the point of the mutation onwards would be different, so the protein produced would be completely different
Would a protein still be affected by a deletion or insertion mutation which wasn’t a frameshift mutation?
Yes, as there would still be a new amino acid added, but the effects would likely be less
What are 3 possible reasons why a mutation may have a neutral effect on a protein’s structure?
- Mutation changes a base, but the amino acid which the triplet codes for is the same (degeneracy)2. Mutation causes a different amino acid to be produced which is chemically similar to the original 3. The triplet affected may code for an amino acid which isn’t essential to the protein’s function, such as one located away from the active site
Would a mutation with a neutral effect affect the whole organism?
No it wouldn’t affect the whole organism
How can a mutation make a protein more or less active?
By changing the shape of its active site
Does a mutation which changes a protein’s active site mean the organism is less likely to survive?
Not necessarily- the mutation may even be beneficial
Give an example of a mutation with a beneficial effect for an organism?
A mutation in proteins of membranes which HIV cannot bind and enter a cell
Give an example of a mutation with a negative effect for an organism?
Deletion mutation causing changes in the CFTR protein which lead to cystic fibrosis
How can a mutation prevent a protein from being produced?
If the mutation is at the start of the gene and RNA Polymerase can’t bind to it, so the protein won’t be produced
What are 2 reasons a mutation may be harmful to an organism?
- Protein may not be produced at all 2. Protein may be produced, but in a non-functional form
What increases the rate of mutation?
Mutagens
What is a mutagen?
A chemical, biological or physical agent which causes mutations
What is depurination?
The loss of a purine base from DNA
What is depyrimidination?
Loss of a pyrimidine base from DNA
How does depurination or depyrimidination usually happen?
Spontaneously
What type of mutation could depurination or depyrimidination lead to?
Insertion if a new base filled the gap left
What are 2 chemical mutagens?
- Free radicals 2. Deaminating agents
What could a deaminating agent do to cytosine?
Change it to uracil
Why are antioxidants also known as carcinogens?
Due to their ability to negate the effects of mutagenic free radicals
What is an example of a physical mutagen?
Ionising radiation such as x-rays
How would x-rays act mutagenically?
Break one or both DNA strands, with the repair of the strand often causing mutations
What are 3 examples of biological mutagens?
- Alkylating agents 2. Base analogues 3. Viruses
How does a virus act as a mutagen?
By inserting viral DNA into the genome
How do alkylating agents act as mutagens?
Attach methyl or ethyl groups to bases, causing incorrect pairing during replication
How do base analogues act as mutagens?
They are incorporated into DNA in lieu of a normal base
What is a chromosome mutation?
One which affects the whole chromosome or a number of chromosomes within the cell
When do most chromosome mutations occur?
During meiosis
What is a deletion chromosome mutation?
A section of a chromosome breaks off and is lost within a cell
What is a duplication chromosome mutation?
Sections of a chromosome duplicated
What is a translocation chromosome mutation?
A section of one chromosome breaks off and attaches to another chromosome
What is an inversion chromosome mutation?
A section of chromosome breaks off, is reversed, and then rejoins onto the chromosome
What is a housekeeping gene?
One which codes for enzymes necessary for metabolic processes such as respiration
What are tissue-specific genes?
Ones which code for protein-specific hormones
What is a transcription factor?
Proteins which bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription
What are the two types of transcription factor?
- Activators 2. Repressors
What do activators do?
Factors which increase the rate of transcription
What do repressors do?
Factors which decrease the rate of transcription
How do transcription factors work?
Bind to specific DNA sites near the start of their target genes (in eukaryotes) and promote/repress the action of RNA Polymerase
What do transcription factors bind to in prokaryotes?
Operons
What 3 things can be contained in an operon?
- Clusters of structural genes 2. Control elements 3. A regulatory gene (sometimes)
What do structural genes do?
a gene (a sequence of DNA nucleotides) that codes for a protein with a metabolic function, e.g. the gene codes for an enzyme or a carrier protein