Mod. 6 genetics of living organisms Flashcards
mutation
a change in the base sequence of DNA caused by substitution, deletion or insertion or one or more of the nucleotides in the gene.
How does substitution mutation affect a gene or DNA sequence?
changes the codon triad that codes for a specific amino acid. This may not affect the amino acid because there can be more than one codon for an amino acid. If it codes for another, the amino acid sequence changes, which will affect the final tertiary structure of the protein, because the R-group affects how an amino acid is used.
How does deletion affect a gene or DNA sequence?
The removal causes a frameshift in the triplet code, a ribosome reads every three pairs, and if one is deleted, then the triplet code is out, and changes the reading frame for every subsequent base. The protein could never perform its function.
How does insertion affect a gene or DNA sequence?
the addition of a nucleotide causes a frameshift. The triplet code no longer reads correctly, since the triplet code has been pushed up one, and codes for a different amino acid completely. Every subsequent codon is affected, and the final protein cannot perform its function.
What is the effect of a mutation?
No effect - if a substitution still codes for the same amino acid, then there is no change to the function of a protein, and they are still synthesised
Damaging - phenotype is affected in a negative way because a protein is not being synthesised or the ones that are are non-functional, interfering with essential processes.
Beneficial - the mutation can create an improvement to the original protein, or creates a new and useful characteristic.
What causes mutation?
Spontaneously - during DNA replication the DNA duplicates incorrectly.
Mutagens - chemical, physical or biological agent.
Give examples of a beneficial mutation.
Lactose digestion - most mammals lose the ability to digest lactose after they are weaned, but some human populations have developed to keep producing lactase. This prevents malnutrition, osteoporosis, starvation etc.
What is chromosome mutation?
mutations in chromosomal structure.
Deletion - a section of chromosome breaks off and is lost in the cell.
Duplication - sections get duplicated on a chromosome
Translocation - a section breaks of a joins a non-homologous chromosome
Inversion - a piece breaks off, is reversed and rejoins the wrong way round.
How are genes regulated?
transcriptional - genes turned on or off
post-transcriptional - mRNA can be modified which regulates translation and types of protein produced.
translational - translation can be stopped or started.
post-translational - proteins can be modified after synthesis to make changes to function.
