M6, C19 Genetics Of Living Systems Flashcards
define mutation
changes (amount or arrangement) to the base (nucleotide) sequence of DNA
define chromosome mutation
changes to parts of or whole chromosomes
define DNA mutation
changes to genes due to changes in nucleotide base sequence
What cause mutations
DNA replication due to change of sequence of bases. Rate of mutation is increased by mutagens (chemical, physical or biological agent such as viruses which insert its dna into a genome changing the base sequence)
Free radicals also can disrupt base pairing during DNA replication
what are the 3 types of gene mutations
substitution - only one nucleotide is affected
insertion - inserting a base which shifts nucleotides to the right
deletion - base or triplet removed
3 effects of the 3 mutation
nonsense - stop codon being coded for due to substitution
missense - different amino acid being coded for, which will alter primary structure of polypeptide and probably change its tertiary structure
silent/neutral - same amino acid being coded for, as genetic code is degenerate, therefore polypeptide will be unaltered
what are the different ways mutations can affect an organism (both beneficially and harmfully)
Beneficial - mutation produces an advantage to the organism, so increase chance of survival
- these are passed onto offspring, by the process of natural selection
(Eg ability to digest lactose, development of antibiotics resistance in bacteria)
Harmful - mutation produces a disadvantage, so decrease chance of survival
- organism may not survive or mate
(Eg albinism, sickle cell anemia (shape of rbc))
what is a conservative mutation
when the amino acid change leads to an amino acid being coded for which has similar properties to the original, this means the effect of the mutation is less severe
what is non-conservative mutation
when the new amino acid coded for has different properties to the original
what are frameshift mutations
adding or deleting a base causes a sift in bases that follow
the base sequence is read differently
the earlier the frameshift, the greater the effect on the protein
(it is NOT a frameshift if a triplet is added)
what are the 4 types of chromosome mutations
Deletion - a section of chromosome breaks off and is lost within the cell
Duplication - sections get duplicated on a chromosome
Translocation - a section of chromosome breaks off and joins another non-homologous chromosome
Inversion - a section of chromosome breaks off, is reversed and then joins back onto the chromosomes
give 3 ways in which a mutation gives a neutral effect on the protein
If the mutation changes a base sequence in a triplet, but the amino acid the triplet codes for doesn’t change
If the mutation produces a triplet that codes for a different amino acid, but the amino acid is chemically similar to the original so it functions like the original amino acid.
If the mutated triplet codes for an amino acid not involved in the proteins function.
Give one example of how a mutation can lead to a protein not being produced
A mutation at the start of a gene could result in RNA polymerase not being able to bind to the gene, which would mean that the protein coded for by the gene wouldn’t be produced.
Outline why the majority of mutations do not have an influence on phenotype
Mutations are random.
Mutations are more likely to occur in non-coding regions.
Majority of DNA is non-coding.
But a mutation on a non-coding region doesn’t affect the phenotype.
define operon
Promoter
Operator
Structural genes
a section of DNA that contains a cluster of structural genes that are transcribed together
Where rna polymerase binds
Repressor protein binds here
Cluster of genes regulated by the same mechanism
what are factors that start transcription called?
what are factors that stop transcription called?
start - activators
stop -repressors
The image for lac operon in E.coli is represented with the letter IPOZYA
what do they all stand for
I - lacI produces lac repressor, which is the transcription factor (REGULATORY GENES)
P - promoter - RNA polymerase binds here to start transcription of structural genes
O - operator- repressor binds here, switch structural genes on and off
Z - lacZ - beta-galactosidase - hydrolyse lactose to glucose and galactose
Y - lacY - lactose permease - allows cell to take up lactose
(A - lacA - enzyme that transfers an acetyl group from acetyl-CoA to beta-galactosides, precise function not known)
at what stages can gene expression be controlled
- transcriptional - genes can be turned on/off
- post-transcription - mRNA can be modified which regulates translation and the types of protein produced
- translational - translation can be stopped/started
- post-translation - proteins can be modified after synthesis which changes their function
how is protein production controlled at the post-transcriptional level
After transcription
1) splicing
- mRNA is edited because it contains sections that don’t code for amino acids (introns)
- the primary mRNA transcript has introns in it so they have to be removed by the process of splicing
- exons (bits that do code for amino acids) and joined together to make mature mRNA
2) capping
- methyl group added to 5- end of transcribed RNA which provides protection against degradation and helps bind to ribosome
3) polyadenylation
- addition of long chain of adenine nucleotides to end of 3- transcript increasing stability of RNA transcript
4) RNA editing
- base addition, deletion or substitution resulting in synthesis of different proteins W differnt functions, increasing range of proteins produced from a single mRNA gene which are catalaysed by enzymes.
