8.1 Alteration of the sequences of bases in DNA can alter the structure of proteins Flashcards
(20 cards)
what is a gene mutation?
- a change in the base sequence of DNA
-they can arise spontaneously during DNA replication (interphase)
what is a mutagenic agent?
A factor that increases rate of mutation e.g ultraviolet (UV) light or alpha particles
Explain how a gene mutation can lead to the production of a non- functional protein or enzyme (general)
1.Changes in base sequence of base triplets in DNA so changes sequence of codons on mRNA
2.Change in sequence of amino acids in the encoded polypeptide
3.Change in the position of hydrogen/ ionic/ disulphide bonds (between amino acids)
4.Change in tertiary structure of protein
5. Enzymes- active site changes shape so substrate can’t bind-> enzyme substrate complexes cannot form
what are the different types of gene mutation?
-subsitution
-addition
-deletion
-duplication/ repetition
-inversion
-translocation
what is a substitution mutation?
-a single letter change when one base/ nucleotide is replaced with another
-caused spontaneously during DNA replication
-the aa can change-> missense effect
what can the effect of missence be ? (when aa is changed)
-severe-> tertiary structure significant difference (completly alter)
-minor->small change to tertiary structure, still some function
-no effect-> tertiary structure altered
-beneficial effect-> enzyme faster, protein is stronger
|> driving force behind natural selection
why are some substitution effects silent?
-they do not change the amino acid
-different codons code for the same aa
= genetic code is degenerate
what is the nonsense effect that some subsitution mutations have?
-this is where the mutation creates a stop codon
what is an addition mutation?
-where one or more bases/ nucleotides are added to the DNA base sequence
-frameshift effect-> where the reading frame/ sets of codons downstream are changed
-frame shift to right
-if 3 extra bases are added, or any multiple of 3 bases, there will not be a frameshift
|> resulting polypeptide will be different from one produced from a non-mutant gene (not to the same extent as if there was a frameshift)
what is a deletion mutation?
one or more bases/ nucleotides are lost from the DNA base sequence and removed
-effect is still a frameshift
what is a duplication mutation?
A sequence of DNA bases (one or more bases)/ nucleotides are repeated
-frame shift to the right
what is an inversion mutation?
- a sequence of bases/ nucleotides detaches from the DNA sequence, then rejoins at the same position in the reverse order
-base sequence of the portion is therefore reversed and effects the amino acid sequence that results
what is a translocation mutation?
- a sequence of DNA bases/ nucleotides become seperated from the DNA sequence on one chromosome and is inserted at a different location within the same or a different chromosome
what is the basic mutation rate increased by?
-by outside factors known as mutagenic agents or mutagens
Example of mutagenic agents
-high energy ionising radiation
|> alpha and beta particles and short wavelength radiation e.g X rays and ultraviolet radiation-> forms radiation tat can disrupt structure of DNA
-chemicals
|> nitrogen dioxide-> directly alter the the structure of DN For interfere with transcription
|> benzopyrene -> mutagen that activates sumo suppressor gene TP53
Cost and benefits of mutagens
-produce genetic diversity needed for natural selection and speciation
-almost always harmful-> produce organism less suited to environment
-mutations occur in body cells not gametes-> disruption of normal cellular activity
Explain why not all gene mutations affect the order of amino acids
-some substitutions change only 1 triplet code/ codon which culled still code for the same amino acid
-as the genetic code is degenerate
-some occur in introns which do not code for amino acids-> removed during splicing
Explain why a change in amino acid sequence is not always harmful
-may not change tertiary structure of protein if position if ionic/ disulphide/ H bonds don’t change
-may positively change the properties of the protein-> giving organism a selective advantage
Explain what is meant by a frameshift
-occurs when mutations (addition, deletion, duplication or translocation) change the number of nucleotides/ bases by a number not divisible by 3
-this shifts the way the eugenic code is read, so all DNA triplets/ mRNA codons downstream from the mutation change
|> significant effects
Explain how mutations can lead to the production of shorter polypeptides
-deletion or translocation-> triplets/ codons missing so amino acid is missing
-subsitution, addition, deletion, duplication, inversion or translocation-> premature stop triplet/ codon (doesn’t code for amino acids; terminates translation) so amino acids missing at the end of polypeptide
