Alteration of the sequence of bases in DNA can alter the structure of proteins Flashcards
Define mutation
- refers to a change to the quantity or base sequence of DNA of an organism
What is a gene mutation?
- Any change to one or more nucleotide bases, or a change in the sequence of bases in DNA
What does a gene mutation result in?
- new allele forming
HIV attaches to a specific protein receptor on helper T cells. A low percentage of people have a mutation of the CCR5 gene which codes for this protein receptor. This mutation results in a non-functional protein receptor.
a) Explain how this mutation leads to production of a non-functional protein receptor.
- Change in DNA base/nucleotide sequence;
- change in amino acid sequence/primary structure;
- alters position of hydrogen/ionic/disulfide bonds;
- change in tertiary structure (of receptor)
b) Explain why people with the mutation show greater resistance to developing AIDS.
- Receptor not complementary OR HIV can’t bind and enter (helper) T cells;
- no replication of virus/destruction of T cell
The frequency of this mutation is highest in Europe. Scientists collected data on the history and number of infections in Europe, and concluded that the high frequency of CCR5 mutation is not due to natural selection in response to HIV
Suggest 2 reasons why scientists suggested that the high frequency of CCR5 mutation was not due to natural selection in response to HIV.
- Low exposure to HIV in Europe OR low number of HIV/AIDS cases;
- HIV only present for short time period;
- mutation been around for many years
What are the types of gene mutations?
- Addition
- Substitution (point)
- Deletion
- Inversion
- Duplication/stutter
- Translocation
What are the possible consequences of substitution (point) mutations?
- Mis-sense
- Nonsense
- Silent
Define addition mutation
- an extra nucleotide is inserted so an extra base is added to the sequence
Define substitution (point) mutation
- a nucleotide is replaced by a nucleotide with a
different base.
What is mis sense mutation?
- results in a different amino acid being coded for
What is a nonsense mutation?
- results in the formation of a stop codon
What is a silent mutation?
- altered base still codes for the same amino acid
Define deletion mutation
- a nucleotide is lost from the normal DNA sequence
How can a silent mutation be possible?
- The genetic code is degenerate, so not every
base substitution changes the amino acid
Why might a deletion mutation be extremely harmful?
- The loss of a single nucleotide can have a significant impact, as it leads to a frame shift, resulting in completely different amino acids being coded for
Define inversion mutation
– a portion of the sequence is inverted
Define duplication/stutter mutation
– there is a repeat of a whole triplet/s
Define translocation mutation
- a base sequence is moved from one position in a DNA molecule to another DNA position, either in the same chromosome or on a different chromosome.
What is translocation mutation caused by?
- mistakes in crossing over (meiosis)
What does translocation mutation lead to?
- leads to abnormal phenotypes, increased risks of cancers and reduced fertility
What are the pros of gene mutations?
- Results in change in polypeptide that positively
changes the properties (of the protein) - May result in increased reproductive success OR increased survival chances - creates new alleles which are more likely to pass offspring e.g., eye colour
What are the neutrals of gene mutations?
- Genetic code is degenerate so amino acid sequence may not change OR mutation is in an intron so amino acid sequence may not change
- Does change amino acid but no effect on tertiary structure
- New allele is recessive so does not influence
phenotype
What are the cons of gene mutations?
- Results in change in polypeptide that
negatively changes the properties of the protein (enzymes may not be able to catalyse reactions, impaired antibody function etc) - May result in reduced reproductive success
OR may result in reduced survival chance
Define chromosome mutations
- These are changes in the structure/number of chromosomes, and can arise spontaneously
What two forms do chromosome mutations take?
- Changes in whole sets of chromosomes
- Changes in the number of individual
chromosomes
What is non disjunction?
- Changes in the number of individual chromosomes. One pair of chromosomes fails to separate, so the gamete and zygote has one more (or one less) chromosome (e.g., Down’s
syndrome)
What is polyploidy?
- an individual has more than 2 full sets of
chromosomes. This is common in plants, with
many modern wheats arising to be polyploidy
