6.1 Flashcards
What is a mutation
A random change to the genetic material, some mutations involve changes to the structure of the number of chromosomes
What is a gene mutation
A change to the DNA
When may mutations occur
Spontaneously during DNA replication before cell division,
What things can be mutagenic
Chemicals like tar in tobacco smoke, and ionising radiation like UV lights, x-rays and gamma rays
What does the structure of DNA make it
Stable and fairly resistant to corruption of the genetic information stored within it, but errors may still occur during the replication of a DNA molecule
What are mutations associated with mitotic division and what does this mean
Somatic mutations, so are not passed to offspring, they may be associated with the development of cancerous tumours
What mutations may be inherited by offspring
Mutations associated with meiosis and gamete formation may be inherited by offspring
What may gene mutations affect
Protein production and function
What are the 2 main classes of DNA mutation
Point mutation (one base pair replaces/substituted for another), insertion or deletion mutation (one or more nucleotides are inserted or deleted from a length of DNA, these may cause a frameshift
What does the genetic code consist of
Nucleotide base triplets within the DNA
What happens during transcription of a gene
this code is copied to a length of mRNA as codons, complementary to the base triplets on the template strand of the length of DNA, the sequence of codons on the mRNA is therefore a copy of the sequence of base triplets on the gene (coding strand of DNA)
What are the 3 types of point mutation
Silent, missense, nonsense
What does it mean that amino acids have more than one base triplets
This reduces the effect of point mutations as they don’t always cause a change to the sequence of amino acids in a protein (degeneracy)
what is a silent mutation
a point mutation involving a change to the base triplet, where the triplet still codes for the same amino acid
what is the result of a silent mutaion on a protein structure
the primary, secondary and tertiary structure is not altered
what is a missense mutation
a change to the base triplet sequence that leads to a change in the amino acid sequence in a protein
what is the effect of a missense mutation
within a gene, this point mutation can have significant effects on the protein produced, it could alter the primary structure altering the secondary and tertiary structure preventing it carrying out its functions
what is sickle cell anemia caused by
the missense mutation, results in deoxygenated haemoglobin crystalising within erythrocytes, causing them to become sickle-shaped, blocking capillaries depriving tissue of oxygen.
what is a nonsense mutation
a point mutation what alters a base triplet to become a stop triplet
what are the effects of a nonsense mutation
it results in a truncated (shortened) protein that will not function, this abnormal protein will likely be degraded in the cells
what disease is caused by nonsense mutation
the genetic disease, Duchenne muscular dystrophy
what are indel mutations
mutations that cause a frameshift
what are the 2 indel mutation
insertion and deletion
what is a frameshift
if nucleotide base pairs (not in multiples of 3) are inserted in the gene or deleted from the gene, as the code is non-overlapping and reads in groups of 3 bases, all subsequent base triplets are altered.
what happens when mRNA is translated after insertion or deletion mutation
the amino acid sequence after the frameshift is disrupted, the primary sequence of the protein and the tertiary structure is much altered, so, the protein can’t carry out its normal function, if the protein was very abnormal it will be rapidly degraded within the cell
what do some forms of thalassaemia (haemoglobin disorder) result from
frameshift due to deletion of nucleotide bases
what may insertion or deletions of a triplet of base pairs result in
the addition/loss of an amino acid and not in a frameshift
what do some genes contain
a repeating triplet like CAG CAG CAG
what is expanding triple nucleotide repeats
the number of CAG (previous flashcard) triplets increases at meiosis and again from generation to generation
what is Huntington disease a result of
an expanding triple nucleotide repeat, if the number of repeating CAG sequences goes above a certain critical number, then the person with that genotype will develop Huntington disease later in life
are all mutations harmful
many are beneficial and driven evolution through natural selection, different alleles of a gene are produced through mutation
what are a neutral mutation and an examples
neither beneficial nor harmful like different shaped ear lobes.
how does regulation of gene expression at transcpiption level work in prokaryotic cells
enzymes that catalyse metabolic reactions involved in basic cellular functions are synthesised at fairly constant rates. Enzymes only needed in certain conditions are synthesised at varying rates according to need of cell
How does the bacterium E. coli normally metabloise glucose
as a respiratory substrate
what happens when glucose is absent in E. coli and dissacharide lactose is present
lactose induces production of 2 enzymes, lactose permease (which allows lactose to enter bacterial cells) and B-galactosidase (hydrolyses lactose to glucose and galactose)
what does the lac operon consist of
a length of DNA, about 6000 pairs long, containing an operator region lacO next to the structural genes lacZ and lacY that code for enzyme B-galactosidase and lactose permease
what is next to the operator region, lacO, in the lac operon
the promoter region, P, that RNA polymerase binds to begin transcription of structural genes lacZ and lacY
what are the operator region and promoter region in lac operon
the control sites
what is the definition of operon
a group of genes that function as a single transcription unit, first identified in prokaryotes.
what is found a small distance away from an operon
the regulatory gene, I, that codes for a repressor protein (LacI), when this regulatory gene is expressed, repressor protein produced binds to the operator, preventing RNA polymerase from binding to promoter region
