6.1 Flashcards
what is a mutation
a mutation is a random change to the genetic material. some mutations involve changes to the structure or number of chromosomes. A gene mutation is a change to DNA
when may mutations occur
mutations may occur spontaneously during DNA replication before cell division.
-during S phase
-during transcription
name some chemicals that may be mutagenic ( increases the chance of mutation)
-tar in tobacco smoke
-ionising radiation such as UV light
- X-rays and gamma rays
mutations associated with what will not be passed onto offspring
mutations associated with mitotic division and somatic mutations will not be passed onto offspring
Though, they may be associated with cancerous tumours
mutations associated with what may be passed onto offspring
mutations associated with meiosis and gamete formation may be passed onto/inherited by offspring
what may gene mutations affect
gene mutations may affect protein production and function
what are the two main classes of DNA mutation
-point mutation- one base pair replaces another (there are 3 types)
-insertion or deletion (indel) mutation- one or more nucleotides are inserted and deleted from a length of DNA. These may cause a frameshift.
what are DNA base triplets then called when a length of DNA is converted to RNA
codons
mRNA is a copy of which strand of DNA
the coding strand
what are the 3 types of point mutations
-silent
-missense
-nonsense
whats a silent mutation
a silent mutation is a type of point mutation that involves a change to the base triplet , where that triplet still codes for the same amino acid. The primary structure, and therefore the secondary and tertiary structure is not altered.
This is due to degeneracy (most amino acids have more than one base triplet code)
what is a missense mutation
a missense mutation is a change to the base triplet sequence that leads to a change in the amino acid sequence in a protein (e.g. TTA is now TCA which codes for a different protein).
-this will have a significant affect on the protein produced because the alteration of the primary structure will lead to alterations in the secondary structure which will alter its shape and make it unable to carry out its function
give an example of a missense mutation
sickle cell anaemia results from a missense mutation on the sixth base triplet of the gene for the B-polypeptide chains of haemoglobin: the amino acid valine, instead of glutamic acid is inserted at this position. This results in deoxygenated haemoglobin crystallising within erythrocytes, causing them to become sickle shaped, blocking capillaries and depriving tissues of oxygen
what is a nonsense mutation
- a nonsense mutation may alter a triplet, so that it becomes a termination (stop) triplet. This particularly disruptive point mutation results in a truncated protein that will not function. This abnormal protein is likely to be degraded within the cell.
what genetic disease is caused by a nonsense mutation?
the genetic disease Duchenne muscular dystrophy is the result of a nonsense mutation
what causes a frameshift
both insertions and deletions cause a frameshift
What are Indel Mutations? (deletions and insertion)
genetic code is non-overlapping. This means it is strictly read in groups of three bases.
a Indel mutation occurs when nucleotide base pairs (one base) are inserted in the gene or deleted from the gene.
this results in a Frameshift and all the subsequent codons will be read incorrectly, producing all different amino acids. This will result in a completely different protein. the tertiary structure is much altered and if very abnormal it will be rapidly degraded within the cell
Indel mutations can also occur when a whole codon is inserted or deleted. This results in one additional or one less amino acid being produced.
what is an example of a disorder resulting from frameshifts
some forms of thalassaemia, a haemoglobin disorder, results from frameshifts due to deletions of nucleotide bases.
What can occur from Expanding triple nucleotide repeats?
Some genes contain a repeating triplet such as -CAG CAG CAG-. In an expanding triple nucleotide repeat, the number of CAG triplets increases at meiosis and again from generation to generation
If the number of repeating CAG sequences goes above a certain critical number, the person will exhibit Huntington’s disease later in life.
how are alleles affected by mutation
different alleles of a particular gene are produced via mutations
what are examples of ‘good’ mutations
people having blue eyes (a mutation) allows people to see better in less bright light (e.g. in temperate regions)
- Darker skin to protect from sun damage and skin caner
- Lighter skin to allow Vitamin D synthesis (vitamin D protects us from rickets and heart disease and cancer)
what are some examples of neutral mutations (neither harmful or beneficial)
-inability to smell certain flowers, including freesias and honeysuckle
-differently shaped ear lobes
at what rate are enzymes synthesised that are needed to catalyse metabolic reactions involved in basic cellular functions
synthesised at a fairly constant rate
at what rate are enzymes synthesised that are only needed for specific conditions
synthesised at varying rates according to the needs of the cell
what are examples of bad mutations
-cancer
-genetic dieases
what does E.coli use as a respiratory substrate
The bacterium E.coli normally metabolises glucose as a respiratory substrate
However, if glucose is absent and the disaccharide lactose is present, lactose induces the production of two enzymes.
what enzymes does the presence of lactose induce in E.coli (when glucose is absent)
lactose induces the production of two enzymes:
-lactose permease, which allows lactose to enter the bacterial cell
-B-galactosidase, which hydrolyses glucose and galactose
whats an operon
an operon is a group of genes that function as a single transcription unit; first identified in prokaryotic cells
whats a lac operon
The Lac Operon is a group of genes present in E.Coli Bacteria that are needed to use Lactose as a respiratory substrate.
what is the structure of the lac operon
-a length of DNA that is about 6000 base pairs long
-a promotor region
-an operator region lacO
- structural genes lac Z and lac Y that code for the enzymes B-galactosidase and lactose permease
what is the role of the regulatory gene
the regulatory gene is a small distance from the lac operon.
The regulatory gene (I) codes for a repressor protein (LacI) when this regulatory gene is expressed, the repressor protein produced binds to the operator region.
