Mutations Flashcards
What is a germinal mutation?
Inheritance of a mutation in a germ cell. This is when an egg or sperm carries the mutation, the embryo will have all cells carrying mutation as one of the copies is mutated.
What is a somatic mutation?
At any possible times of the life of an organism, one somatic cell undergoes mutation. The daughter cells of this specific cell will go on to be mutated as well.
What is a point mutation?
A mutation that only affects a single nucleotide.
What are the 2 types of substitution mutations?
Transition changes a purine for another, or pyrimidine for another.
Transversion changes a purine for a pyrimidine or vice versa.
Describe the functional classes of point mutations.
- No mutation
- Silent - where 1 nucleotide is substituted but makes no final change in amino acid as the genetic code is redundant.
- Nonsense - severe as a stop codon is placed instead of one coding for amino acid, thus an incomplete protein is formed that is useless.
- Missense - different amino acid coded, can be either acidic or basic and depending on the original sequence of amino acids, this can have a large or smaller effect.
- Frameshift - loss or insertion of a DNA sequence that shifts the way the sequence is read.
Desribe how sicke cell anemia results from a point mutation.
Cuased by a mutation in a single nucleotide in the gene coding for globin, leading to the malformation of hemoglobin molecules.
Are mutations generally spontaneous or induced?
Mutations are generally ssoontaneous.
Describe the background of the experiment to show whether mutations are spontaneous or induced.
Performed by Luria and Delbruck.
A culture of bacteria cells exposed to bacteriophage eventually becomes clear, as if all the bacteria in the culture were killed. However eventually the culture would grow cloudy again.
It was surmised that the bacteria acquired resistance to the phage and were able to repopulate the culture. Therefore did a spntaneous mutation occur or dd the viral infection change the DNA of the bacteria?
Describe the experiment to show whether mutations are spontaneous or induced.
Luria set up a large numbers of bacterial cultures containing a small number of bacteria in each, to which bacteriophage was added.
2 hypothesised situations:
- Spontaneous mutations - the number of surviving bacteria would be small in most cultures, but large in a handful.
- Directed mutation - number of surviving bacteria would be evenely distributed.
It was found that the spontaneous mutation model proved true.
Why are rare base forms common base forms?
Sometimes base forms can be present in their rare base formes, i.e. The common form for thymine is its keto form, while the rare form is its enol form.
Why can rare base forms be mutations?
Instead of producing normal base pairs, they can produce different pairs.
Cytosine in its rare form can pair with common form adenine. While guanine in its rare form can pair with thymine.
These base pairings can be transform into a stable mutation via replication. This is because replication maintains mutations in genomes during replication cycles.
Consequently spontaneously mutated DNA can be converted into a permanently mutant copy which is stable after a few rounds of replication.
How do base analogs act as chemical mutagen to DNA?
Base analogs that resembles DNA so are erroneously cooperated. E.g. 5-Bromouracil and 2-Aminopurine.
5-Bromouracil can bond with both adenine and guanine.
How do some molecules induce a mutation chemically when interacting with DNA?
Molecules directly interacting with DNA to induce structural changes.
HNO2 - nitrous acid - a deaminating agent that deaminates aminic group of adenine and cytosine in some cases, changing it into an ether group.
It can transform A into hypoxanthine that base pairs with C. G changed to xanthine, which still base pairs with C. And C to U, which base pairs with A.
NH2OH - hydroxylamine - a hydroxylating agent
How do some molecules indirectly chemically mutate DNA?
Molecules indirectly affect with DNA via induction of mutagenic substances.
Describe the properties of alkalyation agents when interacting with DNA.
Depending on dosage, alkylation agents can have different effects - cytotoxic, carcinogenic or mutagenic effects.
Can work in all cells, but works particularly in cells that divide rapidly.
Can be used as antineoplastic or anticancer drugs. These mutagens can be used to target rapidly dividing cells. Although this means that they do not only target cancer cells, but all other rapidly dividing cells.
