Session 1: Mutations Flashcards
What are mutations?
Mutations are alterations in the DNA of chromosomes. They can be neutral (have no observable affect), harmful (alter the survival capacity of the organism), or beneficial (can give the organism an advantage).
What are the causes of mutation? (overall)
Mutations can be random and spontaneous because of errors in replication, or they can be caused by environmental factors (mutagens) such as exposure to nuclear radiation.
What are cancers?
Cells with uncontrolled cell growth and division. Normally genes control cell division and so damage to genes causes uncontrolled cell division. Any type of cell can develop cancer but it is more common with cells with rapid division.
Overall, describe the impact of radiation (in terms of mutations).
Ionising radiation has high energy and causes reactive
molecules (free radicals) which damage DNA. Nuclear radiation can cause many different cancers, they can be caused by fallout from nuclear weapons and the exposure to nuclear radiation that nuclear workers have.
Overall, describe viruses in terms of mutations.
Viruses insert their genetic material into the DNA of the host cell. This can disrupt the host’s genes and potentially lead to cancer.
Overall, describe chemicals in terms of mutations.
A large number of chemicals may interact directly with DNA. However, many are not necessarily mutagenic by themselves, but through metabolic processes in cells they produce mutagenic compounds.
How does location determine whether or not a cell mutation will be inherited?
Most mutations occur in somatic cells and are not inherited. Gametic (germ line) mutations occur in the cells of the gonads (which produce sperm and eggs) and may be inherited.
What are neutral mutations?
Mutations that produce little or no change in the phenotype. They may have little or no effect on the survival of an
organism or its ability to reproduce. They may be the result of a ‘same-sense’ mutation where a change in the third base of a codon still codes for the same amino acid.
What is missense substitution?
Overall, when a single amino acid may be altered due to mutation. A single base is substituted by another (point mutation). Usually results in coding for a new amino acid in the polypeptide chain. If the third base in a triplet had been substituted, the resulting amino acid may not be altered (due to degeneracy in the code).
What is nonsense substitution?
A single base is substituted by another. This results in a new triplet that does not code for an amino acid. This may be an instruction to terminate the synthesis of the polypeptide chain.
What is reading frame shift?
A single base is inserted or deleted, upsetting the reading sequence for all those after it. A reading frame shift results in new amino acids in the polypeptide chain from the point of insertion onwards. The resulting protein will be significantly different most likely non-functional.
Describe sickle cell mutation.
The mutation responsible for causing sickle cell disease is a point substitution mutation (substitution of a valine for a glutamic acid in the beta-chain). This mutation occurs on hemoglobin and results in less soluble hemoglobin, resulting in blood cells forming in a sickle shape.
Describe cystic fibrosis.
The mutation causing 70% of cystic fibrosis cases is a gene mutation involving a triplet deletion. Other cystic fibrosis cases can be caused by deletions, missense, nonsense, and terminator codon
What are examples of beneficial mutations?
Bacterial resistance to antibiotics, Insecticide (e.g. DDT) resistance in insect pests, and Changes to the make-up of the protein coats of viruses. Beneficial mutations are generally observed in species with short generation times. A larger example of beneficial mutation is evolution.
What are homozygous and heterozygous genes/alleles?
Homozygous genes are when both the alleles in a chromosome pair are the same, e.g. homozygous dominant and homozygous recessive. Heterozygous alleles are when the alleles in a chromosome pair are different, e.g. one is dominant and one is recessive. Heterozygous alleles are carriers for recessive genes.
