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| Frage | Antworten |
| What is a mutation? | any change to the quantity or the structure of the DNA of an organism |
| What is a gene mutation? | Any change to one or more nucleotide bases, or any rearrangement of the bases, in DNA. |
| What is a substitution? | when a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base. |
| What are the 3 things a change to a single base could result in | 1) a nonsense mutation 2) a mis-sense mutation 3) a silent mutation |
| Whats a nonsense mutation | -occurs if the base change results in the formation of one of the 3 stop codons -causing the polypeptide to be stopped prematurely. -the final protein would almost certainly be significantly different and would no longer be functionable |
| What is a mis-sense mutation? | -when the base change results in a different amino acid being coded for -the polypeptide produced will differ in a single amino acid -the significance of the difference depends upon the precise role of the original amino acid. -if the amino acid is important in forming bonds that affect the tertiary structure then this may not form the same bonds and will be a different shape, and therefore not function properly. e.g. in an enzyme its active site may no longer fit the substrate and will not catalyse the reaction |
| What is a silent mutation? | occurs when the substituted base, although different, codes for the same amino acid. This is due to the degenerate nature of the genetic code in which most amino acids have more than one codon will have no effect |
| How does deletion of bases occur? | when a nucleotide is lost from the normal DNA sequence |
| Effect of deletion of bases? | can cause the amino acid sequence of the polypeptide to be entirely different due to the genetic code read in units of 3 bases. causes a 'frame shift' by one letter. will change the entire sequence after that mutation. |
| Causes of mutations: | 1) can arise spontaneously during DNA replication (w/o outside influence) 2) high energy radiation that can disrupt the DNA molecule 3) chemicals that alter the DNA structure or interfere with transcription |
| Mutations | despite being random they occur with a set frequency, the natural mutation rate varying from species to species. around 1/2 mutations per 100,000 genes per generation. this can however be increased by outside factors - mutagenic agents |
| Pros and Cons of mutations | PROS - produce genetic diversity necessary for natural selection + speciation CONS- often produce organism less well suited to its environment mutations that occur in body cells rather than gametes can disrupt normal cellular activities e.g. cell division |
| What is cell division rate controlled by? | Proto-oncogenes - stimulate tumour suppressor genes - slow down |
| Role of Proto-oncogenes | -STIMULATE cell division -in a normal cell, growth factors attach to a receptor protein on the cell-surface membrane and, via relay proteins in the cytoplasm, 'switch on' the genes necessary for DNA replication a gene mutation can cause proto-oncogenes to mutate into oncogenes |
| What are the two ways oncogenes affect cell division | 1) the receptor protein on the cell surface membrane can be permanently activated, so cell division is switched on even in the absence of growth factors 2) the oncogene may code for a growth factor that is then produced in excessive amounts, stimulating cell division |
| What is the result of oncogenes | cells divide too rapidly and a tumour/cancer develops |
| Role of tumour suppressor genes | - they inhibit cell division - a normal tumour suppressor gene will maintain normal rates of cell division and prevent formation of tumours. if it becomes mutated it is inactivated and so cell division starts to increase. -cells formed are structurally and functionally different from normal cells. most mutated cells die ones that survive are capable of making clones of themselves and forming tumours. some tumours are harmless (benign) |
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