Presented To :Sir Khalid Hussain Presented by: 09040606-028 The molecular basis and mutations
The molecular basis and mutations DNA is made of a long sequence of smaller units strung together. There are four basic types of unit: A, T, G, and C. These letters represents the type of base each unit carries: adenine, thymine, guanine, and cytosine.
The sequence of these bases encodes instructions. Some parts of our DNA are control centers for turning genes on and off, some parts have no function, and some parts have a function that we dont understand yet. Other parts of our DNA are genes that carry the instructions for making proteins — which are long chains of amino acids. These proteins help build an organism.
Mutations Mutations are changes in the DNA sequence of genes. Point mutations typically refer to alterations of single base pairs of DNA or of a small number of adjacent base pairs. Mutations in DNA cause substitutions in protein
New mutations are categorized as induced or spontaneous Induced mutations are defined as those that arise after purposeful treatment with mutagens, environmental agents that are known to increase the rate of mutations Spontaneous mutations are those that arise in the absence of known mutagen treatment. They account for the "background rate" of mutation and are presumably the ultimate source of natural genetic variation that is seen in populations
Mutation can be classified as:a- Germline - affecting tissues that produces eggs & sperm ( heritable meiotically between generations)b-Somatic mutations occur in non- reproductive cells and wont be passed onto offspring. For example, the golden color on half of this Red Delicious apple was caused by a somatic mutation. Its seeds will not carry the mutation.
Substitutions: A substitution is a mutation that exchanges one base for another (i.e., a change in a single "chemical letter" such as switching an A to a G). Such a substitution could:
Substitutions 1- Silent substitutions the mutation changes one codon for an amino acid into another codon for that same amino acid 2- Missense mutations the codon for one amino acid is replaced by a codon for another amino acid 3- Nonsense mutations the codon for one amino acid is replaced by a translation termination (stop) codon
Insertion: Insertions are mutations in which extra base pairs are inserted into a new place in the DNA. Deletion: Deletions are mutations in which a section of DNA is lost, or deleted.
Effects of mutation Mutations happen for several reasons.1. DNA fails to copy accurately.2. External influences can create mutations. Mutations can also be caused by exposure to specific chemicals or radiation. These agents cause the DNA to break down.
Biological Repair Mechanisms Living cells have evolved a series of enzymatic systems that repair DNA damage in a variety of ways. The low spontaneous mutation rate is indicative of the efficiency of these repair systems. Failure of these systems can lead to a higher mutation rate.