DNA and Gene Expression.ppt

DNA and Gene Expression Dexoyribonucleic Acid (DNA) Two phosphoric acid sugar strands held apart by pairs of four bases Adenine (A), thymine (T), guanine (G), cytosine (C) A pairs with T, G pairs with C Self replicating molecule Directs protein synthesis DNA Structure DNA Replication Results in two complete double helixes of DNA How nucleotides are added in DNA replication (animation) Genome Maybe 30,000 genes on human genome Gene range from 1000 to 2 million base pairs Protein Synthesis 20 amino acids, despite 64 possible combinations from 4 base pairs; duplication Codons Sequences of three base pairs Each codes for an amino acid (or “stop” signal) Amino acids assembled into proteins Only about 2% of genome involved in protein synthesis Genetic Code Mutations Mistakes made in copying DNA Produces different alleles (called polymorphisms) Mutations in gametes are transmitted faithfully unless natural selection intervenes Single-Base Mutations Can either change or remove a base from a codon Changing one base for another Generally less likely to have an affect Removal of base More problematic; shifts the reading of the triplet code CGA-CTA-TGA -- CAC-TAT-GA… Alanine - aspartic acid - threonine -- valine - isoleucine… Changing amino acid No, small, or large effect on protein production Multi-base Mutations Some genes can have multiple mutations at different locations Complicates matters enormously for functionality and identification of effects by behavioural geneticists RNA Ribonucleic acid Differs from DNA Single-stranded molecule (generally); shorter Ribose, not deoxyribose; RNA is less stable Adenine’s complementary nucleotide is uracil (U), not thymine Various forms: mRNA, tRNA, rRNA, non-coding RNA RNA The original genetic code Still seen in most viruses Single strand vulnerable to predatory enzymes; double stranded DNA gained selective advantage RNA degrades quickly, is tissue-, age-, and state-specific Gene Expression Transcription Production of mRNA in nucleu