Chapter 20: Molecular Genetics Overview DNA Structure and Replication DNA Functions: Carrier of genetic information, regulates proteins, supports cell division, and contributes to genetic diversity. Structure: Double helix with sugar-phosphate backbone and nitrogen bases forming complementary base pairs (A-T, G-C). Anti-parallel strands held by hydrogen bonds. Replication: Semi-conservative process where DNA helicase unzips strands, and DNA polymerase synthesizes new complementary strands. Errors during replication can lead to mutations. Protein Synthesis Transcription (Occurs in the nucleus): DNA is used as a template to synthesize mRNA. RNA polymerase initiates and elongates mRNA, which exits the nucleus to the cytoplasm. Translation (Occurs in the cytoplasm): mRNA codons are translated into amino acid sequences with the help of tRNA and ribosomes. Involves initiation (start codon AUG), elongation, and termination. Genetic Mutations Types: Point mutations (silent, missense, nonsense). Gene mutations (insertions, deletions – frameshift mutations). Chromosomal mutations (translocations, inversions). Causes: Spontaneous errors or mutagenic agents (radiation, chemicals). Impact: Beneficial (selective advantage), harmful (reduce fitness), or neutral. Examples: Sickle-cell anemia, cystic fibrosis. Biotechnology Applications Recombinant DNA: Combines DNA from different sources. Used for cloning genes (e.g., insulin production) and creating transgenic organisms. Polymerase Chain Reaction (PCR): Amplifies DNA fragments. Gel Electrophoresis: Separates DNA fragments by size and charge. DNA Fingerprinting: Used for identification in forensics and paternity tests. Oncogenes and Cancer Mutations in oncogenes disrupt cell division regulation, potentially leading to cancer. Exercises and Labs Activities include labeling DNA structures, simulating DNA replication and transcription, and practical lab techniques like gel electrophoresis.