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Cell Division: Mitosis & Meiosis

• Mitosis yields 2 genetically identical diploid (2n) cells.
• Mitosis phases include Interphase (G1, S, G2), Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.
• Meiosis produces 4 genetically unique haploid (n) cells.
• Meiosis I separates homologous chromosomes.
• Meiosis II separates sister chromatids.
• Crossing over and independent assortment during meiosis contribute to genetic diversity.

Discovery of DNA: Avery et al. Experiment

• Griffith's experiment demonstrated that DNA was the material responsible for bacterial transformation.
• Heat-killed S strain (virulent) mixed with live R strain (non-virulent) killed the mouse, indicating DNA transformed bacteria.
• Avery, MacLeod, and McCarty proved that DNA is the transforming principle in Griffith's experiment.
• Only DNA extract from the S strain could convert R strain into S strain.

DNA & RNA Structure

• Nucleotides are composed of a phosphate group, a pentose sugar, and a nitrogenous base.
• In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).
• In RNA, adenine (A) pairs with uracil (U), and cytosine (C) pairs with guanine (G).
• RNA features ribose instead of deoxyribose.
• RNA is single-stranded.
• RNA contains uracil instead of thymine.
• DNA structure is a double helix with antiparallel strands.
• DNA base pairing is A-T and G-C.

Genome Structure

• Prokaryotic genomes feature a single, circular chromosome in the nucleoid region.
• Some prokaryotes have plasmids.
• Eukaryotic genomes contain multiple linear chromosomes within the nucleus.
• Histones help package eukaryotic DNA into chromatin.
• Eukaryotic DNA is complex with introns, repetitive sequences, and more regulation.

Semiconservative DNA Replication (Meselson & Stahl)

• Meselson & Stahl's experiment proved DNA replication is semiconservative.
• Each new DNA molecule consists of one old (parent) strand and one new (daughter) strand.

Key Enzymes in Replication

• Helicase unwinds DNA.
• DNA polymerase adds new nucleotides.
• Ligase seals gaps in newly synthesized DNA strands.
• Okazaki fragments are short segments of DNA synthesized on the lagging strand.

Transcription: DNA to RNA

• Initiation involves RNA polymerase binding to the promoter and unwinding DNA.
• Elongation involves RNA polymerase synthesizing mRNA in the 5' → 3' direction.
• Termination involves RNA polymerase reaching a termination signal, which releases the mRNA.
• In eukaryotes, mRNA undergoes 5' capping, splicing (removal of introns), and poly-A tail addition for stability.

Translation: RNA to Protein

• Initiation involves ribosome assembling around mRNA, while tRNA carrying methionine binds to the start codon (AUG).
• Elongation involves tRNA bringing amino acids to the A-site, where peptide bonds form.
• Termination occurs when a stop codon (UAA, UAG, UGA) is reached.
• tRNA carries amino acids and has an anticodon that matches the mRNA codons.

Key Concepts

• Mitosis produces identical diploid cells, while meiosis results in genetically diverse haploid cells.
• DNA is the Genetic Material, proven by Avery, MacLeod, and McCarty, and confirmed by Griffith's transformation experiment.
• The Central Dogma is DNA → mRNA → Protein.
• The Genetic Code consists of each mRNA codon corresponding to one amino acid in the protein sequence.
• Post-Translational Modifications involve proteins undergoing folding, cleavage, and chemical modifications (e.g., phosphorylation).

Important Enzymes

• DNA polymerase synthesizes DNA during replication.
• RNA polymerase synthesizes RNA during transcription.
• Helicase unwinds the DNA double helix.
• Ligase seals breaks in the DNA strands.
• tRNA transfers amino acids during translation.