The Central Dogma of Biology among other things…

What is the Central Dogma? The process by which we convert the message stored in DNA into a functional protein DNA  mRNA  tRNA  Protein!

Step 1: DNA  mRNA Transcription (copy the DNA message into an mRNA strand) DNA must “unzip” – Helicase is the enzyme that “unzips” DNA An RNA copy is made – Polymerase – DNA “triplets” (groups of 3 nitrogenous bases in DNA) become mRNA “codons” (complementary groups of 3 nitrogenous bases in mRNA) – Once the RNA copy is made, it travels out into the cytoplasm

Step 2: mRNA  tRNA  Protein Translation – The “language” of the nucleic acids is translated into the “language” of the amino acids (the tRNA acts as a literal “translator”) – “codons” become “anticodons” (3 nitrogenous bases in tRNA that are complementary to the mRNA codons). Each anticodon corresponds to one specific amino acid – When complete, AA chain is released!

Protein Folding Proteins must achieve a specific three- dimensional conformation before they become functional Spontaneous folding (protein folds itself) Chaperoned folding (protein is physically folded by something else)

Organelles Endoplasmic Reticulum – Smooth ER – lipid synthesis and site of chemical rxn’s – Rough ER – protein synthesis (“rough” because covered with ribosomes!) Ribosomes – protein production factories in the cell Nucleus – contains genetic material; command center of cell Golgi Apparatus – responsible for packaging and shipping in the cell Lysosomes – contain digestive enzymes to break down wastes Mitochondria – breaks down glucose to provide cell with ATP Peroxisomes – seek and destroy harmful substances in the cell Centrioles – protein bundles that serve as anchors during cell division

Cytoskeleton Microtubules (hollow cylinders) – Determine shape and distribution of organelles Microfilaments – Cell motility (movement) and changes in cell shape Intermediate Filaments (see Desmosomes) – Help form Desmosomes

Cell Cycle Interphase – period of growth and metabolism in the cell – G1 – cytoplasm doubles in volume, proteins are synthesized, organelles are copied – Synthesis – growth stops, DNA replicates – G2 – centrioles replicate, growth continues Mitosis – division of the nucleus; end result is two identical daughter cells – Prophase – preparation for division: nuclear envelope and nucleolus disappear, chromatin condenses into chromosomes, centrioles migrate to opposite ends of the cell, spindle fibers appear) – Metaphase – spindle fibers attach to chromosomes and align them at the middle of the cell – Anaphase – spindle fibers shorten, drawing sister chromatids to opposite ends of the cell – Telophase – spindle fibers disappear, nuclear envelope and nucleolus reappear, chromatids uncoil into chromatin, cytoplasm begins to pinch Cytokinesis – division of the cytoplasm; cells re-enter interphase

Plasma Membrane Or Selectively Permeable Membrane or Phospholipid Bilayer or Cell Membrane or Membrane or Lipid Bilayer Flexible boundary between the cell and its environment Purpose: maintain homeostasis!

Membrane Junctions Junctions form between adjacent cells Tight Junctions – Impermeable barriers – Their purpose is to bind cells together into “sheets” – Act like “zippers” for adjacent cells Desmosomes – Anchoring Junctions – Prevent tearing of tissues due to mechanical stress Gap Junctions – Allow communication between cells – Made of Connexons Protein channels within gap junctions

Membrane Transport Passive Transport (requires no energy) – Diffusion: random movement of solute particles across a membrane from an area of high concentration to an area of low concentration – Osmosis: diffusion of water – here our focus is on the concentration of solvent particles (not solute!!). Osmosis typically occurs in the opposite direction of simple diffusion Active Transport (requires energy; goes AGAINST a concentration gradient) – Solute Pumping (requires a carrier protein) Sodium-potassium pump – Bulk Transport Endocytosis (cell takes up materials by enveloping it with a membrane) Exocytosis (cell expels materials) Phagocytosis (“cellular eating” – defense mechanism in the cell) Pinocytosis (“cellular drinking” – endocytosis for materials dissolved in solution)