The Central Dogma of Biologyamong 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)