Introduction to Proteins
What do proteins do? Structural proteins Function: Support Example: Collagen and elastin provide a fibrous framework in animal connective tissues such as tendons and ligaments Keratin is the protein of hair, horns, quills, Keratin Collagen injection
What do proteins do? 2) Storage Proteins Function: Storage of amino acids Example: Ovalbumin is the protein of egg whites Casein is the protein is mammal milk
What do proteins do? Transport Proteins Function: transport other substances Example: hemoglobin transports oxygen from the lungs to the other parts of the body Other proteins transport molecules across cellular membranes
What do proteins do? 4) Hormonal Proteins Function: coordination of bodily activities Example: Insulin helps control the concentration of sugar in blood Insulin
What do proteins do? Receptor Proteins Function: response of cell to chemical stimuli Example: neuron receptors respond to chemicals released by other nerve cells
What do proteins do? Contractile proteins Function: Movement Example: Actin and myosin are the proteins responsible for muscle movement
What do proteins do? Defensive Proteins Function: Protection against disease Example: Antibodies combat bacteria and viruses
The Immune System
What do proteins do? Enzymatic Proteins Function: Speed up chemical reactions Example: amylase hydrolyzes sugar polymers in food.
What is a protein? A protein is a linear chain of amino acids 20 species of amino acid, properties dictated by side chain (R) Polar (hydrophillic): contain O and N Nonpolar (hydrophobic) Acidic: negative charge Basic: positive charge H NH3+ C COO- R
Amino Acids
How Complex are Proteins? Example: Average E. Coli protein: 300 a.a. long 20 possible a.a. at each position =20300 possible sequences! DNA: structure is independent of sequence Protein: structure change with sequence change
Polypeptide Chains Enzymes join the carboxyl of one amino acid to the amino group of another amino acid Amino acids are joined in a condensation reaction to form a peptide linkage Polypeptides range in length from a few monomers to thousands of amino acids long
Peptide linkage
Protein Composition Peptide Bond Amino Acid Subunit Proteins are composed of amino acids covalently linked via polypeptide bonds Peptide Bond Amino Acid Subunit R O R C NH C C NH NH C C NH C C O R O R
Protein Have Multiple Levels of Structure Primary Secondary Tertiary Quaternary
Protein Have Multiple Levels of Structure Primary Unique sequence of amino acids Even a slight change can affect the proteins ability to function For example: The disease sickle cell anemia is caused by glutamic acid changing to valine at position 6
Sickle Cell
Proteins Have Multiple Levels of Structure Secondary a-helices, b-sheets, turns, and random coils Controlled by hydrogen bonding network
Protein Have Multiple Levels of Structure Tertiary Interaction of pieces of secondary structure Controlled by side chain interactions and include hydrogen bonds, ionic bonds, hydrophobic interactions, and covalent bonds in the form of disulfide bridges
Protein Have Multiple Levels of Structure Quaternary Interaction of multiple chains Interactions are controlled by shape and chemistry Hemoglobin
Hemoglobin An example of quarternary structure