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4/29/2015 Proteins Chapter 3 An Introduction to Organic Compounds • Most varied of the biomolecules • Also called polypeptides • Make up more than half the dry weight of cells • Categorized by function Lecture 3: Proteins Protein Functions • Storage • Protein Functions • Energy for embryo, young, other organisms Structure • Macroscopic examples: tendons, ligaments, hair, nails (collagen, keratin) • Cellular level examples: actin, actin, tubulin Protein Functions • Transport • Proteins that carry other molecules from one place to another • Examples: hemoglobin, kinesins Protein Functions • Catalysis • Enzymes are proteins 1 4/29/2015 Protein Functions • Defense • Protein Functions • Antibodies, interferons produced in response to infection Coordination and growth (signaling) • Hormones (e.g. insulin, growth hormone) • Communication (receptors) Protein Functions • Buffering • Proteins are both acids and bases at the same time Proteins • Protein monomer = amino acids • 20 amino acids Amino Acids Exam 3! Final Exam! • Can be arranged to form an astounding variety of proteins • Much the way only 26 letters make thousands of words Amino Acids • General structure • Numbers 11-3 are the same for all amino acids • α-Carbon in center • The R group is different for each amino acid • 4 single bonds with other atoms or groups • Significantly change the properties of the amino acid 1. Hydrogen (H) 2. Amine (NH2) 3. Carboxyl (COOH) 4. Variable (R) 2 4/29/2015 Amino Acids • Two amino acids combine by dehydration synthesis to form a dipeptide • Bond is a covalent bond called a peptide bond Amino Acids • The process is repeated to elongate the polymer • polypeptide First makes a dipeptide dipeptide,, then a polypeptide Protein Structure • Protein function depends on 4 levels of structure • Primary – number and order of amino acids • Secondary – local folding patterns • Tertiary – overall 3D folding • Quaternary – interaction of 2 or more fully assembled proteins Example: Hemoglobin Example: Sickle Cell Anemia Normal RBC Sickle RBC 3 4/29/2015 Example: Sickle Cell Anemia Protein Structure • How do these interactions form? • Primary – covalent (peptide) bonds between amino acids • Secondary – hydrogen bonds between R groups • Tertiary and quaternary – interactions between R groups Protein Structure Protein Structure • All proteins have primary, secondary structure • Most proteins do not have quaternary structure • Most have tertiary structure • Fibrous proteins have 1° 1°, 2° 2°, and 4 4°°, but not 3 3°° Polar R groups move out • Water insoluble • Non--polar R groups move in Non • Examples: collagen, keratin • Typically form spherical shape – referred to as “globular” • Soluble in water • Sickle Cell Anemia • Caused by defect in 1° structure • Leads to defect in 4° structure Protein Structure • Biological activity of a protein highly dependent on shape • Changes in shape = denaturation • Protein shape is maintained by hydrogen bonds • Anything that alters hydrogen bonds can denature a protein • Heat, pressure, pH, heavy metals, alcohol, UV light 4 4/29/2015 Denaturation • How does food preservation exploit denaturation? • Blanching, pickling, cheesecheese-making, acid, pressure-canning, pasteurizing pressure- Denaturation • Sometimes denaturation is reversible (sometimes not) • Denatured protein • May fold inappropriately • May not be functional • May disrupt other cellular functions • • • Sickle cell anemia Cystic fibrosis Prions Enzymes Cell Differentiation • Biological catalyst • Binds to substrate by active site Having cells that differ in appearance and function • Product(s) made and released = reusable • • Lowers activation energy but provides no energy • Speeds up reaction • Highly dependent on proteins and enzymes • May require a coco-factor to bring active site to final form (vitamin, mineral) • Major advantage of being multicellular • Specialization – perform very few tasks, but do them well Enzyme Regulation Enzyme Regulation • Cell can micromanage its function by controlling rate of enzyme function • Cell can micromanage its function by controlling rate of enzyme function • Environmental conditions • Environmental conditions • Temperature • pH 5 4/29/2015 Enzyme Regulation • Cellular influences • Enzyme Regulation • Substrate concentration Cellular influences • Enzyme Regulation • Cellular influences • Enzyme Regulation • Competitive inhibition Cellular influences • Enzyme Regulation • Cellular influences • Enzyme inactivation: nonnon-competitive inhibition Enzyme concentration Competitive inhibition Enzyme Regulation • Cellular influences • Enzyme inactivation: nonnon-competitive inhibition 6 4/29/2015 Enzyme Regulation • Cellular influences • Enzyme inactivation: coco-factors 7