Defense Antibodies, interferons produced in response to infection Coordination and growth (signaling) Hormones (e.g. insulin, growth hormone) Communic

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1 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 Storage Energy for embryo, young, other organisms Structure Macroscopic examples: tendons, ligaments, hair, nails (collagen, keratin) Cellular level examples: actin, tubulin Transport Proteins that carry other molecules from one place to another Examples: hemoglobin, kinesins Catalysis Enzymes are proteins 1

2 Defense Antibodies, interferons produced in response to infection Coordination and growth (signaling) Hormones (e.g. insulin, growth hormone) Communication (receptors) Buffering Proteins are both acids and bases at the same time Protein monomer = amino acids 20 amino acids Proteins Exam 3! Final Exam! Can be arranged to form an astounding variety of proteins Much the way only 26 letters make thousands of words General structure α-carbon in center 4 single bonds with other atoms or groups 1. Hydrogen (H) 2. Amine (NH 2 ) 3. Carboxyl (COOH) 4. Variable (R) Numbers 1-3 are the same for all amino acids The R group is different for each amino acid Significantly change the properties of the amino acid 2

3 Two amino acids combine by dehydration synthesis to form a dipeptide Bond is a covalent bond called a peptide bond The process is repeated to elongate the polymer First makes a dipeptide peptide, then a polypeptide peptide 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 Example: Sickle Cell Anemia 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 All proteins have primary, secondary structure Most have tertiary structure Polar R groups move out Non-polar R groups move in Typically form spherical shape referred to as globular Soluble in water Most proteins do not have quaternary structure Fibrous proteins have 1, 2, and 4, but not 3 Water insoluble Examples: collagen, keratin Sickle Cell Anemia Caused by defect in 1 structure Leads to defect in 4 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

5 Denaturation How does food preservation exploit denaturation? Blanching, pickling, cheese-making, acid, pressure-canning, pasteurizing Sometimes denaturation is reversible (sometimes not) Denatured protein May fold inappropriately Sickle cell anemia May not be functional Cystic fibrosis May disrupt other cellular functions Prions Denaturation Biological catalyst Binds to substrate by active site Product(s) made and released = reusable Lowers activation energy but provides no energy Speeds up reaction Enzymes May require a co-factor to bring active site to final form (vitamin, mineral) Cell Differentiation Having cells that differ in appearance and function Specialization perform very few tasks, but do them well Highly dependent on proteins and enzymes Major advantage of being multicellular Cell can micromanage its function by controlling rate of enzyme function Environmental conditions Temperature Cell can micromanage its function by controlling rate of enzyme function Environmental conditions ph 5

6 Substrate concentration Enzyme concentration Competitive inhibition Competitive inhibition Enzyme inactivation: non-competitive inhibition Enzyme inactivation: non-competitive inhibition 6

7 Enzyme inactivation: co-factors 7