P ROTEINS SBI4U Ms. Manning

Most diverse molecules in living organisms. Coded for by genes in the DNA Used as: Structural building blocks Catalysis - enzymes Immunity Transport of other molecules across the cell membrane Monomer: Amino acid

3 F OUR OF THE 7 CLASSES OF P ROTEINS Structural Contractile Storage Transport Copyright Cmassengale

4 20 A MINO A CID M ONOMERS Copyright Cmassengale

5 S TRUCTURE OF A MINO A CIDS Amino group –NH 2 Carboxyl group -COOH Hydrogen -H Side group -R Amino group Carboxyl group R group Side groups Leucine -hydrophobic Serine-hydrophillic Copyright Cmassengale Amino acids have a central carbon with 4 things bonded to it:

6 L INKING A MINO A CIDS Cells link amino acids together to make proteins The process is called condensation or dehydration Peptide bonds form to hold the amino acids together Carboxyl Amino Side Group Dehydration Synthesis Peptide Bond Copyright Cmassengale

P ROTEIN S TRUCTURE 1 A.A. = 1 A.A. monomer 2 A.A.’s = a dipeptide molecule Many A.A.’s = a polypeptide chain 1 or more polypeptide chains = a protein molecule. There are 4 levels of protein structure: 1. Primary Structure 2. Secondary Structure 3. Tertiary Structure 4. Quaternary Structure UYQ&feature=related

L EVELS OF S TRUCTURE Primary A polypeptide chain of A.A’s.

S ECONDARY S TRUCTURE A.A. chain will pleat or coil or form a helix. H bonds!

S ECONDARY S TRUCTURE Alpha helix Flexibility Polypeptide chain tightly coiled held by H bonds i.e. Keratin n4GSA&feature=related

S ECONDARY S TRUCTURE Beta pleated sheet Strength Parallel polypeptide chains H-bonds i.e. silk proteins CTWlrE&feature=related

T ERTIARY S TRUCTURE Folded to form a specific shape (enzymes)

3. TERTIARY – 3D folding (more complex) of polypeptide held in place by: Hydrophobic bonding of non-polar side chains Ionic bonds between charged side chains Covalent disulfide bridges of cysteines

F IBROUS V S. G LOBULAR Fibrous proteins are strong and insoluble in water eg. collagen, silk, keratin (main component in hair) Globular proteins are spherical in shape, Have a hydrophobic group on the inside, hydrophilic group on the outside. Soluble in water. eg. enzymes, antibodies, hormones

Protein consists of one or more polypeptides twisted and coiled into a specific shape Shape is determined by the ORDER of amino acids Many proteins are globular (rounded shape), especially enzymes.

4. QUARTERNARY – Two or more polypeptides wound together

H EMOGLOBIN C 3032 H 4816 O 872 N 780 S 8 Fe 4 Build it!!!

P ROTEIN SHAPE ALSO INFLUENCED BY... Chemical and physical environmental factors i.e. pH and temperature changes in environmental conditions may cause changes in protein shape – called denaturation, protein becomes non-functional Protein can resume shape under normal conditions if primary structure is maintained.

20 D ENATURATING P ROTEINS Changes in temperature & pH can denature (unfold) a protein so it no longer works Cooking denatures protein in eggs Milk protein separates into curds & whey when it denatures Copyright Cmassengale

21 C HANGING A MINO A CID S EQUENCE Substitution of one amino acid for another in hemoglobin causes sickle-cell disease (a) Normal red blood cellNormal hemoglobin (b) Sickled red blood cellSickle-cell hemoglobin Cop yrig ht Cma ssen gale

22 O THER I MPORTANT P ROTEINS Blood sugar level is controlled by a protein called insulin Insulin causes the liver to uptake and store excess sugar as Glycogen The cell membrane also contains proteins Receptor proteins help cells recognize other cells Cop yrig ht Cma ssen gale

23 INSULIN Cell membrane with proteins & phospholipids Copyright Cmassengale