Proteins

Multipurpose molecules Proteins: Multipurpose molecules 2006-2007

Proteins Examples muscle skin, hair, fingernails, claws pepsin insulin collagen, keratin pepsin digestive enzyme in stomach insulin hormone that controls blood sugar levels pepsin collagen (skin)

Proteins Function: many, many functions hormones movement signals from one body system to another insulin movement muscle immune system protect against germs enzymes help chemical reactions

Amino acids H O | H || —C— C—OH —N— R Structure central carbon amino group carboxyl group (acid) R group (side chain) variable group different for each amino acid confers unique chemical properties to each amino acid like 20 different letters of an alphabet can make many words (proteins) —N— H R Oh, I get it! amino = NH2 acid = COOH

Proteins —N— H | —C— C—OH || O Building block = amino acids – 20 different amino acids There’s 20 of us… like 20 different letters in an alphabet! Can make lots of different words —N— H | —C— C—OH || O variable group

Effect of different R groups: Nonpolar amino acids nonpolar & hydrophobic Why are these nonpolar & hydrophobic?

Effect of different R groups: Polar amino acids polar or charged & hydrophilic Why are these polar & hydrophillic?

Sulfur containing amino acids Form disulfide bridges covalent cross links betweens sulfhydryls stabilizes 3-D structure H-S – S-H You wondered why perms smell like rotten eggs?

Amino Acids Essential Amino acids Amino acids that the body cannot synthesize from simpler compounds; they must be obtained from the diet

—N— H | —C— R C—OH || O —N— H | —C— R C—OH || O Amino acid chains Proteins amino acids chained into a polymer —N— H | —C— R C—OH || O —N— H | —C— R C—OH || O

—N— H | —C— R C—OH || O —N— H | —C— R C—OH || O Amino acid chains Proteins amino acids chained into a polymer —N— H | —C— R C—OH || O —N— H | —C— R C—OH || O Carboxyl group Amino group

—N— H | —C— R C— || O —N— H | —C— R C—OH || O OH H Amino acid chains Proteins amino acids chained into a polymer —N— H | —C— R C— || O —N— H | —C— R C—OH || O OH H

—N— H | —C— R C— || O —N— H | —C— R C—OH || O H2O Amino acid chains Proteins amino acids chained into a polymer —N— H | —C— R C— || O —N— H | —C— R C—OH || O Peptide bond- The amide linkage that holds amino acids together in polypeptides H2O

Amino acid chains Proteins Each amino acid is different amino acids chained into a polymer Each amino acid is different some “like” water & dissolve in it some “fear” water & separate from it

Amino acid chains Amino terminus Carboxyl terminus The free amino group at one end of the polypeptide Carboxyl terminus The free carboxyl group at one end of a polypeptide

Water-fearing amino acids Hydrophobic “water fearing” amino acids try to get away from water in cell the protein folds

Water-loving amino acids Hydrophillic “water loving” amino acids try to stay in water in cell the protein folds

For proteins: SHAPE matters! Proteins fold & twist into 3-D shape that’s what happens in the cell! Different shapes = different jobs growth hormone hemoglobin pepsin collagen

It’s SHAPE that matters! Proteins do their jobs, because of their shape (conformation) Unfolding a protein destroys its shape wrong shape = can’t do its job unfolding proteins = “denature” temperature pH (acidity) unfolded “denatured” In Biology, it’s not the size, it’s the SHAPE that matters! folded

Protein Folding Shape comes from how the protein folds There are 4 levels of folding in proteins

Primary (1°) structure Order of amino acids in chain amino acid sequence determined by gene (DNA) slight change in amino acid sequence can affect protein’s structure & its function even just one amino acid change can make all the difference! Sickle cell anemia: 1 DNA letter changes 1 amino acid = serious disease Hemoglobin mutation: bends red blood cells out of shape & they clog your veins. lysozyme: enzyme in tears & mucus that kills bacteria

Secondary (2°) structure “Local folding” folding along short sections of polypeptide interactions between adjacent amino acids H bonds weak bonds between R groups forms sections of 3-D structure -helix -pleated sheet It’s a helix or B sheet within a single region. Can have both in one protein but a specific region is one or another Coiled (α-helix) Hair - Can stretch, perms change the protein structure Hydrogen bonds Between chains and parts of chains Disulfide bonds Occur between chains β-sheet Eg. Silk Doesn’t stretch Hydrogen bonds between side chains

Secondary (2°) structure

Tertiary (3°) structure “Whole molecule folding” interactions between distant amino acids hydrophobic interactions cytoplasm is water-based nonpolar amino acids cluster away from water H bonds & ionic bonds disulfide bridges covalent bonds between sulfurs in sulfhydryls (S–H) anchors 3-D shape How the whole thing holds together Tertiary Structure Globular shape (only helices) enzymes Each protein folds in a specific way Folding of the secondary structure Bonding between R groups (side chains) Hydrophobic interactions Nonpolar side chains, away from water Hydrogen bonds between side groups Ionic bonds between +ve and –ve charged R groups (weak) Disulfide Bridges Strong covalent bonds Between aa with sulfyhdryl groups on their side chains Between cysteine bonds

Quaternary (4°) structure More than one polypeptide chain bonded together only then does polypeptide become functional protein hydrophobic interactions Protein structure video Structure equals function wonderfully illustrated by proteins Collagen is just like rope -- enables your skin to be strong and flexible. hemoglobin collagen = skin & tendons

Protein structure (review) R groups hydrophobic interactions disulfide bridges (H & ionic bonds) 3° multiple polypeptides hydrophobic interactions 1° sequence determines structure and… structure determines function. Change the sequence & that changes the structure which changes the function. amino acid sequence peptide bonds 4° 2° determined by DNA R groups H bonds