Proteins Major group of biological molecules

Proteins Monomers: amino acids ▫Always contain an amino group and carboxylic acid group Polymers: peptides ▫Each different sequence of amino acids is a different peptide Polymerization Rxn: Condensation Reactions Examples: meat, skin, hair, nails, casein

Amino Acids The “R” can be an H or any hydrocarbon or organic functional group Amino acids are classified based on properties of R group

Amino Acid Classifications Type of Amino AcidR group contains Non-polar/hydrophobicHydrocarbon Polar but chargesAlcohol, sulfhydryl (-SH), or amide (-CONH2) BasicAmino (–NH2) AcidicCarboxylic Acid (-COOH)

Zwitterions Amino acids(AA) can become charged in two places – thus making them dipolar ions Zwitterions result from internal acid/base reaction where the carboxylic acid group on the AA transfers an H to the amino group on the same AA

Amino Acids are Amphoteric AA contain both an acid and base group and are therefore amphoteric (able to act as either and acid or a base) As a result, amino acids are very good buffers – resist changes in pH pH changes just affect the charge of the AA

Isoelectric Point Isoelectric point is when the AA is neutral – it is a zwitterion The isoelectric point of each AA is different Changes in pH cause differing charges on the AA

Condensation to make Proteins The bond that results from the condensation reaction of AA to make a protein is called a peptide bond The carboxylic acid group on one AA reacts with the amino group on another AA Literally millions of possible AA sequences of varying lengths

4 Levels of Structure for Proteins Primary- ▫amino acid sequence connected through peptide bonds to form a polypeptide Secondary- ▫through hydrogen bonds between carboxylic groups and amino groups Tertiary- ▫further twisting and folding of polypeptide on itself via interactions of R groups Quaternary- ▫Interactions between polypeptide chains

Primary Structure Dictates rest of protein structure Forms the covalent backbone of the molecule All polypeptide bonds

Secondary Structure Influenced by R groups All hydrogen bonding Types: ▫α-helix ▫β-pleated sheet

Alpha(α) Helix looks like a spiral- forms via hydrogen bonding between AA 4 units apart It’s flexible and elastic Folding of 1 polypeptide (intra-chain H bonds)

Beta (β)- pleated sheets Hydrogen bonding between polypeptides (inter-chain hydrogen bonds) Looks like waves stacked on each other Are inelastic and therefore well defined Aka Fibrous proteins

Tertiary Structure = conformation Results from interactions of R groups All with in the same polypeptide Globular conformations are very common and important ▫Include all enzymes and hormones ▫Water soluble because hydrophilic R groups on outer surface and hydrophobic on interior

Stabilization of Globular Proteins In order of strength: Hydrophobic interactions ▫– between nonpolar side chains Hydrogen bonding – ▫between polar side chains Ionic Bonds – ▫between charged side chains Disulfide bridges – ▫ covalent bonds between sulfur atoms in cysteine

Denaturing of Proteins Denaturing – when a protein loses its tertiary structure Results in protein being inactive/ losing its function Caused by: ▫Temperature changes ▫pH changes

Quaternary Structure Association between different polypeptides Ex: ▫Collagen – triple helix of chains ▫Haemoglobin – 2 alpha and 2 beta chains

Hydrolysis of Proteins Proteins are analyzed by knowing its amino acid composition To do this, the peptide bonds in the polypeptide must be broken Are broken through hydrolysis reaction – adding water back onto the amino acids (OH onto carboxyl group and H onto amino end)

Separation of AA Sequence Chromatography ▫Particularly useful with colorful substances ▫ Electrophoresis ▫Based on movement of charged particles in an electric field ▫ / / ▫

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