Proteins

Extremely important molecule in the body About 50% of a cell’s dry weight is protein Polymers made up of monomer units called amino acids

Important functions of Proteins enzymes (speed up chemical reactions) hormones storage (egg whites of birds, reptiles; seeds) transport (hemoglobin) contractile (muscle) protective (antibodies) membrane proteins (receptors, membrane transport) structural toxins (botulism, diphtheria)

Amino Acids The building blocks of proteins There are 20 different amino acids, each with a unique R-group (what makes the amino acid distinct) Each amino acid contains An amino group (NH2) A carboxyl group (COOH) A central carbon attached to a hydrogen A side chain (R group)

Amino Acid Structure Carboxyl Group Functional Group Central Carbon Functional Group (gives properties) Amino Group

Amino acids may be polar, non-polar, acidic or basic depending on the nature of their side-chains There are 8 essential amino acids that the body cannot synthesize; these must be obtained from the diet

Polypeptides Amino acids are joined by peptide bonds into long chains called polypeptides This bond is formed by a condensation reaction between the amino group on one amino acid and the carboxyl group of another amino acid Two amino acids = dipeptide Three amino acids = tripeptide

Polypeptides Always have an amino group on one end and a carboxyl group on the other end Several amino acids together will produce a repeating sequence of atoms along the chain N-C-C-N-C-C-N-C-C

Proteins consist of one or more amino acid polymers that have twisted and coiled into a specific shape The final shape (conformation) of the polypeptide is determined by the sequence of amino acids it contains A protein’s conformation is critical to its function There are four levels of organization for proteins

Levels of Organization Structural name Structural Description Bonding Characteristics Primary Sequence of amino acids Covalent peptide bonds Secondary Alpha helix Hydrogen bonds   Beta pleated sheet Tertiary Complex folding R-group-R-group interactions (H-bonds, ionic bonds, hydrophobic interactions), disulfide bridges Quaternary Several polypeptides in tertiary structure interacting with one another R-group-R-group interactions between globular polypeptide chains

Primary and Secondary Structure Primary Structure refers to the sequence of amino acids found in a protein. Secondary Structure The oxygen or nitrogen atoms of the peptide bond are capable of hydrogen- bonding with hydrogen atoms elsewhere on the molecule. This bonding produces two common kinds of shapes seen in protein molecules, coils (helices) and pleated sheets

Tertiary Structure Tertiary structure refers to the overall 3-dimensional shape of the polypeptide chain. Hydrophobic interactions with water molecules are important in creating and stabilizing the structure of proteins. Hydrophobic (nonpolar) amino acids aggregate to produce areas of the protein that are out of contact with water molecules. Hydrophilic (polar and ionized) amino acids form hydrogen bonds with water molecules due to the polar nature of the water molecule. Hydrogen bonds and ionic bonds form between R groups to help shape the polypeptide chain. Disulfide bonds are covalent bonds between sulfur atoms in the R groups of two different amino acids. These bonds are very important in maintaining the tertiary structure of some proteins.

How polypeptides are held in place!

Quaternary Structure Some proteins contain two or more polypeptide chains that associate to form a single protein. These proteins have quaternary structure. For example, hemoglobin contains four polypeptide chains

https://www.youtube.com/watch?v=qBRFIMc xZNM

A proteins shape is also determined by the environmental conditions in which it is found The structure is sensitive to pH, temperature, salt, concentration and chemicals If any of the conditions fall outside favourable range, a protein’s shape and therefore function is altered

Denaturation and Inactivation Denaturation of a protein occurs when the normal bonding patterns are physically broken causing the shape of the protein to change. This can be caused by increased temperature Inactivation occurs when the temperature is too low for a protein to function properly Chaperone proteins are molecules that can assist a protein fold properly after it has been slightly damaged or unfolded