Hannah Barreca Daria Lukasz Ian Reucroft Roshelle Belfer Stephanie Puthumana

 Amino Acids contain a central carbon chain with ◦ An amino group NH 2 ◦ A carboxyl group COOH ◦ A hydrogen ◦ Side chain faculty.irsc.edu thefullwiki.org

 Crystalline solids  Very high melting point in excess of 200°C  Very soluble in water, not soluble in organic solutions  Exist as ionic species

 Contain amine (-NH 2 ) and carboxylic acid (-COOH) functional group  The amine is a base, the acid is an acid ◦ This means that protons (H + ) move from the carboxyl group to the amine group ◦ This forms a zwitterion

 Zwitterions have net charge of zero ◦ Are both positively and negatively charged ◦ This is the form of amino acids even when solid ◦ When dissolved, zwitterion ions are formed  If OH¯ ions added, pH rises ◦ NH 3 + loses H + ◦ Amino acid is negative

 Lower pH by adding acid ◦ -COO¯ gains H + ◦ Amino acid is positive  Thus amino acids can be separated by electrophoresis ◦ Positive acids travel to cathode ◦ Negative acids travel to anode

 If positive amino acid has alkali added to it ◦ Ion has two acidic hydrogens ◦ -COOH hydrogen is more acidic and is removed to make water ◦ We have zwitterion again! ◦ Net charge of zero is restored ◦ Acid wouldn’t go anywhere in electrophoresis

 pH which results in lack of movement is isoelectric point ◦ Varies from amino acid to amino acid ◦ Not necessarily at pH 7, more often pH 6 ◦ pH I  Buffer action ◦ - COO¯ is proton acceptor: acts as base ◦ NH 3 + is proton donor: acts as acid ◦ Amino acids thus are amphiprotic and act as buffers, depending on environment

h.gov/books/NBK /

 Amino acids are linked with amide groups, known as peptide bonds ◦ Atoms in the amide group are linked with covalent bonds (Don’t draw peptide bonds as dotted lines, like in bio)  Peptide bonds form during a condensation reaction between the carboxyl group of one amino acid and the amino group of another amino acid ◦ Water is released as a product of this reaction

Condensation reaction between glycine and alanine Image from:

 Primary: ◦ Amino acids link together to form polypeptide chain in a condensation reaction ◦ The order in which amino acids are linked is determined by the genes. Ex: Met is always first. ◦ Peptide bonds link amino acids  Covalent bond  intramolecular

 Secondary: ◦ The polypeptide chain is coiled into either an alpha-helix or beta-pleated sheet ◦ Hydrogen bonds define the structure  Alpha-helix: bonding causes the polypeptide to twist into a helix  Bonds are within a molecule, so could be considered intra-molecular (or intra- chain) forces  Beta-pleated sheets: bonding enables the polypeptide to fold back and forth upon itself like a pleated sheet  Bonds are between chains, so could be called inter-chain forces

 Tertiary: ◦ Alpha-helices and beta-sheets are folded into compact globule ◦ The folding is driven by non-specific hydrophobic interactions  Between non-polar side chains  Ex: Between 2 alkyl side chains in valine. These are attracted by van der Waals forces and create non-polar regions on the interior of the protein ◦ But the structure is stable only when protein parts are locked into place by specific tertiary interactions between the side groups (R groups) of each amino acid

 Tertiary: ◦ Specific interactions between R groups:  Disulfide bonding  Covalent bonds  strongest interactions  Ex: Form between S atoms in cysteine  Hydrogen bonding  Form between polar side chains  Ex: hydrogen bonding is between the R group in serine and aspartic acid  Ionic bonding  Form between charged side chains  Ex: (CH 2 ) 4 NH 3 + in lysine and CH 2 COO - in aspartic acid

 Quaternary: ◦ Multiple polypeptide chains join together ◦ Subunits are formed ◦ The quaternary structure is stabilized by same non-covalent interactions as tertiary structure  Hydrophobic interactions  Disulfide bonding  Hydrogen bonding  Ionic bonding ◦ Examples:  In hemoglobin, each of 4 subunits have heme group containing iron  Collagen has triple helix structure (3 chains of DNA) consisting of many subunits

TypeExampleFunction StructuralCollagenConnective tissue in skin/tendons MyosinControls contraction of muscles EnzymeLactase Breaks lactose into glucose and galactose through hydrolosis HormoneInsulinStores glucose as glycogen ImmunoproteinAntibodies Protect body from foreign substances (e.g. pathogens) TransportHemoglobinCarries oxygen from lung to cells Energy sourceCaseinProtein in milk

 structure.html structure.html  s/proteinstruct.html s/proteinstruct.html  Amino Acids. (n.d.). Lecture 27. Retrieved August 24, 2011, from  the acid base behaviour of amino acids. (n.d.).chemguide: helping you to understand Chemistry. Retrieved August 24, 2011, from