Hannah BarrecaDaria LukaszIan Reucroft

Roshelle BelferStephanie Puthumana

Amino Acids contain a central carbon chain with◦ An amino group NH2

◦ A carboxyl group COOH◦ A hydrogen◦ Side chain

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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 (-NH2) 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◦ NH3

+ 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◦ pHI

Buffer action◦ - COO¯ is proton acceptor: acts as base◦ NH3

+ is proton donor: acts as acid◦ Amino acids thus are amphiprotic and act as buffers,

depending on environment

http://www.ncbi.nlm.nih.gov/books/NBK28418

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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: http://dl.clackamas.edu/ch106-08/images/68025.jpg

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: (CH2)4NH3

+ in lysine and CH2COO- 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

Type Example Function

Structural Collagen Connective tissue in skin/tendons

Myosin Controls contraction of muscles

Enzyme Lactase Breaks lactose into glucose and galactose through hydrolosis

Hormone Insulin Stores glucose as glycogen

Immunoprotein Antibodies Protect body from foreign substances (e.g. pathogens)

Transport Hemoglobin Carries oxygen from lung to cells

Energy source Casein Protein in milk

http://themedicalbiochemistrypage.org/protein-structure.html

http://www.chemguide.co.uk/organicprops/aminoacids/proteinstruct.html

Amino Acids. (n.d.). Lecture 27. Retrieved August 24, 2011, from http://butane.chem.uiuc.edu/cyerkes/

the acid base behaviour of amino acids. (n.d.).chemguide: helping you to understand Chemistry. Retrieved August 24, 2011, from http://www.chemguide.co.uk/org