Amino Acids and Proteins

Enzymes – catalyze enzymatic reactions
Transport proteins – often present in membranes Nutrient/storage proteins – seeds, milk proteins, Fe storage
Contractile or motile proteins – actin, myosin, tubulin, flagella
Structural proteins – tendons, cartilage, cytoskeleton Defense proteins – antibodies, blood-clotting proteins, toxins
Regulatory proteins – hormones, transcription factors

Amino Acids- Monomer
Peptides- Polymer (joined by covalent bond

AAs are ionized in H2O at pH 7 and can act as either acids or bases

Aspartic and glutamic acids

Lysine
arginine- very basic because its positive charge is stabilized by resonance
histidine- these nitrogens have a relatively weak affinity for an H+ and are only partly positive at neutral pH.

Asparagine, glutamine, - although the amide N is not charged at neutral pH, its polar
serine, threonine, tryosine- the -OH is polar

Alanine, Valinem Leucine, isoleucine, proline, phenylalanine, methoinine, glycine, trptophan,cysteine.

Condensation or dehydration reaction-H20 is condensed or formed as a result of polymer formation
Hydrolysis reaction-H20 is split or hydrolyzed as a result of polymer dissociation

1o – linear sequence of amino acids
2o – basic arrangements that form over short regions e.g., α-helix, β-sheets, and turns
3o – 3D arrangement of secondary structure 4o – arrangement of multiple polypeptides

Sequence of amino acids
Number of different combinations
4 AA peptide 20 different AAs
204 = (20 X 20 X 20 X 20) =1.6 X105

Regular, reoccurring arrangements over short distances

3D arrangement of secondary structure

Electrostatic attraction, van der Waals attraction, hydrogen bond
Disulfide bonds help maintain protein structure