AMINO ACIDS

CHARACTERISTICS OF PROTEIN

  • Most abundant substance in the cell next to water

  • All proteins contain C, H, O, N, and most have S

  • Proteins monomer unit is Amino Acid

  • Synthesis of enzymes, hormones, tissue repair and energy

  • Presence of nitrogen 15.4% sets them apart from lipids and carbohydrates.

Casein - Phosphorus (important for infants)

Haemoglobin- Iron (O2 transport)

Amino Acids - Building Blocks of Proteins

  • An amino acid contains both amino group (-NH2) and carboxyl Group (-COOH)

  • a - amino acid = amino and carboxyl groups are attached to a-carbon

  • B - amino acid = amino and carboxyl groups are attached to secondary carbon atoms

  • R group - side chains (distinguishes a - amino acids from each other)

  • Vary in size, charge, functional group, hydrogen bonding and chemical reactivity

FOUR CATEGORIES (OR CLASSIFICATION) ACCORDING TO SIDE CHAIN POLARITY

Nonpolar Amino Acids- (one (-NH2) AND (-COOH) + nonpolar side chain)

-These amino acids have hydrophobic side chains(when in protein), meaning they don't interact favorably with water.

-They tend to be buried within the interior of proteins away from the aqueous environment. (less contact w/ H2O)

  • Glycine

  • Aline

  • Valine

  • Leucine

  • Isoleucine

  • Proline

  • Phenylalanine

  • Methionine

  • Tryptophan

Polar, neutral amino acid(One (-NH2) & (-COOH) group + polar but neutral side chain)

- Polar amino acids have hydrophilic side chains, which means they interact readily with water molecules.

- can form hydrogen bonds with water and other polar molecules.

- often found on the surface of proteins, where they can interact with the surrounding solvent

there are 6 amino polar, neutral amino acids;

  • Serine

  • Cysteine

  • Threonine

  • Asparagine

  • Glutamine

  • Tyrosine

Polar acidic amino acid (one (-NH2) & two (-COOH) group, 2nd (-COOH) group part of the side chain;)

-capable of donating a proton (H+)

-As a result, they are negatively charged at physiological pH

there are 2 polar acidic amino acid

  • Aspartic Acid

  • Glutamic Acid

Polar Basic Amino Acid (two (-NH2 & ONE (-COOH) GROUP)

-Basic amino acids have an amino group (NH2) in their side chains,

-allowing them to accept protons (H+).

there are 3 polar basic amino acid

  • Histidine

  • Lysine

  • Arginine

ESSENTIAL AMINO ACIDS

Essential Amino acids - standard amino acids obtained from dietary sources, Body cannot synthesize it in adequate amounts

  • Complete Dietary Protein

    -contains all essential amino acids in a relative amount the body needs

    -may or may not contain all nonessential amino acid

  • Incomplete Dietary Protein

    -does not contain adequate amounts relative to the body

  • Limiting Amino Acid

    -is an essential amino acid that is missing, or present in inadequate amounts, in an incomplete dietary protein

Examples:

Protein from animal sources is usually a complete dietary protein Casein from milk and proteins found in meat, fish, and eggs except for gelatine Protein from plant sources are incomplete dietary protein except for soy

CHIRALITY OF AMINO ACIDS

  • Four different groups are attached to the a-carbon atom in all of the standard amino acids except glycine.

  • Proteins and Amino Acids are L-isomers by nature

  • Fischer Projection Rules a. b.-COOH put at the top; R group at the bottom

Acid- Base Properties of Amino Acids

  • Both an acidic group (-COOH) and a basic group (-NH the same carbon in an a-amino acid. 2) are present on

  • In a neutral solution, carboxyl groups have a tendency to lose protons (H+)

  • In a neutral solution, amino groups have a tendency to accept protons (H+

zwitterion - molecule that has a (+) charge on one atom & (-) charge on another atom, but which has no net charge

Isoelectric Points - pH at which an amino acid exists primarily in its zwitterion form

Cysteine - Chemically Unique Amino Acid

  • Contain sulfhydryl group (-SH group)

  • Dimerizes with another with cysteine to form cystine

  • Two cysteine residues linked by a disulfide bond