Proteins Structure and Function

Practice flashcards covering the structure, classification, properties, and levels of protein organization based on the lecture module.

Amino acids

The basic monomeric units of proteins consisting of a C-terminus/Carboxyl group, an N-terminus/Amino group, an $\alpha$-carbon, and an R side group.

$\alpha$-amino acid

An amino acid where the C-terminus, N-terminus, and R group are all connected to the $\alpha$-carbon.

Proteinogenic amino acids

The twenty-two (22) amino acids used in protein synthesis, twenty (20) of which are found in the genetic code.

Nonpolar, Neutral Amino Acids (Aliphatic)

A group of amino acids with mostly hydrocarbon R-groups, including Glycine (G), Alanine (A), Proline (P), Valine (V), Leucine (L), Methionine (M), and Isoleucine (I).

Nonpolar, Neutral Amino Acids (Aromatic)

Amino acids containing hydrocarbon aromatic R-groups: Phenylalanine (F) with a Benzyl group and Tryptophan (W) with an Indole group.

Polar, Neutral Amino Acids

Amino acids that are neutral at physiological pH ($6.9-7.4$), including Serine (S), Threonine (T), Cysteine (C), Asparagine (N), Glutamine (Q), and Tyrosine (Y).

Polar, Positively-Charged (Basic) Amino Acids

Amino acids having a positive charge at physiological pH ($6.9-7.4$), including Lysine (K), Arginine (R), and Histidine (H).

Polar, Negatively-Charged (Acidic) Amino Acids

Amino acids having a negative charge at physiological pH ($6.9-7.4$), specifically Aspartate (D) and Glutamate (E).

Essential Amino Acids

Amino acids necessary for growth and normal body functions that cannot be synthesized by the body and must be obtained through the diet.

L-Configuration

The stereoisomer configuration where the amino group is on the left side of the $\alpha$-carbon; all naturally occurring amino acids exist in this form.

Zwitterions

The form amino acids take in aqueous solution, where they possess both positive and negative charges and can act as both proton donors and acceptors.

Amphotericity

The ability of amino acids to act as both an acid and a base.

Isoelectric point (pI)

The specific pH at which the net ionic charge of the amino acid is zero.

Peptide bond

A covalent bond formed via a condensation reaction between the $-COO^{-}$ group of one amino acid and the $-NH_3^{+}$ group of another.

Residues

The term for individual amino acid units once they are joined together through peptide bonds.

Proteins

Biomolecules composed of one or more polypeptide chains with a molecular weight greater than $10,000\,kDa$.

Primary ($1^{\circ}$) Structure

The linear amino acid sequence of a protein held together by covalent peptide bonds, which dictates the protein's final structure and function.

Secondary ($2^{\circ}$) Structure

The local conformation of a polypeptide chain, such as the $\alpha$-helix or $$\beta$-sheet, stabilized by hydrogen bonds.

$\alpha$-Helix

A common secondary structure stabilized by internal hydrogen bonds between the N-terminus hydrogen and the C-terminus carbonyl, with all R groups oriented outward.

$\beta$-Pleated Sheet

A secondary structure where the polypeptide is extended into a zigzag, with hydrogen bonds formed between adjacent parallel or antiparallel segments.

Tertiary ($3^{\circ}$) Structure

The overall three-dimensional shape of a polypeptide resulting from folding, stabilized by intermolecular forces like disulfide bonds, ionic bonds, and hydrophobic interactions.

Fibrous Proteins

Water-insoluble proteins with high tensile strength that usually consist of a single repeating secondary structure, such as $\alpha$-keratin, collagen, and silk fibroin.

Globular Proteins

Spherical, water-soluble proteins where hydrophobic residues are buried inside (e.g., Albumin and Myoglobin), carrying out diverse biochemical reactions.

Quaternary ($4^{\circ}$) Structure

The level of structure in multisubunit proteins (multimers) consisting of multiple polypeptide chains stabilized by various intermolecular forces.

Hemoglobin

A quaternary oxygen-binding protein in erythrocytes consisting of four subunits (two $\alpha$ chains and two $\beta$ chains) and approximately 600 residues.

Protein Denaturation

The disruption of a protein's three-dimensional structure resulting in the loss of biological function, caused by physical agents (heat, UV) or chemical agents (pH, salts).

Protein Hydrolysis

A process that breaks peptide bonds using acids, bases, or enzymes, disrupting the primary structure and producing free amino acids or smaller peptides.