Chapter 3 MCAT Biology

MCAT BIOLOGY

Proteins

Macromolecules that function as enzymes, hormones, receptors, channels, transporters, antibodies, and support structures.

Amino Acid Structure

All 20 amino acids share a nitrogen-carbon-carbon backbone with a variable R group (sidechain).

Peptide Bonds

Link amino acids into polypeptides by forming bonds between carboxyl and alpha-amino groups, losing water.

Disulfide Bridges

Covalent bonds formed between cysteine R-groups that stabilize tertiary protein structure.

Residue

An individual amino acid in a polypeptide chain; the amino terminus is the first, and the carboxyl terminus is the last.

Proteolysis

The hydrolysis of proteins by proteolytic enzymes, resulting in the cleavage of peptide bonds.

Tertiary Structure

The three-dimensional structure of a protein formed by interactions between distantly located amino acid residues.

Quaternary Structure

The highest level of protein structure involving interactions between multiple polypeptide subunits.

Denaturation

The disruption of a protein's shape without breaking peptide bonds, often caused by extremes of pH, temperature, or salt concentration.

Glycosidic Linkage

A covalent bond formed between monosaccharides during the dehydration reaction to create disaccharides and polysaccharides.

Monosaccharide

A simple sugar with the general formula CnH2nOn.

Polysaccharides

Long chains of monosaccharides, such as glycogen (energy storage in animals) and cellulose (structural component in plants).

Fatty Acids

Long unsubstituted alkanes ending in a carboxylic acid, which can be saturated (no double bonds) or unsaturated (one or more double bonds).

Triglycerides

Composed of three fatty acids esterified to glycerol, serving as a major form of energy storage in fat cells.

Terpenes

Compounds made of isoprene units (C5H8) that can be linear or cyclic, including squalene and vitamin A.

Steroids

Hydrophobic compounds characterized by a tetracyclic ring system, including cholesterol and sex hormones like testosterone and estradiol.

Phosphoric Acid

An inorganic acid that can donate three protons and exists largely in anionic forms.

Nucleotides

The building blocks of nucleic acids (RNA and DNA), consisting of a sugar, a base, and one to three phosphate groups.

ATP

Adenosine triphosphate, a universal energy molecule that stores energy in its phosphoanhydride bonds for cellular processes.

Pyrophosphate

Formed by the anhydride linkage of two orthophosphates, containing high-energy phosphate bonds.