Test: Chemistry - 10 - MCAT MCQ

The quaternary structure of a protein refers to the arrangement and interactions of multiple polypeptide chains (subunits) to form a functional protein complex. It is stabilized by various forces, including hydrogen bonding, hydrophobic interactions, and disulfide bonds.

Zwitterions are molecules that possess both a positive and a negative charge within the same molecule. They are often observed in amino acids and other molecules that can act as both acids and bases.

Glutamic acid is classified as an acidic amino acid. It has a carboxyl group (COOH) in its side chain, which can ionize and donate a proton, resulting in a negatively charged carboxylate ion.

An alpha-helix has a planar, rigid structure where the polypeptide chain forms a right-handed helical coil. The hydrogen bonds occur between the carbonyl oxygen of one amino acid and the amino hydrogen of an amino acid four residues down the chain.

Essential amino acids cannot be synthesized by the human body and must be obtained from the diet. Histidine is one of the nine essential amino acids required for protein synthesis.

Enantiomers are stereoisomers that are non-superimposable mirror images of each other. They have the same connectivity of atoms but differ in their spatial arrangement, specifically at chiral centers.

The secondary structure of proteins is primarily determined by the hydrogen bonding between the carbonyl oxygen of one amino acid and the amino hydrogen of another amino acid along the polypeptide backbone, which is facilitated by the peptide bonds.

Disulfide bonds, formed between the sulfur atoms of cysteine residues, contribute to the stabilization of the quaternary structure of proteins. They are covalent bonds that hold different polypeptide subunits together.

An achiral molecule is one that possesses an internal plane of symmetry, which allows it to be superimposable on its mirror image. It does not exhibit optical activity.

Hemoglobin is an example of a protein with a quaternary structure. It is composed of four subunits (two alpha chains and two beta chains) that interact to form the functional protein.

Chiral centers are carbon atoms that are bonded to four different groups. They are responsible for the generation of stereoisomers, including enantiomers, which are non-superimposable mirror images of each other.

Lysine is classified as a basic amino acid due to the presence of an amino group (NH₂) in its side chain. It can accept protons and become positively charged at physiological pH.

Myoglobin is an example of a protein with a tertiary structure. It consists of a single polypeptide chain folded into a specific three-dimensional conformation, which is critical for its function as an oxygen-binding protein.

Peptide bonds are strong covalent bonds formed between the carboxyl group of one amino acid and the amino group of another amino acid. They are stable and resistant to hydrolysis under physiological conditions.

Hydrophobic interactions play a significant role in the folding and stabilization of the tertiary structure of proteins. Nonpolar amino acid side chains tend to cluster together in the protein's interior to minimize contact with water.