Mcat Biochemistry Ch. 1 Amino Acids, Peptides, & Proteins

Amino acids with ionizable side chains have functional groups that can ionize and gain or lose a proton, leading to different charged forms.

Nonpolar amino acids do not contain a charge or hydrophilic groups. Aromatic amino acids have a ring structure that imparts unique properties. Glycine has only a hydrogen atom as its side chain, making it the simplest amino acid. The other nonpolar, nonaromatic amino acids listed lack polar functional groups in their side chains, contributing to their nonpolar nature.

Aromatic amino acids have a specific ring structure that gives them unique properties compared to other amino acids. Tryptophan, tyrosine, and phenylalanine possess this aromatic ring structure.

Polar amino acids have functional groups that interact with water molecules, making them hydrophilic. Serine, threonine, asparagine, glutamine, and cysteine are all examples of polar amino acids because they contain polar side chains or functional groups.

Lysine, Arginine, and Histidine are positively charged (basic) amino acids due to their structures containing basic amino groups. Glutamine, Alanine, and Phenylalanine do not possess positively charged amino groups and are therefore not considered basic amino acids.

Hydrophobic amino acids have nonpolar side chains that are repelled by water, causing them to be located in the interior of proteins.

Hydrophilic amino acids are characterized by charged side chains that interact well with water molecules, making them ideal for the surface of proteins where water is abundant. Amino acids with non-polar, aromatic, or sulfur-containing side chains would not fall under the classification of hydrophilic.

The primary structure of a protein is determined by the linear sequence of amino acids in a peptide, which is stabilized by peptide bonds. The other options provided do not accurately reflect the factors that determine and stabilize the primary structure of proteins.

The tertiary structure of a protein refers to the three-dimensional shape of a single polypeptide chain, which is essential for its proper function. This shape is stabilized by various interactions including hydrogen bonds, hydrophobic interactions, disulfide links, and acid-base interactions (salt bridges). Incorrect options describe other levels of protein structure or incorrect definitions.

The quaternary structure of a protein is primarily stabilized by the interaction between subunits, not by peptide bonds or van der Waals forces, glycosylation and phosphorylation modifications, or transcription and translation processes.

Hydrophobic interactions play a crucial role in determining the folding and structure of proteins by pushing hydrophilic amino acids towards the outer surface, interacting with water, while hydrophobic amino acids are sequestered in the interior of the protein away from the surrounding aqueous environment.

Conjugated proteins are proteins that have additional molecules covalently attached to them, known as Prosthetic Groups. These groups can be various types of molecules such as metal ions, vitamins, lipids, carbohydrates, or nucleic acids. This modification gives conjugated proteins additional functions beyond their primary structure.

A disulfide bond occurs when two cysteine molecules are oxidized to create a covalent bond to form cystine. This chemical bond is important in stabilizing protein structures.

Denaturation of proteins can occur due to various factors, but the most common ones are heat and solutes. Heat increases the average kinetic energy of proteins, disrupting the hydrophobic interactions. Solutes like urea can actively disrupt the bonds holding proteins together. The incorrect options do not directly contribute to denaturation in the same way as heat and solutes do.

The isoelectric point of a neutral amino acid is calculated by taking the average of the pKa values of the NH group and the COOH group.

The isoelectric point (pI) of a basic amino acid is calculated by taking the average of the pKa values of the NH group and the R group. This helps determine the pH at which the amino acid carries no net charge.

Alpha-helices are stabilized by intramolecular hydrogen bonds between a carbonyl oxygen atom and an amide hydrogen atom four residues down the chain. This secondary protein structure helps contribute to the overall folding and stability of the protein.

The correct answer describes the specific structure of β-pleated sheets involving peptide chains forming rows of strands held together by intramolecular hydrogen bonds.

Proteins are made up of primary, secondary, tertiary, and quaternary structures. Denaturation leads to the loss of the three-dimensional (tertiary) structure, rendering the protein inactive.