Biochemistry - Amino acids, Peptides and Proteins

Which of the following statements is CORRECT regarding the R-groups in α-helix structures of polypeptides?

• It extends outward from the central axis to avoid interfering sterically with each other.

• It is located in the interior of the helix to stabilize the structure.

• It forms hydrogen bonds with the backbone of the polypeptide chain.

• It is always hydrophobic in nature.

Myoglobin contains eight α helices, one of which has the following amino acid sequences: -Gln-Gly-Ala-Met-Asn-Lys-Ala-Leu-Glu-His-Phe-Arg-Lys-Asp-Ile-Ala-Ala- (c) Briefly explain the side chains which are likely to be found in the interior of the protein?

• The hydrophilic side chains of asparagine, lysine, and glutamic acid.

• The hydrophobic side chains of glycine, alanine, methionine, leucine, phenylalanine, and isoleucine.

• The charged side chains of arginine, lysine, and histidine.

• The polar side chains of serine, threonine, and cysteine.

In an amino acid zwitterion, the carboxylate end is ______________.

• negatively charged

• positively charged

• neutral

• hydrophobic

A polypeptide can be either generated in vitro (under laboratory conditions) or in vivo (in a living cell). However, the tertiary protein molecules formed in vitro are usually insoluble. On the other hand, the same protein formed in vivo is naturally soluble in the cell. Briefly explain this situation.

• A polypeptide formed in a living cell has a sequence optimized by natural selection for proper folding, while a synthetic peptide with random sequence cannot direct coherent folding.

• Polypeptides formed in vitro are always soluble due to controlled conditions in the laboratory.

• Proteins formed in vivo are less stable than those formed in vitro, leading to better solubility.

• The solubility of polypeptides is unrelated to their formation conditions, as all proteins are soluble regardless of the environment.

In this oligopeptide: Ser-Cys-Ala-Gly, the amino acid on the C-terminal end is ________________.

• serine

• cysteine

• glycine

• alanine

Briefly describe the changes (eg. bond formation, broken bond, etc.) when collagen molecules are heated up for the production of gelatin.

• Chemical bonds between side chains are broken. The covalent bonds like peptide bonds are retained.

• All bonds, including peptide bonds, are broken completely.

• Only hydrogen bonds are formed, while covalent bonds remain intact.

• No changes occur in the molecular structure of collagen.

Myoglobin contains eight α helices, one of which has the following amino acid sequences: -Gln-Gly-Ala-Met-Asn-Lys-Ala-Leu-Glu-His-Phe-Arg-Lys-Asp-Ile-Ala-Ala- (a) Show the direction in which this polypeptide expands.

• ----->

• <-----

• -----<

• >-----

Which of the following amino acids form cystine?

• A. Alanine

• B. Cysteines

• C. Glycine

• D. Serine

Define peptide bond.

• The bond formed between two amino acids when the amino group of one reacts with the carboxyl group of another.

• A type of bond that allows free rotation between amino acids in a protein chain.

• A bond that only exists in the cis configuration between amino acids.

• A bond that is formed by the interaction of two side chains of amino acids.

Myoglobin contains eight α helices, one of which has the following amino acid sequences: -Gln-Gly-Ala-Met-Asn-Lys-Ala-Leu-Glu-His-Phe-Arg-Lys-Asp-Ile-Ala-Ala- (b) What are the functional groups of Lys and Ala that are involved in peptide bond formation?

• Lysine: carboxyl group (-COOH), Alanine: amino group (−NH2)

• Lysine: amino group (−NH2), Alanine: carboxyl group (-COOH)

• Lysine: hydroxyl group (-OH), Alanine: amino group (−NH2)

• Lysine: carboxyl group (-COOH), Alanine: hydroxyl group (-OH)