Biochemistry Protein Structure and Function 1 — Questions and Answers
Question 1: Which level of protein structure refers to the sequence of amino acids in a polypeptide chain?
- Primary structure (Correct answer)
- Secondary structure
- Tertiary structure
- Quaternary structure
Correct answer: Primary structure
Primary structure is the linear sequence of amino acids linked by peptide bonds, which ultimately determines all higher levels of protein structure.
Question 2: Alpha-helices and beta-pleated sheets are examples of which level of protein structure?
- Primary
- Secondary (Correct answer)
- Tertiary
- Quaternary
Correct answer: Secondary
Secondary structure describes local folding patterns stabilized by hydrogen bonds between backbone amide and carbonyl groups.
Question 3: Which bond is primarily responsible for maintaining the tertiary structure of a protein in an aqueous environment?
- Peptide bonds
- Ionic bonds only
- Hydrophobic interactions (Correct answer)
- Covalent disulfide bonds only
Correct answer: Hydrophobic interactions
Hydrophobic interactions drive the burial of nonpolar side chains in the protein core and are the dominant force in tertiary structure stabilization.
Question 4: Hemoglobin is an example of a protein with which level of structural organization?
- Primary
- Secondary
- Tertiary
- Quaternary (Correct answer)
Correct answer: Quaternary
Quaternary structure describes the assembly of two or more polypeptide subunits, as seen in hemoglobin's four globin chains.
Question 5: Which amino acid can form disulfide bonds that stabilize protein structure?
- Serine
- Threonine
- Cysteine (Correct answer)
- Methionine
Correct answer: Cysteine
Cysteine residues contain thiol (-SH) groups that can be oxidized to form covalent disulfide (-S-S-) bonds between chains or within a single chain.
Question 6: Protein denaturation by heat or chemicals disrupts all levels of structure EXCEPT which?
- Secondary
- Tertiary
- Quaternary
- Primary (Correct answer)
Correct answer: Primary
Denaturation disrupts non-covalent interactions and disulfide bonds but does not break the covalent peptide bonds that define primary structure.
Biochemistry Protein Structure and Function 1
Which level of protein structure refers to the sequence of amino acids in a polypeptide chain?