Free BACE Chemistry and Biochemistry Questions and Answers 3 — Questions and Answers
Question 1: What is a buffer in chemistry, and why are buffers critical in biotechnology applications?
- A buffer is a solution that resists changes in pH when small amounts of acid or base are added (Correct answer)
- A buffer is any solution used to dissolve biological molecules for storage
- A buffer is a concentrated salt solution used to prevent protein aggregation
- A buffer is a solution used to dilute samples before analytical measurements
Correct answer: A buffer is a solution that resists changes in pH when small amounts of acid or base are added
Buffers resist pH changes by containing a weak acid and its conjugate base in equilibrium; they are critical in biotechnology because enzymatic activity, protein stability, and cell viability are highly pH-dependent.
A buffer consists of a weak acid (HA) and its conjugate base (A-) in equilibrium. When acid is added, A- reacts with H+; when base is added, HA donates H+. Maximum buffering capacity occurs near the pKa. Common biotech buffers: Tris (pKa 8.1), HEPES (pKa 7.5), PBS (phosphate, pKa 7.2), citrate, acetate. Critical applications include cell culture media, enzyme assays, protein storage, and chromatography.
Question 2: What is the difference between substrate-level phosphorylation and oxidative phosphorylation?
- Substrate-level phosphorylation occurs in mitochondria; oxidative phosphorylation occurs in the cytoplasm
- Substrate-level phosphorylation directly transfers a phosphate group from a substrate to ADP; oxidative phosphorylation uses the proton gradient across the inner mitochondrial membrane to drive ATP synthase (Correct answer)
- Substrate-level phosphorylation requires oxygen; oxidative phosphorylation does not require oxygen
- Both terms describe the same process — synthesis of ATP from ADP and inorganic phosphate
Correct answer: Substrate-level phosphorylation directly transfers a phosphate group from a substrate to ADP; oxidative phosphorylation uses the proton gradient across the inner mitochondrial membrane to drive ATP synthase
Substrate-level phosphorylation directly phosphorylates ADP using a high-energy phosphate group from a metabolic intermediate; oxidative phosphorylation uses the proton gradient created by the electron transport chain to drive ATP synthase.
Substrate-level phosphorylation occurs in glycolysis (phosphoglycerate kinase and pyruvate kinase) and TCA cycle (succinyl-CoA synthetase). A high-energy phosphate is transferred directly from a metabolite to ADP. Oxidative phosphorylation uses NADH and FADH2 to pump protons across the inner mitochondrial membrane; the resulting electrochemical gradient drives protons through ATP synthase. About 90% of aerobic ATP comes from oxidative phosphorylation.
Question 3: What is the role of disulfide bonds in the structure of proteins like antibodies?
- Disulfide bonds provide energy for antibody-antigen binding interactions
- Disulfide bonds form covalent cross-links between cysteine residues that stabilize protein tertiary and quaternary structure (Correct answer)
- Disulfide bonds allow antibodies to flex and change conformation during cell signaling
- Disulfide bonds are required for glycosylation to occur in the Golgi apparatus
Correct answer: Disulfide bonds form covalent cross-links between cysteine residues that stabilize protein tertiary and quaternary structure
Disulfide bonds (S-S covalent bonds between cysteine thiol groups) covalently stabilize protein structure, linking separate polypeptide chains or stabilizing loops within a single chain.
Disulfide bonds form in the oxidizing environment of the ER during protein folding, catalyzed by protein disulfide isomerase (PDI). In IgG antibodies: inter-heavy chain disulfide bonds in the hinge region, inter-heavy-light chain disulfide bonds in each Fab, and intra-chain disulfide bonds within each Ig domain. These bonds maintain the domain topology essential for antigen binding. Proper disulfide bond formation is a key quality attribute monitored in biopharmaceutical manufacturing.
Question 4: In biochemistry, what is competitive inhibition of an enzyme?
- A molecule permanently inactivates the enzyme by covalently modifying the active site
- A molecule that resembles the substrate competes for binding at the active site reducing enzymatic activity but can be overcome by increasing substrate concentration (Correct answer)
- A molecule binds an allosteric site and changes enzyme conformation to reduce activity regardless of substrate concentration
- A molecule binds covalently to the active site only when substrate is also bound
Correct answer: A molecule that resembles the substrate competes for binding at the active site reducing enzymatic activity but can be overcome by increasing substrate concentration
A competitive inhibitor structurally resembles the substrate and competes for the active site; increasing substrate concentration outcompetes the inhibitor, restoring Vmax while Km appears increased.
Competitive inhibition: inhibitor and substrate compete for the active site. Kinetic effects: apparent Km increases (higher substrate concentration needed for half-Vmax), Vmax unchanged. High substrate concentration outcompetes inhibitor. Example: methotrexate competitively inhibits dihydrofolate reductase (DHFR). Non-competitive inhibition: inhibitor binds a separate allosteric site; Km unchanged, apparent Vmax decreases. Uncompetitive: inhibitor binds only the enzyme-substrate complex; both apparent Km and Vmax decrease.
Question 5: What is the difference between hydrophilic and hydrophobic amino acid residues in a protein and how does this affect protein folding?
- Hydrophilic residues carry a positive charge; hydrophobic residues carry a negative charge
- Hydrophilic residues interact favorably with water and are found on the protein surface; hydrophobic residues avoid water and pack into the protein interior during folding (Correct answer)
- Hydrophilic residues are found in alpha helices; hydrophobic residues are found in beta sheets
- Hydrophilic residues form disulfide bonds; hydrophobic residues form hydrogen bonds in the protein interior
Correct answer: Hydrophilic residues interact favorably with water and are found on the protein surface; hydrophobic residues avoid water and pack into the protein interior during folding
Hydrophobic residues with nonpolar side chains minimize contact with water by packing into the protein core; hydrophilic residues with polar or charged side chains interact favorably with water and face the exterior.
The hydrophobic effect is the primary driving force for protein folding. Nonpolar residues (Leu, Ile, Val, Phe, Met) favor the protein interior, reducing the entropically unfavorable ordering of water molecules around exposed nonpolar surfaces. Polar and charged residues are hydrophilic and cluster on the protein surface, interacting with solvent. Protein stability depends on the balance between hydrophobic packing, hydrogen bonds, ionic contacts, and disulfide bonds.
Question 6: What is a recombinant protein and how is it produced in biotechnology?
- A protein that has been chemically modified after extraction from its natural source
- A protein encoded by a gene that has been introduced into a host organism's DNA using recombinant DNA technology allowing production of specific proteins at scale (Correct answer)
- A protein produced by combining two naturally occurring proteins through chemical cross-linking
- A protein that forms naturally in response to DNA recombination during cell division
Correct answer: A protein encoded by a gene that has been introduced into a host organism's DNA using recombinant DNA technology allowing production of specific proteins at scale
Recombinant proteins are produced by cloning the gene of interest into an expression vector, transfecting or transforming a host cell (E. coli, CHO, yeast), and allowing the host to express and produce the protein.
Recombinant protein production steps: (1) clone gene into expression vector, (2) introduce vector into host cell, (3) select stably expressing cells, (4) optimize expression conditions, (5) harvest and purify protein. Common hosts: E. coli (fast, cheap, no glycosylation), yeast (can glycosylate), insect cells (complex folding), CHO/HEK293 (human-like glycosylation — preferred for therapeutics). Examples: insulin, erythropoietin, monoclonal antibodies, growth hormones.
Free BACE Chemistry and Biochemistry Questions and Answers 3
What is a buffer in chemistry, and why are buffers critical in biotechnology applications?