ACS CP ACS CP Biochemistry & Polymer Chemistry 1 — Questions and Answers
Question 1: Which type of bond is primarily responsible for the secondary structure (alpha-helix and beta-sheet) of proteins?
- Disulfide bonds
- Hydrogen bonds (Correct answer)
- Ionic bonds
- Van der Waals forces
Correct answer: Hydrogen bonds
Hydrogen bonds between the backbone amide NH and carbonyl C=O groups stabilize the alpha-helix and beta-sheet secondary structures in proteins.
Question 2: The Michaelis-Menten equation describes the relationship between:
- Enzyme inhibitor concentration and reaction rate
- Substrate concentration and initial reaction velocity for an enzyme-catalyzed reaction (Correct answer)
- Temperature and enzyme activity
- pH and enzyme denaturation
Correct answer: Substrate concentration and initial reaction velocity for an enzyme-catalyzed reaction
The Michaelis-Menten equation v = (Vmax[S])/(Km + [S]) relates the initial reaction velocity to substrate concentration, with Km as the substrate concentration at half-maximal velocity.
Question 3: Which polymer property describes the distribution of molecular weights in a polymer sample?
- Degree of polymerization
- Polydispersity index (PDI) (Correct answer)
- Glass transition temperature
- Crystallinity percentage
Correct answer: Polydispersity index (PDI)
The polydispersity index (PDI = Mw/Mn) describes the breadth of the molecular weight distribution; a PDI of 1.0 indicates a monodisperse (perfectly uniform) polymer.
Question 4: In step-growth polymerization, high molecular weight polymer is obtained only:
- At the very beginning of the reaction when monomer concentration is highest
- At very high conversions (>99%) of functional groups (Correct answer)
- When a large excess of one monomer is used
- When reaction temperature is kept below the ceiling temperature
Correct answer: At very high conversions (>99%) of functional groups
In step-growth polymerization, molecular weight increases slowly and high MW polymer is only achieved at very high monomer conversion (>99%), as described by the Carothers equation.
Question 5: The ATP hydrolysis reaction (ATP → ADP + Pi) releases approximately how much free energy under standard biological conditions?
- -7.3 kcal/mol (Correct answer)
- -14.6 kcal/mol
- -3.6 kcal/mol
- -20.0 kcal/mol
Correct answer: -7.3 kcal/mol
ATP hydrolysis releases approximately -7.3 kcal/mol (-30.5 kJ/mol) of free energy under standard conditions, making it the universal energy currency of cells.
Question 6: Which technique separates proteins based on their isoelectric point (pI)?
- SDS-PAGE
- Isoelectric focusing (IEF) (Correct answer)
- Size exclusion chromatography
- Affinity chromatography
Correct answer: Isoelectric focusing (IEF)
Isoelectric focusing separates proteins in a pH gradient gel based on their isoelectric point — the pH at which the protein carries no net charge and stops migrating.
ACS CP ACS CP Biochemistry & Polymer Chemistry 1
Which type of bond is primarily responsible for the secondary structure (alpha-helix and beta-sheet) of proteins?