Quick questions on Food chemistry: biomolecules, enzymes and energy content: VCE Chemistry Unit 4

Vitamins are small organic molecules required in trace amounts. Two classes:

Enzymes are protein catalysts. Two models for substrate binding:

A bomb calorimeter burns a known mass of food sample in pure oxygen inside a sealed steel "bomb" surrounded by water. The temperature rise of the calorimeter is measured. The calorimeter is calibrated with a known electrical input (heater of known V, I, t) to give a calibration factor (CF) in J deg C^-1 or kJ deg C^-1.

Two models for substrate binding:

rate rises with T up to an optimum (typically around 37 deg C for human enzymes), then falls sharply as the enzyme denatures: the weak bonds holding the tertiary structure together break, the active site distorts, and the enzyme loses activity.

each enzyme has a pH optimum. Pepsin (stomach) optimum ~2; trypsin (small intestine) optimum ~8; salivary amylase optimum ~7. Outside the optimum range, the charge state of the active site residues changes, weakening substrate binding or catalysis.

rate increases with [S] until the enzyme is saturated, at which point the rate plateaus at V_max.

Explain why most enzymes denature above $50^{\circ}\text{C}$. [2 marks]

A $2.50 \, \text{g}$ sample of cheese is burned in a bomb calorimeter ($\text{CF} = 9.85 \, \text{kJ/}^{\circ}\text{C}$) giving $\Delta T = 10.5^{\circ}\text{C}$. (a) Calculate energy content in $\text{kJ/g}$. (b) Estimate fat content if carbohydrate and protein contributions are negligible.

Maltose, a disaccharide, hydrolyses to two glucose units. (a) Write the equation. (b) State the bond that breaks.