Metabolism and Enzymes, practice questions

B, Anabolism builds large molecules and needs energy; catabolism, digestion and respiration all break molecules down.

B, An enzyme is a protein that acts as a biological catalyst, lowering activation energy and remaining unchanged.

C, The substrate fits the active site, whose shape is complementary to it, forming an enzyme-substrate complex.

B, Excess heat changes the shape of the active site, denaturing the enzyme so the substrate no longer fits.

B, Once every active site is occupied at any moment, the enzyme is the limiting factor and the rate cannot rise further.

C, Enzyme names usually end in '-ase' and are built from the substrate; amylase acts on starch (amylum).

B, Pepsin works in the acidic stomach and has a low optimum pH; trypsin works in the mildly alkaline small intestine.

B, Protease and lipase are most active near body temperature, so the wash is effective without a high temperature.

B, An immobilised enzyme can be recovered and reused and is easily separated from the product, lowering cost.

C, Amylase acts on starch; protease acts on protein and lipase on lipids, so only option C is correctly matched.

• (a) The enzyme is most active at its optimum temperature, 40 degrees C.
• (b) As temperature rises from 10 degrees C to 40 degrees C, the enzyme and substrate molecules gain kinetic energy and move faster.
• They collide more often, so more enzyme-substrate complexes form each second and the rate rises.
• (c) Above 40 degrees C the heat changes the shape of the enzyme's active site.
• The substrate no longer fits the active site, so enzyme-substrate complexes cannot form.
• The enzyme is denatured and the change is permanent, so the rate falls to zero.

• (a) As substrate concentration rises, the rate increases at first because more substrate molecules collide with the active sites, forming more complexes each second.
• The rate then levels off into a plateau.
• This is because every active site is occupied at any moment, so the enzyme becomes the limiting factor and more substrate has no further effect.
• (b) As enzyme concentration rises with substrate in excess, the rate increases because more active sites are available for the substrate.
• The rate keeps rising as long as substrate remains in excess.
• Once substrate becomes the limiting factor, adding more enzyme no longer raises the rate.

• (a) Protease removes protein-based stains such as blood or egg.
• Lipase removes fat-based (lipid) stains.
• (b) The enzymes are most active around body temperature, so the detergent cleans effectively at a lower washing temperature, which also saves energy.
• (c) An immobilised enzyme is fixed onto or trapped within an inert support such as alginate beads rather than being free in solution.
• One advantage is that it can be recovered and reused repeatedly, which lowers cost, or that the product is easily separated from the enzyme and not contaminated by it.

Anabolism builds large molecules from small ones (uses energy); catabolism breaks large molecules down (releases energy).

Enzymes are proteins that speed up reactions without being used up, and are specific to one substrate.

A substrate fits the enzyme's active site like a key in a lock, forming an enzyme-substrate complex.

Rate rises to an optimum (around body temperature) then falls sharply as the enzyme denatures at high temperature.

Each enzyme has an optimum pH; away from it the rate drops, and extreme pH denatures the enzyme.

Enzymes are used in detergents, food processing, brewing and medicine.

As substrate concentration increases, the rate of reaction increases because more substrate molecules collide with the available active sites; beyond a certain point the rate plateaus because every active site is already occupied at any moment.

As enzyme concentration increases, with excess substrate present, the rate of reaction increases because there are more active sites available; the rate eventually levels off once substrate becomes the limiting factor instead.

Most enzyme names end in '-ase' and are built from the substrate they act on or the reaction they catalyse, such as amylase for starch, protease for protein and lipase for fat.

Biological detergents contain protease and lipase to remove protein and fat stains at lower washing temperatures; the food industry uses enzymes such as pectinase to clarify fruit juice and rennin in cheese-making.

An enzyme is a globular protein folded into a precise three-dimensional shape; the active site is a small region of this shape whose contours and chemical groups are complementary to one specific substrate.

Enzymes can be fixed onto or within an inert support, such as alginate beads, so they can be reused repeatedly and easily separated from the product, which is common in industrial applications like producing lactose-free milk.

Rate of reaction can be found by dividing the change in the amount of product or substrate by the time taken, or by finding the gradient of the steepest part of a graph of amount against time.