Biology : Enzymes

Bacteria produce enzymes which cause food to decay. Explain how vinegar, which is acidic, can prevent the action of bacterial enzymes in some preserved foods.

(bacterial) active site/enzymes/proteins denatured / tertiary 3D structure disrupted/changed; (ionic) bonds broken; (reject peptide bonds) (ignore other bonds) no enzyme substrate complex formed / substrate no longer fits;

Explain how decreasing the pH affects carbohydrase activity.

(decrease in pH) increases H+ ions/protons; attach/attracted to amino acids; hydrogen/ionic bonds disrupted/broken; denatures enzyme / changes tertiary structure; changes shape/charge of active site; active site/enzyme unable to combine/fit with starch/enzyme-substrate complex no longer able to form; decreases rate of breakdown of starch/rate of reaction/carbohydrase activity;

Use your knowledge of protein structure to explain why enzymes are specific and may be affected by non-competitive inhibitors.

1 each enzyme/protein has specific primary structure / amino acid sequence; 2 folds in a particular way/ has particular tertiary structure; 3 active site with unique structure; 4 shape of active site complementary to/ will only fit that of substrate; 5 inhibitor fits at site on the enzyme other than active site; 6 determined by shape; 7 distorts active site; 8 so substrate will no longer fit / form enzyme-substrate complex;

Suggest a simple method by which you could find out whether an enzyme-catalysed reaction is being inhibited by a competitive or a non-competitive inhibitor.

Addition of extra substrate; Rate of reaction increased if competitive / no change if non-competitive;

Competitive and non-competitive inhibitors affect the activity of enzymes. Explain how.

Competitive inhibitor: 1 Inhibitor similar in shape to substrate; 2 Competes for active site / binds at active site; 3 Less substrate attaches / fewer enzyme-substrate complexes; Non-competitive inhibitor: 4 Inhibitor differs in shape to substrate; 5 Binds at position other than active site/ binds at allosteric site/inhibitor site; 6 Alters active site so substrate cannot bind / substrate attaches but no reaction/product;

'Lock and Key' theory (2)

Enzymes have an active site of specific shape (1); the substrate that is a complementary shape (1) binds the active site

Use your knowledge of the tertiary structure of enzymes to explain how a non-competitive inhibitor could reduce the rate of an enzyme controlled reaction.

Inhibitor is a different shape to substrate; Binds at position other than active site/allosteric site; Alters shape of active site; Substrate cannot bind/enzyme-substrate complex not formed;

Effect of changes in pH on enzyme activity

Ionic bonds holding tertiary structure break; active site distorts and substrate no longer BINDS TO ACTIVE SITE; charges on amino acids in active site affected; so FEWER E-S complexes form

What will happen when increasing substrate concentration

Substrate limiting factor As increase substrate concentration the enzymes active sites all become occupied Graph plateaus as rate of reaction rate constant enzyme is limiting factor

Describe and explain how an increase in temperature affects the rate of an enzyme controlled reaction.

Temperature Rate of reaction increases; Increasing temperature increases rate of movement of molecules/kinetic energy; Collide more often/substrate enters active site more often/more enzyme-substrate complexes formed; Up to optimum; Rate of reaction decreases; High temperatures cause denaturation/loss of tertiary structure/3D structure; By breaking specified bonds (not peptide bond); Active site altered/substrate cannot bind/fit/

Activation energy (2)

The minimum amount of energy required to bring particles into close contact (1); so that they will collide and react (1)

a. Use your knowledge of enzymes to explain i. Why the initial rate of reaction was highest at 55 °C; ii. The shape of the curve for 55 °C after 20 minutes. b. Explain why the curves for 27 °C and 37 °C level out at the same value

a.i. substances/molecules have more (kinetic) energy/moving faster; increased collisions / enzyme substrate complexes formed; ii. causes denaturation/tertiary structure/shape change; H+/ionic bonds break; (shape) of active site changed; substrate no longer binds/not complementary to (active site); b. all substrate changed into product / reaction is complete; same amount of product formed; same initial substrate concentration;

Explain how raising the temperature to 35 °C affects carbohydrase activity

increase in temperature increases kinetic energy; increases collisions (between enzyme/active site and substrate) /increases formation of enzyme/substrate complexes; increases rate of breakdown of starch /rate of reaction/carbohydrase activity;

Explain how methanol inhibits ethanol dehydrogenase.

similar in structure/shape/similar (chemical) group attach to active site; (reject same shape) competitive inhibition/competes for active site OR differ in structure/shape attach away from active site non-competitive inhibition/competing for active site

Explain how the shape of an enzyme molecule is related to its function.

specific 3D tertiary structure/shape; substrate complementary shape; (reject same shape) substrate (can bind) to active site/ can fit into each active site;

'Induced Fit' theory (2)

upon binding the active site of the enzyme moulds around the substrate (1) the active site becomes complementary (1)