IB BIO TOPIC 3.6 : ENZYMES

Question 1

What is an enzyme ?

Answer 1

A globular protein functioning as a biological catalyst, speeding up the reaction rates by lowering the activation energy.

Question 2

What is an active site ?

Answer 2

The site on the surface of an enzyme to which substrate(s) bind.

Question 3

Explain enzyme - substrate specificity :

Answer 3

1. Each globular enzyme includes an active site with a specific 3D shape which is complementary to the shape of the substrate.
2. The globular enzyme active site also includes a specific set of charges which are complementary to the charges of the substrate
3. Through complementarity of shape and charge the substrate is attracted to, and fits precisely into the active site.
4. the precise interactions between enzyme and active site and substrate are essential for the catalytic properties of an enzyme to function. The complementarity is often referred as the fit between lock and key.
5. Enzymes vary in specificity from being exclusive to a single substrate to being generalised to accept any molecule of a certain type.

Question 4

What are the 4 reasons why enzymes are altered by environmental conditions ?

Answer 4

1. • each enzyme has a highly specifically shaped active site which is complementary to the shape of its substrate; catalysis depends on this complementarity
   • the enzyme active site is a product of its tertiary, or three-dimensional structure, which is in turn produced by a variety of bonds: covalent, ionic, and hydrogen bonds, as well as hydrophobic interactions
   • each enzyme active site best fits its substrate at a set of optimum conditions
   • deviation from optimum conditions alter the bonds which produce the tertiary structure of the enzyme, thus altering the shape of the active site and its complementary fit to its substrate

Question 5

Explain the effects of the pH on enzymes :

Answer 5

• both acids and alkalis denature enzymes
• stomach pepsin is optimized at pH=2
• pancreatic lipase is optimized at pH=8

Question 6

Explain the effects of temperature on the enzymes :

Answer 6

• at lower temperatures, all chemical reactions proceed more slowly, with a general rule of doubling reaction rates with each 10 degrees Celcius increase
• at higher temperatures, the excessive energy breaks bonds that would otherwise create the shape of the active site; this denaturing the enzyme

Question 7

Explain the effect of the substrate concentration on the enzymes :

Answer 7

• at low to medium substrate concentrations, enzyme activity is directly proportional to substrate concentration; this is because random collisions between substrate and active site happen more frequently with higher substrate concentrations
• at high substrate concentrations, all the active sites of the enzymes are fully occupied, so raising the substrate concentration has no effect

Question 8

Define denaturation :

Answer 8

• a change in the structure of an enzyme so that it can no longer carry out its function

Question 9

Explain the use of lactase in the production of lactose free milk :

Answer 9

• lactose is the sugar that is naturally present in milk
• lactase is obtained by artificially culturing a fungus, Kluveromyces lactis
• the fungus grows naturally in milk where it uses lactase to hydrolyze lactose into glucose and galactose
• biotechnology companies culture the yeast, extract the lactase from the yeast, and purify it for sale to food manufacturing companies

Question 10

Explain the use of Lactase in food processing :

Answer 10

• some people are lactose-intolerant and cannot drink more than about 250 ml of milk per day, unless it is lactose-reduced
• galactose and glucose are sweeter than lactose, so less sugar needs to be added to sweet foods containing milk, such as milk shakes or fruit yoghurt
• lactose tends to crystallise during the production of ice cream, giving a gritty texture; because glucose and galactose are more soluble than lactose they remain dissolved, giving a smoother texture
• bacteria ferment glucose and galactose more quickly than lactose, so the production of yoghurt and cottage cheese is faster