2.5 enzymes

Question 1

what are enzymes?

Answer 1

• function as biological catalysts by lowering the activation energy needed for a reaction to begin,
• able to increase the rate of a reaction without being consumed by the reaction
• usually made of proteins, although some RNA molecules can function as enzymes.

Question 2

why do enzymes possess high selectivity?

Answer 2

• arises from the shape and properties of the active site on the enzyme

Question 3

what are the 2 models / hypotheses put forward to explain how enzymes function?

Answer 3

• lock and key hypothesis

- induced fit hypothesis

Question 4

what is the lock and key hypothesis?

Answer 4

• hypothesis is that the substrate will match the active site of the enzyme on two different levels
• structurally: substrate is of a shape that will fit into the active site, like a particular key for a particular lock
• chemically: existence of interactions at the molecular level (charged attraction, polar/non-polar interactions) that allows for an attraction between the active site and the substrate
• replaced by the induced fit hypothesis

Question 5

what is the induced fit hypothesis?

Answer 5

• if lock and key hypothesis is true, only one exact type of substrate can bind to a specific enzyme
• reality is that the active site did not start out being completely complimentary to the substrate chemically and structurally
• as substrate approaches the enzyme, the substrate induces a conformational change in structure of the enzyme, and the active site changes to fit the substrate
• different substrates can induce a fit in the same enzyme, but there remains a high level of specificity as only a few substrates can induce the enzyme to fit them

Question 6

how do enzymes work?

Answer 6

1. enzyme available with empty active site
2. substrate binds to enzyme with induced fit
3. substrate is converted to products
4. products are released

Question 7

how does enzyme catalysis occur?

Answer 7

• molecules in water will move about in a random fashion, as determined by the temperature
• hence random level of collision between a substrate molecule and the active site of an enzyme in the solution
• substrate may be at any angle to the active site when the collision occurs
• successful collisions are ones in which the substrate and active site happen to be correctly aligned to allow binding to take place (or more accurately to allow binding after a inducing the enzyme to fit)

Question 8

what 3 factors affect the rate of activity of enzymes?

Answer 8

• temperature
• pH
• substrate concentration

Question 9

how does temperature affect rate of activity of enzymes?

Answer 9

• affects the rate of movement of the substrate and enzyme molecules
• at higher temp, more heat energy present and the molecules are moving at a higher velocity
• increased rate of collision between the substrate and enzyme molecules
• however when temp increases beyond the optimum, bonds within the enzymes will start to break and the enzymes begins to denature
• results in structural changes in the enzyme so that the active site may no longer fit the substrate properly

Question 10

how does pH affect rate of enzyme activity?

Answer 10

• amino acids have different charges based on the pH
• when pH changes, the resultant change in charge can
  break some of the internal bonds within the enzyme
• results in a structural change of the enzyme, as the enzyme will be denatured at pH drastically different from the optimal pH
• leads to a change in shape of the active site which affects the level of successful binding of the substrate to the enzyme

Question 11

how does substrate concentration affect rate of enzyme activity?

Answer 11

• increasing substrate concentration increases the amount of substrate present per unit volume in the solution
• more substrate molecules are present to collide with enzymes, leading to an increased rate of reaction

Question 12

what is denaturation and how does it occur?

Answer 12

• almost all enzymes are made of proteins
• proteins maintain a particular 3 dimensional structure based on internal bonds formed between amino acids
• when such bonds are broken, the protein will assume a different shape, and this is known as denaturation

Question 13

how and why are enzymes immobilised?

Answer 13

• in industries, enzymes are usually immobilised by attaching them to glass surfaces or trapping them in gel beads
• efficient as enzyme can remain fixed in position while the substrate is brought to them
  • either in liquid agitated in a tank, or in a constant flow over the enzyme
• reduces chance that the enzymes are exposed to new substrate molecules, as enzymes are fixed in place and now randomly distributed in a large volume of solution
• enzymes can easily be removed as they are fixed in place, and recycled for the next batch of reaction

Question 14

what are some common uses of immobilised enzymes in industrial use?

Answer 14

• detergents containing enzymes to break down protein and fat stains
• enzymes used to digest starch and even cellulose that can be further fermented to produce biofuels like ethanol
• enzymes help to process fibres to polish cloth to make it shine
• enzymes used to break down and clarify beer in a brewery
• enzymes used to convert glucose into fructose which is a sugar and used in beverages like bubble tea
• enzymes used to process wood pulp in the production of paper
• enzymes used in diagnostic tests in the medical industry
• enzymes used to break down proteins in the cleaning of contact lenses

Question 15

what are the advantages of lactose-free milk?

Answer 15

• lactase is the enzyme that digests lactose to glucose and galactose
• when lactose is not properly digested, the products of digestion are not absorbed and lactose enters into the large intestines
• large intestines contain lots of bacteria that will feed on the lactose to produce a large amount of gas, and can lead to symptoms like abdominal pain and diarrhoea
• lactase production decreases with age, and some people may develop lactose-intolerance later as they grow older

Question 16

how is lactose-free milk produced?

Answer 16

• 1 way to reduce lactose content of milk is to turn the milk into yoghurt, where microorganisms feed on lactose and produce lactic acid which curds the milk
• possible to produce low lactose milk on an industrial scale:
• lactase extracted from a source like yeast or bacteria, and immobilised within alginate beads
• milk passed down repeatedly over a column containing such beads
• such milk tends to be sweeter as glucose and galactose is sweeter than lactose
• can also be more suitable to make ice-cream, as the product sugars are more soluble than lactose and will not easily crystallise when frozen