IB biology: topic 2: enzymes

what are enzymes?

biological catalysts / globular proteins / speed up the rate of breakdown of substrates

what are enzymes specific to?

their substrate

what is enzyme-substrate specificity?

The shapes of the enzyme and substrate and their chemical properties are complementary, to allow the substrate to fit into the active site..

how many enzymes in the body? why?

thousands are needed in the body due to enzyme substrate specificity - each substrate has its own enzyme

what conditions are required for an enzyme-substrate complex to form?

1. substrates collide at random with the enzyme's active site

2. collision at correct orientation and speed.

why may unsuccessful collisions occur?

• when the molecules are not correctly aligned with each other at the moment of collision.

• molecules 'bounce' off each other and no reaction takes place.

what is the specificity of an enzyme dependent on?

the complementary nature between the shape of the active site on the enzyme and its substrate(s)

what is the shape of the active site determined by?

the complex 3D shape of the protein that makes up the enzyme:

• proteins formed from chains of amino acids.

• order of amino acids in this chain determines the shape of an enzyme.

• if the order is altered, the resulting three-dimensional shape changes.

a change to the amino acid order results in…

3D shape of protein/enzyme changing

are enzyme reactions catabolic or anabolic?

enzyme reactions can either be catabolic or anabolic

what is an example of a catabolic enzyme reaction?

cellular respiration and hydrolysis reactions

what is a catabolic enzyme reaction?

the breakdown of complex molecules into simpler products, which happens when a single substrate is drawn into the active site and broken apart into two or more distinct molecules

what is an example of an anabolic enzyme reaction?

protein synthesis and photosynthesis

what is an anabolic enzyme reaction?

the building of more complex molecules from simpler ones when two or more substrates are held in the active site, forming bonds between them and releasing a single product

what factors affect enzyme activity?

Temperature, pH and substrate concentration

what is temperatures effect on enzyme activity?

enzymes have a specific optimum temperature, the temperature at which they catalyse reactions at maximum rate.

lower temperature on enzyme reactivity?

lower temperatures prevent reactions from proceeding or slow them down:

• molecules move slower.

• lower frequency of successful collisions.

• less frequent enzyme-substrate complex formation.

• substrate and enzyme collide with less energy, making it less likely for bonds to be formed or broken.

higher temperature on enzyme reactivity?

higher temperatures speed up reactions:

• molecules move quicker.

• higher frequency successful collisions.

• more frequent enzyme-substrate complex formation.

• substrate and enzyme collide with more energy, making it more likely for bonds to be formed or broken (allowing the reaction to occur).

what happens if temperature is too high?

the rate at which an enzyme catalyses a reaction drops sharply, as the enzyme begins to denature,

hydrogen bonds holding enzyme together start to break,

active site changes shape.

how does pH affect enzyme activity?

each enzyme has an optimum pH:

• extremes of pH can alter hydrogen bonding within an enzyme's structure and cause irreversible denaturation.

• e.g stomach enzyme pepsin is adapted to work best at pH 2.

how does changing substrate concentration affect enzyme activity?

more substrate molecules present = increase in frequency of collisions with the enzyme's active site:

• the more active sites are occupied, the fewer are available to catalyse other substrate molecules.

• as substrate concentration rises, the slower the rise in the rate of the enzyme-catalysed reaction.

• the active sites have become saturated.

what happens when active sites are saturated?

at the point of active site saturation, increasing the substrate concentration will cause no further increase in the rate of reaction.

a method of increasing the rate of reaction would be to make more active sites available by increasing the enzyme concentration.

what happens to enzymes active site when denatured?

• bonds (e.g hydrogen bonds) holding the enzyme molecule in its precise 3D shape start to break.

• causes the 3-dimensional shape of the protein (ie. the enzyme) to change.

• this permanently damages the active site, preventing the substrate from binding.

• denaturation has occurred if the substrate can no longer bind

what might be observed when an enzyme denatures?

denaturation often causes the enzyme to become insoluble and form a precipitate

what is an immobilised enzyme?

an enzyme that is attached to an insoluble material to prevent mixing with the product and through this method, the enzyme can be reused in subsequent reactions

what are examples of immobilised enzyme uses in industry?

Agriculture

Manufacturing processes

Energy generation

Environmental management

Food/drinks industry

Medicines

how can enzymes be immobilised?

Attachment to an inert substance eg. glass

Entrapment within a matrix e.g. alginate gel

Entrapment within a partially permeable membrane

how do immobilised enzymes work?

• the immobilised enzymes are contained within a column.

• substrate is filtered through this column in solution.

• as the substrate runs through the column, enzyme-substrate complexes are formed and products are produced.

• these products then flow out of the column, leaving the enzymes behind to catalyse the reaction again.

what are advantages of immobilised enzymes?

• no enzyme in the product (the product is uncontaminated).

• immobilised enzyme can be reused multiple times which is both efficient and cost-effective.

• immobilised enzymes have a greater tolerance of temperature and pH changes.

• conditions can be controlled carefully, allowing immobilised enzymes to function close to their optimum conditions and be more stable.

what are disadvantages of immobilised enzymes?

• specialist expensive equipment is required.

• immobilised enzymes are more costly to buy, so are unlikely to be financially worthwhile for smaller industries.

• rate of reaction is sometimes lower when using immobilised enzymes as the enzymes cannot mix freely with the substrate.

hoe can lactose free milk be created using immobilised enzymes?

milk passed through column with immobilised lactase in, breaks down lactose (disaccharide) into glucose and galatcose (monosaccharides).

benefit = glucose + galactose sweeter than lactose so less sugar needed to be added!