2.5 enzymes Flashcards
1
Q
what are enzymes?
A
- 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.
2
Q
why do enzymes possess high selectivity?
A
- arises from the shape and properties of the active site on the enzyme
3
Q
what are the 2 models / hypotheses put forward to explain how enzymes function?
A
- lock and key hypothesis
- induced fit hypothesis
4
Q
what is the lock and key hypothesis?
A
- 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
5
Q
what is the induced fit hypothesis?
A
- 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
6
Q
how do enzymes work?
A
- enzyme available with empty active site
- substrate binds to enzyme with induced fit
- substrate is converted to products
- products are released
7
Q
how does enzyme catalysis occur?
A
- 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)
8
Q
what 3 factors affect the rate of activity of enzymes?
A
- temperature
- pH
- substrate concentration
9
Q
how does temperature affect rate of activity of enzymes?
A
- 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
10
Q
how does pH affect rate of enzyme activity?
A
- 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
11
Q
how does substrate concentration affect rate of enzyme activity?
A
- 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
12
Q
what is denaturation and how does it occur?
A
- 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
13
Q
how and why are enzymes immobilised?
A
- 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
14
Q
what are some common uses of immobilised enzymes in industrial use?
A
- 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
15
Q
what are the advantages of lactose-free milk?
A
- 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
