2.5 Enzymes

define: denaturation

structural change in the 3D confirmation of a protein, that results in loss of biological properties

describe effects of heat on protein structure

heat will cause a protein to denature above its optimum temperature -> due to increased vibrations within the protein, which break the intramolecular bonds that stablize its conformation -> changing its conformation

describe effects of deviation from optimum pH on protein structure

deviation from optimum pH will cause protein to denature -> due to gain/loss of hydrogen ions, which breaks the intramolecular bonds that stablize its conformation -> changing its conformation

define: enzyme

globular protein that acts as a catalyst

define: active site

region of surface of enzyme to which substrates bind and which catalyzes a chemical reaction involving that substrate

def: substrate

the substance that the enzyme converts into product(s)

def: metabolic pathway

chemical reaction that consists of chains and cycles of enzyme-catalyzed reactions

def: activation energy

def: activation energy

explain how enzymes increase the rate of chemical reactions (include a graph)

* enzymes increase the rate of chemical reactions by decreasing the activation energy required for the reaction


* they decrease the minimum amount of energy required for the reaction to occur/susbtrate are converted to products more readily
* as a result reactions can occur at lower temps/pressures than they would normally
* happen more quickly bc amount of energy required to bring about the reaction is reduced

summarize the steps in enzyme catalyzed reactions

* substrate collides with and binds to active site of enzyme forming the enzyme substrate complex
* forming enzyme substrate complex
* enzyme catalyze reaction involving that substrate, converting the substrate into products
* products are released from the active site, enzyme is unchanged and free to catalyze another reaction

outline the lock and key model

* enzymes and their active site have a specific 3D shape and chemical properties
* substrate also has specific 3D shape and chemical properties
* properties of substrate and active site match exactly
* molecules of substrate fit with the active site and are chemically attracted to it
* other substrates will not fit or are not attracted
* enzyme can only catalyze reactions involving that specific substrate

outline the induced fit model

* shape of active site is similar to the substrate but does not match it exactly
* once the substrate binds the shape of the active site changes to fit the substrate exactly
* the substrate induces the active site to change shape which weakens the bonds in the substrate in the process

why can enzymes be used again and again?

enzymes remain unchanged in the chemical reactions and once the products are released, the active site is available to catalzye another reaction

benefits of lactase in industry

* lactase intolerance high in some human populations
* lactase used to produce lactose-free milk
* lactase breaks down lactose to glucose and galactose
* source of lactase is usually yeast/bacteria
* milk passed over immobilised lactase
* increase sweetness of milk
* no need to add sugar

def: immobilized enzymes

enzyme that has been trapped in place and so cannot move, by attaching it to an insoluble surface/substance

method by which enzymes are immobilized

enzymes are trapped in tiny pores on bead of alginate

advantages of enzyme immobilization

* the beads (covered in enzymes) can be easily recovered and separated from the products of reaction, allowing them to be reused
* reduces the cost of obtaining new enzymes
* the enzymes can be quickly removed from the products to stop the reaction at the ideal time/prevent contamination
* substrates can be exposed to very high concentrations of enzymes compared to dissolved enzymes
* immobilized enzymes are also more resistant to high temperatures and pH

def: lactose

a disaccharide sugar naturally present in milk

reaction that enzyme lactase catalyzes

lactose -> glucose + galactose

def: lactose intolerance (2)

* lactose intolerance is high in some populations/some people suffer from lactose intolerance


* cannot drink regular milk as causes cramping/bloating/ gas

source of lactase in the production of lactose free milk

microorganisms such as yeast/bacteria

describe the process by which lactose-free milk is produced using immobilized enzymes

* lactase is immobilized in alginate beads or an insoluble surface
* milk is passed slowly over the beads
* converting the lactose into glucose and galactose

what is meant by optimum temperature and pH of in terms of enzymes

the temperature/pH at which the enzymes functions best, where the rate of the reaction it catalyzes is the highest

do all enzymes have the same optimum temperature and pH?

* enzymes may have different optimums depending on the conditions of the location/environment in which they can function
* for example, those in the human body have the same (similar) optimum temperatures (slightly higher than body temp) but different optimum pH depending in the body they are found

def: denaturation

change in the structure of an enzyme or other protein that results in the loss of it's function

draw and annotate graphs to explain the effect of temperature increase on enzyme activity

* at low temp, as temperature increases so does the rate of enzymes activity
* because enzyme and substrate particles gain kinetic energy/move more quickly
* collide more frequently/with greater force
* rate is fastest at optimum temperature
* after optimum, rate begins to decrease

draw and annotate a graph to explain the effect of changing pH of the following on enzyme

* enzyme activity at max at optimum pH
* change in pH (increase/decrease) causes a decrease in enzyme activity
* enzyme denature so can no longer bind to substrate
* due to distortion of tertiary structure by hydrogen ions

annotate a graph of the increase in substrate concentration (starting from 0) on the effect of enzyme activity

* from zero substrate, an increase in substrate concentration will increase rate of enzyme activity
* greater number of enzyme and substrate particles in the same volume/space
* means greater likelihood, more frequent collisions between them
* at a certain point the rate of increase will slow and begin to plateau
* because all the active sites are occupied so no more substrate can be catalyzed