2.5 enzymes Flashcards
enzyme
a globular protein which acts as a biological catalyst by speeding up the rate of a chemical reaction
why are enzymes able to be reused?
Enzymes are not changed or consumed by the reactions they catalyse
substrate
the molecules the enzyme reacts with
active site
the region on the surface of the enzyme which binds to the substrate molecule
where do enzyme reactions typically occur?
in aqueous solutions
catalase
an enzyme found in the blood, and in most living cells, that catalyses the decomposition of hydrogen peroxide into water and oxygen.
denaturation
a structural change in a protein that alters its three-dimensional shape and causes the loss of its biological properties.
enzyme activity
a measure of the ability of an enzyme to catalyse a specific reaction.
hydrolysis
decomposition of a chemical compound by reaction with water.
lactase
the enzyme responsible for catalysing the split of lactose into galactose and glucose.
lactose
a disaccharide (C12H22O11) found in milk that may be hydrolysed to yield glucose and galactose.
membrane-bound
when an enzyme is fixed in its position
describe enzyme catalysis
- first requires that the substrate has close physical proximity with the active site
- When a substrate binds to the enzyme’s active site, an enzyme-substrate complex is formed
- the enzyme catalyses the conversion of the substrate into product, creating an enzyme-product complex
- The enzyme and product then dissociate – as the enzyme was not consumed, it can continue to catalyse further reactions
what does increasing the rate of enzyme catalysis accomplish?
improves the frequency of collisions b/w substrate and enzyme
2 ways to increase rate of enzyme catalysis
- Increasing the molecular motion of the particles (thermal energy)
- Increasing the concentration of particles (either substrate or enzyme concentrations)
how does denaturation affect the enzyme?
negatively affect the enzyme’s capacity to bind the substrate
what factors influence the rate of activity of an enzyme
Temperature, pH and substrate concentration
describe process of denaturation
- the shape and chemical properties of the active site are highly dependent on the tertiary structure of the enzyme
- the chemical bonds which are necessary to maintain the tertiary structure of the enzyme are disrupted
- enzyme cannot bind to substrate
draw graph of The Effect of Temperature on Enzyme Activity
see ipad
how does temperature affect enzyme activity?
- Low temperatures result in insufficient thermal energy for the activation of an enzyme-catalysed reaction to proceed
- Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity
how does pH affect enzyme activity?
- Changing the pH will alter the charge of the enzyme, which in turn will alter protein solubility and overall shape
- Changing the shape or charge of the active site will diminish its ability to bind the substrate, abrogating enzyme function
- Enzymes have an optimal pH (may differ between enzymes) and moving outside this range diminishes enzyme activity
how does substrate concentration affect enzyme activity?
- Increasing substrate concentration will increase the activity of a corresponding enzyme
- More substrates mean there is an increased chance of enzyme and substrate colliding and reacting within a given period
- After a certain point, the rate of activity will cease to rise regardless of any further increases in substrate levels
- This is because the environment is saturated with substrate and all enzymes are bound and reacting (Vmax)
immobilized enzymes
- have been fixed to a static surface in order to improve the efficiency of the catalysed reaction
- widely used in industry
in general, why are immobilized enzymes helpful?
- Enzyme concentrations are conserved as the enzyme is not dissolved – hence it can be retained for reuse
- Separation of the product is more easily achieved as the enzyme remains attached to the static surface
Common Industrial Uses of Enzymes
biocatalysis, food and beverage, animal feed, pharmaceuticals, biofuels, household items
draw the Breakdown of Lactose by the Enzyme Lactase
see ipad
how is lactose-free milk produced?
Lactose-free milk can be produced by treating the milk with the enzyme lactase
The enzyme lactase can be bound to alginate beads and immobilized. The beads are then packed in a container and milk is allowed to flow through it. Lactose is converted to glucose and galactose as it flows through the container with the immobilized enzymes. The solution leaving the container contains the products which are collected
Advantages of Lactose-Free Dairy Products
source of dairy for lactose-intolerant individuals
increases sweetness bc monosaccharides are sweeter tasting
reduces the crystallisation of ice-creams as monosaccharides are more soluble and thus less likely to crystalise
reduce production time for cheeses and yogurts (bacteria ferment monosaccharides more readily)
relationship b/w acidic substances (less than 7) and hydrogen?
donates hydrogen ions (i.e. high H+ concentration)
relationship b/w basic substances (more than 7) and hydrogen?
accept hydrogen ions (i.e. high OH– concentration)
2 models that describe enzyme-substrate reaction
The ‘lock and key’ model
The ‘induced fit’ model
lock and key model
According to the lock and key model, the enzyme’s active site complements the substrate precisely
The substrate fits a particular active site like a key fits into a particular lock
This theory of enzyme-substrate interaction explains how enzymes exhibit specificity for a particular substrate
induced fit model
According to the induced fit model, the enzyme’s active site is not a completely rigid fit for the substrate
Instead, the active site will undergo a conformational change when exposed to a substrate to improve binding
This theory of enzyme-substrate interactions has two advantages compared to the lock and key model:
It explains how enzymes may exhibit broad specificity (e.g. lipase can bind to a variety of lipids)
It explains how catalysis may occur (the conformational change stresses bonds in the substrate, increasing reactivity)
6 types of enzymes
hydrolase, isomerase, lyase, oxidoreductase, synthetases, transferase
reaction & examples of hydrolase enzymes
hydrolysis
- lipase, protease
reaction & examples of isomerase enzymes
rearrangement of atoms w/in a molecule
- phosphohexoisomerase
reaction & examples of lyase enzymes
splitting chemicals into smaller parts w/o using water
- decarboxylases, aldolases
reaction & examples of oxidoreductase enzymes
transfer electrons or hydrogen atoms from one molecule to another
- dehydrogenases, oxidases
reaction & examples of synthetase enzymes
joining of 2 molecules by the formation of new bonds
- DNA ligase, DNA polymerase
reaction & examples of transferase enzymes
moving a functional group from one molecule to another
- kinases, transaminases
draw graph of The Effect of pH on Enzyme Activity
see ipad
draw graph of The Effect of substrate concentration on Enzyme Activity
see ipad
advantages of enzyme-substrate specificity
- the specificity helps to control where a reaction takes place
- the specificity helps to control when reactions takes place
- the specificity helps to control which reactions should take place & prevents unnecessary reactions from taking place
activation energy
the minimum energy required for a reaction to occur. Enzymes lower the activation energy of a reaction.
