2.5 enzymes
TRANSCRIPT
2.5: Enzymes
Understandings• Enzymes have an active site to
which specific substrates bind. • Enzyme catalysis involves
molecular motion and the collision of substrates with the active site.
• Temperature, pH, and substrate concentration affect the rate of activity of the enzymes.
• Enzymes can be denatured.• Immobilized enzymes are
widely used in industry.
Applications and Skills• A: methods of production
of lactose free milk and its advantages.
• S: Design of experiments to test the effect of temperature, pH, and substrate concentration on the activity of enzymes.
• S: Experimental investigation of a factor affecting enzyme activity.
Guidance:- Lactase can be immobilized in alginate beads, and experiments can be
carried out in which the lactose is hydrolyzed.- Students should be able to sketch graphs to show the expected effects of
temperature, pH, and substrate concentration on the activity of enzymes. They should be able to explain the patterns or trends of these graphs.
EnzymesEnzymes are molecules that act as catalysts to speed up biological reactions.
The compound on which an enzyme acts is the substrate.
Enzymes can break a single structure into smaller components or join two or more substrate molecules together.
Most enzymes are proteins.
Many fruits contain enzymes that are used in commercial processes. Pineapple (Ananas comosus, right) contains the enzyme papain which is used in meat tenderization processes and also medically as an anti-inflammatory agent.
Enzyme ExamplesEnzyme Role
PepsinStomach enzyme used to break
protein down into peptides. Works at very acidic pH (1.5).
ProteasesDigestive enzymes which act on proteins in the digestive
system
AmylasesA family of enzymes which assist in the breakdown of
carbohydrates
Lipases A family of enzymes which breakdown lipids3D molecular structures for the
enzymes pepsin (top) and hyaluronidase (bottom).
Enzymes are catalysts• All reactants need to have a certain energy before they will
react. This is like an energy barrier that it has to overcome before a reaction will occur. It is called the activation energy.
• All catalysts lower the energy barrier, allowing the reactants (substrates) to react faster forming the products.
• Enzymes do not participate in the reaction.
Enzymes have a specific region where the substrate binds and where catalysis occurs. This is called the active site.
Enzymes are substrate-specific, although specificity varies from enzyme to enzyme.
When a substrate binds to an enzyme’s active site, an enzyme-substrate complex is formed.
http://isite.lps.org/sputnam/biology/u4metabolism/activesite.gif
Changing the Active Site• Changes to the shape of the active site will result in a loss of
function. Enzymes are sensitive to various factors such as temperature & pH.
• When an enzyme has lost its characteristic 3D shape, it is said to be denatured. Some enzymes can regain their shape while in others, the changes are irreversible.
The Effect of Temperature on Enzyme Action• Speeds up all reactions,
but the rate of denaturation of enzymes also increases at higher temperatures.
• High temperatures break the bonds holding the tertiary structure of the enzyme together thus changing the shape of the enzyme.
• This destroys the active sites & therefore makes the enzyme non – functional.
http://www.bbc.co.uk/schools/gcsebitesize/science/images/add_edex_bio_temp-chart.jpg
The pH scale• Indicates the concentration
of H+ ions• Ranges from 0 – 14• pH of 7 is neutral• pH 0 up to 7 is acid … H+
• pH above 7 – 14 is basic… OH-
• Each pH unit represents a factor of 10X change in concentration
• pH 3 is 10 x 10 x 10 (1000) stronger than a pH of 6
The Effect of pH on Enzyme Action Like all proteins, enzymes are
denatured by extremes of pH (acidity/alkalinity).
The green curve is for pepsin that digests proteins in the stomach.
The red curve represents the activity of arginase that breaks down arginine to ornithine & urea in the liver.
The Effect of Enzyme Concentration on Enzyme Action• Assuming that the amount of substrate is not limiting, an increase in enzyme concentration causes an increase in the reaction rate.
The Effect of Substrate Concentration on Enzyme Action
• Assuming that the amount of enzyme is constant, an increase in substrate concentration causes a diminishing increase in the reaction rate.
• A maximum rate is obtained at a certain concentration of substrate when all enzymes are occupied substrate (the rate cannot increase any further).
http://www.rsc.org/Education/Teachers/Resources/cfb/images/07D.jpg
HomeworkVocab• Enzyme
SubstrateActive siteActivation energyDenaturedImmobilizedLactaselactose intolerantWild-type
Other• Exercises 12-14