Transcript Slide 1

Tuesday, July 21, 2015
Unit 1: Enzymes and the digestive system
Title: Enzyme action
Keywords:
• activation energy
• lock and key model
Learning Objectives:
• induced fit model
We are learning….
• How do enzymes speed up chemical reactions?
• How does the structure of enzyme molecules relate
to their function?
• What is the lock and key model of enzyme action?
• What is the induced-fit model of enzyme action?
Starter:
Write down five things you know about enzymes.
What’s wrong with these statements?
1. Enzymes are biological catalysts which change the rate of
chemical reactions by increasing activation energy.
2. Enzymes are used up during reactions.
3. Enzymes are fibrous proteins made up of amino acids
joined by glycosidic bonds.
4. Each enzyme catalyses many different reactions.
5. Substrates bind with enzymes at the substrate site,
forming a product.
6. Catabolic enzymes build up molecules and anabolic
enzymes break larger molecules into smaller ones.
2.5 Enzymes
Essential idea:
Enzymes control the metabolism of the cell.
Nature of science:
• Experimental design—accurate, quantitative
measurements in enzyme experiments
require replicates to ensure reliability.
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
enzymes.
• Enzymes can be denatured.
2.5 Enzymes
Applications and skills:
• Application: Methods of production of
lactose-free milk and its advantages.
• Skill: Design of experiments to test the effect
of temperature, pH and substrate
concentration on the activity of enzymes.
• Skill: Experimental investigation of a factor
affecting enzyme activity. (Practical 3)
2.5 Enzymes
Guidance:
• Lactase can be immobilized in alginate
beads and experiments can then be carried
out in which the lactose in milk is hydrolysed.
• 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 apparent in these graphs.
2.5 Enzymes
Theory of knowledge:
• Development of some techniques benefits particular human
populations more than others. For example, the
development of lactose-free milk available in Europe and
North America would have greater benefit in Africa/ Asia
where lactose intolerance is more prevalent. The
development of techniques requires financial investment.
Should knowledge be shared when techniques developed
in one part of the world are more applicable in another?
Utilization:
• Enzymes are extensively used in industry for the production
of items from fruit juice to washing powder.
8.1 Metabolism
HL only
Essential idea:
Metabolic reactions are regulated in response to the
cell’s needs.
Nature of science:
Developments in scientific research follow
improvements in computing—developments in
bioinformatics, such as the interrogation of
databases, have facilitated research into metabolic
pathways.
8.1 Metabolism
HL only
Understandings:
• Metabolic pathways consist of chains and
cycles of enzyme-catalysed reactions.
• Enzymes lower the activation energy of the
chemical reactions that they catalyse.
• Enzyme inhibitors can be competitive or noncompetitive.
• Metabolic pathways can be controlled by
end-product inhibition.
8.1 Metabolism
HL only
Applications and skills:
• Application: End-product inhibition of the pathway
that converts threonine to isoleucine.
• Application: Use of databases to identify potential
new anti-malarial drugs.
• Skill: Calculating and plotting rates of reaction from
raw experimental results.
• Skill: Distinguishing different types of inhibition from
graphs at specified substrate concentration.
8.1 Metabolism
HL only
Guidance:
• Enzyme inhibition should be studied using
one specific example for competitive and
non-competitive inhibition.
8.1 Metabolism
HL only
Theory of knowledge:
• Many metabolic pathways have been described following a
series of carefully controlled and repeated experiments. To
what degree can looking at component parts give us
knowledge of the whole?
Utilization:
• Many enzyme inhibitors have been used in medicine. For
example ethanol has been used to act as a competitive
inhibitor for antifreeze poisoning.
• Fomepizole, which is an inhibitor of alcohol dehydrogenase,
has also been used for antifreeze poisoning.
8.1 Metabolism
HL only
Aims:
• Aim 6: Experiments on enzyme inhibition
can be performed.
• Aim 7: Computer simulations on enzyme
action including metabolic inhibition are
available.
Explain the diagram to the person next to you
Use these keywords to help you:
Substrate, active site, enzyme-substrate complex, reactants,
products, protein, pH, temperature, collisions, hydrolysis
What are enzymes?
Enzymes are biological catalysts.
They make chemical reactions go faster but don’t actually
take part in the reaction. They do this by reducing the
activation energy required to initiate the reaction.
What is activation energy?
HL only
Before any chemical reaction can proceed it must initially be
activated, i.e. its energy must be increased.
The energy required is called activation energy.
Once provided, the activation energy allows the products to
be formed.
How do enzymes lower activation energy?
HL only
Heat is often the source of activation energy and enzymes
often dispense with the need for this heat and so allow
reactions to take place at lower temperatures.
Enzymes provide a platform for the reactants of a reaction to
come together at the active site.
Without enzymes, more energy would be required in order for
reactants molecules to collide with one another.
When a chemical reaction involves two or more reactants,
the enzyme provides a site where the reactants are
positioned very close to each other and in an orientation that
facilitates the formation of new covalent bonds.
How do enzymes work?
Enzymes are globular proteins.
Proteins are made from chains of amino acids joined by
peptide bonds.
Each type of enzyme catalyses a specific reaction. The
important part of the enzyme is the active site. The
substrate fits into this part, and an enzyme-substrate
complex is formed.
How are the products of enzyme catalysed reactions
produced?
Once the substrate binds with the active site of the
enzyme and forms an enzyme-substrate complex, a
reaction occurs and the product is released, leaving the
enzyme free to process another substrate molecule.
Enzymes are able to process hundreds of molecules.
The lock and key model of enzyme action
Enzymes are highly specific in the reactions catalysed.
Some enzymes catalyse the transformation of one
particular type of substrate molecule or, at most, a very
restricted group of substrate molecules.
Some catalyse only one type of chemical change.
The specificity of enzymes is
due to the configuration of the
active site.
In the lock and key model, the
substrate is the ‘key’ that fits
exactly into the enzyme ‘lock’
The induced fit model of enzyme action
Evidence from protein chemistry suggests that a small
rearrangement of chemical groups occurs in both the
enzyme and the substrate molecules when the enzymesubstrate complex is formed. This is called induced fit.
The induced fit theory
can be compared
to a hand entering
a glove. The hand
will move slightly to
fit into the glove,
while the gloves’
shape will change
to accommodate
the hand.
Main activity: Using the mini white-boards and working
with a partner….
One person explains the induced-fit model of enzyme
action
The other person explains the lock and key model of
enzyme action.
Use diagrams and keywords from the lesson and
reference activation energy in your explanation.
Anabolic and catabolic enzymes
Anabolic enzymes facilitate reactions that take simple
molecules and join them together to form complex
molecules.
For example, glucose molecules go through a
condensation reaction forming many glycosidic bonds
between molecules and eventually forming the
polysaccharide starch.
Many enzymes are involved in this process, including
starch synthase.
Catabolic enzymes break larger molecules into smaller
ones. Amylase will hydrolyse the glycosidic bonds in a
starch molecule to produce glucose.
Main Activity:
Complete the worksheet ‘enzymes’
How successful were we this lesson?
Learning Objective
We were learning…..