Ch 8: An Intro to Metabolism
2016
Chapter 8: Metabolism
From Topic 2.1
Understandings:
• Metabolism is the web of all the enzyme-catalysed reactions in a cell or
organism.
From Topic 8.1
Understandings:
• Enzymes lower the activation energy of the chemical reactions
that they catalyse.
• Enzyme inhibitors can be competitive or non-competitive.
From Topic 2.5
• Metabolic pathways can be controlled by end-product inhibition.
Essential idea: Enzymes control the metabolism of the cell.
• Metabolic pathways consist of chains and cycles of enzymeFrom Topic 2.5
catalysed reactions.
Nature of science: Experimental design—accurate, quantitative measurements Applications and skills:
in enzyme experiments require replicates to ensure reliability. (3.2)
• Application: Use of databases to identify potential new antiUnderstandings:
malarial drugs.
• Enzymes have an active site to which specific substrates bind.
• Application: End-product inhibition of the pathway that converts
• Enzyme catalysis involves molecular motion and the collision of substrates
threonine to isoleucine.
with the active site.
• Skill: Calculating and plotting rates of reaction from raw
• Temperature, pH and substrate concentration affect the rate of activity of
experimental results.
enzymes.
• Skill: Distinguishing different types of inhibition from graphs at
• Enzymes can be denatured.
specified substrate concentration.
• Immobilized enzymes are widely used in industry.
Guidance:
Applications and skills:
• Application: Methods of production of lactose-free milk and its advantages. • Enzyme inhibition should be studied using one specific example
for competitive and non-competitive inhibition.
• Skill: Design of experiments to test the effect of temperature, pH and
Utilization:
substrate concentration on the activity of enzymes.
• Many enzyme inhibitors have been used in medicine. For
• Skill: Experimental investigation of a factor affecting enzyme activity
example ethanol has been used to act as a competitive inhibitor
(Practical 3).
Guidance:
for antifreeze poisoning.
• Lactase can be immobilized in alginate beads and experiments can then be
• Fomepizole, which is an inhibitor of alcohol dehydrogenase, has
carried out in which the lactose in milk is hydrolysed.
also been used for antifreeze poisoning.
• Students should be able to sketch graphs to show the expected effects of
Aims:
temperature, pH and substrate concentration on the activity of enzymes.
• Aim 6: Experiments on enzyme inhibition can be performed.
They should be able to explain the patterns or trends apparent in these
• Aim 7: Computer simulations on enzyme action including
graphs.
metabolic inhibition are available.
Utilization:
• Enzymes are extensively used in industry for the production of items from
fruit juice to washing powder.
Chapter 8: Metabolism
From Topic 6.1 (further discussed in Digestion Mini-Unit of HL 1)
Understandings:
• The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the
gut.
• The pancreas secretes enzymes into the lumen of the small intestine.
• Enzymes digest most macromolecules in food into monomers in the small intestine.
Utilization:
• Some hydrolytic enzymes have economic importance, for example amylase in production of sugars from starch and in the
brewing of beer.
Guidance:
• Students should know that amylase, lipase and an endopeptidase are secreted by the pancreas. The name trypsin and the
method used to activate it are not required.
Free Energy (G)
• Unstable systems have a lot free energy (G) and have a tendency to change
spontaneously to a more stable state. Cells can then use this release of energy
for cellular work.
Free Energy (G)
• Exergonic
• Endergonic
Activation Energy EA
• Enzyme help lower the Activation Energy of chemical reaction;
thus speeding the process
- Energy of activation (activation energy or EA)= amount of
energy that reactant molecules need to absorb to start a
reaction.
http://www.sumanasinc.com/webcontent/animations/content/enzymes/enzymes.html
EA – Reaching the Transition State
• In order for reactants A+B and C+D to be converted to products, they must
absorb enough energy from their surroundings (pass the EA) to reach the
unstable transition state, where bonds can become unstable and can reform.
Q: Based on this graph, is it an exergonic or
endergonic reaction?
Catalysts
• Catalyst: chemical agent that accelerates a reaction without
being permanently changed in the process.
• Enzymes: are biological catalysts.
- Are proteins.
- Lower activation energy.
- Do not change the nature of the reaction but only speed it up.
- Are very selective
- Can continue their function after a reaction.
Enzymes
• Enzymes are substrate
specific.
• Substrate: the substance
an enzyme acts on.
• Place where enzyme
binds to substrate is
called the active site.
• Usually a pocket or groove
on protein’s surface.
• Formed with only a few of
the enzymes amino acids
(charged etc…)
• Determines specificity.
• Changes shape in response
to substrate.
How Enzymes lower EA
Active site hold two or more reactants in
proper position.
Induced fit may distort bonds making it
easier.
Active site provides proper
microenvironment.
Amino acids may play a direct role in
reaction.
Enzyme Function, pg153
Induced Fit
Rates of Reaction
• The higher the substrate concentration the higher the rate of
reaction up to a certain point.
• Enzymes become saturated at a point.
• Then it depends on how fast the reaction happens.
• The rate of reaction can increase if more enzyme is added
up to a point.
Environmental Factors
1) Temperature: each has an
optimal temperature.
(Mostly between 35-40⁰C).
- Enzymatic activity
increases with temp up
to a certain point.
2) Ph: amount of charge (H+)
in the environment.
3) Salt Concentration: Na+
and Cl- (charged ions)
Environmental Factors Cont.
•
Changes in temperature, pH, and salt concentration
can lead to an enzyme losing its confirmation (shape)
leading to denaturation.
- too hot breaks the bonds within a protein
- charges in H+, Na+, or Cl- can disrupt the bonds
within the protein
Factors affecting Enzymes Graphs
Effect of Temperature
Factors affecting Enzymes Graphs
Effect of pH
Factors affecting Enzymes Graphs
Effect of Substrate
Concentration
Designing an Experiment
Designing an Experiment
Designing an Experiment
Designing an Experiment
Designing an Experiment
Enzyme Inhibitors
• Can be reversible or irreversible.
• Competitive inhibitors: compete
for active site.
Ex. Sulpha drugs.
• Non-competitive inhibitors : don’t
bind to active site.
Ex: Metals, antibiotics, DDT or another
molecule in the metabolic pathway.
http://www.wiley.com/college/pratt/0471393878/student/animations/enzyme_inhibition/
Competitive Inhibition Example
• Sulpha drugs contain
sulfonamide group.
• Act as an competitive
inhibitor to DHPS, which is
an enzyme responsible for
folic acid biosynthesis. Folic
acid is a vitamin needed to
make nucleotides and
amino acids.
• Sulpha drugs are used as
antibiotics to inhibit
bacteria’s ability to make
DNA/RNA and amino acids.
Noncompetitive Inhibition Example
• Isoleucine an
amino acid that
acts as a
noncompetitive
inhibitor to
threonine
deaminase.
• Stopping its own
metabolic
pathway.
Inhibition Graphs
Controlling Metabolism w/ Enzymes
•
Allosteric regulation: activation, inhibition,
or cooperativity.
• Allosteric site: specific site on enzyme other
than active site.
• Allosteric regulator: bind to allosteric site
and can either activate or inhibit the
enzyme activity.
-
•
Activation: turns on the enzyme
Inhibition: turns off the enzyme
Cooperativity- a type of activation; binding
of the substrate may enhance the enzymes
function.
Feedback inhibition: a metabolic pathway
in which it is turned off with its own endproduct; the product attaches to an
enzyme in an earlier reaction
http://bcs.whfreeman.com/thelifewire/content/chp06/0602002.html
http://programs.northlandcollege.edu/biology/Biology1111/animations/enzyme.html
Allosteric Control
http://content.bfwpub.com/webroot_p
ubcontent/Content/BCS_4/Hillis1e/Ani
mated%20Tutorials/at0303/pol_0303.
swf
Feedback Inhibition: Noncompetitive
http://highered.mcgrawhill.com/sites/0072943696/stude
nt_view0/chapter2/animation__f
eedback_inhibition_of_biochemi
cal_pathways.html