Ch 8: An Intro to Metabolism
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 2.5
Essential idea: Enzymes control the metabolism of the cell. From Topic 2.5
Nature of science: Experimental design—accurate, quantitative measurements
in enzyme experiments require replicates to ensure reliability. (3.2)
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.
• Immobilized enzymes are widely used in industry.
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).
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.
Utilization:
• Enzymes are extensively used in industry for the production of items from fruit juice to washing powder.
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.
• Metabolic pathways can be controlled by end-product inhibition. • Metabolic pathways consist of chains and cycles of
enzyme-catalysed reactions.
Applications and skills:
• Application: Use of databases to identify potential new anti-malarial drugs.
• Application: End-product inhibition of the pathway that converts threonine to isoleucine.
• Skill: Calculating and plotting rates of reaction from raw experimental results.
• Skill: Distinguishing different types of inhibition from graphs at specified substrate concentration.
Guidance:
• Enzyme inhibition should be studied using one specific example for competitive and non-competitive inhibition.
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.
Aims:
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:
Free Energy (G)
Free Energy (G)
•
Exergonic
Activation Energy E
A
•
Enzyme help lower the Activation Energy of chemical reaction;
thus speeding the process
-
Energy of activation (activation energy or E
A
)= amount of
energy that reactant molecules need to absorb to start a
reaction.
E
A
– 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 E
A
) to reach the
unstable transition state, where bonds can become unstable and can reform.
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
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.
How Enzymes lower E
A
Active site hold two or more reactants in
proper position.
Induced fit may distort bonds making it
easier.
Active site provides proper
microenvironment.
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.
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.
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
Factors affecting Enzymes Graphs
Factors affecting Enzymes Graphs
Factors affecting Enzymes Graphs
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.
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
Noncompetitive Inhibition Example
•
Isoleucine an
amino acid that
acts as a
noncompetitive
inhibitor to
threonine
deaminase.
•
Stopping its own
metabolic
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
end-product; the product attaches to an
enzyme in an earlier reaction
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