Download Enzymes continued

Enzymes continued
• Some enzymes work together to complete a
series of reactions to produce a given product:
Enzyme 1
Enzyme 2
Enzyme 3
• A + B ------- C ------- D ------------ E
• Collectively, these steps are known as a
metabolic pathway
A metabolic pathway
The entire set of all chemical reactions
being performed by an organism is
called its metabolism
• Anabolism = chemical reactions that
expend energy to make or transform
chemical bonds
• Catabolism = chemical reactions that
harvest energy by breaking chemical bonds
Anabolism involves
endergonic reactions
Catabolism involves
exergonic reactions
Control of Metabolism
• Coenzymes
• Inhibitors
• Allosteric regulation
• Feedback Inhibition
• Cooperativity
Coenzymes
• Coenzymes are bound at the active site in order to
interact with the substrate and play an essential role
in the catalysed reaction.
• They act as carriers of a variety of chemical groups.
.
Most water-soluble vitamins are
components of coenzymes
Vitamin
Thiamine (B1)
Riboflavin (B2)
Nicotinic acid
(niacine)
Coenzyme
Deficiency
Thiamine
Beriberi (weight
pyrophosphate loss,other problems
Mouth lesions,
FAD+
dermatitis
Pellagra (dermatitis,
+
NAD
depression)
Pantohtinic acid
Coenzyme A
Hypertension
Biotin
Biotin
Rash, muscle pain
Inhibitors
• Specific for an enzyme
• Can be reversible or non-reversible
• Competitive inhibitors
• Non-competitive inhibitors
Competitive vs. Non-competitive inhibitors
Many inhibitors are used as
pesticides or drugs
Regulating the rates of enzymedriven reactions
• Cells use inhibitors and activators to turn
off and on enzymes
• Many enzymes are controlled by an
allosteric site remote from the active site
Allosteric regulation of enzyme activity
Many allosterically controlled enzymse show
quaternary structure
Feedback inhibition
Many enzymes are actually regulated by
the end products of the reaction they
catalyze
Enzyme 1
Start of
pathway
X
Enzyme 2
Intermediate
Intermediate
Enzyme 3
Product
Presence of product inhibits enzyme 1
This prevents too much product from
being made
An example of Feedback inhibition