Chapter 8 (Exam 2) Flashcards
How can enzyme activity be modulated?
Temperature, pH, and specific molecules (inhibitors).
How is enzyme activity modulated?
Enzyme activity increases with temperature until the enzyme is denatured.
Explain how enzyme activity is modulated with tyrosinase?
The enzyme tyrosinase is involved in synthesizes of the pigment responsible for dark fur. It is inactive at normal body temperatures but functional at slightly lower temperatures. The extremities of a Siamese cat are cool enough for tyrosinase to gain function and produce pigment.
Why is temperature important?
Temperature of the environment is an important regulator of biochemical and biological activity in many organisms.
What do thermophilic archaea do?
They form an orange mat surrounded by yellow sulfurous deposits in a volcanic vent.
Proteins in these organisms have evolved to be very resistant to thermal denaturation.
These organisms can live at temperatures of 170 F or higher.
What pH do most enzymes have?
An optimal pH.
pH dependence of enzymes is due to the presence of ionizable R groups
What are zymogens?
Activation of inactive precursors by proteolytic cleavage.
Irreversbile Covalent Modification.
Some enzymes are synthesized in an inactive form and need to be activated by cleavage of some covalent bonds.
Inactive forms of enzymes are called zymogens.
What are examples of zymogens?
Enzymes from digestive system, such as trypsin and chymotrpsin.
What is enzyme inhibition?
Inhibitors are compounds that decrease an enzyme’s activity.
Irreversible inhibitors (inactivators).
Reversible inhibitors.
What are irreversible inhibitors?
Inactivators that react with the enzyme.
One inhibitor molecule can permanently shut off one enzyme molecule.
They are often powerful toxins but also may be used as drugs.
What are reversible inhibitors?
Bind to and can quickly dissociate from the enzyme.
Often structural analogs of substrates or products.
Often used as drugs to slow down a specific enzyme.
What can reversible inhibitors bind to?
The free enzyme and prevent the binding of the substrate.
The enzyme-substrate complex and prevent the reaction.
Can an enzyme be irreversibly inhibited?
Yes, by covalent modification of a crucial residue at the active site.
What are the types of reversible inhibitors?
Competitive inhibitor: Inhibitor resembles regular substrate; it binds at the active site.
Uncompetitive inhibitor: Inhibitor binds to the enzyme-substrate complex.
Noncompetitive inhibitor: Inhibitor binds to the regulatory site, not to the active site; it binds enzyme with or without substrate.
What happens to Vmax and Km during competitive inhibition?
No change in Vmax and Km increases.
Inhibition can be overcome by the amount of substrate.
