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27 Cards in this Set

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How does a cell regulate its metabolic pathways?
it does this by either switching on and off the genes that encode specific enzymes or by regulating the activity of enzymes once they're made.
Do molecules that naturally regulate enzyme activity in cell behave like noncompetitive inhibitors or competitive inhibitors?
noncompetitive inhibitors.
Can noncompetitive inhibitors form covalent bonds?
no. they build noncovalent interactions.
What is an allosteric regulation?
When a protein's function at one site is affected by the binding of a regulatory molecule to a separate site.
Does an allosteric regulation result in an inhibition or stimulation of an enzyme activity?
Either inhibition or stimulation.
True or False: Most enzymes known to be allosterically regulated are constructed from subunits with their own active site.
True.
True or False: An enzyme that is allosterically regulated may not change shapes.
False. It has two different shapes, one catalytically active and the other inactive. p. 157
On an enzyme that is allosterically regulated, what is a regulatory site (or allosteic site)?
the site in which an activating or inhibiting molecule binds.
What is an activator?
a regulatory molecule, that stabilizes the shape that has functional active sites.
What is an inhibitor?
a regulatory molecule that stabilizes the inactive form of the enzyme.
On an allosteric enzyme with four subunits, if one subunit changes form, do the others change form as well?
yes. A single activator or inhibitor molecule that binds to one regulatory site will affect the active sites of all subunits. p. 157
True or False: A substrate molecule binding to one active site may stimulate the catalytic powers of multisubunit enzyme by affecting the other active sites.
True. If an enzyme has two or more subunits, a substrate molecule causing induced fit in one subunit can trigger the same favorable shape change in all the other subunits of the enzyme.
What is cooperativity?
the mechanism that amplifies the response of enzymes to substrates: One substrate molecule primes and enzyme to accept additional substrate molecules more readily.
What is a classic example of cooperativity?
vertebrate oxygen transport protein hemoglobin.

p. 158
True or False: The good majority of metabolic enzymes are allosterically regulated.
False. Allosteric regulatory molecules are hard to characterize.
Why are allosterically regulated molecules hard to characterize?
because they tend to bind the enzyme at low affinity and are hard to isolate.
What are caspases?
protein-digesting enzymes that play a role in inflammation and cell death. p. 158 Figure 8.21
What is feedback inhibition?
A metabolic pathway switched off by the inhibitory binding of its end product to an enzyme that acts early in the pathway.
When ATP allosterically inhibits an enzyme in an ATP-generating pathway, what is the result?
feedback inhibition.
How many steps are there in feedback inhibition?
five
How is the amino acid isoleucine is synthesized from threonine?
through feedback inhibition. As isoleucine accumulates, it slows down its own synthesis by allosterically inhibiting the enzyme for the first step of the pathway. Feedback inhibition thereby prevents the cell from wasting chemical resources by making more isoleucine than necessary.
What does it mean when we say the cell is compartmentalized?
Cellular structure helps bring order to metabolic pathways.
What to multienzyme complexes do?
the arrangement facilitates the sequence of reactions with the product from the first enzyme becoming the substrate for the adjacent enzyme in the complex... etc until the product is released.
True or False: Some enzymes and enzyme complexes have fixed locations within the cell and act as a structural components of particular membranes.
True. p. 159
True or False: Enzymes do not exist in any membrane-enclosed eukaryotic organelle.
False. Some ar ein solution with specific membrane-enclosed eukaryotic organelles, each with its own internal chemical environment.
Where do the enzymes for cellular respiration lie?
in the mitochondria
How can an activator and an inhibitor have different effects on an allosterically regulated enzyme?
The activator binds in a way that it stabilizes the active form of an enzyme, and the inhibitor stbilizes the inactive form.