BB 450 Unit 3 questions with verified
solutions A+ graded
How do cells control the activity of an enzyme? - correct answer ✔✔1. Cells use ~Allosteric~ to
control enzyme activity by binding small molecules to the enzyme.
When this happens, it's not completely an on or off mechanism. Instead it just says how much
of the pool of that enzyme gets to be active at any given time.
2. Cells also control enzymes by covalent modifications * Breaking peptide bonds is usually an
activation of the enzyme
* Phosphorylation and dephosphorization are also covalent modifications (These can be
activating or not activating)
3. Controlling synthesis of an enzyme is another mechanism that makes sure that the cell is
allowing the right amount of enzyme to be active. AKA being transcribed, translated, or folded
properly
Whether an enzyme is present at all is clearly a way of controlling its levels
4. Activism can also activate enzymes and not just inactivate them.
How substrate affects enzyme binding
Compare the hyperbolic and sigmoidal plots. - correct answer ✔✔Hyperbolic: Tells us that the
substrate does not change enzyme binding of the substrate
Can read the Vmax and see the Vmax/2 relationship to Km
,Sigmoidal: Tells us that the substrate does change enzyme binding of the substrate. This effect is
allosterism
What are homotropic and heterotropic effectors? How do they differ? - correct answer ✔✔They
are both allosteric effectors:
Homotropic effector: Is both a substrate and has the ability to change the enzyme (regulatory
molecule). * Makes the sigmoidal curve, and is the control on the [S] vs. Reaction Velocity plot.
Heterotropic effector: Is NOT a substrate, it's just something that affects the enzyme. It could be
activating or inhibitory but it's not happening at the active site.
* ATP is an activator
* CTP is an inhibitor
In the case of ATCase: what are the roles of ATP and CTP? - correct answer ✔✔ATP: High Energy,
Purine
Acts as an activator, indicating that there's plenty of energy available
Stabilizes/Favors the R state which increases the reaction rate (shifts/increases the velocity).
CTP: End of Product Pathway (negative feedback)
When CTP is sensed it tells the cell to end the reaction of pyrimidines
Favors the T state, it is a heterotrophic effector and decreases V0
How can the cell tell if there are plentiful amino acids and nucleotides and energy? - correct
answer ✔✔If this reaction is occurring it means that the cell understands that there are enough
amino acids to go around and the energy status is good.
Therefore the cell can undergo DNA replication if it needs to.
,~ It knows this due to the presence of aspartate/aspartic acid ~
How can ATCase shut down pyrimidine synthesis? - correct answer ✔✔Reaction that requires
ATCase:
Starts w/ bicarbonate and then you end up w/ carbamoyl phosphate. Then the carbonyl
phosphate acts w/ ATCase to make carbamoyl aspartate.
What we need to make this whole reaction occur is phosphate, nitrogen, and energy.
As [S] increases, the ATCase goes from being mostly in the T state to mostly in the R state
It can shut down pyrimidine synthesis by being inhibited by CTP (which is a pyrimidine)
CTP creates a negative feedback loop. The large amounts of CTP tell our body that we probably
need more purines. So purine/ATP is what turns the self inhibition on
What is negative feedback? - correct answer ✔✔A response to a change in the body that
counteracts or opposes the initial change.
Negative feedback occurs to reduce the change or output: the result of a reaction is reduced to
bring the system back to a stable state.
Why is aspartate a homotropic effector of ATCase? What state is favored? - correct answer
✔✔Aspartate is a homotrophic effector because it both acts as a substrate and affects the
enzyme
Binding of aspartate favors the R state ---> That means that bc. it favors the R state additional
substrate binding is favored.
, (when aspartate is bound, then the enzyme will be in the R state)
What is a zymogen? Can you give some examples? - correct answer ✔✔Zymogens are...
Precursors of active enzymes, the enzyme is not active if in zymogenic form because you don't
necessarily want all your enzymes active at all times but you want them standing ready
Especially important in digestive enzymes or else it would chew up proteins they encounter that
look specific enough to them or when they're moving through the body btw organs you want
them to not be active.
Suffix: -ogen
Prefix: pro- or prepro -
Examples:
Proenteropeptidase ---> Enteropeptidase
Trypsogen ---> Trypsin
Proelastase ---> Elastase
Procarboxypeptidase ---> Carboxypetdidase
Chymotrypsinogen ---> Chymotrypsin
Prolipase ---> Lipase
Why would an enzyme be held in an inactive state? - correct answer ✔✔Protein digesting
enzymes are secreted in an inactive form to protect the organs and glands from digestion by the
enzymes.
So that the enzyme is not constantly active
* prevent any kind of reaction of the enzymes with other cells or tissues.
solutions A+ graded
How do cells control the activity of an enzyme? - correct answer ✔✔1. Cells use ~Allosteric~ to
control enzyme activity by binding small molecules to the enzyme.
When this happens, it's not completely an on or off mechanism. Instead it just says how much
of the pool of that enzyme gets to be active at any given time.
2. Cells also control enzymes by covalent modifications * Breaking peptide bonds is usually an
activation of the enzyme
* Phosphorylation and dephosphorization are also covalent modifications (These can be
activating or not activating)
3. Controlling synthesis of an enzyme is another mechanism that makes sure that the cell is
allowing the right amount of enzyme to be active. AKA being transcribed, translated, or folded
properly
Whether an enzyme is present at all is clearly a way of controlling its levels
4. Activism can also activate enzymes and not just inactivate them.
How substrate affects enzyme binding
Compare the hyperbolic and sigmoidal plots. - correct answer ✔✔Hyperbolic: Tells us that the
substrate does not change enzyme binding of the substrate
Can read the Vmax and see the Vmax/2 relationship to Km
,Sigmoidal: Tells us that the substrate does change enzyme binding of the substrate. This effect is
allosterism
What are homotropic and heterotropic effectors? How do they differ? - correct answer ✔✔They
are both allosteric effectors:
Homotropic effector: Is both a substrate and has the ability to change the enzyme (regulatory
molecule). * Makes the sigmoidal curve, and is the control on the [S] vs. Reaction Velocity plot.
Heterotropic effector: Is NOT a substrate, it's just something that affects the enzyme. It could be
activating or inhibitory but it's not happening at the active site.
* ATP is an activator
* CTP is an inhibitor
In the case of ATCase: what are the roles of ATP and CTP? - correct answer ✔✔ATP: High Energy,
Purine
Acts as an activator, indicating that there's plenty of energy available
Stabilizes/Favors the R state which increases the reaction rate (shifts/increases the velocity).
CTP: End of Product Pathway (negative feedback)
When CTP is sensed it tells the cell to end the reaction of pyrimidines
Favors the T state, it is a heterotrophic effector and decreases V0
How can the cell tell if there are plentiful amino acids and nucleotides and energy? - correct
answer ✔✔If this reaction is occurring it means that the cell understands that there are enough
amino acids to go around and the energy status is good.
Therefore the cell can undergo DNA replication if it needs to.
,~ It knows this due to the presence of aspartate/aspartic acid ~
How can ATCase shut down pyrimidine synthesis? - correct answer ✔✔Reaction that requires
ATCase:
Starts w/ bicarbonate and then you end up w/ carbamoyl phosphate. Then the carbonyl
phosphate acts w/ ATCase to make carbamoyl aspartate.
What we need to make this whole reaction occur is phosphate, nitrogen, and energy.
As [S] increases, the ATCase goes from being mostly in the T state to mostly in the R state
It can shut down pyrimidine synthesis by being inhibited by CTP (which is a pyrimidine)
CTP creates a negative feedback loop. The large amounts of CTP tell our body that we probably
need more purines. So purine/ATP is what turns the self inhibition on
What is negative feedback? - correct answer ✔✔A response to a change in the body that
counteracts or opposes the initial change.
Negative feedback occurs to reduce the change or output: the result of a reaction is reduced to
bring the system back to a stable state.
Why is aspartate a homotropic effector of ATCase? What state is favored? - correct answer
✔✔Aspartate is a homotrophic effector because it both acts as a substrate and affects the
enzyme
Binding of aspartate favors the R state ---> That means that bc. it favors the R state additional
substrate binding is favored.
, (when aspartate is bound, then the enzyme will be in the R state)
What is a zymogen? Can you give some examples? - correct answer ✔✔Zymogens are...
Precursors of active enzymes, the enzyme is not active if in zymogenic form because you don't
necessarily want all your enzymes active at all times but you want them standing ready
Especially important in digestive enzymes or else it would chew up proteins they encounter that
look specific enough to them or when they're moving through the body btw organs you want
them to not be active.
Suffix: -ogen
Prefix: pro- or prepro -
Examples:
Proenteropeptidase ---> Enteropeptidase
Trypsogen ---> Trypsin
Proelastase ---> Elastase
Procarboxypeptidase ---> Carboxypetdidase
Chymotrypsinogen ---> Chymotrypsin
Prolipase ---> Lipase
Why would an enzyme be held in an inactive state? - correct answer ✔✔Protein digesting
enzymes are secreted in an inactive form to protect the organs and glands from digestion by the
enzymes.
So that the enzyme is not constantly active
* prevent any kind of reaction of the enzymes with other cells or tissues.
