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Biochem MCAT > Enzyme Regulation > Flashcards

Enzyme Regulation Flashcards

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MCAT flashcards
1
Q

Why do enzymes need to be coordinate?

A

In order to work together properly. Activity must be controlled so the reaction happens at the right rate, right time, and the right amount.

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2
Q

What are the three types of enzyme regulation mechanisms?

A

Negative Feedback
Positive Feedback
Feed-Forward

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3
Q

What is the most common way that enzyme activity is regulated?

A

Negative Feedback. Also knows as feedback inhibition

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4
Q

How does Negative Feedback work?

A

It happens when downstream products make a previous step less likely to happen or less efficient. This is known as down-regulating.

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5
Q

How does Positive Feedback work?

A

It happens when downstream product makes previous step better at converting.

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6
Q

How does the Feed-Forward mechanism work?

A

It happens when an upstream compound makes a downstream enzyme better at converting downstream products.

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7
Q

What does it mean for something to be upstream in a metabolic pathway?

A

It describes earlier steps in a pathway (first steps)

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8
Q

What does it mean for something to be downstream in a metabolic pathway?

A

It describes later steps in a pathway (last steps)

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9
Q

What does the word feedback mean in enzyme regulation mechanisms?

A

It refers to when the downstream product of a pathway reaches backwards to regulate the upstream steps.

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10
Q

What is Negative Feedback good for?

A

It is good for maintaining homeostasis (balance within the body). It is extremely common in metabolism and is the default regulatory mechanism for any pathway you may encounter.

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11
Q

What is a popular example of Positive Feeback?

A

Oxytocin in labor and childbirth.
Oxytocin causes uterine contractions and uterine contractions cause more oxytocin to be released which make contractions stronger. The endpoint is childbirth.

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12
Q

What is an example of Positive Feedback that is also regulated by Negative Feedback?

A

Blood clot formation.

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13
Q

Can enzymes have multiple active sites for the same ligand?

A

Yes, because binding at one active site can make it easier to bind at another active site.

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14
Q

When speaking about enzymes, what does cooperativity mean?

A

It is the concept that it is hardest for an enzyme to bind its first ligand, and then it gets easier to bind the second.
Ex. How hemoglobin transports blood throughout the
body (first O2 molecule is hardest to bind)

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15
Q

What does partial pressure of O2 stand for?

A

Oxygen concentration in the blood

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16
Q

What does stronger cooperativity do to the curve on a graph.

A

It makes the curve greater (more s-like,sigmoidal)

17
Q

What does the Hill Coefficient tell us?

A

It tells us about an enzymes cooperativity with a substrate.

18
Q

What does it mean if the Hill Coefficient > 1 ?

A

There is positive cooperativity. The higher the coefficient the sharper the sigmoidal curve.

19
Q

What does it mean if the Hill Coefficient = 1 ?

A

There is no cooperativity

20
Q

What does it mean if the Hill Coefficient < 1 ?

A

There is negative cooperativity (binding the first substrate reduces the affinity for subsequent binding).

21
Q

What type of interactions are MOST enzyme-substrate interactions?

A

Non-covalent. Substrate is put in place by polarity and steric based interactions.

22
Q

What is an example of an enzyme regulation that involves making covalent modification?

A

Phosphorylation - catalyzed by kinases
Attaching a phosphate group to a protein affects the activity of the enzyme. Phosphorylation targets Serine, Threonine, and Tyrosine (In order of probability). These all have a hydroxyl (-OH) group.

23
Q

What does cleavage do?

A

Breaks covalent bonds.

24
Q

Where is the enzyme trypsin produced?

A

The pancreas.

25
Q

What are Zymogens?

A

Inactive precursor forms of enzymes. Usually end in -ogen.

26
Q

Are any covalent bonds formed between an enzyme and its substrate as the substrate enters the active site?

A

No

27
Q

What are cofactors?

A

Another chemical compound that enzymes require to be present in order for the enzyme to function.

28
Q

What are organic cofactors called?

A

Coenzymes

29
Q

What are some examples of inorganic cofactors?

A

Metal ions including:
Mg2+
Zn2+
Cu2+

30
Q

What do multivitamins contain?

A

Many cofactors and coenzymes.

31
Q

Describe coenzymes. How do they usually contribute to the function of enzymes?

A

They are often vitamins or vitamin derivatives. They often contribute to the function of enzymes by carrying functional groups from one place to another in a reaction.

32
Q

What is a popular coenzyme? What does it do?

A 
Coenzyme A (CoA)
This coenzyme transfers acyl groups from one place to another.
33
Q

What are Prosthetic Groups? What is an example?

A

They are coenzymes that are tightly or covalently bonded to their enzymes.
Ex. Heme, which contains an iron ion in the center of a
porphyrin ring and attached to hemo an myoglobin

34
Q

What is a Haloenzyme?

A

Enzyme with the whole set of substances needed for it to be functional.

35
Q

What is an Apoenzyme?

A

Enzyme without the cofactors needed to function properly.

36
Q

Is FAD a coenzyme?

A

Yes

37
Q

Describe allosteric regulation.

A

It involves change in the 3D structure of an enzyme. An allosteric activator binds noncovalently to an allosteric site on an enzyme, which promotes a conformational shift that increases or decreases the enzyme’s affinity for its substrate.

38
Q

Can phosphorylation and cleavage only occur with enzymes?

A

No, they can occur with other proteins as well.

39
Q

What are covalent modification a subset of?

A

Subset of post-translational modifications of proteins.

Biochem MCAT (7 decks)

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