Biochem enzyme regulation questions

feedback inhibition

The regulatory mechanism in which the final product inhibits activity of the first step.

isozymes

Multiple forms of homologous enzymes found within an organism.

zymogens

Enzymes activated by proteolytic cleavage.

T-state

The less active conformational form of an allosteric enzyme

sigmoidal

The shape of the kinetic plot of an enzyme that exhibits cooperative binding.

heterotropic

A type of regulator of an allosteric enzyme that is not a substrate.

protien kinases

The enzymes that catalyze protein phosphorylation.

protien phosphates

Removal of protein phosphates is catalyzed by these.

isozymes

_______________ are multiple forms of homologous enzymes within the same organism that catalyze the same reaction but with different kinetic properties.

p-Hydroxymercuribenzoate reacts with crucial ______________ residues in ATCase.

sulfhydryl

Blood serum analysis of ____________________________ isozymes is used in the diagnosis of a myocardial infarction.

lactate dehydrogenase (LDH)

ATP

____________ is the most common donor molecule in phosphorylation reactions catalyzed by protein kinases.

Protein kinase A is activated by binding ________________ to specific sites on the regulatory subunit.

AMP (cAMP)

zymogen

A ______________ is an inactive precursor of an enzyme that is activated by a proteolytic cleavage

What is the function of aspartate transcarbamoylase?

The enzyme catalyzes the first step in the synthesis of pyrimidines. It condenses carbamoyl phosphate and aspartate to form N-carbamoylaspartate and inorganic phosphate

Give several examples of enzymes and proteins that are activated by proteolytic activation.

Examples include digestive enzymes (trypsin), hormones (insulin), clotting enzymes(fibrinogen), developmental process proteins (collagen), and apoptosis proteins(caspases).

Why was it surprising to find that CTP inhibits ATCase?

The substrates for ATCase are carbamoyl phosphate and aspartate. These molecules do not resemble CTP. Thus, it was clear that the CTP must not bind to the active site, but to a distinct regulatory site.

Do allosteric enzymes follow traditional Michaelis-Menten kinetics?

No, ATCase displays different kinetics. A plot of rate versus substrate concentration is a sigmoidal curve, as opposed to the simple hyperbolic curve obtained by enzymes displaying Michaelis-Menten kinetics

How does the sequential model differ from the concerted model for allosteric enzymes?

The concerted model does not allow for anything other than an "all-or-none" complete tense- or relaxed-form protein. In contrast, the sequential model allows for a mixed type of protein, containing some tense and some relaxed subunits. The form is in response to the ligand binding by a particular subunit

Why is covalent modification advantageous when compared to proteolytic activation?

Covalent modification is usually a reversible process.

Phosphorylation is an extremely effective tool for catalytic control. Explain the reasons.

A phosphoryl group adds negative charges, allowing new electrostatic interactions and new hydrogen-bond formation. The free energy charge of phosphorylation is large, which can affect the conformational equilibrium of different states. Using ATP means that the reaction is linked to the energy status of the cell. Phosphorylation is rapid and reversible and can result in amplified effects. These factors affect structural, thermodynamic, regulatory, and kinetic properties

The most common strategy(ies) for enzymatic regulation:

multiple enzyme forms, allosteric control, reversible covalent modification, proteolytic activation

Allosteric proteins:

contain distinct regulatory sites and have multiple functional sites, and display cooperativity

Many allosteric enzymes have two types of subunits, termed:

catalytic and regulatory

What is PALA?

a bi-substrate analog that resembles the catalytic transition-state intermediate

The relaxed form of an allosteric enzyme has ________ affinity for the substrates.

higher

The regulatory effects of substrates on allosteric enzymes are referred to as _______________ effects.

homotropic

Examples of covalent modification include:

phosphorylation, dephosphorylation, acetylation, ubiquination

Which of the following is an example of a zymogen?

pepsinogen and procarboxypeptidase

The common activator of the pancreatic zymogens is:

trypsin

Is phosphorylation, allosteric control, proteolytic cleavage, and regulatory mechanisms readily reversible:

No

Explain the regulation mechanism for Protein Kinase A: (Also, briefly describe the role of this enzyme in the body)

PKA is a serine/threonine kinase that regulates metabolism, gene expression, and cell signaling. It mediates effects of cyclic AMP (cAMP)

In the body: metabolism, gene expression, cell growth and memory formation

Explain the regulation mechanism for ATC-ase: (Also, briefly describe the role of this enzyme in the body)

Aspartate transcarbamoylase (ATCase) is a classic example of an allosterically regulated enzyme and plays a central role in controlling the pyrimidine biosynthesis pathway

In the body: Catalyzes the first committed step in the synthesis of pyrimidine nucleotides