Biochem 6.2 Enzyme Regulation and Covalent Modifications

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Questions and Answers

What does reversible covalent modification refer to?

The permanent alteration of a protein's structure.

The thermodynamic reversibility of a single enzymatic reaction.

The ability to undo a covalent modification through a separate enzymatic reaction. (correct)

The modification of a protein that cannot be reversed.

Which of the following amino acids can be phosphorylated?

Methionine

Proline

Cysteine

Serine (correct)

What role does a kinase play in phosphorylation?

It hydrolyzes ATP to generate energy.

It adds phosphate groups to proteins. (correct)

It stabilizes protein structures.

It removes phosphate groups from proteins.

How is the phosphate group typically removed from a phosphorylated protein?

Through hydrolysis by a phosphatase enzyme. Signup and view all the answers

What is the primary thermodynamic characteristic of the kinase and phosphatase reactions?

Both reactions are thermodynamically irreversible when considered individually. Signup and view all the answers

What is the effect of phosphorylation on enzymes?

It can control the level of enzyme activity, depending on the enzyme modified. Signup and view all the answers

Which of the following is NOT a type of post-translational modification?

Vitamination Signup and view all the answers

What byproduct is generated during the removal of a phosphate group by phosphatase?

H2O Signup and view all the answers

What are zymogens specifically known for?

Being inactive proteins converted by cleavage Signup and view all the answers

Which of the following statements about pepsinogen is true?

It can self-activate through proteolytic cleavage. Signup and view all the answers

Which of the following is an example of a covalent modification that can regulate enzyme activity?

Zymogen activation Signup and view all the answers

What characterizes dynamic covalent modifications of enzymes?

They can be added and removed to regulate activity. Signup and view all the answers

How do irreversible inhibitors affect enzymes?

They covalently modify an individual enzyme molecule. Signup and view all the answers

Which of the following roles do zymogens play in biological systems?

They are synthesized in an inactive form for regulation. Signup and view all the answers

What results from the proteolytic cleavage of proinsulin?

It is converted into insulin, the active hormone. Signup and view all the answers

What is a key feature of most post-translational modifications?

They can irreversibly change enzyme activity. Signup and view all the answers

What is the primary result of a single activated Kinase A in the signal cascade?

It results in 100 molecules of active Kinase C. Signup and view all the answers

How do feedback or allosteric modulators differ from covalent modifications?

They require binding to the enzyme to exert their effect. Signup and view all the answers

What role do phosphatases play in overriding feedback inhibition during glycolysis?

They prevent the feedback inhibition caused by high ATP levels. Signup and view all the answers

Which of the following statements is true regarding dynamic covalent modifications of enzymes?

They can fine-tune the level of an enzyme's activity. Signup and view all the answers

What is the mechanism by which modulation is achieved in feedback regulation?

Through reversible binding of an effector. Signup and view all the answers

In the context of enzyme activity, how does the signal amplification affect cellular response?

It creates a rapid and increase in the number of active enzymes. Signup and view all the answers

Which statement accurately reflects the comparison between feedback modulation and covalent modification?

Covalent modification often leads to signal amplification. Signup and view all the answers

What effect does high ATP concentration typically have on glycolysis?

It inhibits the glycolytic process via feedback regulation. Signup and view all the answers

What is the effect of phosphorylation on glycogen synthase?

It deactivates glycogen synthase. Signup and view all the answers

How does phosphorylation affect enzyme activity mechanistically?

It induces a conformational change in the enzyme. Signup and view all the answers

What defines an enzyme being 'turned on'?

Its catalytic efficiency rises. Signup and view all the answers

Which statement about phosphorylation sites on enzymes is true?

Phosphorylation at different sites may have opposing effects. Signup and view all the answers

What advantage does covalent modification of enzymes provide?

It supplements and enhances other regulatory mechanisms. Signup and view all the answers

What occurs when glycogen phosphorylase is phosphorylated?

It activates the breakdown of glycogen to glucose. Signup and view all the answers

Which of the following enzymes would be classified as a kinase?

An enzyme that adds phosphate groups. Signup and view all the answers

How can covalent modification amplify a cellular signal?

Through signal cascades involving multiple targets. Signup and view all the answers

Study Notes

Enzyme Regulation by Covalent Modifications

Enzymes are commonly regulated by covalent modifications, in addition to allosteric regulation
Covalent modifications are post-translational modifications that affect enzyme activity
Proproteins are synthesized in an inactive form and converted to an active form by proteolytic cleavage
Zymogens are proproteins that become enzymes after cleavage
Pepsinogen is an example of a zymogen that is cleaved to form the active enzyme pepsin
Pepsin can cleave more pepsinogen, an example of an enzyme that activates its own zymogen precursor
Many zymogens are activated by separate enzymes, like trypsinogen cleaved by enteropeptidase
The synthesis of enzymes as zymogens helps ensure they remain inactive until needed
Zymogens are commonly found in digestion, clotting, and apoptotic pathways
Aberrant early activation of zymogens can cause pathological consequences

Dynamic Covalent Modifications

Some covalent modifications are irreversible, stopping enzyme activity
Inhibitors are exogenous to the organism (e.g., drugs, toxins)
Zymogen activation, part of a post-translational modification, is irreversible
Both irreversible inhibition and zymogen activation are examples of post-translational modifications
Dynamic covalent modifications are reversible, meaning they can be added and removed to regulate enzyme activity
These modifications can be dynamic, adding or removing, which allows for regulation of enzyme activity
Dynamic modification isn't the reversibility of a single enzymatic reaction, but the ability to alter it by another enzyme reaction

Phosphorylation

Phosphorylation is a common dynamic covalent modification
Addition of phosphate group to the hydroxyl of serine, threonine, or sometimes tyrosine
Kinase enzymes catalyze the addition of phosphate using ATP
Phosphate groups are removed by phosphatase enzymes
Phosphate group addition causes a conformational change and affects enzyme activity (kcat/KM values)
Kinase and phosphatase reactions, though individually considered irreversible, can reversibly regulate phosphorylation status
Phosphorylation status of an enzyme can control activity; some are 'on' when phosphorylated, others 'off'
Enzymes may have multiple phosphorylation sites, with effects varying by site

Signal Cascades and Multi-Target Effects

Signal cascades, involving phosphorylation, can amplify cellular responses
Kinases and phosphatases can affect multiple different enzymes and pathways
Covalent regulation can override feedback mechanisms
Phosphorylation plays a central role in hormonal regulation of metabolic processes

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Description

This quiz focuses on the regulation of enzymes through covalent modifications and the role of zymogens in enzymatic activity. It covers key concepts such as proproteins, pepsinogen, and the implications of early zymogen activation. Test your understanding of these vital biochemical processes!