Biochemistry Regulation and Enzyme Kinetics

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Questions and Answers

What is one method of regulating enzymatic function mentioned?

Changing the substrate concentration

Changing the geometry of the enzyme (correct)

Altering the pH level

Modifying the enzyme's temperature

How do conformational changes affect enzyme activity?

They control enzymatic catalysis and action (correct)

They alter the length of enzyme molecules

They enhance the binding affinity of substrates

They permanently deactivate the enzyme

Which of the following best describes enzyme processivity?

The measurement of an enzyme's effectiveness based on substrate concentration

The change in enzyme structure in response to environmental conditions

The ability of an enzyme to catalyze multiple reactions without releasing the substrate (correct)

The speed at which substrates are transformed into products

What does enzyme action primarily refer to?

The overall performance and function of the enzyme Signup and view all the answers

Which aspect is NOT regulated through conformational changes in enzymes?

Protein synthesis rate Signup and view all the answers

What role does phosphorylation play in glucose metabolism?

It activates enzymes that build glucose and inhibits those that degrade it. Signup and view all the answers

Which statement best describes the effect of phosphorylating enzymes during glucose production?

It enhances the activity of enzymes that synthesize glucose. Signup and view all the answers

Why is enzyme inhibition important in glucose metabolism?

It allows the cell to store glucose instead of breaking it down. Signup and view all the answers

What is the overall effect of phosphorylation on glucose levels within a cell?

It increases glucose levels by promoting synthesis. Signup and view all the answers

What is the primary function of glycogen phosphorylases?

To release glucose into the blood Signup and view all the answers

What would likely happen if phosphorylation did not activate glucose-building enzymes?

Cells would primarily break down glucose without synthesizing it. Signup and view all the answers

Under what condition do glycogen phosphorylases particularly release glucose?

When epinephrine concentration is high Signup and view all the answers

What role does epinephrine play in glucose release from glycogen?

It triggers glycogen phosphorylases to release glucose Signup and view all the answers

Which scenario most likely increases the activity of glycogen phosphorylases?

Exercising vigorously Signup and view all the answers

What happens to blood glucose levels when glycogen phosphorylases are activated?

Blood glucose levels increase Signup and view all the answers

What is the role of cAMP in the phosphorylation cascade triggered by adrenaline?

It serves as a signaling molecule that activates protein kinase A. Signup and view all the answers

Which enzyme is primarily responsible for breaking down cAMP into AMP?

Phosphodiesterase (PDE). Signup and view all the answers

What occurs immediately after cAMP activates protein kinase A in the cascade?

Glycogen phosphorylase kinase is phosphorylated and activated. Signup and view all the answers

What is the effect of phosphodiesterase on the phosphorylation cascade?

It breaks down cAMP, converting it into inactive AMP. Signup and view all the answers

What characterizes a phosphorylation cascade?

Sequential phosphorylation events that amplify the signal. Signup and view all the answers

What is the primary function of adenylate cyclase in cellular signaling?

Converting ATP into cAMP Signup and view all the answers

What happens to the alpha subunit after it hydrolyzes GTP to GDP?

It undergoes a conformational change and returns to its original shape Signup and view all the answers

What is the role of cAMP in the signaling pathway mentioned?

It functions as a secondary messenger Signup and view all the answers

How does the alpha subunit affect its interaction with beta-gamma subunits after GDP is produced?

It increases its binding affinity for beta-gamma Signup and view all the answers

What is the enzymatic activity of the alpha subunit in relation to GTP?

It hydrolyzes GTP to GDP Signup and view all the answers

What is the primary function of kinases in biochemical reactions?

To add phosphate groups to molecules Signup and view all the answers

Which enzyme is an example of a kinase that participates in phosphorylation?

Glycogen phosphorylase Signup and view all the answers

What is the role of phosphatases in biochemical reactions?

To hydrolize phosphate groups from molecules Signup and view all the answers

Which statement about phosphorylation is correct?

Phosphorylation can lead to both activation and deactivation of enzymes. Signup and view all the answers

Which of the following statements is false regarding kinases and phosphatases?

Phosphatases add phosphate groups. Signup and view all the answers

Study Notes

Biochemistry Study Notes

Sheet number: 33
Year: 2024
Written by: Lajneh Teejan
Edited by: Lajneh Wisdom
Doctor: Nafez Abotarboush

Regulation Through Conformational Changes

Enzymes can be regulated by altering their geometry (conformational change).
This affects enzymatic catalysis, action, and processivity.
Regulatory mechanisms include:
- Allosteric activation/inhibition (allo-far away, steric-far away)
- Phosphorylation/covalent modification
- Protein-protein interactions (between regulatory/catalytic subunits or proteins)
- Proteolytic cleavage (irreversible)

Not All Enzymes Follow Michaelis-Menten Equation

According to Michaelis-Menten studies, enzymes fall into two classes:
- Simple enzymes: follow Michaelis-Menten kinetics (hyperbolic plot)
- Complex enzymes (allosteric enzymes): don't follow Michaelis-Menten kinetics (sigmoidal plot)
Chymotrypsin is a simple enzyme, with specificity for aromatic residues and hydrolysis of ester bonds.

Allosteric Regulation

Allosteric enzymes have a quaternary structure with multiple subunits.
Regulatory subunits control the enzyme's activity by binding effectors (modifiers).
Effectors can be:
- Inhibitors (negative effect)
- Activators (positive effect)
Binding to regulatory subunits triggers conformational changes in the active site, leading to either activation or inhibition.
Homotropic effectors bind to the same site as the substrate.
Heterotropic effectors bind to a different site than the substrate.

Aspartate Transcarbamoylase (ATCase)

Involved in CTP and UTP synthesis for RNA and DNA.
Displays cooperative behavior (sigmoidal plot).
Has both regulatory and catalytic subunits.

How Do Allosteric Enzymes Work?

Exist in two states: R (relaxed), T (tight).
R state has higher substrate affinity than T.
The equilibrium ratio (T/R) affects the shape of the curve (sigmoidal or hyperbolic). Higher ratio shifts the curve to the right.

Concerted or Sequential Model

Enzymes and proteins with multiple subunits can change their structure through the concerted or sequential models.
Concerted model: all subunits change structure simultaneously.
Sequential model: a change in one subunit's structure triggers a change in the next.

Allosteric Regulation-ATCase (Synthesis of Pyrimidine Nucleotides)

This enzyme makes CTP and UTP used in DNA and RNA synthesis.
Allosterically regulated by product inhibition (feedback inhibition): UTP and CTP
Regulated by an activator (ATP).

Covalent Modification

A common enzyme regulation mechanism.
Enzyme activation or deactivation occurs by binding materials covalently to the enzyme.
Phosphorylation is the most common type of covalent modification, involving the addition of a phosphate group (most often to Serine, Threonine, or Tyrosine residues).
Phosphorylation can activate or inactivate enzymes, depending on the targeted enzyme and the needs of the cell. For instance, when the cells needs glucose, glycogen phosphorylase is phosphorylated and activated.

Phosphorylation:

Common covalent modification.
Modifies enzymes by adding phosphate groups.
Kinases add phosphate, phosphatases remove them.
Acts as a signal to modify enzyme activity, and pathways.

Glycogen Phosphorylase

Example of an enzyme that undergoes phosphorylation.
Phosphorylation converts less-active form (b) to more-active form (a).
Regulation is important pathway control.

Protein Kinase A (PKA)

Enzyme regulated by cAMP (second messenger).
Important in glycogen, sugar, and lipid metabolism regulation.

Other Covalent Modifiers

Other than phosphorylation, other covalent modifications include:
- Adenylylation
- Uridylylation
- ADP-ribosylation
- Methylation
- Acetylation

Conformational Changes from Protein-Protein Interaction

G proteins (transmembrane proteins) regulate cellular signaling by binding to and releasing GTP/GDP. This changes protein conformation.
G proteins are usually trimeric, with alpha, beta, and gamma subunits.
Alpha subunit has intrinsic enzymatic activity.
When G proteins bind GTP, they are activated and can interact with other proteins. It is inactivated once it converts to GDP.

Monomeric G Proteins

Some G proteins are monomeric (non-trimeric).
Monomeric G-proteins also operate by cycling between a GDP-bound (inactive) and a GTP-bound (active) state.

Proteolytic Cleavage Zymogens

Proteins often synthesized in inactive precursor forms (zymogens), which are converted (activated) to active forms through cleavage.
This activation often occurs at a specific place, such as by cleavage of amino acid sequences at the N-terminus.
Examples include pepsinogen, trypsinogen, and chymotrypsinogen.

Blood Clotting

Blood clotting involves converting soluble fibrinogen into insoluble fibrin through the action of thrombin.

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Description

Explore the intricate world of enzymatic regulation through conformational changes in this biochemistry quiz. Delve into mechanisms such as allosteric effects, covalent modifications, and the distinction between simple and complex enzymes. Ideal for students studying biochemistry and enzymology.