Biochemistry Enzyme Mechanisms Quiz

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Questions and Answers

What is the role of glucose binding to hexokinase in the induced fit mechanism?

It prevents glucose from entering the active site.

It facilitates the release of glucose-6-phosphate.

It stabilizes a conformation that promotes catalysis. (correct)

It allows ATP to hydrolyze rapidly.

What occurs due to the exclusion of water from the active site of hexokinase?

Facilitation of glucose-6-phosphate formation.

Inhibition of glucose binding.

Promotion of glucose phosphorylation. (correct)

Enhancement of ATP hydrolysis.

How does the conformation of hexokinase change upon glucose binding?

The enzyme becomes inactive.

The C6 hydroxyl of glucose is positioned near ATP's terminal phosphate. (correct)

The enzyme is unable to bind ATP.

The active site becomes too large.

What is the primary function of hexokinase in the presence of ATP?

To transfer a phosphate group to glucose. Signup and view all the answers

Why is it important that water is excluded from the active site of hexokinase?

It ensures the enzyme only catalyzes phosphorylation. Signup and view all the answers

What type of bond is cleaved during the reaction catalyzed by Hexokinase?

Phospho-anhydride bond Signup and view all the answers

Which enzyme catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate?

Phosphoglucose Isomerase Signup and view all the answers

What is the function of Phosphofructokinase in glycolysis?

It regulates the rate of glycolysis. Signup and view all the answers

What is the intermediate formed during the isomerization of fructose-6-P by Phosphoglucose Isomerase?

Enediolate Signup and view all the answers

Which reaction is considered the rate-limiting step of glycolysis?

Conversion of fructose-6-phosphate to fructose-1,6-bisphosphate Signup and view all the answers

What kind of reaction does Aldolase catalyze?

Aldol cleavage Signup and view all the answers

What is formed as a product when Aldolase catalyzes the breakdown of fructose-1,6-bisphosphate?

Dihydroxyacetone-P and glyceraldehyde-3-P Signup and view all the answers

Which enzyme catalyzes a spontaneous reaction in glycolysis and is regulated locally by substrate concentrations?

Phosphofructokinase Signup and view all the answers

What type of control over glycolysis is primarily associated with hormone-activated signal cascades?

Global control Signup and view all the answers

Which of the following enzymes is NOT one of the three key enzymes regulating the glycolytic pathway?

Aldolase Signup and view all the answers

Which enzyme in glycolysis experiences a negative standard free energy change (DG) during its reaction?

Pyruvate Kinase Signup and view all the answers

Which enzyme is associated with a positive standard free energy change (kJ/mol) during its reaction?

Phosphoglycerate Mutase Signup and view all the answers

What is the primary role of lactate after being released into the blood?

It may be converted back to pyruvate in other tissues. Signup and view all the answers

In which process is lactate converted back to glucose?

Gluconeogenesis Signup and view all the answers

Which enzyme is responsible for the conversion of lactate to pyruvate?

Lactate dehydrogenase Signup and view all the answers

What is the net ATP yield of anaerobic catabolism of glucose?

2 ATP Signup and view all the answers

What is one of the primary functions of lactate in cardiac muscle?

As a fuel source. Signup and view all the answers

Which of the following statements about fermentation is true?

It results in the production of lactate and 2 ATP. Signup and view all the answers

Which byproduct is produced when some anaerobic organisms metabolize pyruvate?

Ethanol Signup and view all the answers

What happens to NADH during the conversion of ethanol?

It is converted into NAD+. Signup and view all the answers

Which of the following tissues primarily ferments glucose to lactate?

Brain astrocytes Signup and view all the answers

During glycolysis, what is the product of the enzymatic reaction involving glucose?

Pyruvate Signup and view all the answers

Study Notes

Hexokinase and Its Mechanism

Hexokinase catalyzes the conversion of glucose to glucose-6-phosphate through the transfer of a phosphate group from ATP.
Glucose binding promotes a conformational change, placing the C6 hydroxyl close to ATP's terminal phosphate, facilitating catalysis.
Active site water exclusion prevents ATP hydrolysis, directing the reaction toward glucose phosphorylation.
The reaction is highly spontaneous; ATP's phospho-anhydride bond is cleaved, resulting in a product with a lower free energy of hydrolysis.

Phosphoglucose Isomerase

Catalyzes the interconversion of glucose-6-phosphate (aldose) to fructose-6-phosphate (ketose).
Utilizes acid/base catalysis and involves an enediolate intermediate, leading to ring closure.

Phosphofructokinase

Converts fructose-6-phosphate and ATP into fructose-1,6-bisphosphate and ADP.
This reaction is highly spontaneous and serves as the rate-limiting step of glycolysis, showing similarity to hexokinase's mechanism.
Phosphofructokinase activity is tightly regulated.

Aldolase

Facilitates the aldol cleavage of fructose-1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.
Lactate, produced during glycolysis, can be converted back to pyruvate by lactate dehydrogenase, linking to energy metabolism through the Krebs Cycle and gluconeogenesis in the liver.

Lactate as a Metabolite

Lactic acid serves as a fuel source for cardiac muscle and brain neurons.
Neurons convert lactate back to pyruvate for energy production via the Krebs Cycle.

Alcohol Fermentation

Anaerobic organisms convert pyruvate to ethanol, excreting it as a waste product.
Alcohol dehydrogenase converts NADH to NAD+, facilitating cellular respiration processes.

Glycolysis Overview

Glycolysis converts one glucose molecule into two pyruvate, yielding 2 ATP and 2 NADH.
Key reactions involve enzymes that mediate spontaneous transformations, showing significant changes in Gibbs free energy (ΔG°').

Regulation of Glycolysis

Key enzymes including hexokinase, phosphofructokinase, and pyruvate kinase regulate glycolysis through local and global controls.
Local regulation occurs with variations in substrate concentration, while global control often involves hormone-mediated signaling, especially in liver cells for blood glucose maintenance.

Glucokinase

A liver-specific variant of hexokinase with a high KM for glucose, active only at elevated glucose levels.
Insulin enhances glucokinase gene expression, promoting glucose uptake and phosphorylation regardless of glucose-6-phosphate levels.
Glucokinase activity is regulated by glucokinase regulatory protein (GKRP), adjusting glucose metabolism based on metabolic state.

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Description

Test your understanding of induced fit mechanisms in biochemistry, focusing on the role of ATP and ADP. This quiz will challenge your knowledge of chemical structures and enzyme dynamics.