91Ó°ÊÓ

Describe the urea cycle. a. The urea cycle is the mechanism of conversion of urea to ammonia involving five intermediate steps catalyzed by five different enzymes. Of the five steps, the first two occur in the mitochondria and the last three in the cytosol. b. The urea cycle is the mechanism of conversion of ammonia to urea involving five intermediate steps catalyzed by five different enzymes. Of the five steps, the first two occur in the mitochondria and the last three in the cytosol. c. The urea cycle is the mechanism of conversion of ammonia to urea involving five intermediate steps catalyzed by five different enzymes. Of the five steps, the first two occur in the cytosol and the last three in the mitochondria. d. The urea cycle is the mechanism of conversion of ammonia to urea involving five intermediate steps all catalyzed by one enzyme. Of the five steps, the first two occur in the mitochondria and the last three in the cytosol.

Step by step solution

01

Understand the Options

Carefully read each option to understand the mechanism described and the locations of where the steps occur.

02

Identify Key Facts

Take note that the urea cycle converts ammonia to urea and involves five intermediate steps with five different enzymes.

03

Check Location of Steps

Determine the correct location of the steps. The first two steps should occur in the mitochondria, and the last three steps should occur in the cytosol.

04

Analyze Each Option

Evaluate each option based on the key facts and the correct locations. Identify which option accurately describes the conversion mechanism and correctly locates the steps.

05

Select the Correct Option

Based on the analysis, choose the option that meets all the criteria: Option b) The urea cycle is the mechanism of conversion of ammonia to urea involving five intermediate steps catalyzed by five different enzymes. Of the five steps, the first two occur in the mitochondria and the last three in the cytosol.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

ammonia conversion

The urea cycle is an essential biochemical process that converts toxic ammonia into urea. Ammonia, produced from the breakdown of proteins, is harmful to our bodies in large amounts. The urea cycle ensures this toxicity is neutralized. This cycle is vital for keeping the body's nitrogen balance in check. By converting ammonia into urea, which is then excreted through urine, the body efficiently manages excess nitrogen.
This process allows organisms to live without being poisoned by their own waste products.
Remember: The urea cycle operates mainly in the liver.

mitochondria

The mitochondria, often described as the powerhouse of the cell, play a critical role in the urea cycle. The first two steps of the urea cycle occur within these organelles.
Inside the mitochondria, ammonia begins its transformation into urea.
Here’s a brief overview:

• Step 1: Ammonia combines with carbon dioxide to form carbamoyl phosphate through the action of the enzyme carbamoyl phosphate synthetase I.
• Step 2: Carbamoyl phosphate then reacts with ornithine to produce citrulline, catalyzed by ornithine transcarbamylase.

These preliminary steps set the stage for the subsequent reactions that occur in the cytosol.

cytosol

After the initial reactions in the mitochondria, the next phases of the urea cycle take place in the cytosol. The cytosol is the liquid component of the cytoplasm where most cellular activities occur.
In the cytosol, the following key steps finish the urea conversion process:

• Step 3: Citrulline moves into the cytosol and reacts with aspartate to form argininosuccinate, a reaction catalyzed by argininosuccinate synthetase.
• Step 4: Argininosuccinate is then broken down by argininosuccinate lyase to release arginine and fumarate.
• Step 5: Finally, arginine is converted to urea and ornithine by the enzyme arginase.

The urea is then transported to the kidneys for excretion, while ornithine is recycled back into the mitochondria to begin the cycle anew.

intermediate steps

The urea cycle is composed of five intermediate steps, each meticulously orchestrated to ensure efficient conversion of ammonia to urea. These steps involve the formation and processing of various intermediate compounds. Knowing these steps and their sequence is essential for understanding the urea cycle's intricacies.
Here's a concise breakdown:

• 1. Formation of carbamoyl phosphate from ammonia and carbon dioxide.
• 2. Synthesis of citrulline from carbamoyl phosphate and ornithine.
• 3. Citrulline's reaction with aspartate to produce argininosuccinate.
• 4. Breakdown of argininosuccinate into arginine and fumarate.
• 5. Conversion of arginine to urea and ornithine.

Each step is vital for the cycle to culminate in the production of non-toxic urea.

enzymes

Enzymes are the biological catalysts that drive the urea cycle forward. Each step of the cycle is facilitated by a unique enzyme, without which the process would be inefficient or impossible.
Here is a list of the key enzymes involved:

• 1. Carbamoyl phosphate synthetase I catalyzes the first step.
• 2. Ornithine transcarbamylase catalyzes the formation of citrulline.
• 3. Argininosuccinate synthetase mediates the synthesis of argininosuccinate.
• 4. Argininosuccinate lyase breaks down argininosuccinate.
• 5. Arginase completes the final conversion of arginine to urea and ornithine.

Understanding the role of these enzymes helps explain how the urea cycle operates seamlessly within our cells, ensuring the detoxification of ammonia.