Problem 18 - Objective Biology for NEET

Question

Urea is derived from (a) Fats (b) Amino acids (c) Carbohydrates (d) Uric acid

Step-by-Step Solution

Answer

The answer is (b) Amino acids.

Step 1: Identify the Origin of Urea

Urea is a compound that is produced in the liver and is a waste product of protein metabolism. Specifically, it is produced in the urea cycle, where ammonia is converted to urea. The major sources of ammonia are amino acids and other compounds, which contain nitrogen.

Step 2: Analyze the Answer Options

Now, looking at the list of options, we need to select the one which is most directly associated with the production of urea. Here are the four options: Fats, Amino acids, Carbohydrates and Uric acid. Fats and carbohydrates are primarily sources of energy and are not directly involved in providing ammonia for the urea cycle. Uric acid is another nitrogenous waste product and is not associated with the production of urea.

Step 3: Select the Correct Option

As a result, based on the information above, the only viable option left is Amino acids. Therefore Amino acids are the primary source of urea.

Key Concepts

Protein Metabolism

Protein metabolism is a fundamental biological process involving the breakdown of proteins into their constituent amino acids. This occurs when the body requires energy or when it needs to recycle or dispose of nitrogen-containing molecules.

During digestion, enzymes called proteases break down dietary proteins into amino acids. These amino acids can either be used to synthesize new proteins or to produce energy. If there is an excess of amino acids, they are deaminated by the liver, which means the amino group is removed. This process produces ammonia, a toxic compound that needs to be eliminated from the body.

Urea Cycle as a Detox Mechanism

The liver converts this ammonia into a less toxic compound called urea via the urea cycle. The urea cycle is the primary pathway for the disposal of excess nitrogen in humans and is an essential part of protein metabolism. Once formed, urea is transported in the blood to the kidneys and excreted in the urine.

Amino Acids

Amino acids are the building blocks of proteins and play a crucial role in various metabolic pathways. Most proteins are composed of 20 different amino acids that can be linked in varying sequences to produce a vast array of proteins with different functions.

Essential vs. Non-Essential Amino Acids

There are essential amino acids, which cannot be synthesized by the human body and must be obtained from the diet, and there are non-essential amino acids, which the body can produce.

Once proteins are ingested and digested, these amino acids can serve numerous functions besides being the precursors for protein synthesis. They can be converted into glucose or fatty acids, or used to produce energy directly. Importantly, the nitrogen contained within amino acids leads to the production of ammonia in the liver when they are deaminated, which feeds into the urea cycle, eventually resulting in the formation of urea.

Nitrogenous Waste Products

Nitrogenous waste products are a result of protein and nucleic acid metabolism. Since the human body cannot store excess nitrogen, it must convert it into a less harmful form for excretion.

Forms of Nitrogenous Waste

The main forms of nitrogenous waste are ammonia, urea, and uric acid.

• Ammonia is very toxic and is quickly converted into urea via the urea cycle.
• Urea is less toxic, soluble in water, and is the primary nitrogenous waste in humans.
• Uric acid is less soluble in water than urea and is excreted mainly by birds and reptiles.

The kidneys play a vital role in filtering these waste products from the blood and expelling them through urine. Proper functioning of this excretory system is critical for maintaining a balance of nitrogenous compounds and for overall health.