Video Transcript
After protein digestion, the
product is transported from the gastrointestinal tract, GIT, to the liver. The excess of it is metabolized and
detoxified to blank. (A) An amino group, (B) urea, (C)
ammonia, or (D) uric acid.
To answer this question, let’s
revise some key facts about metabolism in the liver. The liver is a large lobed organ
found in the human abdomen, and it has many roles, including bile production,
detoxification, and excretion. This question is asking about the
metabolism and detoxification of proteins, so let’s take a closer look at these
processes.
Metabolism is the term used to
describe all of the chemical reactions that occur within a living organism to
maintain life. These reactions produce metabolic
waste products that need to be excreted, many of which are broken down by the liver
before they are removed from the body. The liver is also responsible for
neutralizing toxic substances through a process called detoxification. A blood vessel called the hepatic
portal vein carries these wastes and toxins, along with nutrients and excess amino
acids from organs such as those of the gastrointestinal tract to the liver.
Having looked at metabolic waste
products in general, let’s focus on the excess proteins mentioned in the
question. Not all of the amino acids that are
produced during protein digestion in the gastrointestinal tract can be stored. And they need to be broken down by
the liver to form molecules that can be used by, or excreted from, the body. The cells of the liver that carry
out this function are called hepatocytes. The prefix hepat- means liver,
while the suffix -cyte means cell. In the hepatocytes, amino groups
are removed from the excess amino acids, converting them into organic acids that can
now be used by the body cells.
This process is called deamination,
and it produces a highly toxic byproduct called ammonia. As this product is so toxic,
ammonia needs to be detoxified in the hepatocytes through a series of reactions
known as the ornithine cycle. The final product of the ornithine
cycle is a comparatively less harmful molecule called urea. Urea is transported to the kidneys
to be excreted from the body as a part of urine.
Now, let’s take a look back at the
question. It asks us what the excess of the
product of protein digestion is metabolized and detoxified to. So let’s recap what is produced in
each of these stages. The products of protein digestion
are amino acids, which are transported to the liver from the gastrointestinal
tract. The amino acids are deaminated,
which produces the byproduct ammonia. Finally, ammonia is detoxified to
produce urea. Therefore, the correct answer to
this question is (B), urea.
