Proteins

12,213views

00:00 / 00:00

High Yield Notes

7 pages

Questions

USMLE® Step 1 style questions USMLE

of complete

A group of researchers are investigating the digestion and absorption of proteins in the gastrointestinal tract of the human body. Which of the following is true regarding protein digestion and absorption?  

External Links

Transcript

Watch video only

Protein is an essential part of the human diet. It’s found in a variety of foods like eggs, dairy, seafood, legumes, meats, nuts, and seeds.

Regardless of the source, the protein that we eat gets broken down and reformed into new proteins in our bodies.

These proteins do everything from fighting infections to helping cells divide. You name it, they’re doing it.

At its simplest, a protein is a chain of amino acids, bound to one another by peptide bonds. Like a string of beads.

These strings get twisted and folded into a final protein shape.

When we eat protein, it gets broken down into its individual amino acids.

Most amino acids have a central carbon atom bonded to one amino or nitrogen-containing group and one carboxylic acid group - that’s why it’s called an amino acid.

The carbon also has one hydrogen atom and a side chain which is unique to each amino acid. The exception to this is proline which has a tiny little ring structure instead.

Although there are hundreds of amino acids in nature, humans use only about 20 of them to make basically every type of protein.

They include: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. Phew, that’s 20.

One way to divide them is by defining which ones our bodies can make ourselves, and which ones we cannot.

There are 5 amino acids - alanine, asparagine, aspartic acid, glutamic acid, and serine - that we can get from foods, but we can also make ourselves. These are called nonessential amino acids.

Then, there are 6 of them that we call conditionally essential because healthy bodies can make them under normal circumstances - arginine, cysteine, glutamine, glycine, proline, and tyrosine. But we can’t make them in cases like starvation or certain inborn errors of metabolism.

Finally, there are 9 of them that we can only get from food - histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. We call these the essential amino acids.

Dietary protein provides the essential amino acids that are needed to make our own proteins, hormones, and other important molecules. A circle of life, of sorts. But to do so, we need to break the dietary protein down first, through a process called proteolysis.

When we eat a protein-containing food, proteolysis begins when the food reaches the stomach.

First, hydrochloric acid denatures the protein, unfolding it and making the amino acid chain more accessible to enzymatic action.

Then, pepsin, which is a protein itself made by gastric chief cells, enters the picture.

Summary

Proteins are an essential part of the human diet. They are found in a variety of foods like eggs, dairy, seafood, legumes, meats, nuts, and seeds. They are complex biomolecules made up of chains of amino acids, the specific sequence of which determines the three-dimensional structure of the protein and its unique functions within the cell. Although there are hundreds of amino acids in nature, humans use only about 20 of them to make basically every type of protein.

Some amino acids are at the same time obtained from food and synthesized by our body. These amino acids are referred to as non-essential. They include alanine, asparagine, aspartic acid, glutamic acid, and serine. Other amino acids are strictly obtained from food because our body can't synthesize them. They include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Sources

  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Amino Acid Metabolism in Pediatric Patients" Nutrition (1998)
Elsevier

Copyright © 2024 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.

RELX