Venom scorpion

show/hide words to know

Amino acid: molecules that contain carbon, oxygen, hydrogen, and nitrogen. These are the building blocks of protein......more

Enantiomer: one of a pair of molecules that are mirror images of each other, but not identical... more

Essential: required, or necessary.

Hydrophobic: any molecule or object that does not mix or repels water... more

Molecule: a chemical structure that has two or more atoms held together by a chemical bond. Water is a molecule of two hydrogen atoms and one oxygen atom (H2O)... more

Protein: a type of molecule found in the cells of living things, made up of special building blocks called amino acids.

Protein Parts

Johnson Righeira Lego portrait

Proteins are not the same as Lego building blocks, but proteins do have special shapes that can be used to build parts of the body. Johnson Righeira Lego portrait via Wikimedia. Click the image to see full size.

Just like a Lego house is made of bricks, proteins are made up of lots of tiny building blocks. These building blocks are called amino acids.

To build a protein, first the amino acids are connected into long chains. These chains of amino acid building blocks can then fold into all types of shapes. Some chains fold into spirals. Other chains make zigzag sheets, and loops.

Combining these spirals, sheets, and loops is how the three-dimensional shape of the protein is made. You can also combine multiple strands of amino acids to make even bigger protein shapes.

21 Is All It Takes

The human body uses just 21 amino acids to make all the proteins it needs to function and grow. Because amino acids can be arranged in many different combinations, it's possible for your body to make thousands of different kinds of proteins from just the same 21 amino acids. You may see books that say there are only 20 amino acids. Don't worry, that's just because the 21st one was discovered pretty recently and not all the books have caught up yet.

21 Amino Acids

21 Amino Acids. Click on the image to see a a larger version.

Essential Amino Acids

There are nine amino acids that your body can’t make. They are called essential amino acids, meaning you must have them to live. They are found in foods like milk, eggs and meat and also a wide variety of plants. This is part of why you can’t survive on a diet of just corn chips for very long. Essential amino acids were actually discovered in an experiment testing something very similar to a "corn chip diet".

Scientists fed rats a diet that had only corn protein in it and observed the results. What they noticed was that rats on this diet got sick and would eventually die. When the sick rats were fed protein from milk, however, they would get better. This told the scientists that something in milk protein was essential to health of rats, that it was something they couldn't live without.

Where Do Amino Acids Come From?


High protein foods include meat, fish, eggs, nuts, spinach asparagus, beans and brussels sprouts.

Just like a Lego house built with Lego bricks can be taken apart, and the bricks used to build something completely different (like a really cool T-Rex), your body can take apart the amino acid building blocks that make up protein and re-use these to make new, totally different proteins. Even your body knows that recycling is really cool!

But where do these amino acid building blocks come from? As it turns out, your cells can make most of the amino acids it needs from other molecules in your body. Nine of these amino acids it can’t make though, so you have to get these from the food you eat. Otherwise, it would be like a Lego set missing nine kinds of bricks to be a complete set. There are certain things you just couldn't build without the missing building blocks.

View Citation

You may need to edit author's name to meet the style formats, which are in most cases "Last name, First name."

Bibliographic details:

  • Article: Protein Parts
  • Author(s): Marcella Martos, Meredith Turnbough
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: June 28, 2012
  • Date accessed: May 15, 2024
  • Link:

APA Style

Marcella Martos, Meredith Turnbough. (2012, June 28). Protein Parts. ASU - Ask A Biologist. Retrieved May 15, 2024 from

American Psychological Association. For more info, see

Chicago Manual of Style

Marcella Martos, Meredith Turnbough. "Protein Parts". ASU - Ask A Biologist. 28 June, 2012.

MLA 2017 Style

Marcella Martos, Meredith Turnbough. "Protein Parts". ASU - Ask A Biologist. 28 Jun 2012. ASU - Ask A Biologist, Web. 15 May 2024.

Modern Language Association, 7th Ed. For more info, see
amino acid alanine

Two versions of the amino acid alanine. Each is the mirror image of the other. Click to image to learn more.

Be Part of
Ask A Biologist

By volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteers page to get the process started.

Donate icon  Contribute

Share this page:


Share to Google Classroom