Amino Acid Structure
Regardless of whether a protein is found in the food on your dinner plate or within your body, it is made up of a chain of amino acids. There are 20 different amino acids needed by your body; some of them are made in your body while others must come from your diet.
All of the amino acids have the same basic structure. We see a central carbon atom, which is represented by the letter C, bonded to four different components. We see a hydrogen atom, which is represented by this letter H. We also have a carboxyl group, which is the COOH seen here; and an amino group, which is this NH2 on the other side.
Amino acids are composed of a few different atoms
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So we have a bunch of C's, some O's, H's and N's in the basic structure of an amino acid, which means the most common atoms in amino acids are carbon, oxygen, hydrogen and nitrogen, but you probably also noticed the R Group. This represents a side chain, and it is the side chain that makes the 20 amino acids different from each other. However, what we are concerned about in this lesson is how the different amino acids come together to form proteins. So let's stay on that track.
Amino Acid Sources
We mentioned that some of the amino acids are made by your body, while others come from your diet. Now, we don't really think in terms of eating different amino acids. What we eat is protein, which is found in foods like meat, fish, eggs and some plant foods, such as beans and nuts.
Your digestive system takes in these protein-containing foods and breaks them down into the individual amino acids, which are then taken up by your body cells and reassembled into new proteins, much like a builder might demolish a building and then salvage the parts to build a new structure.
Inside your cells, the individual amino acids can bond together by forming a peptide bond, which is simply a chemical bond that joins amino acids together. More specifically, peptide bonds join the carboxyl group of one amino acid with the amino group of another.
For example, the amino acid called glycine can bond with the amino acid called alanine to form a dipeptide. The prefix 'di' means two, so, a dipeptide is defined as a compound consisting of two amino acids. Now, amino acids cannot just join together by holding hands; they actually have to give something up in order to live their lives together.
In our dipeptide example, glycine gives up an atom of hydrogen and an atom of oxygen, while alanine loses an atom of hydrogen. Together they release a molecule called H2O, and I bet you recognize that as a water molecule. This loss of water to form a bond is called a dehydration synthesis reaction. This is a big term, but it's easy to remember if you recall that dehydration is the loss of water, and synthesis means to build. So, a protein is built through dehydration synthesis.
Of course, simply joining two amino acids together is still a long way off from having a protein. More amino acids need to join up until you have a chain of amino acids joined together by peptide bonds, which gives us a polypeptide. Polypeptides are important to the body and can be found in places like the oxygen-carrying hemoglobin of your blood.
Now proteins, well, they are also long chains of amino acids, and there is some debate over the distinction between a small protein and a polypeptide, yet we do see that some larger proteins can contain many polypeptides folded and coiled together.
Lesson Summary
Let's review. Proteins are the true workhorses of the body, needed for building structures and maintaining life. The basic building blocks of proteins are amino acids.
The 20 different amino acids needed by your body all have the same basic structure, which is a central carbon atom attached to a hydrogen atom, a carboxyl group, an amino group, and a variable R group or side chain that gives the amino acid its uniqueness.
A peptide bond is a chemical bond that joins amino acids together where the carboxyl group of one amino acid bonds with the amino group of another. This forms a dipeptide, which is simply a compound consisting of two amino acids. It requires the loss of water to form a bond, which is a process called a dehydration synthesis reaction.
More amino acids can join up in a similar fashion until you have a chain of amino acids joined together by peptide bonds, which results in a polypeptide. Proteins are also long chains of amino acids, and some larger proteins can contain many polypeptides folded and coiled together.
Learning Outcomes
Once you have finished this lesson you should be able to:
- Define proteins and amino acids and the purpose of each
- Explain the process that results in amino acid formation
- Describe how amino acids result in proteins
