You may have been told proteins are good for you. Do these look good to you?
Proteins as food. To you, these may not look appetizing (or they might), but they do provide a nice supply of amino acids, the building blocks of proteins. Proteins have many important roles, from transporting, signaling, receiving, and catalyzing to storing, defending, and allowing for movement. Where do you get the amino acids needed so your cells can make their own proteins? If you cannot make it, you must eat it.
Proteins
A protein is an organic compound made up of small molecules called amino acids. There are 20 different amino acids commonly found in the proteins of living organisms. Small proteins may contain just a few hundred amino acids, whereas large proteins may contain thousands of amino acids. The largest known proteins are the titins, found in muscle, which are composed from almost 27,000 amino acids.
General Structure of Amino Acids. This model shows the general structure of all amino acids. Only the side chain, R, varies from one amino acid to another. For example, in the amino acid glycine, the side chain is simply hydrogen (H). In glutamic acid, in contrast, the side chain is CH2CH2COOH. Variable side chains give amino acids acids different chemical properties. The order of amino acids, together with the properties of the amino acids, determines the shape of the protein, and the shape of the protein determines the function of the protein.
Protein Structure
When amino acids bind together, they form a long chain called a polypeptide. A protein consists of one or more polypeptide chains. A protein may have up to four levels of structure. The lowest level, a protein’s primary structure, is its sequence of amino acids. Higher levels of protein structure are described in Figure below. The complex structures of different proteins give them unique properties, which they need to carry out their various jobs in living organisms.
Protein Structure. The structure of a protein starts with its sequence of amino acids. What determines the secondary structure of a protein? What are two types of secondary protein structure?
The following activity will help you remember a bit about proteins and amino acids. Click on the button below to download the file and print out the 2 pages:
Instructions:
Activity 1: Make a chain of amino acids to learn that proteins are “chains” of amino acids.
Activity 2: Cut out the “boxcar” strips of the 20 amino acids your body needs. Boxcars are labeled with the amino acids. Essential amino acids are blue. The others are red. Paste the strips together and fold accordion-style.
Activity 3: Make a pocket to store the amino acids. Learn that each amino acid can link to 2 other amino acids just like a boxcar in a train. Put the amino acids from the previous step into the pocket.
Functions of Proteins
Proteins play many important roles in living things. Some proteins help cells keep their shape, and some make up muscle tissues. Enzymes are proteins that speed up chemical reactions in cells. Other proteins are antibodies, which bind to foreign substances such as bacteria and target them for destruction. Still other proteins carry messages or transport materials. For example, human red blood cells contain a protein called hemoglobin, which binds with oxygen. Hemoglobin allows the blood to carry oxygen from the lungs to cells throughout the body.
As you view Protein Functions in the Body, think about these things:
- the amount of protein in each cell,
- the roles of different types of proteins.
Proteins and Diet
Proteins in the diet are necessary for life. Dietary proteins are broken down into their component amino acids when food is digested. Cells can then use the components to build new proteins.
Humans can synthesize 11 of the 20 common amino acids. These are known as the non-essential amino acids because our bodies can produce them. The remaining nine amino acids are called essential amino acids, which we must obtain from our diet. Like dietary carbohydrates and lipids, dietary proteins can also be broken down to provide cells with energy.
This text is Creative Commons BY-NC 3.0 Source: CK-12 and edited / added to by Guest Hollow, LLC. The amino acid printables are © Guest Hollow, LLC.