What is a Protein??

Proteins are important substances that your cells produce in response to the orders given by the DNA that is present inside a cell. Every day, your cells produce thousands of different proteins to do thousands of different jobs. For example, your pancreas produces a protein known as insulin for your other cells. Your red blood cells produce a protein known as hemoglobin to carry oxygen to different parts of your of body. And the list goes on and on. In this section of Genetics R Us, we are going to take an up close look at proteins, and learn about their important role in sustaining life as we know.

At this point, the most important concept that should be floating around in your heads should be what is shown toward your left. The instructions present within DNA are carried out by your cells. The result is that your cells creates a substance called a protein.

Cells then use that protein to actually perform the work which DNA commands. In other words, you can think of the cell as a worker or builder. You can think of the protein as the builder’s tool, such as a hammer or saw that one uses to do work.

Let’s take a closer look at proteins. Shown toward your left is a typical protein. All proteins are composed of smaller units which are called amino acids. To make it easier for you to understand, you can think of a protein as a string of beads. Like something similar to a necklace that you might wear around your neck, proteins can be thought of as the same.

In nature, there are 20 amino acids. Of the thousands of proteins that exist, they are all made up of 20 simple amino acids. A cell knows what amino acid to connect to one another thru the instructions it receives from DNA. Here’s a diagram of the known amino acids toward your right.

From the diagram above, it is quite apparent that the names of some these animo acids are hard to say. For instance, can you pronounce the name, Asparagine. Don’t worry!! I myself have trouble saying these names. Because of this, amino acids are given certain letters of the alphabet in order to make them easy to remember and refer to. For example, the amino acid known as Histidine, is referred to as “H” (However, there are two amino acids, lysine and tryptophan, that you might want to remember. Those two amino acids aren’t present much within plants. Thus strict vegetarians should ensure that their diet contains sufficient amounts of these two amino acids.)

DNA holds the instructions that are needed by your cells to make a protein. Basically, a cell knows which amino acid to connect to one another thru the commands it receives from DNA. Any change in DNA usually, (not always), results in a change in the amino acid sequence.

The result after a cell connects different amino acids togther is a protein that has a certain amino acid sequence. In fact, it is the sequence that determines what the protein is. For example, insulin has a certain sequence that is different from say hemoglobin.

All proteins have a chemical structure that is very important to its existence. The name of that structure is the a peptide bond. Shown toward your left are two amino acids which are joined togther by a peptide bond. The purpose of the peptide bond is to connect two more amino acids.

Every peptide bond is formed when two amino acids are joined together. This reaction takes place when water, H20 is removed. If look in the model toward your left, you can see this. Every peptide bond consists of a single nitrogen (N), hydrogen (H), carbon (C), and oxygen (O) atom.

While the peptide bond is important, the shape of protein is equally important. The shape of a protein is important because it is what gives a protein its function. In order to understand a protein’s shape, you first must understand the different visual levels that a protein can be viewed as having.

A Shy Protein

If you ever took a chemistry class, then your chemistry book probably used a lot of “models” to describe what a protein looks like. The same is true for Genetics R Us. Many times I used models to you, so that you would be able to understand the concepts. This is no coincedence. There is a good reason for the use of models in science Here’s why!!!!!

Simply put, no one actually knows what a substance’s structure actually looks like. The structure of substances such as DNA, RNA, & proteins are way too small for anyone to actually see, as you might be able to see someone in plain vision. Even the most powerful tool we have, the electron microscope, cannot give us a plain view picture of the structures of substances.

This why we use models to describe the structures of substances. It is the best that we can do at the present time. Eventually powerful tools will come along and use of models will probably cease. So with that in mind, let’s take a look at the four levels of a protein.

At the most basic level, a protein can be viewed as being simply a string of a amino acids that have their names written short-handed form.

In addition, each of the 20 amino acids may be assigned a single letter from the alphabet. For example, the amino acid, Histidine, is assigned the letter, “H”. This level is where the protein’s primary structure exists. The primary structure gives a protein’s amino acid sequence as well as sulfur bridges. The element sulfur is present in many proteins. When two sulfur atoms connect to each other, they are called a “sulfur bridge”.

At the second level is a protein’s secondary structure. This level reveals a protein’s structure in 3-D or three dimensional space. The structure is usually a computer generated picture through the use of a technique called X-ray crystalization, in which x-rays are shot into a protein to reveal the location of its atoms.

At the second level, a protein has two basic shapes or conformations they take on. The first shape is called an alpha helix. The second shape is called a beta sheet conformation.

An alpha helix means that a protein takes on a spiral, coiled shape in three dimensional space. An example of this is shown toward your right. Some times, supercomputers are used to give a 3-D picture. This is done using a techinque known as X-ray crystalization.

In a beta sheet conformation, a protein basically folds back on itself in three dimensional space. In many cases, a beta sheet conformation consists of multiple protein chains lying side by side in a parallel fashion. An example of this is shown toward your left. Once again, supercomputers are used to give a detailed three picture.

At the third level is a proteins’s tertiary structure. This is simply a three dimensional picture of the entire structure of a protein. It is a computer generated picture like in the previous level. The tertiary structure is very important because a protein gets its function from its tertiary structure.

When a protein loses its teritiary structure, we say that a protein is denatured, which basically means a protein that has lost its function. This can be caused by a number of things, from extreme heat, to a change in DNA which is called a mutation.

The fourth and final level is where a protein’s quaternary structure lies. In this arrangement, two or seperate teritary proteins are linked together in a certain pattern. In reality, proteins have very complex structures, and the quaternary structure reveals that structure.

Another interesting property that is worth mentioning is a protein’s size, which refers to the number of amino acids that make up the protein. For example, insulin is composed of 63 amino acids, whereas hemoglobin is composed of 248 amino acids.

With that, we’ll end our discussion on proteins. Proteins represent DNA commands in action. The passing of commands from DNA to the protein can summarized into a neat little equation that you may want to commit to memory. (And remember, all of this takes place inside of the cell).

The above equation is what is referred to as the Central Dogma of Life. This equation describes the flow of information from DNA to cell, with the end result being the formation of a protein by the cell. Today, life is defined, biologically, as this above equation. However, there is one slight problem. You’re probably wondering what the heck is RNA? In the next section we are take an upclose look at RNA, and see how it fits into our understanding of genetics.