You Are Your Proteins Reading



You Are Your Proteins Reading

You have probably heard many times that “your DNA determines your characteristics.” Did you ever wonder how DNA does that? DNA determines all your characteristics (and the characteristics of every plant, animal, fungus, bacterium, etc., in the world) by determining what proteins your cells will synthesize (make).

Why are proteins so important? Because of the many things they do. There are many types of proteins, and each of these types performs an important kind of job in your body. Structural proteins help build parts, carrier proteins help transport nutrients and enzymes help with chemical reactions. For example, structural proteins form the “bricks and mortar” of your tissues. Two of them, actin and myosin, enable your muscles to contract. Another type of structural protein, keratin, is the basic component of hair. Carrier proteins transport important nutrients, hormones, and other critical substances around your body. One of these proteins is hemoglobin, which carries oxygen through your blood to your tissues.

Another large class of proteins is the enzymes. Enzymes are the body’s workhorses. They carry out chemical reactions in your body. Enzymes digest your food, synthesize fats so your body can store energy, and carry out the work of making new cells. They make molecules and perform activities necessary for life. In fact, if you want to sum up the importance of proteins in your body, you could say: “Nearly every biological molecule in my body either is a protein or is made by proteins.” So, by telling your cells what proteins to synthesize (make), DNA controls your characteristics.

What Proteins Are

What exactly is a protein? A protein is a biological molecule made of many small units linked together in a chain (rather like beads on a string). The units are amino acids, small molecules composed of carbon, hydrogen, oxygen, and nitrogen. There are 20 different amino acids that can be used in making up your proteins.

Imagine sitting down to make a string of beads with 20 containers, each filled with a different type of bead. You may use as many or as few of each kind of bead as you wish. You may string them in any order you wish, and you may use any number of beads you wish. The beads represent amino acids, and any string of them represents a protein. You can get an idea of the infinite variety of proteins that could be made!

However, in the cell, one thing is different from our example. The cell is handed an instruction sheet that tells it what beads (amino acids) to string to make a particular chain. The instructions come from the cell’s DNA.

How DNA Directs Protein Synthesis

Each strand of DNA contains millions or even billions of nucleotides. The order of these bases makes up the code for specific characteristics in the body like eye color or nose-hair length. Just as we use 26 letters to code for what you are now reading, our DNA uses 4 letters (A, T, C and G) to code for millions of different characteristics.

DNA contains a genetic code or instructions for the order of amino acids. Different segments or parts of a DNA molecule code for different characteristics in the body. A GENE is a segment of DNA that is the directions for making a specific protein. A chromosome is made up of many genes.

In your cells, the DNA is located within the chromosomes in the nucleus. DNA contains all the instructions for making every protein in your body. However, your cells assemble (put together) proteins at the ribosomes, located in the cytoplasm. An individual ribosome makes only one protein at a time, so when your cell needs to make a protein, a “working copy” of the instructions for that one protein is copied from the DNA and sent to the ribosome for use. This working copy is “messenger” RNA (mRNA).

After the base sequence of a gene (DNA) is copied into mRNA, the mRNA travels to the ribosome, where its code is “translated” into protein. The translation step is carried out by a second type of RNA called transfer RNA (tRNA). The tRNA matches the correct amino acids to the codons (3 nucleotides) in the mRNA. The amino acids are linked together to make the new protein.

Wait a Minute—Isn’t Protein a Kind of Food?

Most of us have heard that “protein is part of a healthy diet.” In fact, most people think of food when they hear the word “protein.” So what’s going on? How does protein in the diet fit into a discussion of genes?

The protein you eat is composed of individual protein molecules made by plant and animal cells. Animal muscle tissue (meat) is particularly rich in protein (remember actin and myosin, mentioned above?). When you eat protein, regardless of its source, your digestive enzymes break the individual protein molecules down into amino acids (like taking the beads off the string). The individual amino acids are used by your cells to make your proteins— a form of biological recycling—or can be further broken down for energy.

Questions:

1. What does DNA determine?

a.

2. Name a few main types of proteins.

3. Sum up the importance of proteins.

a.

4. What is a protein?

a.

5. Where are the instructions for making proteins found?

a.

6. What is a gene?

a.

7. Explain the relationship between chromosomes and genes.

a.

8. Where are proteins put together?

a.

9. DNA cannot leave the nucleus so you make a “working copy” of the DNA. What is this called?

a.

10. What is a codon made of?

a.

11. How are our proteins related to foods we eat?

a.

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