Protein plays a huge role in our bodies, but how it is made? This lesson describes how ribosomes read the message hidden within our genetic code in order to produce protein. A lesson summary and brief quiz are included.
DNA, Ribosomes, and Proteins
Have you ever wondered how DNA is actually used to create your unique features? After all, DNA is simply a collection of molecules put together in a specific sequence. How can this assortment of information actually be decoded to create the characteristics of living organisms?
Well, it has to do with a cellular component called a ribosome. Ribosomes are cellular organelles that interpret our genetic sequence and produce a protein. Proteins are large molecules made from subunits called amino acids. It is proteins that create things like eye color or hair color. But they’re also responsible for many other factors, such as aiding in digestion, building and/or repairing tissue, and transporting material into our cells. In this lesson, we’ll explore how this happens, how protein produced from our DNA, and what the ribosome’s roleis in this process.
Before we get down to the business of decoding our DNA and making a protein, let’s first recap some basic biology. DNA is the genetic material found within living things – yourself included. This DNA is double stranded and looks much like a twisted ladder. It exists within the cells of your body.
Inside those cells is a region called the nucleus. The nucleus is the cellular organelle where DNA is housed inside the cell – think of it as a room inside your house. The house is analogous to a cell, and the room inside represents the nucleus.
Now, an important note: DNA does not leave the nucleus. Instead, it remains inside where it is safe and less likely to be damaged. This seems like a good idea; however, ribosomes cannot enter the nucleus! This creates a problem. How can ribosomes decode the message DNA contains if they can’t get to it?
Enter a new molecule called messenger RNA, or mRNA for short. mRNA is a single stranded molecule created using the DNA template. It, therefore, contains the same information as DNA, but it is smaller than DNA. This process of making mRNA from DNA is called transcription. And because the mRNA created through transcription is smaller than DNA, it means that mRNA can exit the nucleus and come into contact with ribosomes – problem averted. Just remember that mRNA carries DNA’s message to the ribosome for decoding. The name is perfect; mRNA truly is a messenger molecule.
Double stranded DNA (inside the nucleus) gets transcribed into single stranded mRNA (leaves the nucleus) and then connects with ribosomes.
Now that mRNA has carried its message outside the nucleus, it’s ready to be read by ribosomes. The process of ribosomes decoding the mRNA message and creating protein is called translation. Here’s how translation works.
First, understand that mRNA is a specific sequence of molecules, just like DNA. These molecules are represented using the letters A, U, C, and G. So for our example, let’s suppose the mRNA sequence being read by our ribosome is AUGGGCAAAUACUGA. In reality the sequence would be much longer, but for demonstration purposes this sequence is sufficient. A ribosome would read this sequence three letters (called bases) at a time. So to a ribosome, our initial sequence would look something like this: AUG GGC AAA UAC UGA. These three letter sequences are called codons. Ribosomes create chains of amino acids based on the sequence of codons they read. We can determine this amino acid’s sequence by using a codon table. You’ll read it from the inside out.
To begin, we have the codon AUG. This is known as a start codon. It tells our ribosome to start making a protein. The codon GGC then calls for the amino acid Glycine (Gly). AAA calls for Lysine (Lys), UAC for Tyrosine (Tyr), and UGA finishes by coding for a stop codon, which tells our ribosome to stop making the protein. So, our example protein would consist of three amino acids strung together in a chain: Glycine – Lysine – Tyrosine. Again, remember that actual proteins are thousands of amino acids long, but the process described here is how ribosomes produce them.
To recap, our DNA is housed inside the nucleus of our cells. The message coded for by this DNA must be converted into the messenger RNA molecule before it can leave the nucleus. This coding process is called transcription. Once outside, the newly transcribed mRNA is read by a ribosome. Ribosomes are the cellular organelle responsible for making proteins. Proteins are large molecules comprised of long chains of subunits called amino acids. The process of a ribosome reading an mRNA molecule and producing a protein is called translation. It involves using codons.