Genes, proteins, and traits | Inheritance and variation | Middle school biology | Khan Academy

• [Instructor] Hi, everyone. This video is all about how the information in an organism's genes is expressed as its traits. This occurs through the action of molecules called proteins. But before we get into the details, let's start with the basics. What are traits? Well, traits are an organism's observable characteristics, and there are some really weird but really cool traits out there in the animal kingdom.

Spiders, for example, can make seven different types of silk. Elephants have an amazingly low risk of developing cancer. And some jellyfish have the ability to glow. That's right! The crystal jelly can bioluminesce, or glow in the dark, all on its own. So now let's dive into the details of how these traits are expressed. Specifically, let's look at the jellyfish trait of bioluminescence.

We know that an organism's traits are affected by its genes. So let's travel into the nucleus of the crystal jelly's cells to where its genes are found, on chromosomes. A chromosome shown here is a cell structure that contains a coiled-up DNA molecule. I personally like to think of chromosomes as the packaged and organized version of DNA.

A DNA molecule is made up of subunits, called nucleotides. Nucleotides are often called A, T, C, and G, which stand for adenine, thymine, cytosine, and guanine. A gene is a specific stretch or a chunk of nucleotides within a DNA molecule. So a chromosome and its DNA are like a cookbook that contains recipes for making an organism. Genes are the recipes.

And just like how letters are arranged in a specific order to form words in a recipe, the nucleotides in a gene are also arranged in a specific order to convey information. So what does the cell make with these gene recipes? The cell uses the information in genes to make other molecules called proteins.

So our crystal jelly must have genes on its chromosomes that are responsible for its trait of bioluminescence. Because of work done by scientists, we now know that the jellyfish's bioluminescence involves one gene in particular. The coding sequence of this gene is made up of roughly 700 nucleotides, all arranged in a specific order.

And this gene acts like a recipe for making a protein called green fluorescent protein, or GFP, for short. Whenever you hear the word fluorescent, just think glowy. GFP is a glowy protein that can emit green light. And it's this presence of GFP in the jellyfish's cells that allows the jellyfish to bioluminesce.

But proteins can do so much more than glow. There are thousands of tasks that different proteins carry out in order for cells to function. Some proteins help provide structure, some help move substances into and out of the cell, and others help carry out chemical reactions. All proteins are made up of subunits called amino acids which are connected in a chain.

It's the order of nucleotides in a gene that determines the order of amino acids in a protein. And the order of amino acids is important because it determines the 3D shape that the protein will take on. And a protein's shape, in turn, affects its function.

For the GFP protein, this protein has a special sequence of three amino acids that end up in the middle of a barrel-like structure when the protein takes on its 3D shape. These amino acids form the part of the protein that can fluoresce. They can absorb energy and then emit that energy as green light. So to sum it all up, genes affect traits through the actions of the proteins that they encode.

The order of nucleotides in a gene determines the order of amino acids in a protein. And a protein's amino acids determine its structure and its function. The crystal jelly's bioluminescence and the discovery of GFP highlight why this knowledge is so important.

Scientists have used the GFP gene and protein to make countless discoveries. Now, researchers can attach GFP to other things, such as other proteins or viruses, making them visible through bioluminescence and easy to track. GFP has made the invisible visible, and it's allowed researchers to learn how neurons develop and how cancer cells spread.

And all of this research started with wondering about a single trait observed in the crystal jelly. Similarly, scientists are studying the properties of spider silk proteins in order to make new biocompatible materials. And they're also studying elephants for clues about how to prevent cancer in humans.

What animal trait do you think will lead to the next big discovery?