RNA
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LearningTranscript
00:00Protein, got to get your protein.
00:11Dear Tim and Moby, I get that DNA holds the instructions for your cells, but how do the
00:16instructions get carried out?
00:18From Olive.
00:19Good question, Olive.
00:21It sounds like you already know the basics.
00:24Almost every living cell contains DNA, or deoxyribonucleic acid.
00:29It's responsible for the differences between organisms, and it also controls how cells
00:33differ within an organism.
00:37Think about it.
00:38Cells are incredibly diverse.
00:40Motor nerves are long strings that transmit signals throughout your body.
00:44They're almost nothing like white blood cells, which are tiny spheres that help you fight
00:48infections.
00:49So what makes one a germ-killing machine while the other acts like an electric wire?
00:55The difference lies in molecules called proteins, the building block of all cells.
01:00DNA tells your cells which proteins to make, when to make them, and what to do with them.
01:06It tells your lens cells to form out of clear proteins so light can shine in.
01:10It tells cells in your pancreas to make insulin, which lets your body process sugar.
01:15All of these proteins are assembled right where they're needed, inside the cell.
01:21They're made out of simpler molecules called amino acids.
01:25The average human protein consists of hundreds of amino acids linked together.
01:31That's why protein is such an important part of the diet.
01:34Your body breaks it down into amino acids, the raw materials for, well, you.
01:40So assuming you eat right, your cells are swimming with amino acids.
01:44Structures called ribosomes stand ready to string them together into proteins.
01:49All they need are some instructions to follow.
01:53The protein recipes are encoded in DNA's unique structure.
01:57It's kind of a spiral staircase shape called a double helix.
02:01Each step is made up of a pair of molecules called bases.
02:05There are four different bases, and they stick together like puzzle pieces, always in the
02:08same pairs.
02:11You can think of bases as the words in a special kind of language.
02:16Each set of three bases translates to a specific amino acid.
02:20These base triplets are called codons.
02:23Hundreds or thousands of codons in a row form a gene, the recipe for a full protein.
02:29Here's the thing, though.
02:30DNA is trapped inside the nucleus, never leaving.
02:33How does it get the recipe out to the rest of the cell, where proteins are made?
02:37How indeed, Moby.
02:40Not a bad guess.
02:41DNA creates a sort of copy of the gene.
02:44The first step is transcription, which is just a fancy word for copying.
02:49A specially shaped molecule moves along the gene, unzipping the double helix.
02:54That exposes the bases on each strand.
02:58Using one strand as a guide, the molecule assembles a copy of the opposing strand.
03:03The copied strand is RNA, or ribonucleic acid.
03:07RNA is basically a half-DNA with a single helix instead of a double.
03:12And rather than pairs, RNA has exposed bases, just waiting to stick to their opposites.
03:17The RNA version of a full gene is called messenger RNA, or mRNA.
03:23Yep, because that's its job, telling the cell to build a specific protein.
03:29So mRNA leaves the nucleus and heads for a ribosome.
03:33This is the start of the translation stage, when the gene gets decoded into a protein.
03:38Well, you remember all those amino acids floating around the cell?
03:42There's something I didn't tell you about them.
03:44Each is attached to a short strand of RNA.
03:48Transfer RNA, or tRNA, is specially shaped to expose three bases at its tip.
03:53These are anticodons.
03:55They match up with the codon for the amino acid they're attached to.
03:59The ribosome holds the mRNA in place to expose its leading codon.
04:04When the matching anticodon comes along, they link up.
04:08The attached amino acid is left behind, and the mRNA advances.
04:12A new chunk of tRNA locks in place, and another amino acid is left behind.
04:17This repeats over and over, adding amino acids to the chain until the full protein is built.
04:24It is pretty involved, and that's just to build a single protein.
04:28Now think about this.
04:29Our cells are cranking out millions of proteins every second.
04:33Hence this protein shake.
04:42Well, that's barfy.