Placeholder Image

字幕列表 影片播放

  • How do you make a human? I mean, after the fertilization part. How does your body know

  • exactly where to put each finger and how to orient the heartThat's where our genetic

  • instructions, or DNA comes in. But to understand DNAwe need to talk about creme brulee.

  • I have no idea how to make one of these tasty morsels, so I check out a recipe site, scroll

  • through a bunch of ads and boring stories, and I'll get an ingredients list and instructions.

  • Now, imagine instead of doing this with the big letters and words in an online recipe

  • list, you're doing the same thing at the tiny, molecular level. You have cellular machinery

  • that reads the instructions, and machinery that copies it, and separate pieces that assemble

  • the ingredients into bigger pieces. The list of ingredients in the recipe that makes our

  • bodies is called DNA. Today we're talking about the genetic instructions for your body,

  • the cookbook that makes the ingredients that make up you. We'll talk about the structure

  • of DNA and how you go from gene to those beautiful brown eyes of yours.

  • So you're not a delicious

  • dessert, sadly. The ingredients that go into you are a little more complicated. Remember

  • back to episode one when we talk about biological hierarchyyour body is a collection of

  • organ systems, which are collections of organs, which are made of tissues, which are made

  • of cells. That whole thing? Well those cells are made of nonliving things like water, lipids,

  • and proteins. And our cells make proteins to do different jobs around the bodyThese

  • proteins aren't alive, they're complex bundles of amino acids that serve different

  • purposes. And they're not just for building musclesThe pigment that makes your eye

  • color is a protein. The keratin that builds your hair is a proteinBut you also need

  • to build proteins for a normal physiology, so you have instructions for proteins like

  • antibodies and enzymes in your genes as wellWe have about twenty to twenty five thousand

  • genes, or recipes, in our cookbookGenes are the genetic instructions that tell your

  • cell to make a specific proteinSo your genes don't tell your body to make brown

  • eyes, they tell it to make a specific protein, which collectively look like brown eyes at

  • the large scaleIt's like you inherited this cookbook from your parents. Or rather, a copy of your

  • mom's cookbook, and a copy of your dad's cookbook. The vast majority of recipes were

  • the same, but a few might be slightly different. Let's say on page five hundred thirty two

  • in the cookbooks, there's a section for some kind of crunchy tortilla based food.

  • In your dad's cookbook is a recipe for tacos, in your mom's cookbook is tostadas. You'll

  • end up making one of those recipes. These are alleles, variations in the same gene.

  • In your body, this might be an allele for freckles from your dad but an allele for no

  • freckles from your mom. Two versions of the same gene, but your body either has freckles

  • or it doesn't. Both fulfill the same role but end up with slightly different results.

  • Each of those recipes has to be written in a language that the reader can understand,

  • and in this case, the recipe is written in DNA. DNA stands for Deoxyribonucleic Acid,

  • it's this long molecule with the classic double helix shape. And DNA is made from smaller

  • molecules called nucleotides, which have a few important piecesIts backbone is made

  • up of a sugar called deoxyribose, the D in DNA, and a phosphate. Together, these give

  • the DNA molecule some structure. Between these backbones are four nitrogen basesadenine,

  • thymine, cytosine, and guanine, or A, T, C, and G which are held together with weak hydrogen

  • bonds. Because of their complementary shape, A will always hook up to T, and C will always

  • hook up with G. So if you know what one side of the DNA strand looks like, you can tell

  • what the other side will look like too. ACA on one side will be met with TGT on the other.

  • We call these A-T and C-G pairs base pairs. As a result of DNA's structure, these opposing

  • strands of nucleotides have specific directions. And just like how we need to know if the language

  • in our recipe should be read left to right or right to left, our cellular machinery needs

  • to know the direction of DNA too. To tell which part is the front and which is the back,

  • we need to look at the sugars in the DNA backboneOne end is called the five prime while the

  • other is called three primeIf you were to dissect one of the sugar-phosphate backbones,

  • you'd see the carbons atoms in the sugar molecule arranged in a certain pattern. Biologists

  • assign them a number, so this one is one prime, this is two prime, all the way to five prime.

  • To determine DNA's direction, you have to look at which end is leading the sequence.

  • One end will have the five prime sticking out, and the other will have the three prime.

  • DNA is usually written starting with five prime and ending with three prime. So you

  • could have a sequence that goes 5 prime TTAGGG 3 prime. Bonus points if anybody can tell

  • me what that sequence refers to in the comments. Example aside, all the base pairs in your

  • DNA make up a code. They're the genes that tell your body what proteins to make. Some

  • genes are short , but one gene, the gene that codes for a protein called dystrophin, is

  • over two million base pairs long. But how do our cells read DNA and make proteins? First,

  • I want to show you what's actually making the protein. It's this little guy called

  • a ribosomeIn our cookbook example, the ribosome is the chef who actually puts the

  • recipe together. It takes amino acids and assembles them into bigger proteinsHere's

  • the thingribosomes read RNA, not DNASo DNA goes through a process called transcription

  • where it's rewritten as RNA or ribonucleic acid. It's chemically similar to DNA but

  • instead of deoxyribose sugar, it's made of ribose. Also, instead of the Thymine, or

  • T base, it has Uracil. But structurally they're quite different. DNA has double strands, RNA

  • has single strands and can be tweaked into different shapes. Transcription starts when

  • enzymes called RNA polymerase move along the DNA strand from five prime to three prime,

  • unwinding the DNA into two pieces. Now, remember how each base pair can only pair with one other

  • specific base? A with T and C with G? That comes in handy again. We can use these newly

  • unwound strands as templates to create new RNA. So if you know what one side is, you

  • know the other side will be a sequence of opposite basepairs.

  • These new RNA strands are made in little sections at a time. So while we

  • might have DNA strands that are hundreds of millions of base pairs long, most RNAs top

  • out at a few thousand base pairs. Some of these RNA are the end product and are useful

  • in the cell but otherscalled messenger RNA, or mRNA, go onto the next step to code

  • for specific proteinsThese things are going to take the message from the DNA in the nucleus

  • out to the cytoplasm. At this point we have mRNA that's been transcribed from DNA. This

  • new structure is ready to be fed into those ribosomes in a process called translation

  • to generate some proteins. For those wondering, the whole ribonucleic acid and ribosome thing

  • isn't a coincidence. Again, these ribosomes are the chefs in our cookbook analogythey're

  • where our cells actually make the proteins, and we have millions of them per cell. When

  • an mRNA enters a ribosome, the ribosome reads the mRNA three letters, or bases, at a timeEach

  • of those three letter combinations, or codons, codes for a new amino acidSome amino acids

  • like tryptophan can only be coded by one combination of bases, in this case, UGG. But some amino

  • acids can be coded by multiple combinations. Like tyrosine can be coded by a sequence of

  • UAC or UAU. This process of translation and protein building repeats, grabbing new amino

  • acids to throw on the growing protein. It continues until the ribosome reads a codon

  • that tells it to stop. Then translation is over. Our cells made the protein and it's

  • off to wherever it's supposed to go. What I find so interesting is how universal this

  • genetic code is. That code of amino acids coded by codons is used by almost a hundred

  • percent of lifeIt doesn't matter if it's in our bodies, your cat, or an E Coli bacteria.

  • The same three letter codes tell ribosomes to make the same amino acids. This genetic

  • code was discovered back in the mid 1900s and we still don't have an answer for why

  • it's so common or how it came to beGenetics is one of the coolest studies in biology and

  • is obviously much bigger than one video can contain. Next time, we'll dive into how

  • DNA makes copies of itself so efficiently, and where that fits in with the growth and

  • copying of cells themselves. Thanks for watching this episode of Seeker Human, I'm Patrick Kelly.

How do you make a human? I mean, after the fertilization part. How does your body know

字幕與單字

單字即點即查 點擊單字可以查詢單字解釋

B2 中高級

你的DNA是如何造就你的 (This Is How Your DNA Made You)

  • 22 2
    Summer 發佈於 2021 年 01 月 14 日
影片單字