下面有8段文字,同学们按班长排的顺序进行录音讲解(只需要音频),每4个同学一段。比如1-4号同学录第一段,5-8号同学录第二段,以此类推...... 1 Swap one of those fatty acids for a phosphate group and you have a phosph o lipid . these make u p cell membrane walls. Since that phosphate group gives that end polarity , it’s attracted to water. And the other end is non polar and it avoids water. So if you were to scatter a bunch of phospholipids into some water they would automatically arrange themselves like this , with hydrophobic ends facing each other, and hydrophilic ends sticking out to face the water . Every cell in your body uses this natural structure to form its cell wall in order to keep the bad stuff out and the good stuff in . 2 A nother class of lipids is the steroids . Steroids have a backbone of four interconnected carbon rings ,which can be used to form hundreds of variations. The most fundamental of them is chol e sterol , which binds with phospholipids to help form cell walls. But they can also be activated to turn into different lipid hormones. 3 And so now we appro a ch the most complicated, powerful, polymorphously aw e some chemicals in our body: the protein. And by complicated I mean that they are probably the most complicated chemical compounds on the planet. In fact, they are so amazing that we’re going to so a separate episode on them,and how they’re created by DNA. 4 But right now , in you, there are tens of thousands of proteins doing everything they can to keep you alive. There are enzymes regulating chemical processes, helping you digest food. There are antibodies connecting themselves to invaders like bacterium and viruses so that your immune system can get them . There are protein endorphins that mess around with your brain and make you feel emotions. But they’re everywhere,they do everything! And proteins do all of this stuff using only 20 differ ent ingredients.And these are the amino acids. 5 Just like fatty acids, amino acids have a carboxyl group on one end.On the other end they have an amino g r oup.Amino acid! Now hey!,I don’t k n ow if you’ve noticed this, bu t this is the fist time nitrogen has shown up in our food This is super important, beca u se despite the fact that nitrogen is everywhere,it’s like 80% of the air we can’t just pull it out of the air and pull it into our bodies. We have to get nitrogen from food. And so we have to eat foods that are high in protein like this egg which by it’s very virtue, because all the white part is protein, it contains a goodly amount of nitrogen. 6 Now in the middle of the amino and the acid group is a carbon. It shares one of electrons with good old hydrogen and the other electrons free to be shared with “R” which is just a kind of fill in the blank. We call it “ The R group”.It can be also called a side chain, and there are 20 different kinds of side chains.Whatever fits in that blank will determine the shape, and the function, of that amino acid.So if you put this in there you get V aline , an amino acid that does a lot of stuff like protecting and building muscle tissue.If you put this in there,you get tryp t ophan,which may be best kno w n for its role in helping you regula te mood and ener g y levels. 7 Amino acids form long chains called polypeptides. Proteins are formed when these polypeptides not only connect but elaborate and frankly really elegant structures. They fold, They coil. They twist. If they were sculptures I would go museum every day just to look at them.And I’d walk straight past the nudes without even looking. 8 But protein synthesis is only poss ib le if you have all of the amino acids necessary, and there are nine of them, that we can’t make ourselves. Histidine, isoleucine, leucine lysine methionine phenylalanine threonine tryptophan and valine. By eating foods that are high in protein we can digest them down into their base particles and then use these essential amino acids in building up your own protein . Some food, especially ones that contain animal protein, have all of the essential amino acid including this egg.