 Hello. Today we are going to talk about proteins and as macromolecules, proteins have structure of the monomers that are called amino acids. Very important large biological molecules. Now you can see here some of the names of the amino acids like alanine, valine, organine, sustain and so forth. They are different but they all have something is in common which makes them to be monomer. Okay? So as you see here I'm trying to code in different colors to emphasize that those molecules are amphoteric. That means that they're both bases and acids as you can see. There is a carbon molecule which is the same for each and every amino acid that has connection with amino group. This is amino group and this is carboxyl group which when you see something like this that means that it's organic acid. There is hydrogen and something that we label as R which is a side group. Even though it looks small it is actually critically important and you will see in a short while why. So what is happening? Remember what we said about macromolecules that monomers are put together to dehydration reaction and taken apart through hydrolysis. So where is that happening? This is a little bit differently stated the structure of the amino acid and if you take a look here we have OH from one amino acid that will become water and we have H from the amino group. So is it happening just that? No we have to have enzyme that is putting them together like a soldering iron. Okay? And they are so we have one water here one molecule water and the rest of it is forming peptide bond. Okay? Now the next monomer we are going to the next amino acid the same situation is happening these are going to form the molecule of water and the rest will have peptide bond. That peptide bond is why we call the base of the proteins actually polypeptides because each and every protein has to be polypeptide but not all of them are just one polypeptide it could be more than one. So polypeptide that comes from peptide bonds that are built chemical bonds that are built from what is left over of the amino acid after taking the water away. Now what we saw there that is the primary structure. So primary structure of the protein very important is only peptide bonds between them. Now when we have many parts of one polypeptide they can be in the form of beta sheets. Okay? Or they can form alpha helix so there are spiral spirals between them. Which bonds are these? Hydrogen bonds. Hydrogen bonds are strong enough to hold the structure together but they're not chemical bonds that are stable enough if there is something like for instance if there is a heat that can be applied and break them apart. Okay? Now alpha helix are here but the sheets are nails it's all the same. Right? Now proteins are if you take a look here spiderweb is one of the proteins. Silk is the protein but the proteins have a variety of the functions and they are enzymes which we are going to talk a little bit more later which enzymes are mostly in a globular form so those that we mentioned about like hair and nail those are structural proteins and tertiary structure is the one when actually all the fun comes. And where is that fun coming from? You remember from lipids that we may have say like hydrogen hydrophilic and hydrophobic interactions. So if these two amino acid if they're acids if there are group is hydrophobic okay? That means that they're going to get to each other and hold that. That is one of the bonds. The other bond could be that here for instance we can have disulfide bridge where say like this thing and methionine which have sulfur in them they can form the bridge of the two sulfur atoms in their structure. Very important. We may have hydrophilic interactions we have Wanderwald's forces and so forth. So all this gives the globular structure which looks pretty much like egg white so it can be moved around change the shape. Please remember everything that is in biology has to do with shape. So here we can actually see how quaternary structure so this would be additional structure and not every protein actually has this structure. As you can see these here are built from two different polypeptides in the case of hemoglobin we have four of these so this would be another two polypeptides okay? That are bring together and they're forming functional protein. In the case of hemoglobin there are four iron atoms that are embedded in each and every of the polypeptides. Now regarding denaturation you may heard about that denaturation that means breaking down all of these bonds that we mentioned and getting it back to that primary structure. Primary structure bringing back to primary structure that is denaturation. What happens when a boil egg? Can that egg white be runny and jiggly again? No because it was denaturated and that is what is happening usually when we boil something to kill bacteria and so forth. What we actually do we denaturate speaking of the temperature the fever that is above 42 degrees Celsius is very dangerous because of that fever is actually enough to do denaturation of the proteins that are in our brain and basically kill us by disabling function of the brain. That would be short about the proteins. Thank you.