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Proteins

Protein is the main structural material of eukaryotic cells, and it performs a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific three-dimensional structure that determines its activity. Proteins are also important for the immune response in defending the body against pathogens.

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Florida State University

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Video Transcript

In this video, we will cover proteins so proteins are going to make up approximately 50% of the dry mass of a cell. And they are going to have a lot of different functions within those cells and within biological systems in maintaining either regulatory levels or Homo static levels within those cells, or being catalysts in different reactions or facilitating different processes. Acting as signals acting as receptors, they carry out a whole range of functions. But to understand how those functions are performed, we have to have a fundamental understanding of how proteins are structured and how they function. So proteins are going to be similar to other polymers in that a protein itself is going to be a poly peptide, and a poly peptide is basically going to be a chain of amino acids. And what are these amino acids? Well, amino acids are going to be these organic molecules that contained both a car boxful group and in amino group. And these amino acids will serve as the Monem Eric sub units of our Polly peptide chain or of our protein. So how would we define them? Amino acids are going to be the monomers that make up our protein. And as we said, it's important to note that they have a car boxful group on one end and an amino group on the other, and there will be a chain that will hang off of the essential carbon. And actually, to understand the way that these amino acids are structured, let's just draw out a sample amino acid. So the amino group that we discussed, he's going to be right here, connected to a central carbon which is also called the Alfa Carbon, and that carbon will be connected to what is called this our group right here and that our group is going to be variable. And then there will be this car boxful group on this end and this our group, as we said, is going to be variable and it is also referred to as this side chain. So what side chain you have will determine what kind of amino acid you will have, and they're going to be different kinds of amino acids. They're going to be polar amino acids. There will be charged amino acids, so they'll actually either be, uh, negatively charged or positively charged, acidic or basic and there will also be non polar amino acids. And once again, the side chain right here. This our group will determine what kind of amino acid we have. So how do we make a protein? Like we said, the poly peptide is going to be this chain or linkage of a bunch of amino acids and the same way that we would link together carbohydrates to form a long Polly Sacha ride linking together Monem Eric sugar molecules, we can link these amino acids together using a condensation reaction so condensation reactions will allow for protein synthesis and specifically if we are to look at our amino acids, we remember that right here we have this Ohh that will depart once we try to add another another amino acid to the chain. So the hydrogen on the amino group on that and terminus as we refer to that amino group as the end terminus, this hydrogen right here of a nearby amino acid. So right here. So this draw this out really quickly here. This hydrogen is going to pair up with the O. H from our car boxful group on a nearby amino acid. And thus we have water that is going to leave and a chain that has formed and how do we form this chain? Well, there's going to be a peptide bond, so let's just redraw this here. And of course, this one is going to be attached to another one. Um, but let's just draw this out right here is going to be what is called the peptide Bond, and it will attach to amino acids together and hold them in place. And as you can see, these ones right here are also going to be peptide bonds because they are going to link to the next amino acid in that chain. So we know about the polarization. And as we said, this is going to be condensation reaction so water is going to be released, and it's important to note that these require energy to occur. They're not going to occur spontaneously. We need to put energy in in order to link up our amino acids, and the last thing that we have to note about our proteins is the fact that there will be different kinds of structure to protein, and these levels of structure will provide for the many different functions that proteins carry out. So let's call this the four levels of protein structure. So the first one is going to be primary structure, and the primary structure relates to the sequence of amino acids. So the sequence of amino acids that you have is going to be unique tau a protein and that will determine the primary structure. Then our secondary structure refers to Alfa he losses and beta sheets. And basically, if we're talking about the secondary structure, it is how these amino acid side chains will interact to form Alfa Hero season beta sheets and these, um, different arrangements. Now, fuel season data sheets will lead to different shapes that the protein conform. And then we have tertiary structure, which is going to refer to the three dimensional folding of our protein. So this will be three D folding of the protein in question, and there will be things like die sulfide bonds that will kind of hold this in place or maintain that shape. And there will also be hydrophobic interactions as well as other week non co violent bonding that occurs, for example, vander Waals interactions. And like we said, these hydrophobic interactions also will maintain the proper protein shape, and finally, the last level of organization will be This Quaternary structure and the Quaternary structure refers to groups of protein, uh, areas, so these are going to be called protein domains. So if we have different areas of the protein, say there's going to be an area that is going to be a beta chain area, there's another area that's going to be an Alfa chain area. We would refer to these areas as domains, and the way that our protein will arrange into domains will be governed by the co ordinary structure off that protein. So this was a brief overlook at how proteins are structured.

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JG
Julie G.

Millikin University

Dr. Bridgette D.

University of North Carolina at Wilmington

Molly F.

Florida State University