The Importance Of Polymers In Living Organisms

The Importance Of Polymers In Living Organisms Polymers are fundamental to all living organisms; they are structures that, without which, the world could not exist as it does today. They constitute the building blocks of everything living:
DNA and RNA; they form proteins and carbohydrates; and they have given us the ability to craft synthetic polymers to perform all kinds of crucial roles in modern life. Polymers are made up of many individual monomer units joined together in a long line. These monomers, which are defined simply by their ability to bind to themselves in a chain, don’t all have to be the same, so there are an almost infinite number of structures formable. This explains the huge variety of roles that polymers play, and their existence in everything living.
Whilst two polymers may be extremely distinct from each other, just small differences in their structure can completely alter their properties. For example, both starch and cellulose are made from the same monomer, glucose, and have the same glucose­based repeat units.
There is only one difference. In starch, all the glucose repeat units are oriented in the same direction (they are all α­glucose). But in cellulose, each successive glucose unit is rotated 180 degrees around the axis of the polymer backbone chain, alternating between α­glucose and β­glucose. Polynucleotides (made up of nucleotides) such as DNA and RNA, are perhaps the most fundamental of all polymers. DNA codes for every living organism known to man, possessing genes determining everything from behavioural characteristics to food metabolisation.
Together with RNA, strings of three nucleotides (any of adenine, cytosine, guanine and thymine) known as codons code for a single amino acid, which in turn join together form another polymer known as a protein. The only way for DNA to hold the huge amount of information required is for it to be a polymer. There is no way that a single molecule could hold enough information to fight off infection, for example, let alone control every single one of an organism’s properties. DNA has a helical structure: this means two DNA strands form a spiral, winding with the two polynucleotide chains running in opposite directions. The sugar­phosphate backbones of the two DNA strands wind around the helix axis like the railing of a spiral staircase, whilst the bases of the individual nucleotides are on the inside of the helix, stacked on top of each other like the steps of a spiral staircase. This allows the genetic code to be stored in an extremely secure, rigid manner, only accessible when carefully unzipped by the enzyme (another polymer) DNA polymerase to undergo transcription into mRNA, before being and translated into a chain of amino acids. Proteins are perhaps the next most crucial polymer. Built from a collection of 20 amino acids joined together by peptide bonds into a polypeptide, and folded into a 3D shape, they perform a huge variety of tasks within an organism. Almost everything that happens in a cell happens because of one or more proteins. Glycolysis is catalyzed by a set of 10 different enzymes, which are proteins. The Kreb's cycle requires protein enzymes, as does ATP synthesis in mitochondria. DNA replication and regulation of gene expression also involves proteins. They are not just enzymes though; there are structural proteins, motility proteins, regulatory

proteins, transport proteins, hormonal proteins, receptor proteins, defensive proteins, and storage proteins.
The human immune system wouldn’t be able to function without proteins as there are proteins known as antigens on each cell/molecule to identify if the molecule is foreign or not. If the proteins are foreign then the immune system will send antibodies
(proteins produced by B­lymphocytes that are specific to the foreign antigens) to bind to the antigens, thereby clumping them together and allowing them to be engulfed. Proteins have a structure that is very specifically tailored to their duties. Their primary structure is the sequence of amino acids, determining what actually makes up the protein.
The secondary structure is how they’re folded: either as an alpha helix or beta sheet. The tertiary structure is how it is folded: this is a crucial part as it controls the ability of the protein to bind to another molecule. For example, an enzyme becomes denatured when its tertiary structure is altered and it is no longer able to bind a substrate to its active site. Finally, the quaternary structure is how subunit polypeptides come together to form one molecule. In haemoglobin, four haem groups join together; each are able to bind to a single oxygen molecule. This means that one protein can carry four O molecules.
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On top of these are carbohydrates.
Carbohydrates are molecules made solely up of Carbon,
Oxygen and Hydrogen. Their monomer is known as a monosaccharide, with a full polymer called a polysaccharide, which is formed via glycosidic bonds. One of their more important uses is as a storage molecule such as starch or glycogen, which, as mentioned earlier, have very similar structures to each other. Starch consists of glucose molecules, which can be easily broken down by amylase into maltose (a disaccharide). This maltose is then broken down by maltase into glucose, which undergoes glycolysis to release energy. As it is a large molecule it is insoluble in water which means that it doesn’t affect the water potential in cells.
This is beneficial as if glucose (a monosaccharide) was stored in the cells on its own it would dissolve and form a sugary solution that would then draw water into the cell and could potentially cause osmotic lysis. Another key polysaccharide is chitin which consists of many
N­acetylglucosamine (which unlike other carbohydrates contains Nitrogen). The main property of chitin is the fact that it forms Hydrogen bonds between molecules, enhancing the strength of the polymer. Due to this property it is found in the exoskeletons of crustaceans and other arthropods, the cell walls of fungi and the beaks of cephalopods such as fungi.