How the structures of different polymers are related to their functions

Polysaccharides

• The polymer/polysaccharide cellulose is formed from a beta-glucose monomer bonded by 1,4 glycosidic bonds, where every alternate monomer is inverted to form the glycosidic bond. These 1,4 glycosidic bonds mean that cellulose is a straight chain, unbranched polymer, and therefore hydrogen bonds form between parallel chains to create fibrils and microfibrils
  These cross linkages make cellulose strong, which is important as it is a component of plant cell walls, and must remain turgid to withstand osmotic pressure and prevent the cell from bursting. This structural support is important in plants to prevent leaves and stems from wilting, ensuring that the have the greatest surface area to obtain maximum sunlight exposure for photosynthesis

• Glycogen is a polysaccharide formed from the monomer alpha glucose, bonded by both 1,4 and 1,6 glycosidic bonds. This makes glycogen a highly branched polymer, which is important as it provides more ends and a larger surface area for faster hydrolysis via enzyme action. This releases more glucose as a respiratory substrate to produce ATP that can be hydrolysed and release energy. Glycogen is also helical and coiled, which makes it compact so that it can maximise energy storage, which is important for its function as the main storage polysaccharide in humans and animals

DNA replication/transcription

• DNA is a polymer made up of repeating nucleotide monomers. Each nucleotide in DNA is covalently bonded to the adjacent nucleotide by a phosphodiester bond between the deoxyribose and the phosphate group (to create the sugar-phosphate backbone). This phosphodiester bond is formed in a condensation reaction by DNA polymerase and is a strong covalent bond, leading to the formation of the DNA polymer 
  The sugar-phosphate backbone and creation of the double helix means that the stronger covalent bonds are on the outside of the DNA polymer, and the weaker hydrogen bonds are at the centre - providing protection of the genetic code within the polymer

• The two DNA strands of the double helix are held together by hydrogen bonding between complementary base pairs, where adenine pairs with thymine via 2 hydrogen bonds, and cytosine pairs with guanine via 3 hydrogen bonds 
  Hydrogen bonds are weak in isolation (although strong collectively) allowing easy unzipping by DNA helicase to expose the template strand for DNA replication
  The complementary base pairing via hydrogen bonding is necessary to help maintain the order of the genetic code for DNA replication to produce an identical DNA copy. This is because it enables one strand of DNA to acts as a template for the other during semi-conservative replication. This is vital in ensuring genetic consistency between generations of cells, and the passing on of genes to offspring.  

Proteins

• Proteins are polymers made up of repeating amino acid monomers. The primary sequence of these amino acid monomers determines the bonds that form in the tertiary structure, and therefore the overall functioning of the polymer

• The tertiary structure of the protein is the 3D folding of the polypeptide chain, as determined by interactions between the R groups. The structure of enzymes as a polymer of amino acids is related to its function through the tertiary structure of the active site. If the tertiary structure of the active site of an enzyme (for example maltase) is not complementary to the shape of the substrate maltose, then they are unable to bind and form an ESC. This decreases the hydrolysis of the glycosidic bond in maltose to release 2 alpha glucose monomers, and therefore reduces the absorption of glucose into the ileum epithelial cell.
  Tertiary structure of the active site of enzymes is important for specificity = acetylcholinesterase as an example of the induced fit model of enzyme action. Once bound to the substrate acetylcholine, a slight conformational change is induced to the tertiary structure of the active site to make it more complementary to the substrate (increases efficiency and specificity of the enzyme - increased ability to stop nervous impulses continuing indefinitely by breaking down the neurotransmitter)

• Carrier proteins have a binding site with a specific tertiary structure that is a complementary shape to the shape of the substrate it transports. Once the substance has bound to the binding site, it induces a conformational change to the shape of the carrier protein in such a way that the substrate is released to travel through the protein across the phospholipid bilayer
  Na+, coupled with the active uptake of glucose, is transported by facilitated diffusion through SGLT1 (a symporter) which is embedded in the ileum epithelial cell membrane. This creates a concentration of glucose higher in the epithelial cell than in the blood, so glucose is able to be transported by facilitated diffusion through GLUT2 and be absorbed into the bloodstream.

Cell recognition and the immune system

• Antibodies are globular proteins and polymers made of amino acid monomers that are joined by peptide bonds. They have a quaternary structure, consisting of four polypeptide chains – 2 heavy chains and 2 light chains – and two variable regions, each with a unique tertiary structure 

  The tertiary structure of the binding sites on each antibody are complementary to a specific antigen, allowing them to bind and form an antigen-antibody complex. Each antibody has two binding sites, meaning each antibody can bind to two identical antigens – thus enabling agglutination to occur. This clumps pathogens together to make it easier for them to be located by phagocytes for hydrolysis. The structure of antibodies as polymers are essential to their function, because if they are not a complementary shape to the antigens, it would result in no immune response against the pathogen or abnormal self-cells when autoimmune diseases like lupus occur. This in turn would cause damage to body tissues (e.g. when pathogens release toxins or when abnormal cells divide uncontrollably and negatively impact normal bodily function).