Polymers

• there are two different methods of forming polymers

  • addition polymerisation
  • condensation polymerisation
• addition polymers are made from alkene monomers. they are formed when the double bond breaks
• addition polymers are saturated (single bond) which makes them unreactive, as wells as long-lasting and non-biodegradable
• addition polymers can be incinerated but produces toxic greenhouse gases
• recycling of addition polymers is expensive but it is an alternative solution to landfill or incineration. one issue with recycling is that different types of plastic must be recycled in different ways
• condensation polymers are formed from two monomers with functional groups at both ends. as monomers join together, a small molecule such as water is eliminated
• polyamides are formed when a dicarboxylic acid reacts with a diamine. the reaction releases water and forms an amide linkage. the water is formed from the OH from carboxylic acid and a H from the amine
• polyesters are formed when a dicarboxylic acid reacts with a diol. the reaction releases water and forms an ester linkage. the water is formed from the OH from carboxylic acid and a H from the diol
• both polyesters and polyamides are biodegradable. they can be hydrolysed in presence of an acid or alkali
• Amino acids have an amine group at one end and a carboxylic acid at the other end
• When amino acids join they form a peptide link (CON)
• Amino acids join to form polypeptides
• A zwitterion is a species that has both a positive and negative change on different parts of the particle. Amino acids form zwitterions when the carboxylic acid group gives a Hydrogen to the amine group
• Peptide links can undergo hydrolysis to break down into amino acids. This occurs when the polypeptide is heated under reflux with 6M HCl
• amino acids consist of a central carbon atom which is directly bonded to an amine group, a carboxylic acid group, a hydrogen atom and one changeable R group
• The R group determines the size, polarity and name of the amino acid
• glycine is the only amino acid that does not display optical isomerism as the central atom is bonded to two hydrogen atoms
• the body only uses 21 different amino acids
• Peptide links can undergo hydrolysis to break down into amino acids in the presence of 6M HCl under reflux
• 2 amino acids form dipeptides. 3 amino acids form tripeptides
• Proteins are molecules which contain more than 50 amino acids. A particular protein has a fixed sequence of amino acids
• Primary proteins have one long chain of amino acids
• Secondary proteins form when peptide links form hydrogen bonds with each other. Results in a chain which isn't a straight line.
• Secondary protein shapes

  • Alpha helix - DNA but one
  • Beta pleated sheet - folds into parallel strands
• R groups on amino acids point to the outside of the protein helix
• Tertiary protein structures

  • Chain of amino acids are coiled and folded
  • Forms extra bonds between parts of the polypeptide chain
• Tertiary proteins have hydrogen bonding, covalent disulfide bonds (stronger than H bonding) between sulfurs, and ionic interactions between acidic amino acids
• In alkaline conditions amino acids become anions
• In acidic conditions amino acids become cations
• Amino acid + alcohol --> ester
• Amino acids have a chiral carbon so can form optical isomers
• Nucleic acid (DNA) is made of monomers called nucleotides
• Nucleotides are made of

  • Sugar - deoxyribose
  • Phosphate group
  • Nitrogen containing a base (adenine, guanine, cytosine, thymine)
• Nucleotides link to form polynucleotide by condensation polymerisation. Ester link forms between phosphate and sugar
• Nucleotides form when phosphates and bases join with sugar by condensation
• The sugar and phosphate form the backbone of the nucleotide
• One turn in the DNA double helix contains 10 complementary base pairs. The bases are connected by hydrogen bonding
• Enzymes are a type of protein which increase the rate of certain reactions in the body. They do this without being used up so we call them biological catalysts
• when an enzyme is involved in a reaction, we call the reactants substrates. even though the enzyme acts as a catalyst, we still include it as a reactant and product in the equation
• Since enzymes only act upon one optical isomer, but not the other, they are called stereospecific