2.1.3 Biology

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  • Created by: LivviR123
  • Created on: 19-11-16 12:37

Nucleic Acids

  • Two types: RNA and DNA, both have roles in storage and transfer of genetic information and synthesis of polypeptides (proteins)
  • Contain elements carbon, hydrogen, oxygen, nitrogen and phosphorus
  • They are large polymers formed from many nucleotides linked together in a chain
  • An individual nucleotide is composed of: a pentose monosaccharide, a phosphate group (PO42-) and a nitrogenous base.
  • Nucleotides are joined by condensation reactions to form a polymer called a polynucleotide. The phosphate group at the fifth carbon of one nucleotide forms a covalent bond with the OH group at the thurd carbon of the pentose sugar of an adjacent nucleotide
  • BONDS ARE CALLED PHOSPHODIESTER BONDS
  • This forms a long, strong sugar phosphate backbone with a base attached to each sugar. The phosphodiester bonds are broken via hydrolysis reactions.

Deoxyribonucleic Acid (DNA) - the sugar in DNA is deoxyribose, a sugar with one fewer oxygen atoms than ribose. The nucleotides in DNA have one of four different bases, which are divided into two groups:

PYRIMIDINES: the smaller bases, which contain single carbon ring structures- thymine (T) and cytosine (C)

PURINES: the larger bases, which contain double carbon ring structures- adenine (A) and guanine (G)

The Double Helix: DNA is made up of two strands of polynucleotudes coiled into a helix. The two strands of the double helix are held together by hydrogen bonds between the bases. Each strand has a phosphate group (5') at one end and a hydroxyl group (3') at the other end, the two strands are ANTIPARALLEL. The pairing between the bases allows DNA to be copied and transcribed.

Base Pairing Rules: Adenine and thymine join and form two hydrogen bonds, cytosine and guanine form three hydrogen bonds and bind to each other- this is COMPLEMENTARY BASE PAIRING. So a small pyrimidine base always binds to a large purine base, this maintains a constant distance between DNA backbones . It is the sequence of bases along a DNA strand that carries the genetic information of an organism in the form of a code.

Ribonucleic Acid (RNA)- essential role in transfer of genetic info from DNA to the proteins that make up enzymes and tissues. DNA of each eukaryotic chromosome is a very long molecule, comprising many hundreds of genes, it is unable to leave the nucleus to supply the info directly to the sites of protein synthesis. So, the section of DNA that corresponds to a single gene is transcribed into relatively short mRNA. Each individual mRNA is therefore shorter than the whole chromosome of DNA- it is a polymer composed of many nucleotide monomers. RNA nucleotides vary from DNA nucleotides as the pentose sugar is is ribose rather than deoxyribose and the thymine bases is replaced with uracil. Uracil forms two hydrogen bonds with adanine so the base pairing rules still apply. RNA nucelotides form polymers by the formation of phosphodiester bonds in condensation reactions, the RNA polymers formed are small enough to leave the nucleus and travel to ribosomes for the process of…

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