2.1.3 nucleotides and nucleic acids

• in eukaryotic cells DNA is found in the nucleus
• chromatin is made up of DNA and histone proteins
• DNA stands for deoxyribonucleic acid and acts as an information store
• RNA stands for ribonucleic acid and has three different forms mRNA, rRNA and tRNA
• RNA is needed to translate the code from DNA to make proteins
• a nucleotide is made up of an inorganic phosphate group, a pentose sugar and a nitrogen containing base
• the pentose sugar in DNA is deoxyribose
• the pentose sugar in RNA is ribose
• the difference in structure of ribose and deoxyribose is that deoxyribose doesn’t have a hydroxyl group below carbon 2 only a hydrogen
• individual bases are joined together by a condensation reaction to form a phosphodiester bond
• there are five types of nitrogen-containing bases adenine (A), guanine (G), thymine (T), uracil (U) and cytosine (C)
• adenine and guanine are purine bases as they have 2 rings
• thymine, cytosine and uracil are pyrimidine bases as they only contain one ring
• guanine is found in DNA and RNA
• thymine is only found in DNA
• cytosine is found in both DNA and RNA
• uracil is only found in RNA as it replaces thymine
• when forming a nucleotide like adenosine monophosphate two water molecules are produced
• adenosine is formed when adenine are ribose are joined
• ATP stands for adenosine triphosphate
• ADP stands for adenosine diphosphate
• ATP and ADP are phosphorylated nucleotides
• nucleotides are joined together to form polynucleotides by condensation reactions
• phosphodiester bonds join nucleotides together
• phosphodiester bonds form when the phosphate group at the 5th carbon of the pentose sugar on one nucleotide forms a covalent bond with the hydroxyl group at the 3rd carbon of pentose sugar of an adjacent nucleotide
• phosphodiester bonds can be broken by a hydrolysis reaction
• the 2 strands that make up DNA are antiparallel to each other as one runs from 5’ to 3’ and the other runs from 3’ to 5’
• 3’ is the end which is closest to carbon 3 in ribose
• 5’ is the end which is closest to carbon 5 on ribose
• antiparallel is when one strand runs the other way around to the second strand
• the four bases in DNA are A,T,G,C
• adenine binds with thymine
• guanine binds with cytosine
• specific base pairing is the fact that A and T always bind together and so do G and C.
• one purine base bonds to one pyrimidine base.
• a hydrogen bond is a weak bond within or between molecules and result from an interaction of polar covalent bonds
• between G and C there are 3 hydrogen bonds
• between A and T there are 2 hydrogen bonds
• the phosphate group in DNA is acidic and the nitrogenous base is alkaline
• in solution the phosphate groups easily loses a H to become negatively charged, this is why DNA carries a large charge, the loses of a H /proton makes DNA an acid