2.1.3 Nucleotides and Nucleic Acids

• Nucleic Acids - elements


  • carbon
  • hydrogen
  • oxygen
  • nitrogen
  • phosphorous
• Nucleic Acids - elements


  C,H,O,N,P
• Nucleotide Structure


  • pentose sugar
  • phosphate group
  • nitrogenous base
• DNA


  
  

  • holds genetic information
  • found in the nucleolus
• DNA (deoxyribonucleic acid) - bases


  • adenine
  • guanine
  • thymine
  • cytosine
• RNA


  • transfers information to ribosomes to make proteins
  • found in the cytoplasm
• RNA (ribonucleic acid) - bases


  • adenine
  • guanine
  • uracil
  • cytosine
• Purines

  • 2 carbon-nitrogen rings
  • adenine and guanine
• Pyrimidines

  • 1 carbon-nitrogen ring
  • cytosine, thymine and uracil
• Adenine bonds to Thymine with 2 hydrogen bonds
• Adenine bonds to Uracil with 2 hydrogen bonds
• Guanine bonds to Cytosine with 3 hydrogen bonds
• Hydrogen bonds between bases 


  Complimentary base pairing
• DNA structure

  • double helix
  • two polynucleotide chains joined together by hydrogen bonds (complimentary base pairing)
  • chains run antiparallel to each other, they run in opposite directions
  • 3' and 5' - carbons are numbered 1' is by the nitrogenous base and 5' is by the phosphate group, 3' will bond to the neighbouring nucleotide's phosphate group
• Phosphate Group

  • inorganic ion
  • acidic
  • negatively charged (3-)
• RNA structure

  a relatively short, single polynucleotide chain
• Properties of ATP

  • water soluble
  • easily regenerated
  • releases energy in small quantities, in a single step reaction
  • small
• ATP can provide energy for chemical reactions


  • ATP + H2O -> ADP + Pi + energy
  • ATP is broken down into ADP and an inorganic phosphate
  • hydrolysis
  • exothermic
• ADP - adenosine diphosphate
• ATP - adenosine triphosphate
• Purifying DNA

  1. break up cells in sample - blend or grind
  2. make a solution of detergent, salt and distilled water
  3. add broken up cells to beaker containing detergent solution - incubate beaker in a water bath at 60C for 15 mins
  4. put beaker in an ice bath to cool
  5. filter mixture and put into a boiling tube
  6. add protease enzymes
  7. slowly dribble cold ethanol to form a layer on top of the DNA detergent mixture
  8. a white ppt will form (DNA)
• DNA 🧬 replication - in cell division

  1. DNA HELICASE uncoils DNA and breaks hydrogen bonds between the two polynucleotide strands, unzipping it
  2. each original single strand acts as a template for a new strand, free floating DNA nucleotides join exposed bases on each original template strand by complimentary base pairing
  3. nucleotides of the new strands are joined together by DNA POLYMERASE - forms the sugar-phosphate backbone - hydrogen bonds form and strands twist to form a double helix
  4. each new DNA molecule has one old strand and one new strand (semi-conservative replication)
• SEMI-CONSERVATIVE REPLICATION


  Half of the strands are from an original piece of DNA
• DNA replication - in cell division

  • very accurate - to conserve genetic information
  • random, spontaneous mutations may occur - can alter the sequence of amino acids in a protein, producing an abnormal protein
• Meselson-Stahl Experiment

  • bacteria is grown in 15N and then transferred to 14N
  • sample is taken after first and another after the second division
  • DNA is extracted and put into a centrifuge to identify 14N and 15N
• Protein Synthesis - DNA is copied into RNA

  • DNA in the nucleus is too large to leave via nuclear pores
  • instead it is copied into mRNA (transcription)
  • mRNA can leave the nucleus to go to a ribosome (ready for translation)
• mRNA - messenger


  • made in the nucleus
  • carries genetic code to the cytoplasm, to ribosomes
  • 3 adjacent bases are called a codon
• tRNA - transfer


  • found in cytoplasm
  • carries amino acids to ribosomes
  • amino acid binding sites on one end and an anti-codon on the other
• rRNA - ribosomal


  • forms the two subunits in ribosomes
  • helps to catalyse the formation of peptide bonds
• Genetic code - sequence of base triplets

  • non-overlapping
  • degenerate
  • universal
• Universal


  Same base triplets code for the same amino acids in all living things
• Degenerate


  More combinations of triplets than amino acids, amino acids can be coded by more than one codon
• Non-overlapping


  Base triplets don't share bases, sequential
• Start and stop codons


  Signal the start and end of a gene and protein production
• DNA triplet

  3 bases code for 1 amino acid
• TRANSCRIPTION


  making a mRNA copy of a gene in the nucleus
• TRANSLATION


  protein synthesis at a ribosome
• TRANSCRIPTION


  1. DNA HELICASE breaks hydrogen bonds in DNA and unzips a section of DNA, uncoiling and unzipping it
  2. one strand is used as a template to make an mRNA copy
  3. RNA POLYMERASE lines up free RNA nucleotides
  4. specific bases are paired together (complimentary base pairing) and the RNA nucleotides are joined together to form mRNA
  5. RNA POLYMERASE moves along, making mRNA until it reaches a stop codon, it stops and detaches
  6. hydrogen bonds reform in DNA and recoils once RNA POLYMERASE has passed
  7. mRNA leaves the nucleus and attaches to a ribosome in the cytoplasm, ready for translation
• TRANSLATION

  1. mRNA attaches to a ribosome and tRNA carry amino acids towards the ribosome
  2. tRNA with an anti-codon that is complementary to the start codon attaches to the mRNA (complementary base pairing)
  3. a second tRNA molecule attaches to the next codon, in a similar way
  4. rRNA in the ribosome catalyses the formation of a PEPTIDE BOND that joins amino acids together, the tRNA is free to leave
  5. a third tRNA molecule binds to the next codon and the amino acid binds to the neighbouring amino acid
  6. this process continues to form a polypeptide chain until a stop codon is reached on the mRNA molecule,
• What bond joins two nucleotides together?

  PHOSPHODIESTER