DNA & RNA

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DNA & RNA Function

  • both types of nucleic acid 
  • DNA stores genetic info
  • RNA transfers genetic info from DNA to ribosomes 
  • ribosomes read RNA & make polypeptides - translation 
  • ribosomes are made from RNA & proteins  
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Nucleotide Structure

  • molecules of DNA & Rna are polymers of nucleotides
  • nucleotide is made from a pentose sugar, a nitrogen-containing base & a phosphate group 
  • they are monomers that make up DNA & RNA 
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Polynucleotide Structure

  • many nucleotides join together to form polynucleotide chains/strands
    • via condensation reaction between phosphate group of one & sugar of another
      • forms phosphodiester bond 
  • chain of phosphates & sugar is known as sugar-phosphate backbone 
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DNA Structure

  • double helix
    • formed from 2 seperate strands which wind round eachother to form a spiral 
    • strands - polynucleotides 
    • made up of lots of nucleotides joined together in long chain
  • really long & coiled up very tightly so lots of genetic info can fit in to small space in cell nucleus 
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DNA Nucleotide Structure

  • made from a phospahte group, pentose sugar - deoxyribose & a nitrogen-containing organic base
  • each has same sugar & phosphate 
  • bases on each can vary 
    • 4 possible bases
      • adenine 
      • thymine
      • cytosine
      • guanine 
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Complementary Base Pairing

  • 2 DNA polynucleotide strands join together by hydrogen bonds between bases
  • each base can only join with1 particular partner 
    • complementary base paring 
  • adenine - thymine 
  • cytosine - guanine 
  • this means there are always equal amounts of adenine and thymine & cytosine and guanine 
  • 2 hydrogen bonds form between A & T 
  • 3 hydrogen bonds form between C & G
  • 2 polynucleotide strands are antiparallel - run in opposite directions 
  • 2 antiparallel strands twist to form a DNA double helix
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RNA structure

  • RNA is made of nucleotides that contain a sugar, a phosphate group & 1 of 4 different bases 
  • nucleotides form polynucleotide strand with sugar-phosphate backbone 
  • pentose sugar - ribose sugar 
  • uracil replaces thymine as a base
  • single polynucleotide strand 
  • RNA strands are much shorter than most DNA polynucleotides 
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DNA as Carrier of Genetic Code

  • DNA first observed in 1800s - scientists doubted that it could carry genetic code - relatively simple chemical composition
  • 1953 - experiments had shown that DNA was the carrier of the genetic code 
    • also the double helix structure was determined by Watson & Crick
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