Nucleic acids 3.1.5.1

• Draw the structure of a nucleotide

  
• Role of DNA in living cells

  Base sequence of genes- codes for functional RNA and amino acid sequence, genetic info determines characteristics
• Structure of RNA

  
• 3 types of RNA

  Messenger RNA -copies a section of DNA (gene) -takes it to a ribosome -codes for a particular proteinRibosomal RNA-makes up ribosomesTransfer RNA-makes amino acid
• Structure of DNA

  
• How do polynucleotides form?

  Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone)Have anti-parallel strands, each strand goes in opposite directions
• Pyrimidines


  Single ring:Cytosine ThymineUracil
• Purines


  Doubles ring:Adenine Guanine
• How many hydrogen bonds are between the complementary base pairs?

  A-T = 2A-U= 2C-G= 3
• What can make a DNA molecule more stable?

  The higher the proportion of C-G pairings, the more stable the DNA molecule (more bonds require more energy to break)
• How is DNA adapted to its function?

  Stable structure=so can pass from generation to generation without changingHeld together by hydrogen bonds=so they can be separated during DNA replication and protein synthesisLarge molecule=can carry a large amount of genetic informationComplementary base pairs=so DNA is replicated accuratelyBase sequence=decides function of gene/proteinHelix= so compactDouble stranded=so replication can occur semi conservatively
• Why is DNA so stable?

  -sugar phosphate backbone protects the bases to provide stability -many hydrogen bonds are strong together
• Process of semi-conservative DNA replication

  1)the enzyme, dna helicase causes the double helix to unwind and separate into two strands by breaking the hydrogen bonds between complementary base pairs2)both strands then act as template for DNA replication to occur3)free activated nucleotides in the nucleoplasm are attracted to and hydrogen bond to their complementary bases4)phosphodiester bonds are then formed by the enzyme, dna polymerase5)this results in two identical DNA molecules
• Discovery of DNA replication

  
• Experimental evidence validating Watson and Crick's model of semi conservative DNA replication

  
• Describe the Meselson-Stahl experiment

  
• Analysing the results from centrifugation

  
• What direction can nucleotides be added in?

  5' to 3' prime direction