Information of life

  • The structure of DNA and RNA
  • Evidence that DNA is the hereditary material
  • Genes and Proteins
  • DNA replication
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RNA

  • RNA is a polymer of nucleotides.
  • Nucleotides are made of phosphate, 5 carbon sugar i.e. ribose and an organic base i.e. AU CG.
  • RNA is single stranded.
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DNA

  • DNA is a polymer of nucleotides
  • Nucleotides are made of a 5 carbon sugar i.e. deoxyribose, an organic base i.e. AT CG and a phosphate
  • The nucleotides are arranged in two chains which coil up and form a double helix

DNA polymerase - bonds nucleotides together.

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Evidence that DNA is genetic material

Explanation of structure related to function

  • The sugar phosphate backbone makes the molecule stable
  • The molecule coils up so that it is compact, i.e. it can store a lot of information in a small space
  • The sequence of bases allows it to carry coded information for making proteins
  • It is a very long molecule so it can store a lot of information
  • Complementary bases pairing allows the molecule to replicate itself accurately
  • The double helix makes the whole molecule stable, as the base pairs are on the inside of the molecule where they are less likely to be damaged
  • The bases are held together by weak hydrogen bonds, which allow the molecule to 'unzip' easily when it replicates
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Griffith experiment

  • Experimented on different strains of Diplococcus pneumoniae
  • Some virulent i.e. cause disease and some were non-virulent i.e. do not cause disease 
  • Virulent strains had a slimy capsule but the non virulent did not
  • When he injected a virulent S-strain of the bacteria into some mice they died
  • When he injected a non-virulent R-strain into some mice they survived
  • Then he killed some S-strain bacteria by heating them, injected them into some mice and they survived 
  • Finally, he mixed the dead S-strain with some living R-strain and injected it into the mice, they died, he found living S-strain bacteria from the dead mice

Somehow the dead S-strain bacteria had 'transformed' the R-strain into the virulent S-strain.

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Genes and proteins

  • The base sequence of amino acids determines the base sequence of the gene which codes for proteins.
  • Gene -  a section of DNa that carries coded information about a characteristic.
  • Allele - an alternative form of a gene. For example, the gene coding for eye colour may have alleles coding for brown or blue eyes.
  • Homologous chromosomes - paired chromosomes where genes occur at the same locus, but alleles are not the same.
  • Phenotype -  the observable traits or characteristics of an organism e.g. hair colour, eye colour or weight.
  • Alkaptonuria - suffers have an allele that produces a faulty enzyme, which means they cannot break down homogentisic acid.
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DNA replication

Semi-conservative replication

One strand of the molecule is kept the same and the other is newly made.

  • DNA molecule 'unzips', hydrogen bonds between complementary bases break
  • Free nucleotides align alongside their complementary bases
  • DNA polymerase joins these new nucleotides together
  • Each new strand is complementary to the old strand, and each of the new molecules formed are identical

Conservative replication

  • Same as above but one helix formed would be entirely made of new material and other other of old

Dispersive replication

  • Both DNA molecules are made up of a mixture of old and new DNA
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