RNA and DNA

RNA and DNA

DNA

  • This is used to store the genetic information which contains all the genetic information from the fertilised egg.
  • DNA has – deoxyribose sugar, nitrogen containing organic base and a phosphate group.
  • These include four bases- adenine, thiamine, cytosine and guanine.

RNA

  • This transfers genetic information from RNA to ribosomes- which make polypeptides through a process called translation.
  • RNA contains a ribose sugar, phosphate group.
  • Uracil replaces thiamine.

Polynucleotides

  • Two nucleotides are joined via a condensation reaction (this is between the phosphate group of one nucleotide and the sugar.
  • A phosphodiester bond forms between both of these.
  • DNA and RNA nucleotides form polynucleotides.

the double Helix structure of DNA

  • Two DNA polynucleotide strands are joined together by hydrogen bonding.
  • The bases form complementary base pairs.
  • All the bases are present in equal amounts.
  • Two anti-parallel twist to form a double helix.
  • This was carried out by Watson and crick

Exam Question and tips

  • Name part F of each nucleotide.

Although the diagram is not shown – you would be expected to label the part of the DNA or RNA molecule.

…………………………………………………………………………………………………………………….(1)

(b) Scientists determined that a sample of DNA contained 18% adenine.

What were the percentages of thymine and guanine in this sample of DNA? (2)

Remember the bases are present as equal amounts and therefore you have to be clear about the percentages.

A pairs with T – therefore each has 18%/18%- total 36%

C pairs with G – therefore each has 32%/32%- total 64%

Exam Tip the total has to be out of 100%

 

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