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  • Created by: parrot16
  • Created on: 28-02-16 17:00

Nucleic acids

DNA holds an immense amount of genetic information wheras RNA transfers the genetic info from the nucleus to the ribosomes.

A nucleotide consists of a sugar called deoxiribose, a phosphate group and a nitrogen containing organic base- bases in DNA are Adenine, Thymine, Cytosine and Guanine.

These 3 parts are joined together to form a mononucleotide in a condensation reaction.

When 2 momonucleotides join together a dinucleotide is formed and a phosphodiester bond is formed betwen the sugar of one nucleotide and the phosphate group of another. A polynucleotide forms when more than 2 nucleotides join together in a condensation reaction.

RNA is shorter than DNA and consists of a sugar called Ribose and the nitrogen containing organic bases are called Adenine, Guanine, Cytosine and Uracil which replaces Thymine.

  • mRNA transfers info from DNA to the ribosomes.
  • Ribosomes consist of rRNA.
  • Protein synthesis involes tRNA.

DNA is a double helix and the backbone has 2 antiparallel strands. The rungs of the ladder contain H bonded base pairs formed by complementary base pairing due to the structure of the bases. A and G are named the double ringed bases as they literally have a double ring structure and they are therefore longer molecules than the single ringed bases which are C and T. Additionally, A and G are named purines and C and T are names pyrimidines. Due to their structure C and G can form 3 hudrogen bonds between each other wheras A and T form 2 hydrogen bonds between each other.

DNA is an extremely stable molecule because the phosphodiester backbone protects the chemically reactivfe organic bases inside the double helix. Also, the higher the proportion of C-G pairings, the more stable the DNA molecule as 3 H bonds form between them. Also base stacking holds the bases together as well as the H bonds but DNA is still able to unravel during replication and protein synthesis. DNA never really mutates as the base pairs containing the genetic information of the organism are within the helical cylinder of the sugar phosphate backbone so genetic info is protected from corruption by exterior physical and chemical forces. 

If there is 14% Adenine in DNA there is also 14% in Thymine. However, this means that 36% must be Guanine and Cytosine to must add up 2 100 and percentage of the base pairs is the same. Ratio of the base pairs varies depending on species. The sequence of bases determine which amino acid will be coded for by the triplet code in the RNA. Each protein contains a different amount and order of amino acids.

DNA replication

Nuclear division consists of the nucleus itself dividing by mitosis or meiosis whereas


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