DNA vs RNA

Learn.

It is conventional to write DNA polymer from left to right which is from the 5′ region to the 3′ region. Proteins are synthesized from the 5′ prime region to the 3′ region hence we also write proteins from the N-terminus (or amino terminus) to the C-terminus (or carboxy terminus).

Proteins are built from amino acid repeating units of amino acids through a polymerization reaction since the amine reacts with carboxylic acid creating a continually growing chain – note this requires energy input hence it is anabolic. This results in a residue being left over and incorporated into the polymer.

Nucleic acid contains a sugar phosphate backbone with nucleobases. Since the phosphate is negatively charged it is hydrophilic.

This negative nature of a phosphate in the sugar phosphate backbone allows electrophoresis. When placed in gel and put in an electric field the nucleic acid will migrate along the gel. Using a dye, the size of a chain can be determined since the lighter molecules will migrate longer distances. Additionally, mixing salt and alcohol into a nucleic acid solution precipitates the nucleic acid, centrifuging this can allow for extraction of nucleic acid.

Proteins generally have more then 50 amino acids whereas polypeptides contain fewer the 50 amino acids. Due to the range of amino acids available, they have a range of properties.

In 1928, Griffith performed a Bacterial transformation experiment which resolved the debate as to whether DNA contained genetic information. Through injecting mice with:

  • Rough non-virulent bacteria into a healthy mouse – mouse survived
  • Smooth virulent bacteria into a healthy mouse – mouse died
  • Heat killed smooth virulent bacteria into a healthy mouse – mouse survived
  • Then he added Heat killed smooth virulent bacteria with Rough non-virulent bacteria into a healthy mouse – mouse died and he extracted Smooth virulent bacteria.

The results of the experiment demonstrated that the genetic information for the virulent bacteria was passed into the non-virulent bacteria making a virulent bacteria.

As previously stated

Nucleobases include Adenine (A) and Guanine (G) which are purines because they contain a double ring and are flat aromatic compounds. Cytosine (C), thymine (T) and uracil (U) which are pyrimidines since they are single ringed, planar and aromatic.

This means the A and T pair up together and G and C pair up together. In RNA, however, T is swapped with U. This means A and U pair together and G and C pair together. C and G are conected by three hydrogen bonds as opposed to A and U/T only having two. This means the more G and C nucleobases present, the greater the melting temperature since the sugar phosphate backbones are held together better.

Note that DNA forms a double helix structure (known as it’s B-type structure) and the two rungs of the ladder go in opposite directions. The double helix contains a major and minor groove. Note RNA contains an extra oxygen in its sugar hence it can not form the helix DNA forms, however, A and U as well as G and C can still pair up together.

RNA is more prone to mistakes. In DNA cytosine undergoes spontaneous deamination changing into uracil. Since uracil shouldn’t be in DNA, this mistake is recognized and corrected. However, when this occurs in RNA it doesn’t look out of place hence it is not corrected. This occurs in each cell close to 100 times per day. For this reason RNA is more prone to mistakes.

Memorise.

Master.

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