Nucleic Acids and Cell Division

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  • Created by: georgia s
  • Created on: 24-01-13 18:36

Nucleotide structure and nucleic acids

Individual nucleotides are made up of three components that combine by condensation reactions. These are:

  • A phosphate group (H3PO4). This has the same structure in all nucleotides.

  • A pentose sugar

  • An organic base which contains nitrogen.

An organic base belongs to one of two different groups:

  • The pyrimidine bases are thymine and cytosine

  • The purine bases are adenine and guanine

(http://scienceaid.co.uk/biology/genetics/images/nucleotide.jpg)

The structure is DNA

  • DNA is a double stranded polymer of nucleotides or polynucleotide.

  • Each polynucleotide may contain many million nucleotide units.

  • It is in the form of a double helix, the shape is maintained by hydrogen bonding.

  • The pentose sugar is always deoxyribose.

  • DNA contains four organic bases. These are adenine, guanine, cytosine and thymine.

  • Each strand is linked to the other by pairs of organic bases.

  • Cytosine always pairs with guanine, adenine always pairs with thymine, and the bases are joined hydrogen bonds. As a result of these pairings adenine is said to be  complementary of thymine and guanine is said to be complementary to cytosine.

    (http://www.chemguide.co.uk/organicprops/aminoacids/doublehelix.gif)

How DNA is well suited to carry out its functions?

  • It is a very stable molecule and can pass from generation to generation without change.

  • It is a very large molecule and can carry a large amount of genetic information.

  • The two strands are able to separate easily as they are held together by weak hydrogen bonds.

  • As the base pairs are held within the deoxyribose-phosphate backbone, the genetic information is protected from outside forces.

The structure of RNA

  • RNA is a single stranded polymer of nucleotide.

  • RNA contains the pentose sugar, ribose.

  • RNA contains the organic bases adenine, guanine, cytosine, and uracil (in place of thymine).

There are three types of RNA are involved in the process of protein synthesis:

  • Messenger RNA (mRNA) is a long, single stranded molecule formed into a helix, it is manufactured in the nucleus and carries the genetic code from the DNA to the ribosomes in the cytoplasm.

  • Ribosomal RNA (rRNA) is found in the cytoplasm and is a large, complex molecule made up of both double and single helices. Ribosomes are made up of ribosomal RNA and protein. It is the site of translation of genetic code.

  • Transfer RNA (tRNA) is a small single stranded molecule. It forms a clover leaf shape, with one end if the chain ending in a cytosine-cytosine-adenine sequence at which point the amino acid it carries attaches itself. At the opposite end of the chain is a sequence of three bases called the anticodon. tRNA molecules transport amino acids to the ribosome so that proteins can be synthesised.

Comparison of DNA and RNA:

Sugar:

DNA= Deoxyribose RNA= Ribose

Bases:

DNA= CGAT RNA= CGAU

Helix:

DNA= Double RNA= Single

Scientists initially thought that proteins played a role in the transfer of hereditary material from one generation to the next. Although we now take for granted that DNA is the hereditary material…

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