Nucleotides and nucleic acids

• Both DNA and RNA carry information, for instance DNA holds genetic

  information whereas RNA then transfers this genetic information from DNA to ribosomes made of RNA and proteins.
• Both deoxyribonucleic and ribonucleic acid are polymers of

  nucleotides.
• Nucleotides consist of pentose which is a 5 carbon sugar, a

  nitrogen containing organic base and a phosphate group
• The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine.
• The components of an RNA nucleotide are ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil.
• Nucleotides join together by phosphodiester bonds formed in condensation reactions.
• A DNA molecule is a double helix composed of two polynucleotides joined together by hydrogen bonds between complementary bases whereas RNA is a relatively short single polynucleotide chain.
• Adenosine triphosphate is a nucleotide derivative and consists of ribose, adenine and three phosphate groups.
• Energy is released when ATP is hydrolysed to form ADP and a phosphate molecule. This process is catalysed by ATP hydrolase.
• The inorganic phosphate formed from ATP can be used to phosphorylate other compounds, as a result making them more reactive.
• Condensation of ADP and inorganic phosphate catalysed by ATP synthase produces ATP during photosynthesis and respiration.
• DNA replication:

  1. The double helix unwinds and the hydrogen bonds between the complementary bases break using DNA helicase thus separating the two strands of DNA
  2. • Both strands are used as templates and complementary base pairing occurs between the template strands and free nucleotides
• DNA replication:

  3) Adjacent nucleotides are joined by phosphodiester bonds formed in condensation reactions using DNA polymerase
• 1. The order of bases on DNA is called the genetic code which consists of triplets of bases, each triplet of bases codes for a particular amino acids and is known as a codon.
• 2) The amino acids are then joined together by peptide bonds and form a polypeptide chain
• 3) Therefore, a gene is a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain.
• 4) However, not all the genome codes for proteins – the non-coding sections of DNA are called introns and the coding regions are called exons
• There are two stages of protein synthesis. Transcription which occurs in the nucleus and involves DNA and mRNA and translation which involves mRNA, tRNA and ribosomes.