nucleic acids

• Nucleic acid


  The molecules of heredity
• Each cell of our bodies contains thousands of different proteins
• From the end of the 19th century, biologists suspected that the transmission of hereditary information took place in the nucleus, more specifically in structures called chromosomes

  
• The hereditary information was thought to reside in genes within the chromosomes
• Chemical analysis of nuclei showed chromosomes are made up largely of proteins called histones and nucleic acids
• By the 1940s, it became clear that deoxyribonucleic acids (DNA) carry the hereditary information

  
• Other work in the 1940s demonstrated that each gene controls the manufacture of one protein
• The expression of a gene in terms of an enzyme protein led to the study of protein synthesis and its control
• Nucleic acids


  Molecules that store the patterns of life and these patterns are passed from one generation to the next
• Nucleic acids


  A polymer in which the monomer units are nucleotides

  
• Nucleotides


  Joined together by phosphodiester bonds
• Nucleic acids


  Found in cells as nucleoproteins

  
• Nucleosides


  A combination of N-base (heterocyclic base or amine base) and pentose sugar

  
• Nucleotides


  Building blocks of nucleic acid composed of N-base and pentose sugar and phosphate or phosphoric acid

  
• Three components of a nucleotide

  • Pentose sugar: Monosaccharide
  • N-bases – heterocyclic amines derived from purine and pyrimidine
  • Phosphate Group (PO4^3-)

  
• Nitrogen-containing heterocyclic bases


  • Purine bases: adenine (A) and guanine (G)
  • Pyrimidine bases: thymine (T), cytosine (C), and uracil (U)
• Adenine (A), guanine (G), and cytosine (C) are found in both DNA and RNA
• Uracil (U) is found only in RNA, and thymine (T) is found only in DNA
• Phosphate


  The third component of a nucleotide, is derived from phosphoric acid (H3PO4)
• Under cellular pH conditions, the phosphoric acid is fully dissociated to give a hydrogen phosphate ion (HPO4^2-)
• DNA and RNA are called nucleic acids because of the phosphate group, and every residue in a DNA or RNA molecule is negatively-charged at physiological pH

  
• Nucleoside


  A two-subunit molecule in which a pentose sugar is bonded to a nitrogen-containing heterocyclic base

  
• The base is attached to C1' position of the sugar (β-configuration), and it is a condensation reaction
• Nucleotide


  A nucleic acid constituent consisting of a sugar residue bonded to both a heterocyclic purine or pyrimidine base and to a phosphate group

  
• Two types of nucleic acids

  • DNA: Deoxyribonucleic Acid - Found within cell nucleus, storage and transfer of genetic information, passed from one cell to other during cell division
  • RNA: Ribonucleic Acid - Occurs in all parts of cell, primary function is to synthesize the proteins

  
• Adenosine 5'-triphosphate (ATP)


  Serves as a common currency into which energy gained from food is converted and stored
• Differences between DNA and RNA

  • Structure: DNA is double stranded, RNA is single stranded
  • Sugar: DNA has deoxyribose, RNA has ribose
  • N-bases: DNA has A, G, C, T, RNA has A, G, C, U
  • Function: DNA stores genetic information, RNA transmits genetic information

  
• Structural organization of DNA

  • Primary
  • Secondary
  • Tertiary
  • Quaternary
• Primary structure of nucleic acids

  The sequence of nucleotides, beginning with the nucleotide that has the free 5' terminus

  
• The strand is read from the 5' end to the 3' end
• A polynucleotide has a sense of directionality and individuality determined by the sequence of its bases

  
• The sugar-phosphate groups are referred to as the nucleic acid backbone, found in all nucleic acids
• The sugars are different in DNA and RNA
• Secondary structure of DNA

  The ordered arrangement of nucleic acid strands, involving two polynucleotide chains coiled around each other in a helical fashion

  
• The polynucleotides run anti-parallel (opposite directions) to each other, i.e., 5' - 3' and 3' - 5'
• The bases are located at the center and hydrogen bonded (A=T and G≡C)
• Base composition: %A = %T and %C = %G
• The DNA sequence on one polynucleotide is complementary to the other polynucleotide

  
• Tertiary structure of DNA


  The 3-D structure that involves a higher-order folding of elements of regular secondary structure, the supercoiling of the DNA
• Histones


  Small proteins that participate in forming the nucleosomal structure of the chromatin