Nucleotides

Nucleic Acids: Brief History

Friedrich Miescher - discovered nucleic acids in 1869 while studying the nuclei of white blood cells

Nucleotides: Structural Building Blocks for Nucleic Acids

Nucleic acid - unbranched polymer

Nucleotide - three subunit molecule: pentose sugar bonded to both phosphate group and a nitrogen-containing heterocyclic base

Nucleoside - molecule without phosphate group

Pentose Sugar - Structural difference occurs at carbon 2’ (deoxy - without oxygen) Deoxyribose in DNA & Ribose in RNA

Phosphate Group - Under cellular pH conditions, the phosphoric acid loses two of its hydrogen atoms to give a hydrogen phosphate ion HPO4

Nitrogen-Containing Heterocyclic Bases - contain basic amino functional groups (proton acceptors)

  • Pyrimidine = monocyclic base, 6 membered ring (Thymine (T), Cytosine (C), Uracil (U))

  • Purine = bicyclic base w/ fused 5 & 6 membered rings Adenine (A), Guanine (G)

Nucleoside Formation

Nucleoside Formation - Base attached to C-1 of sugar in β-configuration, N-9 in purine while N-

1 for pyrimidine connected through β-N-glycosidic linkage

  • Condensation reaction occurs as water molecule is formed upon bonding of base and sugar

Nucleotide Formation

Nucleotide Formation - phosphate group is attached to the sugar at the C-5’ position through a phosphate-ester linkage

  • Condensation reaction occurs, overall two water molecules are produced in combing bonding base, sugar and phosphate

Types of Nucleic Acids

DEOXYRIBONUCLEIC ACID (DNA): Primary function is the storage and transfer of genetic information

  • Information used to control many cell functions

  • DNA passed from existing to new cells during cell division

RIBONUCLEIC ACID (RNA): Primary function is the synthesis of proteins

  • RNA Occurs in all parts of the cell

  • Proteins carry out essential cellular functions

Levels of Nucleic acid Structure

Primary - The order of the base pairs in a polynucleotide sequence

Secondary -Is the three-dimensional conformation of the backbone

Tertiary - The supercoiling of the molecule

Quaternary - the interaction of nucleic acids to other molecules

Primary Nucleic Acid Structure - sequence in which nucleotides are linked together in nucleic acid

  • Nucleic acid backbone - alternating sugar-phosphate chain

Secondary Structure - The DNA Double Helix

  • The concentration of ADENINE and THYMINE are identical as are the

    amounts of CYTOSINE and GUANINE.

  • The base-pairing pattern ( A to T, G to C ) is the same in all molecules of DNA

  • The information encoded by that sequence is the basis of traits that define

    species and distinguish individuals.

  • VARIATIONS IN ITS NUCLEOTIDE SEQUENCE ARE THE FOUNDATIONS OF

    LIFE'S DIVERSITY

Factors that stabilizes the helix

Hydrogen Bonding Interaction -Stabilizes helix structure, although weak force number of base pairs result to significant strength

Base Stacking Interactions - Stacking interactions as purines and pyrimidines are hydrophobic

Pi-pi interactions - Happens between the aromatic rings of the bases

KINDS OF RNA (product of DNA transcription)

Transfer RNA (tRNA) or soluble RNA - Holds a specific amino acid for incorporation into a protein molecule

Ribosomal RNA (rRNA) - the most abundant RNA, constitutes 80% of the total RNA(guanylic acid is most abundant) , Combines with protein to form the ribosome

Messenger RNA (mRNA) - Concerned with the transmission of genetic information from DNA to the site of protein synthesis

Heterogeneous nuclear RNA (hRNA) - A precursor of mRNA, found in the nucleus of cell