4.5 - Nucleic Acids

Structure of Nucleic Acids

Nucleic acids are one or two polymer chains consisting of nucleotide monomers.
They contain carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and phosphorus (P).
Each nucleotide consists of a pentose sugar, a nitrogenous base, and a phosphate group combined through condensation.
Pentose sugars: Ribose and deoxyribose.
Nitrogenous bases: Adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U).

Contains deoxyribose sugar.
Consists of two polynucleotide chains intertwined in opposite directions to form a double helix.
Nitrogenous bases on the two chains are matched and joined by hydrogen bonds.
Contains adenine (A), guanine (G), thymine (T), and cytosine (C).
Adenine pairs with thymine; guanine pairs with cytosine.

Contains ribose sugar.
Consists of a single polynucleotide chain that is shorter than DNA.
Contains adenine (A), guanine (G), cytosine (C), and uracil (U); uracil replaces thymine.
The three main types are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA); all are involved in protein synthesis.

DNA carries hereditary information and determines characteristics in living organisms.
The sequence of nitrogenous bases in DNA carries the genetic code for synthesising polypeptides that form proteins.
Each three-base sequence determines an amino acid in the protein; for example, the mRNA codon AUG codes for methionine.
A three-base sequence in DNA is transcribed into an mRNA codon and then translated into an amino acid sequence to form a polypeptide chain.
The nucleotide sequence in DNA therefore determines the amino acid sequence in the polypeptide chain of the corresponding protein.

DNA polynucleotide chains wind around histone proteins; histones do not carry genetic information.
DNA molecules and histone proteins form nucleosomes.
Nucleosomes coil to form the chromosome structure.