Nucleotides and Nucleic Acids
Here are some brief points on Nucleotides and Nucleic Acids
Functions of nucleic acids are:
- Informational biomolecules – DNA, RNA
– Function as polymers in the storage and transmission (expression) of the genetic information. (giant molecules)
- Electron carriers – NAD+, FAD
- Carriers of high energy intermediates
– UMP, CMP, GTP
- Energy currency of the cell – ATP
- Signaling molecules – cAMP, AMP, etc
The monomeric units of a nucleotide polymer contain 3 components:
- 1. A nitrogenous heterocyclic base, either:
- 2. A pentose sugar which is either:
- Ribose (furanose form)
- 2-deoxy-ribose (furanose form)
- 3. A phosphoric acid group in ester linkage at C-5 of the pentose
- The phosphoester bond
Double Helical DNA:
- 2 complementary anti-parallel strands – right-hand coil along a common axis
- Held together by H-bonds – A-T & G-C
- Bases on the interior – planes are perpendicular to helix axis
- Sugar and P-groups on the outside, exposed to H2O
- Sugar rings almost at right angles to the planes of the bases
- DNA – adenine, guanine, cytosine, thymine
– A, G, C, T
- RNA – adenine, guanine, cytosine, uracil
– A, G, C, U
- A and G – purines
– Purines are bicyclic fused rings of a pyrimidine & a 5-membered imidazole
- U, T, C – pyrimidines
– 6-membered ring
- Analysis of DNA from most species –
– 4 bases are not equal
– Base composition varies between species
- But, different tissues of the same species
– Same base comp.
- And always: A = T and G = C
– sum of purines = sum of pyrimidines
- Related species, similar base composition
- nucleotides are the building blocks for DNA and RNA
- nucleotides are carriers for activated intermediates
- nucleotides are structural components of coenzyme A, FAD, NAD+, and NADP+
- defects in nucleotide metabolism are associated with several common and rare human disorders
- several drugs used to treat cancer and bacterial infections function at the level of nucleotide metabolism
- Nucleotides are composed of a nitrogenous base, a pentose monosaccharide, and 1, 2, or 3 phosphate groups.
- The nitrogenous bases are derived from 2 families called purines and pyrimidines.
There are 5 common bases found in DNA and RNA:
- Purines Adenine and Guanine common to both DNA and RNA
- Pyrimidines Thymine and Cytosine are found in DNA
- Pyrimidines Cytosine and Uracil are found in RNA
- Addition of a pentose sugar to the base produces a nucleoside. Base + ribose = nucleoside
- Addition of a ribose sugar to the bases A, G, C, T, and U produces adenosine, guanosine, cytidine, thymidine, and uridine, respectively.
- If the pentose sugar is a deoxyribose, then a deoxyribonucleoside is produced.
- Addition of either 1, 2, or 3 phosphate groups to a nucleoside produces a nucleoside. Monophosphate, nucleoside diphosphate, or a nucleoside triphosphate, respectively. Base + sugar + phosphate = nucleotide.
- The phosphate groups are responsible for the negative charges associated with RNA and DNA.