A1.2 Nucleic acids

Nucleic Acid: A nucleic acid is a complex biological polymer made of nucleotide monomers, responsible for storing, transmitting, and expressing genetic information. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Nucleic acids are the fundamental molecules of heredity , they carry the instructions that cells need to build proteins and regulate biological processes.

• DNA is the long-term storage molecule of genetic information, found primarily in the nucleus of eukaryotic cells.
• RNA acts as a working copy of that information, shuttling instructions from DNA to the ribosomes where proteins are made.

In eukaryotes, DNA is packaged inside the nucleus as chromosomes. Smaller DNA molecules also exist in mitochondria (mtDNA) and, in plants and algae, in chloroplasts (cpDNA).

RNA is found in both the nucleus and the cytoplasm, and exists in several functional forms:

• mRNA (messenger RNA): carries the genetic code from DNA to ribosomes
• tRNA (transfer RNA): delivers amino acids to the ribosome during protein synthesis
• rRNA (ribosomal RNA): forms part of ribosomes and catalyses peptide bond formation

The monomer unit of all nucleic acids is the nucleotide. Every nucleotide consists of three components bonded together:

1. A phosphate group (represented by a circle in diagrams)
2. A pentose sugar , a 5-carbon sugar (represented by a pentagon)
3. A nitrogenous base (represented by a rectangle)

The phosphate group is attached to the 5' carbon of the pentose sugar. The nitrogenous base is attached to the 1' carbon of the sugar.

The two pentose sugars:

• Deoxyribose , found in DNA; lacks an –OH group at the 2' carbon (has only –H)
• Ribose , found in RNA; has a full –OH group at the 2' carbon