DNA structure

Biological functions of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)

2 types of nucleic acids are the most important macromolecules for the continuity of life.

The main function of nucleic acids is to store and transfer the genetic blueprint of all living organisms.

Nucleic acids use their stored genetic information to guide the synthesis of new proteins within the cell.

The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

Deoxyribonucleic acid, known as DNA, stores hereditary information in small segments called genes inside long polymer strands.

Ribonucleic acid (RNA) transfers gene information from DNA to create functional products.

Such field of biology as molecular genetics studies the structure and function of genes, how genes control the development and function of organisms. It employs methods of molecular biology and genetics.

Rna and its types

There are four major types of ribonucleic acid: messenger RNA (mRNA), ribosomal RNA (rRNA), transfer RNA (tRNA), and microRNA (miRNA).

Functions and types of ribonucleic acid (RNA)

Type of RNAAbbreviationFunction(s)
Messenger RNA mRNA Transfers genetic information from genes to ribosomes to synthesize proteins.
Heterogeneous nuclear RNA hnRNA Serves as precursor for mRNA and other RNAs.
Transfer RNA tRNA Transfers amino acid to mRNA for protein biosynthesis.
Ribosomal RNA rRNA Provides structural framework for ribosomes.
Small nuclear RNA snRNA Involved in mRNA processing.
Small nucleolar RNA snoRNA Plays a key role in the processing of rRNA molecules.
Small cytoplasmic RNA scRNA Involved in the selection of proteins for export.
Transfer-messenger RNA tmRNA Mostly present in bacteria. Adds short peptide tags to proteins to facilitate the degradation of incorectly synthesized proteins.

Three parts of a nucleotide – a building block of nucleic acids (DNA and RNA)

DNA and RNA are polymers.

Nucleic acids are made up of monomers called nucleotides. The nucleotides combine with each other to form a polynucleotide.

Basic building blocks of nucleic acids are three different components:

  1. a nitrogenous base,
  2. a pentose (five-carbon) sugar,
  3. a phosphate group.

Each nitrogenous base in a nucleotide is attached to a sugar molecule, which is attached to one or more phosphate groups. 

Each nucleotide in DNA contains one of four possible nitrogenous bases:

  1. adenine (A),
  2. guanine (G),
  3. cytosine (C),
  4. thymine (T).

Nucleotides of RNA contain uracil (U) instead of thymine.

Adenine and guanine are classified as purines. The primary structure of a purine is two carbon-nitrogen rings.

Cytosine, thymine, and uracil are classified as pyrimidines which have a single carbon-nitrogen ring as their primary structure.

Nitrogenous building blocks of nucleic acids (DNA and RNA)

Pentose sugar in DNA and RNA

The pentose sugar in DNA is deoxyribose, and in RNA, the sugar is ribose.

The difference between the sugars is the presence of the hydroxyl group on the second carbon of the ribose and hydrogen on the second carbon of the deoxyribose.

The carbon atoms of the sugar molecule are numbered as 1′, 2′, 3′, 4′, and 5′ (1′ is read as “one prime”).

The phosphate residue is attached to the hydroxyl group of the 5′ carbon of one sugar and the hydroxyl group of the 3′ carbon of the sugar of the next nucleotide, which forms a 5′–3′ phosphodiester linkage.

Structural elements of nucleic acids (DNA)

Double-Helix structure of nucleic acids - DNA

DNA has a double-helix structure.

The backbone of a nucleic acid molecule is made of the sugar and phosphate lying on the outside of the helix.

The nitrogenous bases are stacked in the interior; the pairs are bound to each other by hydrogen bonds.

Every base pair in the double helix is separated from the next base pair by 0.34 nm.

The two strands of the helix run in opposite directions, meaning that the 5′ carbon end of one strand will face the 3′ carbon end of its matching strand.

The Double-Helix Structure of nucleic acids (DNA)

Only certain types of base pairing are allowed. For example, a certain purine can only pair with a certain pyrimidine.

This means:

  • A can pair with T,
  • G can pair with C.

Molecular structure of ribonucleic acid (RNA) is usually single-stranded.