Monomers of DNA and RNA | Their Chemistry & Shape

Monomers are single-unit molecules that combine with each other to form Polymers. Both the DNA and RNA are polymers made of 4 types of nucleotide monomers.

The monomers of DNA are

1. Deoxyadenosine monophosphate (dAMP)
2. Deoxyguanosine monophosphate (dGMP)
3. Deoxycytidine monophosphate (dCMP)
4. Deoxythymidine monophosphate (dTMP)

Thus, each monomer is made of a

• Deoxyribose sugar,
• One nitrogenous base (viz. adenine, guanine, thymine, and cytosine) and
• One Phosphate groups

The monomers of RNA are

1. Adenosine monophosphate (AMP)
2. Guanosine monophosphate (GMP)
3. Cytidine monophosphate (CMP)
4. Uridine monophosphate (UMP)

Each of the monomers is made of

1. Ribose sugar molecule
2. nitrogenous base (viz. Adenine, Guanine, Cytosine, and Uracil) and
3. Phosphate group.

As the name indicates, DNA (deoxyribonucleic acids) and RNA (ribonucleic acids) have similar structures and are made of similar monomers.

They are made of nuclear bases and carbohydrate monomers.

These nucleic acids, DNA and RNA, are found in all living cells, including viruses, and it is believed that they can even be made in space (as per NASA).

Most organic compounds, like carbohydrates, amino acids, nucleic acids, etc., can be isolated as monomers.

Formation of Monomers of DNA and RNA

Each monomer described above has 3 basic parts.

Three parts of DNA Monomer

• DNA is a double-stranded structure with two strands aligned in a helix.

The DNA monomers have

1. Ribose sugar,
2. Nitrogenous bases and
3. A Phosphate group.

Deoxyribose sugar

• DNA monomers have deoxyribose sugar, a five-carbon sugar (carbohydrate).

• Unlike ribose sugar, this is devoid of one oxygen at the 2′ carbon position, as shown in the image above.

Nitrogenous base

• Besides, four nuclear bases are part of these monomers, and they include two purine bases, namely

1. Adenine
2. Guanine

and two pyrimidine bases, namely

1. Thymine
2. Cytosine

Phosphate group (PO₄^–³)

• The phosphate group is critical in the nucleotide structure.

• It connects sugar molecules through phosphodiester bonds and also helps form the sugar-phosphate nucleic acid backbone of DNA and RNA strands.

Three parts of RNA Monomers

• Each RNA monomer has a sugar, nitrogenous base, and phosphate group.

Ribose sugar

• Unlike DNA, RNA has ribose sugar, which is a five-carbon sugar.

Also, there are four nuclear bases, of which two are purine bases like

a) Adenine

b) Guanine

and two pyrimidine bases as

C) Uracil

d) Cytosine.

• So, the purine bases are the same in monomers of both the DNA and RNA, but the pyrimidine bases are different between these two nucleic acids.

• There is uracil instead of thymine in the RNA strand.

How do these components bind to form monomers?

• Both DNA and RNA monomers have the same patterns of component binding.

• The nitrogenous bases are bound to 1′ carbon of sugar molecule.

• Meanwhile, the phosphate group binds to the 5′ carbon of sugar molecules.

Polymerization to nucleic acids.

• The monomer forms a long strand through a phosphodiester bond.

• The 3′ hydroxyl of sugar reacts with 5′ phosphate of another by dehydration, forming a sugar-phosphate backbone.

• The DNA molecule is a double-strand structure, possibly due to the hydrogen bonds between the nuclear bases of both chains.

• DNA is the genetic material and is more stable than single-stranded RNA.

• Interestingly, the DNA is double-stranded in the nucleus but is a single-strand structure in mitochondria.

• RNA is a less durable genetic material and is present mainly in the cell’s cytoplasm.

Frequently asked questions and answers

References:

• NASA Researchers: DNA Building Blocks Can Be Made in Space