Nucleic Acids

4.5

Nucleic Acids

Introduction

Nucleic acids are one or two polymer chains comprising of nucleotide monomers.
Nucleic acids are formed from the elements of carbon, hydrogen, oxygen, nitrogen and phosphorus.
Each nucleotide consists of a pentose sugar (5-carbon sugar), a nitrogenous base and a phosphate group that are combined together through the condensation process.
There are two types of pentose sugars, that are, ribose and deoxyribose.
The nitrogenous base consists of adenine (A) guanine (G), cytosine (C), thymine (T) and uracil (U).
There are two types of nucleic acids:
- deoxyribonucleic acid (DNA).
- ribonucleic acid (RNA).
Ribonucleic acid (RNA) contains ribose sugar while deoxyribonucleic acid (DNA) contains deoxyribose sugar.

Deoxyribonucleic Acid (DNA)

DNA consists of two polynucleotide chains that are intertwined in opposite directions and form the double helix.
The nitrogenous base groups on both polynucleotide chains are matched and bound together by hydrogen bonds.
The nitrogenous bases for DNA are adenine (A), guanine (G), thymine (T) and cytosine (C).
Adenine will pair with thymine while guanine will pair with cytosine.

Ribonucleic Acid (RNA)

The RNA structure is a single polynucleotide chain which is shorter compared to DNA.
The nitrogenous bases for RNA are adenine, guanine, cytosine and uracil.
Thymine in DNA is replaced by uracil in RNA.
The three main types of RNA, are messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA).
These three RNAs are involved in the protein synthesis process.

Importance of Nucleic Acids in a Cell

DNA is important as a carrier of hereditary information and a determinant of characteristics in living organisms.
DNA contains genetic codes carried by nitrogenous bases (A, G, C and T) for the synthesis of polypeptides which form proteins.
The genetic code is written as a series of three bases that determine the sequence of amino acids in proteins to be synthesised.
For example, the AUG codon (base sequence: adenine, uracil and guanine) on mRNA is the code for methionine amino acid.
The three-base sequence in DNA is transcribed into mRNA codons which are then translated into the amino acid sequence to form a single polypeptide chain (refer image below).
This means that the sequence of nucleotides in DNA determines the amino acid sequence in the polypeptide chain that builds the corresponding protein.

Formation of Chromosomes from DNA and Proteins

Chromosomes are formed from DNA polynucleotide chains that are wound around a protein called histone.
Histones do not carry genetic information.
DNA molecules combine with histone proteins to form nucleosomes.
Nucleosomes are intertwined to form the chromosome structure.

4.5

Nucleic Acids

Introduction

Nucleic acids are one or two polymer chains comprising of nucleotide monomers.
Nucleic acids are formed from the elements of carbon, hydrogen, oxygen, nitrogen and phosphorus.
Each nucleotide consists of a pentose sugar (5-carbon sugar), a nitrogenous base and a phosphate group that are combined together through the condensation process.
There are two types of pentose sugars, that are, ribose and deoxyribose.
The nitrogenous base consists of adenine (A) guanine (G), cytosine (C), thymine (T) and uracil (U).
There are two types of nucleic acids:
- deoxyribonucleic acid (DNA).
- ribonucleic acid (RNA).
Ribonucleic acid (RNA) contains ribose sugar while deoxyribonucleic acid (DNA) contains deoxyribose sugar.

Deoxyribonucleic Acid (DNA)

DNA consists of two polynucleotide chains that are intertwined in opposite directions and form the double helix.
The nitrogenous base groups on both polynucleotide chains are matched and bound together by hydrogen bonds.
The nitrogenous bases for DNA are adenine (A), guanine (G), thymine (T) and cytosine (C).
Adenine will pair with thymine while guanine will pair with cytosine.

Ribonucleic Acid (RNA)

The RNA structure is a single polynucleotide chain which is shorter compared to DNA.
The nitrogenous bases for RNA are adenine, guanine, cytosine and uracil.
Thymine in DNA is replaced by uracil in RNA.
The three main types of RNA, are messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA).
These three RNAs are involved in the protein synthesis process.

Importance of Nucleic Acids in a Cell

DNA is important as a carrier of hereditary information and a determinant of characteristics in living organisms.
DNA contains genetic codes carried by nitrogenous bases (A, G, C and T) for the synthesis of polypeptides which form proteins.
The genetic code is written as a series of three bases that determine the sequence of amino acids in proteins to be synthesised.
For example, the AUG codon (base sequence: adenine, uracil and guanine) on mRNA is the code for methionine amino acid.
The three-base sequence in DNA is transcribed into mRNA codons which are then translated into the amino acid sequence to form a single polypeptide chain (refer image below).
This means that the sequence of nucleotides in DNA determines the amino acid sequence in the polypeptide chain that builds the corresponding protein.

Formation of Chromosomes from DNA and Proteins

Chromosomes are formed from DNA polynucleotide chains that are wound around a protein called histone.
Histones do not carry genetic information.
DNA molecules combine with histone proteins to form nucleosomes.
Nucleosomes are intertwined to form the chromosome structure.