Let me tell you about an incident to you. A family immigrated to the United Kingdom and became citizens. However, one of the sons visited his parent's ancestral house and returned back to the UK. Alas, he was denied entry to the UK stating he had a forged passport. He has to prove that his mother lived in the UK while his father is no more. The family's lawyer was looking for proof that the boy was indeed the UK mother's son and not her nephew.
But do you know the technique which was used to address this problem?
DNA samples were collected from the mother and the son whose identity was disputed, and the mother's other three undisputed children. The patterns confirmed the mother-son relationship under consideration. Furthermore, the testing revealed that all four children shared the same father and got him his entry to the UK.
This immigration case paved the way for the use of DNA fingerprinting in forensic cases and for determining identity.
But what is this DNA and how it could give the clinching evidence about the relationship?
Nucleic acids are biopolymers and macromolecules that are fundamental to all known life forms. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the two main types of nucleic acids (RNA).
Let's learn about the functions of nucleic acid in this article.
Table of content
Nucleic acids are large polymers of nucleotides that are found in the nucleus of cells. This macromolecule was given the name nucleic acid because it was discovered in the cell nucleus and had acid-like properties. It is a polymer composed of smaller subunits (nucleotides) that are linked together.
Nucleic acid is a naturally occurring chemical compound that can be broken down to produce phosphoric acid, sugars, and a mixture of organic bases (purines and pyrimidines). Nucleic acids are the primary information-carrying molecules in the cell, and they determine the genetic characteristics of all living things by directing the process of protein synthesis.
Classification and structure of nucleic acids
There are two types of nucleic acids: DNA and RNA, and they are responsible for storing a cell's genetic information. The two nucleic acids have minor structural differences but perform vastly different functions in the biological system.
Structure of DNA
A double-helical structure makes up DNA. The outer edges of the sugar-phosphate backbone are formed by alternating deoxyribose sugar molecules and phosphate groups. The two parallel strands run in opposite directions. The strand is antiparallel, which means that the phosphodiester bonds (3'-5') are in the opposite direction, and the 3' end of one strand is next to the 5' end of the other. This means that the nucleotides in one strand of DNA are the same as those in the other. The DNA molecule contains four nitrogenous cyclic bases: adenine (A), thymine (T), guanine (G), and cytosine. Adenine and thymine are joined by two hydrogen bonds, while cytosine and guanine are joined by three hydrogen bonds. Within the helix structure, the nitrogenous bases are arranged. Inside the double helix, the bases are stacked. Twists or turns occur every ten bases in the double helix's two sugar-phosphate backbones.
Structure of RNA
Ribonucleic acid (RNA) is a single-stranded helix composed of nucleotides containing a complete pentose sugar, and nitrogenous bases which includes uracil (U), adenine (A), cytosine (C), and guanine (G), and a phosphate group. In RNA, uracil(U) replaces thymine(T), which is found in DNA, as a nitrogen base. The major building blocks of RNA are uracil (U) and adenine (A), which form base pairs linked by two hydrogen bonds. The cell contains several types of RNA, including tRNA, rRNA, and mRNA, which serve various functions for the cell. Other non-coding RNAs can be found in the cell.
There are two types of nucleic acid and it is important to know the functions of both types of nucleic acids as it can also be considered the function of the nucleic acid.
Function of deoxyribonucleic acid (DNA)
Q1. Which of the following intermolecular force of attraction holds the nitrogenous base together in DNA molecules?
A. Ionic bond
B. Covalent bond
C. Vanderwaal force of attractions
D. Hydrogen bonding
Solution: The DNA molecule contains four nitrogenous cyclic bases: adenine (A), thymine (T), guanine (G), and cytosine. Adenine and thymine are linked together by two hydrogen bonds, whereas cytosine and guanine are linked together by three hydrogen bonds within the helix structure, and the nitrogenous bases are arranged. Therefore, option(D) is correct.
Q2. Which nitrogenous base is only present in an RNA molecule and not in a DNA molecule?
Solution: The DNA molecule contains four nitrogenous cyclic bases: adenine (A), thymine (T), guanine (G), and cytosine. Adenine and thymine are joined by two hydrogen bonds, while cytosine and guanine are joined by three hydrogen bonds.. Whereas, in the case of an RNA molecule nitrogenous bases include uracil (U), adenine (A), cytosine (C), and guanine (G). In RNA, uracil(U) replaces thymine(T), which is found in DNA, as a nitrogen base. Therefore, option(C) is correct.
Q3. Select the correct option which signifies the importance of DNA molecules.
A. It aids in the synthesis of ribosomal small and large subunits
B. It is responsible for biochemical reactions in cells such as gene splicing
C. It helps in the transfer of amino acids to the ribosomal subunit at the site of protein synthesis
D. It aids in the transmission of genetic information from the parent cell to the daughter cell.
Solution: Some important function of RNA includes:
It aids in the synthesis of ribosomal small and large subunits,
it is responsible for biochemical reactions in cells such as gene splicing and helps in the transfer of amino acids to the ribosomal subunit at the site of protein synthesis. Whereas, chromosomes are tightly packed DNA structures found in the nucleus of our cells DNA which aid in the transmission of genetic information from the parent cell to the daughter cell.
Therefore option (D) is correct.
Q4. What is the difference between purines and pyrimidines?
Purines are large-sized heterocyclic molecules which has two rings and therefore bicyclic molecule.
Purines are small-sized heterocyclic molecules which have a single ring and therefore are monocyclic in nature.
Rings are formed from 9 atoms which are numbered in an anticlockwise direction.
Rings are formed from six atoms and numbered in the clockwise direction.
Nitrogen atoms are at the 1st, 3rd, 7th and 9th positions
Nitrogen atoms are at the 1st and 3rd position
Guanine and adenine are the examples of purine molecules
Thyamine, cytosine and uracil are the examples of pyrimidines molecules.
Q1. What is a nucleotide?
Answer: A nucleotide is the fundamental component of nucleic acids (RNA and DNA). A nucleotide is composed of a sugar molecule (ribose in RNA or deoxyribose in DNA) that is linked to a phosphate group and a nitrogen-containing base. Adenine (A), cytosine (C), guanine (G), and thymine(T) are the bases used in DNA. In RNA, the base uracil (U) is replaced by thymine(T). DNA and RNA are polymers made up of long nucleotide chains.
Q2. what are the functions of a nucleotide?
Answer: Some important functions of nucleotides are:
Q3. Can DNA survive on the surface of clothes?
Answer: DNA survival in summer and winter results differed significantly, as did pond and river results. For a sample with skin cells in the pond during winter, the longest exposure time that still resulted in a complete profile was 2 weeks. In the summer, the time required to erase the majority of DNA from epithelial samples was 4 hours and more than 1 day for blood samples in pond and river environments. Overall, the findings show that DNA can still be recovered from clothes that have been submerged in water for more than a week.
Q4. How to define the complementary base pairing rule?
Answer: Chemical cross-links formed by pairs of nucleotide bases exist between the two strands of DNA. They always pair up in the same way, which is known as a complementary base pairing or Chargaff's rule. Complementary base pairing occurs when guanine always binds to cytosine and adenine always binds to thymine in DNA. Guanine and cytosine have three hydrogen bonds in common, whereas adenine and thymine always have two. RNA replaces thymine (T) with uracil, a different pyrimidine base (U). The complementary base pairing of DNA strands in a double-helix allows one strand to be used as a template to construct the other. Only a subset of DNA's nitrogenous bases can interact with one another to form a stable DNA molecule.