Molecular Basis of Inheritance

Introduction

The process by which offspring inherit the characteristics of a parent is called inheritance. Molecular basis of inheritance deals with the study of heredity, variation in genetics, and also genes. The most crucial heredity determiner is known as genes. Genes carry messages from one generation to another from cell to cell.

To specify biological and physical traits, genes send information from parents to offspring. Most of the genes contain the information required to make a functional molecule which is known as a protein. But all the genes do not code for proteins. There are roughly 20000 protein-coding genes present in the human body. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) and genetic codes constitute the molecular basis of inheritance.

Importance of DNA

The importance of deoxyribonucleic acid is listed below −

• Deoxyribonucleic acid codes for protein synthesis.

• Deoxyribonucleic acid carries genetic information.

• Deoxyribonucleic acid provides information on life and processes.

Structure of DNA and RNA

The most important nucleic acids confirmed by many biologists are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The basic structural unit of DNA and RNA is nucleotides. Long chains of nucleotides constitute both DNA and RNA. Nucleotides are composed of a sugar molecule that is linked to a phosphate group and a nitrogenous base. The nucleoside is the subunit of a nucleotide.

Structurally deoxyribonucleic acid (DNA) is constituted of two strands that wind around each other like a twisted ladder. This type of shape of DNA is known as a double helix.

Nitrogenous Base

• In a nucleotide structure, the nitrogenous base is the crucial information-bearing part.

  

• Nitrogen base is attached with sugar at its number 1- carbon position.

• The nitrogenous base contains a pyrimidine or purine base.

• Bases containing one carbon-nitrogen ring are known as pyrimidines while two ring bases are purine.

• Cytosine, thymine, and uracil are the pyrimidines.

• Cytosine is present in both DNA and RNA.

• Thymine is present only in DNA while uracil is in RNA.

• Purine mainly comprises guanine and adenine.

• Adenine and guanine present both in DNA and RNA

• Nucleotides can pair up with each other.

Sugar

• A nucleotide contains two important pentose sugar molecules namely ribose and deoxyribose.

• The sugar contains five carbon, ten hydrogen and five oxygen and is known as ribose or lacking one oxygen atom is known as deoxyribose.

• Ribose is found in RNA

• Deoxyribose is found in DNA.

Phosphate group

• The phosphate group of each nucleotide is attached to the sugar at its number 5 carbon position.

• The phosphate group is acidic in nature.

Characteristics of Nucleotide

• N-glycosidic bond link nitrogenous base with pentose sugar.

• The important pyrimidine bases are cytosine, thymine, and uracil. Cytosine and thymine are present in DNA while RNA contains cytosine and uracil.

• The purine bases of DNA and RNA comprise guanine and adenine.

• Thymine and adenine are attached by two hydrogen bonds.

• Three hydrogen bonds connect guanine and cytosine.

• The chain of nucleotides attach to each other to form the backbone of DNA.

• The consecutive nucleotides in DNA and RNA are linked together by phosphodiester linkage.

Genetic Code

The genetic code is constituted of a four-letter set of nucleotides known as codons. Each codon is linked to particular amino acids or stop signals. The concept of genetic code was first put forward by Francis Crick and his colleagues in 1961. Marshall Nirenberg and Heinrich Matthaei conducted an experiment on genetic code in the same year. From their experiment, they came to the conclusion that RNA sequences UUU specifically code for the amino acid phenylalanine. After this finding scientists, Philip Leader, Govind Khorana, and Nirenburg recognized the remaining genetic code and explained the three-letter codons that are associated with amino acids. There are approximately 64 codons present. Out of which 61 codons are linked with amino acids while three are stop signals. Genetic codes never overlap with each other. That means a single nucleotide is only part of a single codon even if it can be part of the two adjacent codons. Genetic code is universal and variation is almost rare. For example, mitochondria have different genetic codes with very minimum variations.

Human Genome Project

The human genome project was a well-organized, big, and highly collaborative effort made by international organizations to produce the first sequence of genomes of humans and several other well-developed organisms. It was carried out between 1990- 2003.

Conclusion

Molecular basis of inheritance deals with the study of heredity, variation in genetics, and also genes. The most crucial heredity determiner is known as genes. Genes carry messages from one generation to another from cell to cell. To specify biological and physical traits, genes send information from parents to offspring. The most important nucleic acids confirmed by many biologists are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The nucleotide is the basic structural constitution of nucleic acid i.e. DNA and RNA. Long chains of nucleotides constitute both DNA and RNA. Nucleotides are composed of a sugar molecule that is linked to a phosphate group and a nitrogenous base.

FAQs

Q1. State three functions of nucleotides.

Ans. The three functions of nucleotides are listed below −

• Nucleotides are the building blocks of life.

• A nucleotide can base the ATP molecule, which is the main source of energy in the cell. It can store energy in the body and acts as an energy reservoir.

• It is essential for many activities of enzymes. They are found in coenzymes like NAD and NADP and take part in metabolism.

Q2. Why do nucleotides only pair with a certain type of nucleotide?

Ans. Nucleotides' molecular structure allows them to bond with certain types of nucleotides. Adenine can only pair with thymine and is attached by two hydrogen bonds. While cytosine and guanine are connected with each other by three hydrogen bonds.

Q3. What do you understand by being acidic in nature?

Ans. Acidic nature possesses the properties of acids (high concentration of H+ ions). It has a pH value lower than 7. Lower the pH value higher will be the concentration of H+ ions hence higher will be the acidic property

Q4. What are the functions of ribonucleic acid?

Ans. The main function of ribonucleic acid is protein synthesis with a process known as translation. Apart from these ribonucleic acid conveys genetic information which is translated by ribosomes into different types of proteins. The three different types of RNA i.e. mRNA, tRNA, and rRNA are used in the process of protein synthesis.

Q5. What is nucleoside?

Ans. A nucleoside is a combination of pentose sugar and a nitrogenous base. The phosphate group is absent in nucleosides.