Gene – Structure, Types & Characteristics

Gene is defined as the fundamental unit of inheritance because it is transferred from parents to offspring. A gene is a basic unit of heredity in biology. It carries instructions encoded in DNA that control the manufacture of particular proteins or useful RNA molecules. As the molecular blueprints for an organism’s growth, operation, and regulation, genes are essential for transferring genetic information from one generation to the next.

In this article, we will read about genes, their history, gene structure and composition, types of genes, the characteristics determined by genes, their function, and much more.

Gene Definition

Gene is the fundamental unit of DNA that encodes all the genetic information in the form of nucleotides.

What is a Gene?

The term “Gene” was coined by Johanssen in 1909. A gene is a unit of inheritance that is composed of DNA and carries all the genetic information. The gene consists of DNA nucleotides and serves as the basic unit of heredity. These nucleotides code for an amino acid and form a functional protein. The gene has a set of coding regions, promoters, and termination sequences.

History

The invention of the microscope played a significant role in visualizing the intracellular structure and led to the discovery of the cell. In 1842, Karl Wilhelm von Nageli found the existence of thread-like structures inside the plant cell nucleus and called them “transitory cytoblasts” which are now known as “chromosome”. At first, chromosomes were thought to be responsible for inheritance. After the introduction of inheritance theory by Mendel in 1865, it was well understood that some elements are responsible for inheritance in organisms and these units of inheritance are now called “genes”.

Gene Composition and Structure

Genes are built up of DNA, which is a long strand of nucleotide monomers. A phosphate group, pentose sugar (deoxyribose), and one of the nitrogenous bases—adenine (A), thymine (T), cytosine (C), or guanine (G)—compose these monomers. The structure of the gene consists of four nucleotides.

Composition

Genes are present in the chromosomes, are made up of DNA and in some viruses, genes are made of RNA. The two chains of nucleotides winded together forming DNA. The nitrogenous base, a sugar molecule and phosphate group together forms a nucleotide. DNA differs from RNA in the nitrogenous base and sugar. The sugar molecule in DNA is deoxyribose sugar while the sugar molecule in RNA is ribose sugar. DNA contains Adenine (A) , Guanine (G) , Thymine (T) and Cytosine (C) as nitrogenous bases while RNA contains Adenine (A) , Guanine (G) , Cytosine (C), and Uracil (U) as nitrogenous bases.

Structure

Genes contain both coding regions and non-coding regions. The coding regions are called exons while the non-coding regions are called introns.

Types of Genes

Some of the types of Genes are discussed below:

• Chromosomal Genes: Genes that retain information and pass it on to the following generation are known as chromosomal genes.
• Structural Genes: These genes encode RNA and proteins other than regulatory proteins.
• DNA repair Genes: These genes control how damaged DNA is repaired during mitosis.
• Operator Genes: These are regulatory genes that give a transcription factor a binding site through which to control the expression of a gene.
• Synthetic Genes: Genes created artificially in a lab are referred to as synthetic genes.
• Epistatic Genes: Genes that express themselves when a modifier gene is present are known as epistatic genes.

Regulation and Expression of Genes

Genes are expressed only when needed and the expression of genes are regulated by certain factors. Experimental studies have shown that the gene carrying information is not active all the time. It can be activated or deactivated in both prokaryotic and eukaryotic organisms.

Regulation of Genes in Prokaryotes

The regulation of genes in bacteria is distinct. The structural, regulator and operator are the three types of genes present in the bacteria.

• The structural genes control the polypeptide synthesis.
• The operator genes are required to initiate the transcription of DNA in the structural genes.
• The structural genes and the operator genes are linked together through an elemental unit called “operon”.
• The operon’s activity is managed by the regulator genes that produce the repressor.
• The repressor is nothing but a small molecule of protein. The presence or absence of the repressor determines the activeness or inactiveness of an operon.

Regulation of Genes in Eukaryotes

The eukaryotic genes do not contain operon. The coding region, the promoter region and the termination sequence are the three regions of a eukaryotic gene. The eukaryotic gene expression is regulated at multiple stages and the presence or absence of the transcription factors regulates their expression. Transcription factors may get attached to the regulatory region or the promoter region influences the transcription rate thereby acting as enhancers or activators.

Characteristics Determined By Genes

Each and every trait of an individual is determined by genes. Genes decide the characteristics of an individual such as:

• Height
• Eye Color
• Blood Group
• Immunity
• Genetic disease

Functions of Gene

Genes play a crucial role in the inheritance of an organism.

• They are located in the chromosomes and are responsible for determining the phenotype of the organism.
• The proteins regulating the function of the cell are encoded by genes.
• The genetic information carried by the base sequence of each gene decides the amino acid sequence of a protein.
• Mutation in the genes is responsible for genetic diversity and evolution.
• The similarity and difference between organisms is originated by genes.
• Genetic disease or disorder arises when genes don’t function properly.
• The presence of both introns and exons in genes is mandatory for the regulation and functioning of the cells.
• Genes are responsible for the transcription and translation process.

Thus, genes regulate each and every trait of the organism at molecular level. Without proper regulation and expression of genes, proteins cannot be synthesised.

FAQs on Gene

What are Gene and Genomes?

Gene is the fundamental unit of DNA that encodes all the genetic information in the form of nucleotides. All the genetic material of an organism as a whole is called the genome.

Which is an Example of a Gene?

Genes carry the genetic information of organisms. The human insulin gene is written as INS and the human insulin receptor gene is written as INSR.

What are the Three regions of a Gene?

Gene contains the coding region, the promoter region and the termination sequences. In order to initiate transcription, the proteins like RNA polymerase and transcription factors bind to the upstream region of the gene and this region is called the promoter region.

What is the Function of a Gene?

Genes are responsible for carrying hereditary information from one generation to the other. It also decides the physical appearance of an individual.

Where is the Gene Located?

Genes are found in the nucleus. To be more specific, genes are located in chromosomes and chromosomes are inside the nucleus.