Difference Between DNA and Genes

Main Difference – DNA vs Genes

DNA is the genetic blueprint of most organisms. DNA exists in a comparatively stable structure called double-helix and is organized into chromosomes. A chromosome is a higher order structure which is composed of a single DNA molecule. Genes are the hereditary molecules which transfer traits to the progeny. Genes are composed of DNA or RNA stretches. The key difference between DNA and genes is that DNA is a chemical structure which stores the genetic instructions and genes are small DNA stretches which determine a specific trait.   

This article studies, 

1. What is DNA
     – Definition, Structure, Features
2. What are Genes
     – Definition, Structures, Features
3. What is the difference between DNA and Genes

What is DNA

Deoxyribonucleic acid (DNA) is the genetic material of most organisms. DNA is located in nucleus and nucleoid. Mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA) also can be found in a cell. DNA stores the genetic information for long-term which is necessary for the development, functioning and reproduction. The nucleotide is the monomer of DNA which consists of three groups: pentose sugar, nitrogenous base, and phosphate group. Nitrogenous base and phosphate group are attached to the pentose sugar. The 3′ OH group of pentose sugar of one nucleotide forms a covalent bond with the phosphate group of the adjacent nucleotide to produce the sugar-phosphate backbone. The covalent bond forming here is referred to as phosphodiester bond. Deoxyribose is the pentose sugar shared by DNA. Thus, DNA lacks the 2′ OH group on the pentose ring which makes the DNA much reactive. DNA is also stable in alkaline conditions.

Four different nitrogenous bases that can be identified in DNA are cytosine (C), guanine (G), adenine (A) and thymine (T). These bases are arranged in different orders in order to store the genetic information. The order of the nucleotide sequence on the sugar-phosphate backbone is identified as genes. Two polynucleotide chains are joined together by hydrogen bonds between complement base pairs. This process is called complement base pairing and it produces a double-stranded DNA molecule where each strand is complementary. Double-stranded DNA is further coiled to form a double-helix structure. The two strands of a double-helix run into opposite directions, making them antiparallel. The asymmetric ends of the strand are called 3′ and 5′ ends. The DNA double-helix prefers the B-form geometry. Hence, major and minor grooves in DNA are narrow, preventing the enzymatic degradation.

An organism’s complete set of DNA is called a genome. The size of the human genome is 3.2 billion base pairs and it consists of about 25,000 genes. Polynucleotide chains of DNA are organized into structures called chromosomes within the cell. DNA synthesize their identical copy by replication. DNA is more prone to damage by UV.

Figure 1: DNA structure

What are Genes

A gene is a region (locus) or a specific nucleotide sequence on the DNA strand. Genes encode an amino acid sequence of a specific protein. Thousands of genes can be found within a single DNA molecule of higher organisms. Genes are recognized as the molecular unit of hereditary since the genetic instructions transfer into progeny via reproduction through genes. Gene sequence is transcribed into mRNA; mRNA is transcribed into proteins which determine the trait. This is called as the central dogma of molecular biology. The concept of the gene and its pattern of inheritance originated with the findings by Gregor Mendel in 1860s.

Most of the genes are made up of DNA but a few may share RNA. Some viruses are made up of RNA genes since their genetic material is RNA. Functionally related prokaryotic genes group to form units called operons. The multiple protein-coding sequences are transcribed together. Eukaryotic gene structure is mainly composed of two regions: coding sequence and the regulatory sequence. Eukaryotic coding sequence consists of exons, introns and untranslated regions whereas prokaryotic genes lack introns. Genes are transcribed with introns. Consequently, they are removed by splicing the exons. On the contrary, multiple proteins can be produced by alternative splicing.

Regulatory sequences are composed of the promoter region for the initiation of transcription, enhancers, and inhibitors. Perhaps, both enhancers and inhibitors may be found on a separate chromosome. Gene expression is regulated at transcriptional and translational level. Variations of a gene are referred to as alleles.

Figure 2: Gene Structure

Difference Between DNA and Genes

Definition

DNA: DNA is a chemical which stores the genetic information of an organism.

Genes: Genes are the DNA stretches which are encoded for different proteins.

Role

DNA: DNA determine many functions such as gene regulation.

Genes: Genes determine the traits of an organism.

Size of the molecule

DNA: DNA is a long chain polynucleotide.

Genes: Genes are small stretches of DNA. A single DNA molecule may carry thousands of genes and other non-coding regions.

Genetic Material

DNA: DNA is not the only genetic material shared by organisms.

Genes: Genes are made up of either DNA or RNA.

Studies

DNA: The studies about DNA are recently developed.

Genes: The studies have started a long time ago.

Conclusion

Genomic DNA is mainly composed of genes and junk DNA. All types of non-coding DNA are collectively called as junk DNA. These junk DNA also play a vital role in the functioning of an organism. They are mainly involved in the gene regulation. For example, cis- and trans- regulatory elements are important in controlling the transcription of genes. Thus, the key difference between DNA and gene is that genes are only one specific sequence of DNA which determines the traits.

Reference:
1. “DNA”. Wikipedia. 2017. Accessed 13 Feb. 2017
2. “What is DNA?”. Genetics Home Reference. 2017. Accessed 13 Feb. 2017
3. Susman M. “Genes: Definition and Structure.” ENCYCLOPEDIA OF LIFE SCIENCES, Nature Publishing Group, 2001. Accessed 09 Feb. 2017
4. Schleif R. “Genetics and Molecular Biology“. 2nd ed., The Johns Hopkins University Press, 1993, pp. 22-47, Accessed 09 Feb. 2017

Image Courtesy:
1. “DNA simple2”. By Forluvoft – Own work (Public Domain) via Commons Wikimedia
2. “Gene”. By Di Courtesy: National Human Genome Research Institute (Public Domain)  via Commons Wikimedia