DNA is a fundamental biological molecule that encompasses the essential instructions required for the development, survival, and reproduction of organisms. It exists universally in all life forms on our planet and holds the distinctive genetic code of each individual organism.
In essence, deoxyribonucleic acid (DNA) is found in practically every cell of the body. This genetic code is responsible for the uniqueness of every person. DNA carries the intricate instructions necessary for the growth, reproduction, and proper functioning of all living organisms.
These genetic instructions account for the diverse characteristics observed in individuals, such as eye color variations between people or the presence of only two wings in birds. They also explain the distinctive traits of certain species, such as the elongated necks of giraffes. Additionally, deviations or alterations in the genetic code can contribute to an increased susceptibility to specific diseases.
Moreover, it is fascinating to note that DNA is not only present in nearly all cells within the body but also has an extraordinary length. If unraveled and stretched end-to-end, the DNA in a single cell would extend over 6.5 feet (ft) in length.
This article aims to provide a comprehensive overview of DNA, including its composition, functioning, and its impact on overall health.
What is DNA?
In summary, DNA is a lengthy molecule that carries the distinct genetic code of each individual. It serves as the blueprint for constructing the vital proteins necessary for the body’s proper functioning.
The transmission of DNA instructions occurs from parents to their offspring, with approximately half of a child’s DNA deriving from the father and the other half from the mother.
How is DNA structured?
DNA takes the form of a double-stranded molecule with a distinct twisted structure known as the double helix.
Each of the two strands consists of a lengthy sequence of nucleotides, which are the fundamental units of DNA. These nucleotides are composed of a phosphate molecule, a sugar molecule called deoxyribose (comprising five carbons), and a nitrogen-containing region.
There are four types of nitrogen-containing regions known as bases, namely adenine (A), cytosine (C), guanine (G), and thymine (T).
The arrangement of these four bases establishes the genetic code, which serves as the instructions for life.
The bases of the two DNA strands are paired together, forming a ladder-like structure. In this ladder, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C), creating the “rungs” of the ladder. The length of the ladder is formed by the sugar and phosphate groups.
What is a gene?
A gene refers to a specific segment of DNA that contains the instructions for producing a particular protein. For example, the gene responsible for insulin production controls the levels of sugar in the bloodstream. In humans, there are approximately 30,000 genes, although the exact number may vary according to different estimates.
Interestingly, it is believed that only around 1% of DNA consists of protein-coding genes. The remaining 99% of DNA has a less understood function but is thought to play a role in regulating the processes of transcription and translation.
Among the chromosomes, chromosome 1 is the largest and contains approximately 2,800 genes. On the other hand, the smallest chromosome, chromosome 22, has around 750 genes.
How does DNA work?
The majority of DNA resides within the nuclei of cells, while a portion is also found in mitochondria, which are the cell’s powerhouses.
Due to the significant amount of DNA present in human cells and the relatively small size of cell nuclei, DNA requires highly compact packaging. The DNA strands undergo looping, coiling, and wrapping around proteins known as histones. This tightly coiled DNA-protein complex is referred to as chromatin.
Further condensation of chromatin occurs through a process called supercoiling, resulting in the formation of structures called chromosomes. These chromosomes take on the recognizable “X” shape.
Each chromosome contains a single DNA molecule. Humans possess 23 pairs of chromosomes, totaling 46 chromosomes. Different species have varying numbers of chromosomes. For example, fruit flies have 8 chromosomes, while pigeons have 80 chromosomes.
Protein creation
To enable the production of proteins from genes, two essential steps take place:
Transcription: During transcription, the genetic code encoded in DNA is copied into messenger RNA (mRNA). Unlike DNA, mRNA is typically single-stranded and serves as a replica of the DNA code. However, there are a few differences. RNA lacks the base thymine (T) found in DNA and instead utilizes uracil (U). Transcription allows for the transfer of genetic information from DNA to mRNA.
Translation: Following transcription, the mRNA undergoes translation, where it is utilized as a template for the synthesis of amino acids. This process involves the participation of transfer RNA (tRNA). The mRNA contains three-letter segments called codons, which provide information about specific amino acids. Each codon corresponds to a particular amino acid or serves as a building block for protein synthesis. For example, the codon GUG codes for the amino acid valine.
There are a total of 20 different amino acids that can be incorporated into proteins during translation.
Telomeres
Telomeres are specialised regions consisting of repeated nucleotides located at the ends of chromosomes.
Their primary function is to safeguard the chromosome ends from damage and prevent them from fusing with other chromosomes.
Scientists often compare telomeres to the plastic tips found on shoelaces that prevent them from fraying.
As an individual ages, these protective regions gradually decrease in size. With each round of cell division and DNA replication, telomeres undergo shortening.
How does DNA affect health?
As individuals age, DNA undergoes degradation, contributing to the aging process.
Occasionally, random changes in a person’s DNA sequence occur, known as mutations. Some mutations within a person’s genetic code can lead to the development of various diseases or conditions.
Alternatively, individuals may inherit genes that can impact their health adversely. Environmental factors can influence how these mutated genes manifest.
Damage to the structure of DNA can happen through different mechanisms, such as incorrect base pairing during replication, missing or extra base pairs, malfunctioning DNA replication or recombination, exposure to environmental factors like radiation or heavy metals, mutations in DNA repair processes, or changes in the number or structure of chromosomes.
Diseases or health conditions can arise from damage to a single gene, as seen in cystic fibrosis, or from damage occurring in multiple regions of a person’s DNA, such as in cancer. Additional examples include Down syndrome, autoimmune conditions, chronic inflammatory conditions, and neurodegenerative diseases like Huntington’s disease.
Frequently Asked Questions
Who discovered DNA?
The credit for the discovery of DNA is attributed to Friedrich Miescher, a Swiss scientist. In the late 1860s, Miescher successfully isolated DNA from human pus cells, marking a significant milestone in the understanding of this fundamental molecule.
What are the different types of DNA?
DNA exhibits various types or forms, each characterized by its distinct structure. The most prevalent type of DNA is known as B-DNA, which is commonly found in the genome. However, there are other types of DNA that have been identified, including A-DNA, H-DNA, and Z-DNA.
A-DNA is a right-handed double helix with a slightly different conformation compared to B-DNA. It typically occurs under specific physiological conditions or in complexes with proteins.
H-DNA refers to a three-stranded DNA structure that can form when certain DNA sequences adopt unusual conformations. It involves the formation of DNA loops and is associated with genetic instability and DNA rearrangements.
Z-DNA is a left-handed double helix with a zigzag shape. It can form in regions of DNA that have alternating purine-pyrimidine base sequences. Z-DNA is less common than B-DNA and may have regulatory roles in gene expression.
These different forms of DNA contribute to the structural diversity and functional complexity of genetic material.
What is DNA replication?
DNA replication is a crucial process in which DNA within cells undergoes a duplication or self-copying. This process is essential to ensure that each new cell formed during cell division possesses a complete and accurate copy of the genome.
During DNA replication, the two strands of the double helix separate, and each strand serves as a template for the synthesis of a new complementary strand. Enzymes called DNA polymerases facilitate the addition of nucleotides to the growing strands, following the base pairing rules (A with T, and G with C).
The result of DNA replication is the formation of two identical DNA molecules, each consisting of one original strand and one newly synthesized strand. This process ensures the preservation and inheritance of genetic information across generations of cells.
Can genetic diseases be cured?
Currently, medical professionals can primarily address the symptoms associated with conditions caused by genetic mutations, as the underlying genetic changes are often challenging to reverse. However, ongoing research is dedicated to the development of gene therapies that hold the potential to halt or prevent the progression of such diseases.
Gene therapy involves introducing healthy genes into cells to replace or supplement faulty genes, aiming to restore normal functioning. This field has shown promising advancements, and certain gene therapy drugs have gained approval from the U.S. Food and Drug Administration (FDA) for specific conditions. These approved therapies have demonstrated their safety and effectiveness through rigorous clinical trials.
Furthermore, numerous other gene therapy approaches are undergoing active clinical trials to assess their potential benefits and ensure their safety. These trials serve as vital steps in evaluating the feasibility and efficacy of various gene therapy strategies for a wide range of genetic disorders.
The continuous efforts of researchers and regulatory bodies like the FDA contribute to the advancement of gene therapies, offering hope for potential future treatments that may address the root cause of genetic diseases.
Summary
DNA is a remarkable molecule present in the majority of cells, containing the distinctive genetic code of each individual. Its primary role is to encode proteins, which play vital roles in cellular growth and development.
DNA is organised into structures called chromosomes, which consist of tightly coiled DNA strands. Within the DNA sequence, specific segments known as genes are responsible for coding individual proteins. Furthermore, DNA carries crucial genetic information necessary for the survival and functioning of all life forms on our planet.
In essence, DNA serves as the comprehensive blueprint for life on Earth, providing each living organism with its unique genetic code. When there are disruptions or abnormalities in this blueprint, it can lead to the occurrence of diseases and health issues. Understanding and deciphering DNA are essential for unravelling the complexities of life and addressing the underlying causes of various health conditions.
