DNA Definition

• DNA is a molecule that contains the instructions necessary for an organism’s development, survival, and reproduction.
• These instructions are transferred from parents to children and are present in every cell in the body.
• Nucleic acid is one of the four fundamental varieties of macromolecules recognized as essential for all forms of life.
• A small quantity of DNA can also be found in the mitochondria of eukaryotes, in addition to the nucleus.

DNA Structure

• In 1953, Francis Crick and James Watson established the DNA structure.
• The finding was made by Watson and Crick thanks to Rosalind Franklin’s writings. The DNA is composed of two spirals, as Franklin initially noted.
• Because DNA has a double helix structure it resembles a twisted ladder.
• The levels of the ladder are composed of two nitrogen bases, while the sides are composed of sugar (deoxyribose) and phosphate molecules that alternate.
• Adenine (A), Thymine (T), Guanine (G), and Cytosine (C) are the four types of nitrogen bases in DNA paired. Nitrogen bases pair in a specific manner.
• Because the amounts of adenine and thymine are equal, as well as guanine and cytosine, this pairing pattern develops.
• Hydrogen bonds keep the pairs attached to one another.

Detailed Structure and Composition of DNA

• A double-stranded helix makes up the DNA. To put it another way, every DNA molecule consists of two long polymer strands which coil around each other to create a double helix structure. Given that they are constructed of less complex monomer units known as nucleotides, these two DNA strands are known as polynucleotides.
• Each strand has a 3′-end and a 5′-end containing a phosphate group (with a hydroxyl group).
• The strands are anti-parallel, so one goes from 5 to 3 and the other from 3 to 5; this is referred to as a direction difference.
• The two strands are joined by hydrogen bonds, which also permit them to support each other.
• In essence, deoxyribonucleotides make up DNA.
• By 3′–5′ phosphodiester linkages, the deoxyribonucleotides are joined.
• The deoxyribonucleotides are made up of the nitrogenous bases adenine, cytosine, thymine, and guanine.
• The nitrogenous bases are responsible for the complimentary nature of the strands. Adenine creates two hydrogen bonds with thymine (A-T) on the opposite strand, whereas cytosine creates three hydrogen bonds with guanine (C-G) on the other strand.
• Hydrogen bonding and hydrophobic interactions between bases maintain the structure of the helix.
• The double helix comprises a 2 nm diameter and repeats at a 3- 4 nm distance, or ten base pairs, between each repetition.

Major and Minor Grooves of the DNA

• Due to DNA’s double helix structure, the molecule has two asymmetric grooves. One groove is more diminutive than the other.
• This asymmetry is caused by the geometrical structure of the bonds between the phosphate, sugar, and base groups, which compels the base groups to bind at 120-degree angles as opposed to 180-degree angles.
• The wider groove, known as the major groove, happens when the backbones are widely separated, whereas the smaller groove, known as the minor groove, occurs when the backbones are close together.
• Due to the fact that the major and minor grooves show the margins of the bases, they may be utilized to determine the base sequence of a particular DNA molecule.
• Proteins must be able to detect certain DNA sequences to which they may bind in order for the body and cell to carry out their respective duties.

Properties of DNA

• Both right- and left-handed DNA helices exist. The most stable form of DNA is the B conformation, which has right-handed helices.
• The two strands of DNA separate when heated, and they rehybridize when cooled.
• Melting temperature is the temperature at which the two strands entirely separate (Tm). For each distinct sequence, a unique melting temperature applies.
• As a result of the C-G pair’s three hydrogen bonds, the B sample of DNA’s higher melting point must include a larger concentration of C-G.
• Each protein in every creature is made up of a specific sequence of amino acids, which is encoded by the bases along the DNA molecule.

Types of DNA

• The bulk of the DNA in eukaryotic species, which include animals, plants, and fungi, is kept in the cell nucleus, although some DNA is kept in organelles like the mitochondria.
• Depending on the site, DNA might be:

Nuclear DNA

• situated in eukaryotic cell’s nuclei.
• typically has two copies of each cell.
• The nuclear DNA chromosomes possess a linear, open-ended structure with 46 chromosomes and three billion nucleotides in total.
• Nuclear DNA is diploid and frequently contains genetic material from both parents. The mutation rate of nuclear DNA is less below 0.3 percent.

Mitochondrial DNA

• The mitochondria possess mitochondrial DNA.
• 100–1,000 copies are present in each cell.
• For instance, human mitochondrial DNA chromosomes include 16,569 nucleotides and often have closed, circular shapes.
• The only source of mitochondrial DNA, which is haploid, is the mother.
• Nuclear DNA often has a mutation rate lower than mitochondrial DNA.

Forms of DNA

• The majority of DNA is in the traditional Watson-Crick model and is referred to as B-DNA or B-form DNA.
• Various types of DNA, like A-DNA, Z-DNA, C-DNA, D-DNA, and E-DNA, are found to arise under particular circumstances.
• Their structural variety is what accounts for this variation in shapes.

1. B-DNA

 Most typical, initially derived from DNA fiber sodium salt X-ray diffraction at 92 percent relative humidity.

2. A-DNA

It was discovered by an X-ray diffraction study of DNA fibers at a relative humidity of 75%.

3. Z-DNA

A left-handed double-helical construction winds zigzag to the left.

4. C-DNA

formed with a relative humidity of 66 percent and the presence of the ions Li+ and Mg2+.

5. D-DNA

Rare variation without guanine forms in structure with 8 base pairs per helical turn.

6. E- DNA

Extended or eccentric DNA.

Functions of DNA

• DNA is essential as the genetic building block of the majority of living things. It transmits genetic data from one generation to the next and from one cell to another.
• Consequently, its primary roles include:
• Preserving genetic data
• Control of protein production.
• Genetic code determination
• Accountable directly for differentiation, heredity, evolution, and metabolic processes.
• Because it is a stable molecule, it can store more complicated information for longer.

References

• http://www.differencebetween.net/science/difference-between-mitochondrial-dna-and-nuclear-dna/
• https://en.wikibooks.org/wiki/Structural_Biochemistry/Nucleic_Acid/DNA/DNA_structure#Major_and_Minor_Grooves
• https://en.wikipedia.org/wiki/Nuclear_DNA
• https://www.slideshare.net/vinithaunnikrishnan16/forms-of-dna-49312507
• David Hames and Nigel Hooper (2005). Biochemistry. Third ed. Taylor & Francis Group: New York.
• Bailey, W. R., Scott, E. G., Finegold, S. M., & Baron, E. J. (1986). Bailey and Scott’s Diagnostic microbiology. St. Louis: Mosby.