The sugar-phosphate backbone of DNA is double-helix in structure, with sugar and phosphate on the helix’s outside. The nitrogenous bases are stacked in pairs in the interior, similar to stair steps, and are linked by hydrogen bonds.
Structure of Polynucleotide Chains
A nucleotide is made up of a nitrogenous base, a pentose sugar, and a phosphate group.
Nitrogenous bases are classified into two types: purines and pyrimidines.
- Purines: The two purines are adenine and guanine.
- The three pyrimidines are cytosine, uracil, and thymine. Cytosine is found in both DNA and RNA, and Thymine is found in DNA. Thymine is replaced by Uracil in RNA.
Nucleosides generated by an N-glycosidic link between a nitrogenous base and a pentose sugar include adenosine or deoxyadenosine, guanosine or deoxyguanosine, cytidine or deoxycytidine, and uridine or deoxythymidine.
Polynucleotide Chain
When a phosphate group is connected to the 5′-OH of a nucleoside by phosphodiester linkage, a matching nucleotide is formed. A nucleotide is composed of two nucleotides linked by a 3′-5′ phosphodiester linkage.
By linking more nucleotides in this manner, a polynucleotide chain can be produced. A free phosphate moiety at the 5′-end of ribose sugar is formed at one end of the polymer. The 5′ end of a polynucleotide chain is referred to as such. At the other end of the polymer, ribose has a free 3′-OH group. This is the 3′ end of the polynucleotide chain.
The backbone of a polynucleotide chain is made up of sugar and phosphates. Nitrogenous bases linked to the sugar moiety project from the backbone.
In prokaryotes, DNA is not distributed throughout the cell. A negative charge exists on the DNA molecule. It is held together in a ‘nucleoid’ area by some positively charged proteins. The nucleoid’s DNA is organised in a massive loop that is held together by proteins.
DNA and The Histone Octamer
The organisation of DNA in eukaryotes is far more intricate. Histones are a type of protein that is positively charged and basic. Histones are organised into eight-molecule units called histone octamers. When negatively charged DNA is wrapped around a positively charged histone octamer, a nucleosome is created.
What Factors Contribute to The Formation of a Double Helix in DNA?
Each DNA molecule is a double helix composed of two complementary strands of nucleotides linked together by hydrogen bonds formed by the base pairs G-C and A-T. The use of one DNA strand as a template for the production of a complementary strand results in genetic material duplication.
Because it resembles a twisted stairway, DNA’s structure is known as a double helix. A DNA molecule is made up of two strands that are coiled around each other like a twisted ladder, with each strand containing an alternating phosphate and sugar group backbone. The following are the primary features of DNA’s double helix structure: Two polynucleotide chains make up a double-stranded DNA molecule. The backbone is made from sugar phosphate. Because the two strands are antiparallel, one chain has 5′-3′ polarity and the other has 3′-5′ polarity.
Conclusion
A nucleosome is made up of 200 base pairs (bp) of DNA helix. Nucleosomes are the chromatin structure’s repeating units in the nucleus. Chromatins are thread-like stained (coloured) structures in the nucleus. When viewed through an electron microscope, the nucleosomes have a ‘beads on string’ structure. Non-Histone Chromosomal (NHC) Proteins: Higher-level chromatin packing needs the usage of a separate set of proteins. These proteins are referred to together as non-histone chromosomal proteins. Some chromatin portions in a normal nucleus are loosely packed, referred to as euchromatin. Euchromatin is a material that stains the light. Euchromatin is transcriptionally active chromatin. Heterochromatin is a term used to describe tightly packed chromatin. Heterochromatin is a protein that is dark in colour. Transcription is unaffected by heterochromatin.