Nucleic acid molecules maintain details of cell growth and reproduction. These are polymers that contain long chains of monomers called nucleotides. Nucleotide has a base of nitrogenous, pentose sugar and phosphate group .There are two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

  • Purines: Adenine (A) and Guanine (G)
  • Pyrimidine: Cytosine (C), Thymine (T) and Uracil (U)
  • Pentose Sugars: There are two related pentose sugars:
  • RNA contains ribose
  • DNA contains deoxyribose

Sugar contains its carbon atoms composed of primes to separate them from nitrogen bases


The nucleoside contains a nitrogen base attached to the glycosides bond to C1 ’of ribose or deoxyribose.Nucleosides are named for the substitution of the nitrogen base ending in -osine purines and -idsine pyrimidine


Nucleotide is a nucleoside that forms a phosphate ester with the C5 ‘OH group of ribose or deoxyribose.Nucleotide is named after the nucleoside term followed by 5’-monophosphate. Additional phosphate groups can be added to nucleoside 5’-monophosphates to form triphosphates and triphosphates. ATP is a major source of energy for cellular activity

The main structure of Nucleic Acids:

The main structure of nucleic acid is the nucleotide sequence. Nucleotides in nucleic acids are associated with phosphodiester bonds. Group 3’-OH sugar in one nucleotide forms an ester bond in the phosphate group to 5’-carbon sugar for the next nucleotide. The nucleic acid polymer has a free 5′-phosphate group at one end and a free 3′-OH group on the other. Sequences are learned from 5′-end free using base characters.

 In RNA, A, C, G, and U a 3′-5 ‘ester bond is connected between ribose and phosphate

In DNA, A, C, G, and T are linked by 3’-5’ ester bonds between deoxyribose and phosphate


DNA Double Helix

In 1953 Watson and Crick wrote a three-dimensional model of the DNA structure (The Double Helix) In DNA there are two strands of polynucleotides that combine around the same axis to form a double right helix. The hydrophilic nuclei of deoxyribose groups interacting with phosphates are outside the double helix, facing the surrounding water. The strands work on opposite sides of the bases arranged in pairs such as steps .two bases are held together by binding hydrogen. The pairing of the bases from both ropes is very clear

Two basic compliments are A-T and G-C

The two forms of hydrogen bond are between A and T

The three forms of hydrogen bond are between G and C

Each pair contains purine and pyrimidine, so they have the same width, keeping the two strands the same distance from each other. In the first type proposed by Watson and Crick, the adjacent bases are separated by 3.4Å.

In eukaryotic cells (animals, plants, fungi) DNA is stored in the nucleus, which is separated from the cell by an entire insignificant membrane. DNA is organized only by chromosomes during cell duplication. During reproduction, DNA is stored in a compound ball called chromatin, and it is wrapped in a protein called histones to form nucleosomes

DNA types:

The Watson-Crick structure is also called B form DNA, or B-DNA. Form B is the most stable structure. The two structural variations that are best represented in crystal structures are types A and Z. Form A is popular in many waterless solutions. DNA is still arranged with a double helix of the right hand, but the helix is ​​wider and the number of base pairs per helical turn is 11, rather than 10.5 as in B-DNA. The base pair of A-DNA pairs is approximately 200 in relation to the helix axis. These structural changes deepen the large groove while making the small groove less shallow. The Z-form DNA difference is within the left helical exchange. There are 12 basic pairs per helical curve, and the structure appears very small and compact. The DNA sequence assumes a zigzag pattern. The large groove is hardly visible in Z-DNA, while the small groove is small and deep. Whether A-DNA is derived from cells is uncertain, but there is evidence of some simple Z-DNA strands in both prokaryotes and eukaryotes.

Differences between RNA and DNA:

o pentose sugar in RNA is ribose, in DNA is deoxyribose

o In RNA, uracil replaces basic thymine (U pairs in A)

o RNA is left alone while DNA is doubled

RNA molecules are much smaller than DNA molecules

Three main types of RNA:

Ribosomal (rRNA), messenger (mRNA) and transmission (tRNA)

Ribosomal RNA

It is part of the RNA of the ribosome

It is a large part of the ribosomes. Protein synthesis is important. Ribosomes are areas of protein synthesis. They contain ribosomal rRNA (65%) and protein (35%).Ribosomal RNAs make up two subunits, a large subunit (LSU) and a small subunit (SSU).

Messenger RNA

      They are RNA strands that attach to the DNA of a component so that the protein is synthesized .They carry details (genetic code) of protein synthesis from DNA in a fraction of the nucleus to ribosomes.

Transfer RNA

RNA transfer translates genetic code from the RNA messenger and delivers certain amino acids to the ribosome for protein synthesis. Each amino acid known as one or more tRNA.tRNA has an L-shaped higher education structure. The structure is compacted and reinforced with foundation bonding and foundation installation. One end binds to amino acids and the other binds to mRNA in a favorable 3-base sequence.

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