It consist of two steps process that called transcription and translation. It represents the flow of genetic material in an organism, in a sequence, in biological system.
Process:
- DNA is transcribed into RNA by RNA polymerase enzyme and than RNA is translated with the help of ribosome into proteins. This is the whole process.
- Plants are made up of cells
- ·And cells have nucleus
- And nucleus have chromosome
- Gene is made up of DNA and is the part of chromosome
- DNA is double stranded and made up of bases include adenine, guanine, cytosine and thymine.
Nucleic acid:
it includes RNA and DNA.
The deoxyribonucleic acid:
DNA is the store house for genetic information in any living organism. It plays a basic role in cell’s process regulation. As DNA has all the information for synthesis and proper functioning of living organism so it act as source of providing codes for protein synthesis and as a template for DNA replication.
The primary structure of DNA:
- It has linear sequence of nucleotides that are connected with each other through phosphodiester bonding.
- It has two anti-parallel strands that run in opposite directions and have 3-OH and 5-PO4 groups attach.
- And nucleotides are made up of three components:
- Pentose sugar, one or more phosphate group attach, and nitrogenous base.
Specific base pairing:
- In DNA guanine base paired with cytosine through 3 hydrogen bonding between them.
- And adenine form pair with thymine through 2 hydrogen bonding between them.
Formation of phosphodiester bond in DNA:
A chemical reaction called condensation reaction take place between two nucleotides and phosphodiester bond formation take place between hydroxyl group attach at carbon-3 of one nucleotide and a phosphate group’s hydroxyl group , that phosphate group attach at the carbon 5 of second nucleotide and the phosphodiester bond formation take place leading to the removal of water.
Chargaff’s rule:
Erwin Chargaff gave two rules called Chargaff’s rules.
In the double strands of DNA the number of guanine bases present are equal to the number of cytosine bases similarly the number of adenine bases are equal in number to the thymine bases.
The second rule is that the formation or composition of the molecule of DNA changes among specie to specie.
Thus facts from rules are:
- Cytosine -Guanine base pairs= Adenine-Thymine base pairs
- Thymine+ Adenine=Guanine + Cytosine
- Thymine=Adenine & Cytosine=Guanine
- Ration(A+T/C+G) it is constant for a specie and changes from one specie to another one
Different forms of DNA:
There are known 3 different types of DNA. Including A type, B type and Z type of DNA.
A form DNA:
- It is right handed in helix senses.
- It has 11 base pairs per helical turn
- ≈ 26Å is its diameter
- 2.6Å is the helix rise per base pair.
- It has anti glycosyl bond conformation.
- It is common in the RNA-RNA and DNA-RNA helices.
B form DNA:
- It is the common type of DNA. That is right-handed in helical senses.
- Its diameter is ≈ 20Å
- It has 10.5 pair of base occur per helical turn
- It has 3.4 Å rise in helix that is per base pair.
- It also has anti glycosyl bond conformation
Z form DNA:
- It is the left handed DNA.
- Its diameter is ≈ 18Å
- It has 12 pairs of bases that are present per helical turn
- Its rise in helix that is per base pair is 3.7 Å
- It has anti glycosyl bond conformation for pyrimidines and parallel for purines.
DNA supercoiling:
- DNA in both prokaryotic and eukaryotic organisms is maintained in supercoiled form.
- The parameters that are used to know the extend of supercoiling are “writhes” and “twists”.
- These both parameters, twists and writhes combines to form linking number which is how many times one DNA strand wrapped around the other strand.
Equation will be as follow for linking number:
Linking number = writhe + twists
Packing of DNA molecule in chromosome:
- DNA that is present in eukaryotes Packed into the chromosomes that are present in diploid or polyploid form.
- The prokaryotic E.coli bacteria has chromosome that is 1.5mm in length.
- The DNA that is present in the nucleus of human is about 2 m in length that further divided and subdivided to form 23 chromosome.
- One large molecule of DNA is present on single chromosome that extend from one end to another end through centromere.
Eukaryotic DNA is packed by . Nucleosome is the structure in which DNA is wrapped around a histone protein this occur after every 200 Base pairs. Nucleosomes combine with each other turn into higher denser structure that is chromatin these are actually responsible for the exact packing of chromosome in eukaryotic cells during mitosis of cell division.
The nuclear DNA consist of gene but rather than this there are other region that cause replication and compact packing of DNA. These regions are: heterochromatins, scaffolding DNA region, telomers centromeres and DNA replication region and euchromatins.