HSEB Notes on Process of DNA Replication
Class : 12
The process of synthesis of DNA molecule from preexisting dna is called dna replication. NA replication may occur by following process:
1.semi-conservative replication
2.conservative replication
3.dispersive replication
Semi-conservative mode of DNA replication
Enzymes involved in semi conservative DNA replication:
Helicase- helicase enzyme breaks the hydrogen bonds formed between bases of nucleotides Topoisomerase- topoisomerase enzyme breaks and reseals one strand of DNA
DNA polymerase- it connects the nucleotides to form DNA polymer nucleotides. It forms RNA primer in DNA strand which is like a knot formed o thread. Due to its formation, newly formed DNA strands cannot separate.
Ligase- ligase binds the fragments of DNA strand together
Repair enzyme- this enzyme cuts off wrong base of nucleotide and rejoin correct base in newly formed DNA
Process:
DNA replication in eukaryotes may begin at several points. in replication ,the helicase enzyme breaks the hydrogen bond between the bases of nucleotides. due to breaking of hydrogen bonds of nucleotides, the two strands separate. The process of separation of DNA strands also supported by enzyme topoisomerase. This enzyme breaks and reseals one strand of dna molecule.
Now the bases of DNA strands become exposed and joins with the free nucleotides present in nucleoplasm only in 5’-3’ direction. This process or formation of polynucleotide chain takes place in the presence of enzyme DNA polymerase. The four types of nucleotides are present in nucleus in the form of datp, dgtp; dttp and dctp.THESE molecules are triphosphates and break down into monophosphates damp, dtmp, dcmp and dgmp with the release of energy. These monophosphates nucleotides make hydrogen bonds with the complementary nucleotides of DNA strand.
According to base pairing rule the nucleotides are arranged. As DNA strand formation occurs only in 5’-3’ direction,in on strand of DNA a continuous strand is formed called leading strand ehereas in other strand of DNA,fragments of strands are formed,these fragments are called okazaki fragments named after Japanese scientist okazaki.the strand with okazaki fragments is called lagging strand.
Here,both DNA strands take part in replication process,so they are called as templates.the segments of strands are joined by the help of enzyme ligase.at the beginning of strand formation, RNA primer is formed at the DNA strand and it is due to the enzyme primase.sometime a wrong base maybe linked with the DNA nucleotide. When it occurs,the repair enzyme replaces the wrong base by correct base.
In the above process,newly formed DNA have one strand of old DNA and one of new formed polynucleotide chain. Hence the process is called as semi conservative process of DNA replication.
It means half of parent DNA is conserved in new formed DNA.
Read this also :
- Physiology of Digestion | Class 12 Zoology Notes
- Digestive Grands Associated with Alimentary Canal of Human | Class 12 Biology Notes
- Alimentary Canal in Digestive System of Human Beings | HSEB Notes Class 12 Zoology
- Physiology of Respiration | HSEB Notes of Biology Class 12
- Difference between Inhalation and Exhalation | Class 12 Biology Notes
- Respiratory Organs and Mechanisms of Breathing | HSEB Notes of Biology Class 12
- Respiration and Its Types | HSEB Notes of Biology Class 12
- Urine Formation | HSEB Notes of Biology, Zoology Class 12
- Structure of Kidney and Nephron | HSEB Notes of Biology Class 11 Zoology
- Physiology of Excretion | HSEB Notes of Biology Class 12 | Zoology
- HSEB Notes on Venous System of Circulatory System of Human Beings Class 12
Don't forget to LIKE, SHARE and COMMENT. Please Join with us on FACEBOOK and GOOGLE+ for daily notes.
No comments:
Post a Comment
Don't forget to leave your comment.