Pages

Genetic Engineering : Cutting & joining DNA

 Genetic Engineering : Cutting & joining DNA 




The science in molecular biology flourished in full throttle in
the 1970s with the discovery that DNA sequences can be cut and
religated at specific target sequences by a group of enzymes
known as restriction endonuclease, for which W. Artier, D. Nathans
and H. Smith received Nobel Prize in 1978. It was observed in
1950s that certain bacteria can exhibit immunity to phage infection.
For example if bacteriophage infects E.coli strain K, it will cause

lysis of that bacterial strain. The progeny phages infect the same
strain with higher efficiency. However, if the progeny phages
grown on strain K are used to infect another E. coli strain B, growth
of phage population is restricted. This phenomenon, known as
‘host controlled restriction modification’ is observed due to presence of restriction enzymes in bacterial cells. When phage A attacks strain B, a site specific restriction enzyme EcoB cuts A DNA as its recognition sequences are present on A DNA, thereby restricting infection. To protect its own DNA from restriction, the bacterium methylates its own DNA by using a methylase enzyme. During this process a small number of phage DNA also gets methylated and avoids restriction. These progeny phages will infect E. coli strain B with much higher efficiency, as they have been modified by host enzyme so that further phage DNA restriction in strain B does not take place. However, if these phage particles attack another strain K that contains a different restriction enzyme
recognizing another sequence, the phage DNA in strain K will be
restricted.


      The restriction endonucleases are classified into three major
groups depending on their sequence specificity, nature of
restriction and structural differences (Table 1). Type I and type III
restriction endonucleases have limited use in DNA cloning and
genetic engineering. Type II restriction endonucleases (Type II R.
E.) are widely used for their sequence specificity, cleaving of
dsDNA within recognition sequence, separate methylation and
no additional requirement of energy.The recognition and restriction sequences of type Ii R. E. are very precise and do not match with one another. The enzymes may further be classified as tetracutter, hexacutter, octacutter etc. depending on the size of the recognition sequence (4, 6 and 8 respectively). For genetic manipulation, hexacufters and tetracutfers are most widely used. Besides, depending on the nature of cut produced by these enzymes. two broad groups may be identified. Some of the restriction enzymes cut exactly at the mid point of the dyad symmetry recognition sequence producing two fragments sequence and cuts at the midpoint to produce two blunt ends with no free nucleotide for hydrogen bonding. For this reason these enzymes are termed as blunt end cutters. Sticky end cutters, on the other hand produce 5’ or 3’ overhangs as the cleavage site 






3 comments:

  1. An hacker helped me to spy on my wife’s WhatsApp,mails and every text message that was sent to her iPhone and every deleted messages of the past six months you can message him through this number (+13852501115) or contact him via email at brillianthackers800@gmail.com

    ReplyDelete
    Replies
    1. Happiness is all i see now, i was herpes sicker for 6 years but i thank God for directing my footsteps to Dr Emu, he gave me instructions and i followed and in 2 weeks i was completely cured using his medicine, I am now Herpes Negative Contact Dr Emu for more information, He also has other cure to other ailment, HIV AIDS, CANCER, DIABETES, HEART DISEASE, HEPATITIS B/C And also restore broken relationships such as Ex HUSBAND, Ex WIFE, BROKEN MARRIAGES, Any kind of Problem in any relationship can be restore back in 24hours, Just Email: emutemple@gmail.com  Whatsapp or call: +2347012841542

      Delete
  2. I want to share this wonderful testimony to the Good people all over the world on how I was able to Enlarge my Penis by Dr. zubby. I was living a shameful life from my young age, just last month as I was browsing on the internet about Penis size and Enlargement Products, I saw a testimony of a Man called George , testifying of how he was able to get his penis Enlarged by Dr. zubby and I decided to also Email Dr.zubby for my small penis size and he quickly respond to me and gave me the normal instructions which i did and then he shipped the product to me here in the united state which i received in just 3 working days and today i am very happy because i started seeing positive changes in my penis size in just 7 days of use. Dr zubby herbal product is the best recommended for you and to whom ever suffering from this shame or having any other diseases as well should Contact this great herbal doctor via his Email :
    dr.zubbysolutionhome@gmail.com and WhatsApp Him on +2348070673249


    ReplyDelete