Turn on thread page Beta
    • Thread Starter
    Offline

    10
    ReputationRep:
    Hi, in the AQA textbook it says "if a plasmid with the required gene is present in a bacterial cell, the colonies grown from it will not produce lactase. Therefore, when these bacterial cells are grown on the colourless substrate they will be unable to change its colour" - I understand this as the required gene has disrupted the lactase. However, the next sentence is "Where the gene has not been taken up by the bacteria, they will not turn the substrate blue. These bacteria can be discounted." I don't understand this - surely if the bacteria have not taken up the required gene then the lactase will not be disrupted and so it will be able to turn the colourless substrate blue ??

    Thanks!
    Offline

    11
    ReputationRep:
    (Original post by 0hhowinteresting)
    Hi, in the AQA textbook it says "if a plasmid with the required gene is present in a bacterial cell, the colonies grown from it will not produce lactase. Therefore, when these bacterial cells are grown on the colourless substrate they will be unable to change its colour" - I understand this as the required gene has disrupted the lactase. However, the next sentence is "Where the gene has not been taken up by the bacteria, they will not turn the substrate blue. These bacteria can be discounted." I don't understand this - surely if the bacteria have not taken up the required gene then the lactase will not be disrupted and so it will be able to turn the colourless substrate blue ??

    Thanks!
    So, I did this stuff years ago (I'm 21 now haha), but as far as I remember, the technique you are referring to is a rudimentary way of determining whether bacteria have taken up a gene you are trying to replicate. You need to determine 2 things, 1) whether the plasmid has incorporated the gene, and 2) whether the bacteria has taken up the plasmid. What you'll have is a plasmid with a lactase gene, and if the lactase is produced then it will change the substrate from colourless to blue. There will be 2 circumstances where the substrate remains colourless; either the bacteria hasn't taken up the plasmid, or the bacteria has taken up the plasmid with the desired gene spliced into the lactase gene. So what you do is you initially test to see which bacteria have taken up the plasmid by seeing which colonies turn the substrate blue. You want to keep these bacteria because they're the ones who have taken up the plasmid with the lactase gene in it. You would then splice the desired gene onto the plasmid with endonucleases, but what you have to remember is that there are 3 possible results from plasmid recombination, 1) the plasmid just closes up again, 2) the gene forms its own plasmid or 3) you get the recombinant plasmid. So what you do is you see which colonies turn the substrate blue, these will be the ones without the recombinant plasmid. The colonies which keep the substrate colourless are the ones you want to keep and replicate.

    So it's a 2 step process that can be quite hard to understand. If there's any bit of it you're confused about then let me know
    • Thread Starter
    Offline

    10
    ReputationRep:
    Oh my gosh this has cleared it up for me completely!! Thank you so much
    (Original post by AortaStudyMore)
    So, I did this stuff years ago (I'm 21 now haha), but as far as I remember, the technique you are referring to is a rudimentary way of determining whether bacteria have taken up a gene you are trying to replicate. You need to determine 2 things, 1) whether the plasmid has incorporated the gene, and 2) whether the bacteria has taken up the plasmid. What you'll have is a plasmid with a lactase gene, and if the lactase is produced then it will change the substrate from colourless to blue. There will be 2 circumstances where the substrate remains colourless; either the bacteria hasn't taken up the plasmid, or the bacteria has taken up the plasmid with the desired gene spliced into the lactase gene. So what you do is you initially test to see which bacteria have taken up the plasmid by seeing which colonies turn the substrate blue. You want to keep these bacteria because they're the ones who have taken up the plasmid with the lactase gene in it. You would then splice the desired gene onto the plasmid with endonucleases, but what you have to remember is that there are 3 possible results from plasmid recombination, 1) the plasmid just closes up again, 2) the gene forms its own plasmid or 3) you get the recombinant plasmid. So what you do is you see which colonies turn the substrate blue, these will be the ones without the recombinant plasmid. The colonies which keep the substrate colourless are the ones you want to keep and replicate.

    So it's a 2 step process that can be quite hard to understand. If there's any bit of it you're confused about then let me know
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 16, 2018

University open days

  • University of Lincoln
    Mini Open Day at the Brayford Campus Undergraduate
    Wed, 19 Dec '18
  • University of East Anglia
    UEA Mini Open Day Undergraduate
    Fri, 4 Jan '19
  • Bournemouth University
    Undergraduate Mini Open Day Undergraduate
    Wed, 9 Jan '19
Poll
Were you ever put in isolation at school?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.