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    When lactose is absent
    1. The regulator gene is expressed and the repressor protein is synthesised. It has two binding sites. One binds to lactose and one that binds to the operator
    region
    2. In binding to the operator region, it covers part of the promoter region where RNA polymerase normally attaches
    3. RNA polymerase cannot bind to the promoter region so the structural genes cannot be transcribed into mRNA
    4. Without mRNA the genes cannot be translated and the enzymes cannot be synthesised

    When lactose is added
    1. Lactose binds to the other site on the repressor protein, causing the molecule to change shape. This prevents the other binding site from binding to the operator region. The repressor dissociates from the operator region
    2. The leaves the promoter region unblocked. RNA polymerase can now bind to it and initiate the transcription of mRNA.
    3. The operator- repressor- inducer system acts as a molecular switch. It allows synthesis of the structural genes
    4. As a result, the bacteria can now use the lactose permease enzyme to take up lactose from the medium into their cells. They can then convert it to glucose and galactose using the β-galactosidase enzyme. These sugars can then be used for respiration

    I don't quite understand the difference, whether lactose is present in the medium or not it still binds to the repressor protein please help me understand this
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    (Original post by WoopWoop1212)
    When lactose is absent
    1. The regulator gene is expressed and the repressor protein is synthesised. It has two binding sites. One binds to lactose and one that binds to the operator
    region
    2. In binding to the operator region, it covers part of the promoter region where RNA polymerase normally attaches
    3. RNA polymerase cannot bind to the promoter region so the structural genes cannot be transcribed into mRNA
    4. Without mRNA the genes cannot be translated and the enzymes cannot be synthesised

    When lactose is added
    1. Lactose binds to the other site on the repressor protein, causing the molecule to change shape. This prevents the other binding site from binding to the operator region. The repressor dissociates from the operator region
    2. The leaves the promoter region unblocked. RNA polymerase can now bind to it and initiate the transcription of mRNA.
    3. The operator- repressor- inducer system acts as a molecular switch. It allows synthesis of the structural genes
    4. As a result, the bacteria can now use the lactose permease enzyme to take up lactose from the medium into their cells. They can then convert it to glucose and galactose using the β-galactosidase enzyme. These sugars can then be used for respiration

    I don't quite understand the difference, whether lactose is present in the medium or not it still binds to the repressor protein please help me understand this
    It's just the way that it is worded. When it says "one binds lactose", what it really means is that "one can bind lactose if it is present". As far as you're concerned (I assume you're doing A-level), then the repressor protein does not bind lactose if lactose is absent. I hope this makes sense.
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    so it should say 'and the repressor protein is synthesised, which has two binding sites, one binds to lactose when present and one binds to the operator region' thank you
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    (Original post by WoopWoop1212)
    so it should say 'and the repressor protein is synthesised, which has two binding sites, one binds to lactose when present and one binds to the operator region' thank you
    Yes
 
 
 
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