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Joseph Roleda

1. Presence of lactose and absence of glucose, transcription takes place, synthesis of b-galactosidase, permease and transacetylase, due to presence of lactose molecules that bind to lac repressor protein, distorting shape, preventing it from binding to operator region.

2. Presence of lactose and glucose, cAMP levels fall, and glucose is used first instead of lactose, therefore RNA polymerase is inhibited from binding to promoter regulatory gene, as lac repressor protein binds to operator region freely. No synthesis of the three structural genes.

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If lactose is present and glucose levels are low, then allolactose binds the lac repressor, causing it to dissociate from the operator region. Under these conditions, the cAMP-bound CAP can bind to the operator in lieu of the repressor protein

If both glucose and lactose are both present, lactose binds to the repressor and prevents it from binding to the operator region. The block of lac gene transcription is thus lifted, and a small amount of mRNA is produced

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When the glucose is not present/low , cAMP is produces and binds to the catabolite activated protein (CAP), allowing the CAP to bind to DNA which helps RNA polymerase bind to the promoter resulting in transcription and if glucose is high less cAMP produced

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Scenario 1

The lac repressor is inactivated by allolactose, allowing transcription to proceed.

The CAP-cAMP complex enhances transcription by assisting RNA polymerase binding.

The lac operon is highly expressed, allowing the organism to metabolize lactose efficiently.

Scenario 2

When lactose is present and glucose is scarce, the lac operon is highly activated in the organism. Lactose inactivates the repressor, unblocking the operon, while low glucose levels create a boost through the CAP-cAMP complex. This combination fully activates the operon, allowing the cell to produce enzymes that digest lactose for energy. This regulation helps the cell save energy by only making lactose-digesting enzymes when they’re actually needed.

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1. Glucose absent, lactose present: Strong transcription of the lac operon occurs. The lac repressor is released from the operator because the inducer (allolactose) is present. cAMP levels are high because glucose is absent, so CAP is active and bound to the DNA. CAP helps RNA polymerase bind to the promoter, permitting high levels of transcription.

2. Glucose present, lactose present: Low-level transcription of the lac operon occurs. The lac repressor is released from the operator because the inducer (allolactose) is present. cAMP levels, however, are low because glucose is present. Thus, CAP remains inactive and cannot bind to DNA, so transcription only occurs at a low, leaky level.

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Dwaine -

In scenario 1, glucose is scarce and lactose is abundant. The lack of glucose means the cell does not respire glucose, as it was the first choice. This means the cell will resort to metabolising lactose. In this situation, allolactose will bind to the repressor protein, changing its shape and allowing the transcription of the structural proteins to allow the breakdown of lactose and its use in respiration.

In scenario 2, there is an abundance of lactose, but also an abundance in glucose. Because glucoseis the first choice of the cell as it does not need to undergo any further steps to be involved in respiration, the glucose will be used in respiration in the cell, and the lactose will not be broken down. The repressor protein stays attached to the operator and the transcription of the structural gene is prevented as glucose is metabolised.

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1. When lactose is present but glucose is scarce, the lac operon is activated. The lactose binds to the repressor protein, preventing it from blocking the operator, allowing RNA polymerase to transcribe the structural genes (lacZ, lacY, lacA) and produce lactase.

2. The presence of glucose inhibits the activation of the lac operon. As it is a preferred energy source. When glucose is present, it is typically used for respiration instead of lactose.

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1)Strong transcription of the lac operon occurs. The lac repressor is released from the operator because the inducer (allolactose) is present. cAMP levels are high because glucose is absent, so CAP is active and bound to the DNA.

2) lactose binds to the repressor and prevents it from binding to the operator region. The block of lac gene transcription is thus lifted, and a small amount of mRNA is produced.

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1. When lactose is present and glucose is scarce, transcription of the structural genes in the lac operon will take place. Some lactose molecules will diffuse into the cell across the cell surface membrane, and allolactose will bind to the allosteric site on the repressor molecules. This will change the repressor molecule's configuration, so it cannot bind to the operator gene anymore. This allows RNA polymerase to move ahead and transcribe the structural genes.

2. When lactose is present and glucose is present as well, the lac operon is repressed. Glucose will be used as a respiratory substrate so lactose will not need to be broken down. The repressor molecule will therefore prevent RNA polymerase from transcribing the structural genes, so no B-galactosidase will be produced, and as a result lactose will not be broken down.

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1. transcription of the lac operon occurs. The lac repressor is released from the operator because the inducer (allolactose) is present.

There is an uptake of lactose by the bacterium

The lactose binds to the second binding site on the repressor protein, distorting its shape so that it cannot bind to the operator site

RNA polymerase is then able to bind to the promoter region and transcription takes place

The mRNA from all three structural genes is translated

Enzyme lactase is produced and lactose can be broken down and used for energy by the bacterium

2. Less transcription of lac operon occurs