Which of the following statements describes prokaryotic...

Which of the following statements describes prokaryotic transcription of the lac operon? a. When lactose and glucose are present in the medium, transcription of the lac operon is induced. b. When lactose is present but glucose is absent, the lac operon is repressed. c. Lactose acts as an inducer of the lac operon when glucose is absent. d. Lactose acts as an inducer of the lac operon when glucose is present.

Which of the following statements describes prokaryotic transcription of the lac operon?
a. When lactose and glucose are present in the medium, transcription of the lac operon is
induced.
b. When lactose is present but glucose is absent, the lac operon is repressed.
c. Lactose acts as an inducer of the lac operon when glucose is absent.
d. Lactose acts as an inducer of the lac operon when glucose is present.

Key Concepts

Prokaryotic Transcription

Prokaryotic transcription refers to the process in which messenger RNA (mRNA) is synthesized from a DNA template within bacterial cells. This process is regulated by various factors including promoters, repressors, activators, and inducers, which enable the cell to respond swiftly to environmental changes.

Operon Model (Lac Operon)

The operon model is a genetic regulatory system common in prokaryotes, and the lac operon is a classic example that controls the metabolism of lactose. It includes genes that encode enzymes for lactose uptake and breakdown, and its regulation involves a repressor that binds to the operator region to prevent transcription when lactose is not available.

Inducible Operon

An inducible operon is one that is normally repressed and can be activated (or induced) when an inducer molecule, such as lactose, binds to a repressor or other regulatory proteins. This interaction relieves repression and allows transcription of the genes required for the metabolism of the inducer substrate.

Catabolite Repression

Catabolite repression is a regulatory mechanism where the presence of a preferred carbon source, like glucose, inhibits the transcription of operons responsible for the metabolism of alternative carbon sources, such as the lac operon. This ensures that the cell prioritizes energy-efficient metabolic pathways.

Transcript

00:01 Let's take a look at the lac operon.

00:04 The lack operon is what governs whether a bacterium will consume lactose or not.

00:12 Why does the bacterium need to choose whether it will consume lactose or not? why can't it just consume it all the time? well, because glucose, it's a much simpler sugar than lactose, and it takes less effort to break down.

00:27 So when glucose is present, it would rather not make this.

00:31 The enzymes responsible for breaking down lactose because that is energy spent.

00:36 However, when you don't have glucose but you have lactose, then you do want to make the enzymes that break down lactose because lactose is better than nothing.

00:45 So that's kind of what we're talking about here.

00:47 So you need those two factors to basically turn on the lack operon.

00:55 You need the absence of glucose and the presence of lactose.

00:59 The cell needs to be able to tell that both of those conditions are met.

01:03 And this is how that happens.

01:05 So up here, we are just showing the general structure of the lac operon with its promoter region, repressor region, and the actual genes.

01:15 And the first scenario is the scenario that we talked about where we have low glucose and high lactose available.

01:23 And in this instance, you have the cap protein, which acts as the promoter.

01:28 So the cap protein is the promoter for the lap operon.

01:31 So when you have low glucose, the cap protein binds.

01:36 And when you have lactose available, the repressor, which is this brown guy down here, it's not on because lactose is available.

01:45 So the genes will be expressed.

01:50 In a scenario where we have high glucose and low lactose.

01:55 So we're talking about scenario two here.

01:57 The promoter is not on, so you don't have the cap there and the repressor is on.

02:04 So that is not being expressed.

02:08 When lactose is unavailable and also glucose is unavailable, that means that you are going to have the promoter because the promoter comes on when glucose is low, but lactose is also not there.

02:21 So there's no point in transcribing, so the repressor is on.

02:25 And when we have high glucose and high lactose, this is basically low expression because you don't have a repressor there stopping things, but you don't have the promoter there helping things along.

02:40 So how does glucose and lactose actually govern whether the promoter and the receptor are on or off? real quickly, glucose stops the production of cyclic amp...

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