lac operon as a model of gene regulation Quiz - Free Printable

Let’s solve this step by step.

This diagram shows how the lac operon works in bacteria — specifically, when lactose is present and when it’s absent. The lac operon controls whether genes for breaking down lactose are turned on or off.

We need to match each blank box with the correct label from the list on the right.

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First, let’s look at the top part of the diagram (when there’s NO lactose):

- There’s a green cylinder → that’s the Regulator gene. It makes the repressor protein.
- The purple shape attached to the DNA near the operator → that’s the Repressor protein. When no lactose is around, it binds to the operator and blocks RNA polymerase.
- The orange oval floating nearby → that’s Lactose. But in the top scene, it’s NOT bound to anything yet — so we’re looking at the “no lactose” state.
- The brown U-shaped thing binding to the operator → that’s the active Repressor protein blocking transcription.
- The yellow section on the DNA → that’s the Promoter, where RNA polymerase tries to bind.
- The purple section next to it → that’s the Operator, where the repressor sits.
- Since the repressor is blocking, nothing gets made → so the outcome is No transcription and translation.
- The long wavy line being made below? That only happens in the bottom part — not here.

Now the bottom part (when lactose IS present):

- Lactose (orange sunburst) binds to the repressor → changes its shape → now it can’t stick to the operator anymore.
- So the repressor falls off → now RNA polymerase can move along the DNA.
- RNA polymerase (blue blobs moving along DNA) starts making mRNA → which becomes proteins (the colored squiggles).
- Those proteins break down lactose into smaller pieces (purple dots).
- So the outcome here is Transcription and translation.
- The repressor now has lactose stuck to it → so it’s an Inactive repressor.
- The blue boxes pointing to the enzymes being made → those are the products of the structural genes (like beta-galactosidase), but since the labels don’t include enzyme names, we focus on what’s given.

Also note:

- The green cylinder appears twice — once above, once below — always labeled as Regulator.
- The brown U-shape without lactose = active repressor; with lactose = inactive repressor.
- The arrow showing RNA polymerase moving → that means transcription is happening.

Let’s assign each blank based on position:

Top row (left to right):

1. Green cylinder → Regulator
2. Orange oval → Lactose
3. Brown U-shape bound to DNA → Repressor protein (active)
4. Yellow region on DNA → Promoter
5. Purple region on DNA → Operator
6. Outcome arrow → No transcription and translation

Bottom row:

7. Green cylinder again → Regulator (same as before)
8. Sunburst with lactose bound to repressor → Inactive repressor
9. Blue blobs moving on DNA → RNA polymerase
10. Wavy line being produced → leads to protein synthesis → outcome is Transcription and translation
11. Bottom-left: repressor with lactose attached → Inactive repressor (already used, but same concept)

Wait — let’s count the blanks carefully.

Looking at the image structure:

There are 10 blank boxes total.

From left to right, top to bottom:

Box 1 (top left, green cylinder): Regulator

Box 2 (above orange oval): Lactose

Box 3 (pointing to brown U-shape on DNA): Repressor protein

Box 4 (yellow segment on DNA): Promoter

Box 5 (purple segment on DNA): Operator

Box 6 (arrow going down from top operon): No transcription and translation

Box 7 (bottom left, green cylinder): Regulator (again)

Box 8 (sunburst with lactose bound to repressor): Inactive repressor

Box 9 (blue blob on DNA in bottom part): RNA polymerase

Box 10 (arrow going down from bottom operon): Transcription and translation

And one more? Wait — actually, looking again, there’s also a box pointing to the repressor after it releases — that’s already covered as “inactive repressor”.

Actually, let me recount visually:

In the original image description, there are 10 empty blue boxes.

Based on standard lac operon diagrams and matching positions:

Final assignment:

Top-left green cylinder → Regulator
Above orange molecule → Lactose
Pointing to repressor bound to operator → Repressor protein
Yellow DNA region → Promoter
Purple DNA region → Operator
Arrow downward from top → No transcription and translation
Bottom-left green cylinder → Regulator
Sunburst + repressor complex → Inactive repressor
Blue enzyme on DNA → RNA polymerase
Arrow downward from bottom → Transcription and translation

That’s 10.

But wait — in some versions, the last box might be pointing to the released repressor — still “inactive repressor”.

All labels are accounted for.

So final mapping:

Blank 1 (top left green tube): Regulator
Blank 2 (above orange pill): Lactose
Blank 3 (to brown clamp on DNA): Repressor protein
Blank 4 (yellow DNA patch): Promoter
Blank 5 (purple DNA patch): Operator
Blank 6 (down arrow top): No transcription and translation
Blank 7 (bottom left green tube): Regulator
Blank 8 (sun + repressor): Inactive repressor
Blank 9 (blue motor on DNA): RNA polymerase
Blank 10 (down arrow bottom): Transcription and translation

Yes — all match.

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Final Answer:
Top row (left to right):
1. Regulator
2. Lactose
3. Repressor protein
4. Promoter
5. Operator
6. No transcription and translation

Bottom row (left to right):
7. Regulator
8. Inactive repressor
9. RNA polymerase
10. Transcription and translation