Problem 35: DNA responds to signals from outside the cell.
Explore signal transduction.
You're a researcher studying a new signal transduction pathway in eukaryotes.
You already know that the signal binds to a receptor in the cell membrane, and this signal causes protein production. The receptor remains in the membrane.
After a signal binds to a receptor, how many more molecules transport the message to the cell's DNA?
0 (No, the signal does not carry the message.)
1 (No, how do you know there's only one?)
1 or more (That is correct.)
2 (Maybe, but how do you know there's only two?)
2 or more (Maybe, but how do you know?)
At least one molecule carries the message to the DNA.
Suppose you replace the inner part of the red receptor with the inner part of the blue receptor. The blue receptor initiates a pathway leading to blue protein production.
When you add the original signal, which protein(s) will be produced?
None. (No, something is produced.)
Red protein only. (No, that is incorrect.)
Blue protein only. (That is correct.)
Red and blue proteins. (No, that is incorrect.)
Though the outer part of the receptor receives the signal, the inner part initiates the signal transduction pathway. Only blue protein is produced.
If a signaling pathway results in protein synthesis, the last molecule in the signaling pathway is...
a transcription activator. (That is correct.)
a JAK. (No, there may not be a JAK in this pathway.)
a receptor. (No, the receptor stays in the membrane.)
a signal transducer. (No, this isn't the last molecule.)
double-stranded RNA. (No, that is incorrect.)
Though other molecules may also carry the message from the receptor to the nucleus, the transcription activator is the final molecule that tells the DNA what to do.
To find the transcription activator, you make a DNA probe to bind the protein. Which part of the DNA can you use?
The promoter of the activated gene. (That is correct.)
Any promoter. (No, the promoter sequences differ gene by gene.)
The operator. (No, an operator binds a repressor.)
The gene that's turned on. (No, this sequence doesn't bind the activator.)
The activator binds to the promoter to turn on protein production. Therefore, a probe made from this sequence will isolate the activator from other proteins in the cell.
You use DNA footprinting to locate the promoter sequence. After radioactively labeling one end of the DNA segment that contains the promoter, you incubate the DNA with cell extract containing the transcription activator. What happens to each DNA molecule when a small amount of DNase is added?
DNase cuts between every every base inside the promoter. (No, the DNase does not cut inside the promoter.)
DNase cuts between every base outside the promoter. (No, that is incorrect.)
DNase cuts the molecule once outside the promoter. (That is correct.)
The activator binds to the promoter and protects it from DNase attack. It is also important to adjust the concentration of DNase so that it only makes one cut in each DNA strand. Otherwise, we will not be able to sequence the entire strand.
After you remove the protein and run the DNA on a gel, you find that the promoter sequence is C T G T T C. What does your footprinting gel look like?
Because the DNA is not cut anywhere in the promoter, there are no fragments that correspond to this sequence.
YOU'RE SO SMART!
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In this section learn that the binding of growth factors outside the cell causes receptors ends to intertwine and activate each other, and once active, the modified receptor ends interact with messenger proteins.
Journey inside a cell as you follow proteins and learn about cellular interactions. This 3-D animation brings to life the inner workings of a fibroblast cell as it responds to external signals. Created by Cold Spring Harbor Laboratory and Interactive Know