Question for DAT

[chance8]

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Can someone please help me with this problem?

"A scientist does a study on TCA cycle ezymes. She discovers that a gene for dehydrogenase spans over 4000 base pairs of DNA. She discovered that 7 introns and 11 exons were present. The number of nucleotides most likely to be found in the mature mRNA after post-transcriptional processing could be?"

Answer: 1150

How?

 

[PrinceJ]

You have to look at this one as a conceptual problem with all of the answer choices. How many will be found in the mature mRNA after post-transcriptional processing? Since it will be processed, the introns will be cut out. Introns are not expressed and will be spliced out in processing, while exons are genes that will be expressed and found in the mature mRNA. Because of this, we know the mature mRNA will have less nucleotides than it does before processing. 1150 will be the only answer that could possibly work. Just keep in mind it is not a math problem, just making sure you know what happens during processing and that introns are not found in mature mRNA.

 

[chance8]

Thanks, but what if the answer choices were 1150 and 2440?

When I do the math, it should be 2440. I understand that from the answer choices, only 1150 is the only possible answer b/c everything is off but it does not match up with my calculation.

You have to look at this one as a conceptual problem with all of the answer choices. How many will be found in the mature mRNA after post-transcriptional processing? Since it will be processed, the introns will be cut out. Introns are not expressed and will be spliced out in processing, while exons are genes that will be expressed and found in the mature mRNA. Because of this, we know the mature mRNA will have less nucleotides than it does before processing. 1150 will be the only answer that could possibly work. Just keep in mind it is not a math problem, just making sure you know what happens during processing and that introns are not found in mature mRNA.

 

[herkulease]

Thanks, but what if the answer choices were 1150 and 2440?

When I do the math, it should be 2440. I understand that from the answer choices, only 1150 is the only possible answer b/c everything is off but it does not match up with my calculation.

you are unlikely to get such a choice.

there will only be 1 answer choice that is possible there will not be any gray area.

There is 1 definite exception to this for the test. # of ATP generated. go with 36 for eukaroytes and 38 for prokaryotes when asked.

Its not factually true as it varies but its an accepted one that is drilled into your head as early as junior high or high school.

sometimes its just easier to just go with what is presented and what you know has been drilled into your head then start coming up with exceptions and all that stuff you'll only stress out and confuse yourself more.

 

[PrinceJ]

Thanks, but what if the answer choices were 1150 and 2440?

When I do the math, it should be 2440. I understand that from the answer choices, only 1150 is the only possible answer b/c everything is off but it does not match up with my calculation.

Like Herc said, they would never give you two choices like that. And you didn't actually "calculate" it. There is no set number of nucletoides for an intron/exon, so they could be a tiny gene with a few or a huge gene with 1000 or more. All you need to know is that it will be less because introns get spliced out.

 

[Lysie]

Resurrecting this thread in case anyone is still around to see it - if each base pair contains 2 nucleotides, wouldn't there be 8000 nucleotides in the 4000 base pairs?

What am I missing?

 

[WaveRace]

Resurrecting this thread in case anyone is still around to see it - if each base pair contains 2 nucleotides, wouldn't there be 8000 nucleotides in the 4000 base pairs?

What am I missing?

The question is asking how many nucleotides are in the mature mRNA after post-transcriptional processing. This is testing your understanding of the central dogma of molecular biology and of how transcription works. After transcription, the resulting mRNA is single stranded. They are asking about how many nucleotides are on that strand after introns are spliced out.