DNA question from TBR

[Meredith92]

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Not entirely sure why choice D is the best answer here.. I also dont think i really understand what the question is trying to get at... are they asking about an accurate aspect of DNA that is unnecessary?

DNA is the carrier of genetic information during cell growth and division. which of the following characteristics of dna is not essential for the accurate transmission of this information?

A) a genetic code that is degenerate
B) a mechanism for self replication
C) a low mutation rate
D) a conformationally variable molecule

Answer: D is correct. In order to transmit info from one cell to the next there must be an alphabet that makes the communication possible. in dna this alphabet is composed of A G C and T . a triplet of these bases= a codon and a codon specifies an amino acid. there are 64 diff codons and among these 64 there is redundancy. in other words, more than one codon can code for the same amino acid. because of this, the genetic code is referred to as being degenerate. (... goes on to explain B and C which i understand..) DNA can exist as single or double stranded. in the double stranded form it can exist in a number of diff states. dna is said to have variable conformations. this info passed on to the next generation is still contained in these diff forms of dna. its just a matter of having the appropriate mechanism to transmit that info. dna, as a conformationally variable molecule, would not pose a problem for the transmission of genetic information.


Do they mean if dna WASNT a conformationally variable molecule it wouldnt matter?
Why does it NEED to be degenerate? wouldnt it be just as accurate if it wasnt degenerate?
I think I'm missing the way we are supposed to look at this problem.
Thanks!

 

[Hemorrage]

Not entirely sure why choice D is the best answer here.. I also dont think i really understand what the question is trying to get at... are they asking about an accurate aspect of DNA that is unnecessary?

DNA is the carrier of genetic information during cell growth and division. which of the following characteristics of dna is not essential for the accurate transmission of this information?

A) a genetic code that is degenerate
B) a mechanism for self replication
C) a low mutation rate
D) a conformationally variable molecule

Answer: D is correct. In order to transmit info from one cell to the next there must be an alphabet that makes the communication possible. in dna this alphabet is composed of A G C and T . a triplet of these bases= a codon and a codon specifies an amino acid. there are 64 diff codons and among these 64 there is redundancy. in other words, more than one codon can code for the same amino acid. because of this, the genetic code is referred to as being degenerate. (... goes on to explain B and C which i understand..) DNA can exist as single or double stranded. in the double stranded form it can exist in a number of diff states. dna is said to have variable conformations. this info passed on to the next generation is still contained in these diff forms of dna. its just a matter of having the appropriate mechanism to transmit that info. dna, as a conformationally variable molecule, would not pose a problem for the transmission of genetic information.


Do they mean if dna WASNT a conformationally variable molecule it wouldnt matter?
Why does it NEED to be degenerate? wouldnt it be just as accurate if it wasnt degenerate?
I think I'm missing the way we are supposed to look at this problem.
Thanks!

Think about it this way.

B and C are easy to cross out because replication and a low mutation rate are key to accurate DNA transfer from generation to generation. A is also just as vital because degeneracy in DNA is an evolved mechanism. We only need 20 codons to encode every amino acid, however since there are 4 bases and codons are read in groups of 3 (64 total), over time the DNA code degenerated and instead of strictly using 20 codons to encode each amino acid we can use all 64 to represent amino acids. My reasoning on why I wouldn't pick A is because the code is by default assumed to be degenerate, transmission of a non degenerate code could result in implications we simply can't predict therefore its better to keep what evolution has naturally selected for. D is more correct in my opinion primarily because 3D conformation of DNA won't affect much other than the rate of mRNA synthesis and will still result in accurate genetic information transfer.

 

[drspacheman]

DNA needs to be degenerate because there are 20 different amino acids needed to be accounted for and it has only 4 bases (ATCG). If these 4 bases were arranged in combinations of 2, then we would get 4^2=16 different possibilities, which is not enough to code for the 20 different amino acids. So we would need to arrange the 4 bases in combinations of 3, which would give 4^3=64 different combinations. Since this is over the 20 amino acids possible, we get some redundancy in the genetic code (i.e. different sets of codes that code for the same AA), which is why DNA is degenerate.

Yes, it would not matter (in terms of transmission for DNA) if it were a conformationally variable molecule. Conformationally variable is just pointing to the different packaging that DNA can exists - it can be folded into chromosomes by histones, or stretched out for transcription or replication. This all is not essential to its transmission though. Hope this helped 👍

 

[Meredith92]

Great! Thanks to both of you!

 

[Postictal Raiden]

Not entirely sure why choice D is the best answer here.. I also dont think i really understand what the question is trying to get at... are they asking about an accurate aspect of DNA that is unnecessary?

DNA is the carrier of genetic information during cell growth and division. which of the following characteristics of dna is not essential for the accurate transmission of this information?

A) a genetic code that is degenerate
B) a mechanism for self replication
C) a low mutation rate
D) a conformationally variable molecule

Answer: D is correct. In order to transmit info from one cell to the next there must be an alphabet that makes the communication possible. in dna this alphabet is composed of A G C and T . a triplet of these bases= a codon and a codon specifies an amino acid. there are 64 diff codons and among these 64 there is redundancy. in other words, more than one codon can code for the same amino acid. because of this, the genetic code is referred to as being degenerate. (... goes on to explain B and C which i understand..) DNA can exist as single or double stranded. in the double stranded form it can exist in a number of diff states. dna is said to have variable conformations. this info passed on to the next generation is still contained in these diff forms of dna. its just a matter of having the appropriate mechanism to transmit that info. dna, as a conformationally variable molecule, would not pose a problem for the transmission of genetic information.


Do they mean if dna WASNT a conformationally variable molecule it wouldnt matter?
Why does it NEED to be degenerate? wouldnt it be just as accurate if it wasnt degenerate?
I think I'm missing the way we are supposed to look at this problem.
Thanks!

This is one of the question that is better solved by POE than looking for the correct response.

 

[BerkReviewTeach]

Great explanations using the context of the question. That's what is so important when preparing. Knowing the information is nice, but applying it requires a process just like this.

 

[ChemTutor]

Think about it this way.

B and C are easy to cross out because replication and a low mutation rate are key to accurate DNA transfer from generation to generation. A is also just as vital because degeneracy in DNA is an evolved mechanism. We only need 20 codons to encode every amino acid, however since there are 4 bases and codons are read in groups of 3 (64 total), over time the DNA code degenerated and instead of strictly using 20 codons to encode each amino acid we can use all 64 to represent amino acids. My reasoning on why I wouldn't pick A is because the code is by default assumed to be degenerate, transmission of a non degenerate code could result in implications we simply can't predict therefore its better to keep what evolution has naturally selected for. D is more correct in my opinion primarily because 3D conformation of DNA won't affect much other than the rate of mRNA synthesis and will still result in accurate genetic information transfer.

The relation between the genetic code degeneracy and accuracy of genetic info was missed somehow during this discussion.

A mutation in DNA that changes GAA codon into GAG does not affect the amino-acid encoded (Glu). As this example demonstrates, the degenerate code contributes directly to the accuracy of genetic info transmission (by making some mutations in DNA harmless).