DNA Structure and Function - SAT Subject Test in Biology
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If a structural gene in an organism's genome is comprised of 33% adenine nucleotides, what percentage of the gene is comprised of cytosine nucleotides?
If a structural gene in an organism's genome is comprised of 33% adenine nucleotides, what percentage of the gene is comprised of cytosine nucleotides?
According to Chargaff's rule, DNA nucleotides pair in a 1:1 ratio. Therefore, if we know how much of the particular gene is made up of one nucleotide, we can extrapolate that known variable to find the other three unknown variables.
To do so, you must remember that adenine pairs with thymine, and cytosine pairs with guanine (A-T, C-G), and that since the ratio between each pair is 1:1 then a gene with 33% adenine must also have 33% thymine. Combine these numbers and subtract from 100: the number leftover is the % of total cytosine and guanine in the gene.
100% - 66% = 34%
Finally, since we know that 34% of the DNA is both C and G, and that the ratio between C-G is 1:1, C and G must both be 17%.
According to Chargaff's rule, DNA nucleotides pair in a 1:1 ratio. Therefore, if we know how much of the particular gene is made up of one nucleotide, we can extrapolate that known variable to find the other three unknown variables.
To do so, you must remember that adenine pairs with thymine, and cytosine pairs with guanine (A-T, C-G), and that since the ratio between each pair is 1:1 then a gene with 33% adenine must also have 33% thymine. Combine these numbers and subtract from 100: the number leftover is the % of total cytosine and guanine in the gene.
100% - 66% = 34%
Finally, since we know that 34% of the DNA is both C and G, and that the ratio between C-G is 1:1, C and G must both be 17%.
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If a structural gene in an organism's genome is comprised of 29% guanine nucleotides, what percentage of the gene is comprised of cytosine nucleotides?
If a structural gene in an organism's genome is comprised of 29% guanine nucleotides, what percentage of the gene is comprised of cytosine nucleotides?
This question is designed to catch a) students who are not reading the question carefully, and b) students unsure of which nucleotides pair with which.
The correct answer is 29%, because cytosine pairs with guanine in a 1:1 ratio. If you answered 21%, then you likely thought the question was more complex than it was.
This question is designed to catch a) students who are not reading the question carefully, and b) students unsure of which nucleotides pair with which.
The correct answer is 29%, because cytosine pairs with guanine in a 1:1 ratio. If you answered 21%, then you likely thought the question was more complex than it was.
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There is a certain type of chemical bonding between the paired nucleotides on each strand of DNA which helps maintain the double-helix structure of DNA by attracting each strand to the other. What type of bonding is responsible for this?
There is a certain type of chemical bonding between the paired nucleotides on each strand of DNA which helps maintain the double-helix structure of DNA by attracting each strand to the other. What type of bonding is responsible for this?
The correct answer is hydrogen bonding, and each nucleotide attracts its pairing mate because they have corresponding number of hydrogen bonds. Adenine is attracted to thymine to create two hydrogen bonds, and cytosine is attracted to guanine to form three hydrogen bonds. While phosphodiester bonds are very important in creating the strand of DNA, they are not the bond that keeps the two strands in the double helix structure.
The correct answer is hydrogen bonding, and each nucleotide attracts its pairing mate because they have corresponding number of hydrogen bonds. Adenine is attracted to thymine to create two hydrogen bonds, and cytosine is attracted to guanine to form three hydrogen bonds. While phosphodiester bonds are very important in creating the strand of DNA, they are not the bond that keeps the two strands in the double helix structure.
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With respect to DNA, the terms 3' and 5' (pronounced 3-prime and 5-prime, respectively) are used in order to refer to one strand or the other. What do these two terms signify?
With respect to DNA, the terms 3' and 5' (pronounced 3-prime and 5-prime, respectively) are used in order to refer to one strand or the other. What do these two terms signify?
When nucleotides bond together and form DNA strands, the first and last nucleotides in the strand have slightly different structures than the rest of the nucleotides between them. On one end of the strand, the nucleotide has an exposed hydroxyl group bound to the third carbon in the carbon ring: this end of the strand is thus called 3'. On the opposite end of the strand, the nucleotide has a phosphate group attached to the 5' carbon in the carbon ring, and is thus called the 5' end. These two groups are exposed because they are used in the bonding of nucleotides to one another to form the strand, but each strand ends with one nucleotide that only is bound on one side: thus, leaving either the hydroxyl or phosphate group exposed (depending on which end you are observing).
These terms are useful because they allow us to discuss the directionality of DNA-related events- if we didn't have terms for directionality the concept would be much more confusing. Example: "DNA polymerase synthesizes the new DNA strand in the 5'-3' direction." Without 3'/5' how would we determine which way the reaction occurs?
When nucleotides bond together and form DNA strands, the first and last nucleotides in the strand have slightly different structures than the rest of the nucleotides between them. On one end of the strand, the nucleotide has an exposed hydroxyl group bound to the third carbon in the carbon ring: this end of the strand is thus called 3'. On the opposite end of the strand, the nucleotide has a phosphate group attached to the 5' carbon in the carbon ring, and is thus called the 5' end. These two groups are exposed because they are used in the bonding of nucleotides to one another to form the strand, but each strand ends with one nucleotide that only is bound on one side: thus, leaving either the hydroxyl or phosphate group exposed (depending on which end you are observing).
These terms are useful because they allow us to discuss the directionality of DNA-related events- if we didn't have terms for directionality the concept would be much more confusing. Example: "DNA polymerase synthesizes the new DNA strand in the 5'-3' direction." Without 3'/5' how would we determine which way the reaction occurs?
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Which type of bond makes up the backbone of DNA strands by linking together adjacent nucleotides?
Which type of bond makes up the backbone of DNA strands by linking together adjacent nucleotides?
DNA and RNA nucleotides are linked together through phosphodiester bonds. A strong covalent bond (ester bond) forms between the 3' carbon atom of the sugar pentose of one nucleotide and a phosphate group, and a second ester bond forms between the phosphate group and the 5' carbon atom of the sugar pentose of another nucleotide. This alternation of sugar and phosphate groups forms a strong backbone and is also the reason why DNA is antiparallel and forms in the 5' to 3' direction.
DNA and RNA nucleotides are linked together through phosphodiester bonds. A strong covalent bond (ester bond) forms between the 3' carbon atom of the sugar pentose of one nucleotide and a phosphate group, and a second ester bond forms between the phosphate group and the 5' carbon atom of the sugar pentose of another nucleotide. This alternation of sugar and phosphate groups forms a strong backbone and is also the reason why DNA is antiparallel and forms in the 5' to 3' direction.
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When synthesizing a strand of double-stranded DNA, which of the following could be a plausible combination of nitrogen bases?
When synthesizing a strand of double-stranded DNA, which of the following could be a plausible combination of nitrogen bases?
DNA nucleotides all contain one of four possible nitrogen bases: adenine (A), thymine (T), cytosine (C), or guanine (G). In forming base pairs, an A must always pair with a T and a C must always pair with a G: \[A-T\], \[C-G\]. This means that for any DNA composition, the percent of adenine (A) must be equal to the percent of thymine (T) and, likewise, the percent of cytosine (C) must be equal to the percent of guanine (G). Looking across the answer choices, there is only one choice that satisfies this condition while also correctly summing to 100%. The choice with uracil can be eliminated immediately, since uracil only replaces thymine in RNA and is not present in DNA.
DNA nucleotides all contain one of four possible nitrogen bases: adenine (A), thymine (T), cytosine (C), or guanine (G). In forming base pairs, an A must always pair with a T and a C must always pair with a G: \[A-T\], \[C-G\]. This means that for any DNA composition, the percent of adenine (A) must be equal to the percent of thymine (T) and, likewise, the percent of cytosine (C) must be equal to the percent of guanine (G). Looking across the answer choices, there is only one choice that satisfies this condition while also correctly summing to 100%. The choice with uracil can be eliminated immediately, since uracil only replaces thymine in RNA and is not present in DNA.
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A sample of DNA is sequenced and found to contain 
guanine. What percentage of thymine does it contain?
A sample of DNA is sequenced and found to contain 
In DNA, guanine pairs with cytosine and adenine pairs with thymine. In RNA, which does not have thymine, adenine pairs with uracil. Thus, if a sample contains 
guanine, it also contains 
cytosine. Together, the two make up 
of the 
total. The remaining 
is divided evenly between the paired adenine and thymine molecules, so the DNA sample contains 
percent each of adenine and thymine. 
is the correct answer.
In DNA, guanine pairs with cytosine and adenine pairs with thymine. In RNA, which does not have thymine, adenine pairs with uracil. Thus, if a sample contains 
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Which of the following is NOT found in DNA?
Which of the following is NOT found in DNA?
DNA and RNA are both made of sugar-phosphate backbones. Ribose is the sugar found in RNA; deoxyribose is the sugar found in DNA. DNA also contains the nucleic acid bases adenine, guanine, cytosine, and thymine. Both DNA and RNA contain phosphate groups as part of the backbone.
DNA and RNA are both made of sugar-phosphate backbones. Ribose is the sugar found in RNA; deoxyribose is the sugar found in DNA. DNA also contains the nucleic acid bases adenine, guanine, cytosine, and thymine. Both DNA and RNA contain phosphate groups as part of the backbone.
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