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Assertion : The sugar phosphatebackone o...

Assertion : The sugar phosphatebackone of two chains in DNA double helix show anti-parallel polarity.
Reason : The phosphodiester bonds in one strand go from a 3' cardon of one nucleotide to a 5, carbon of adjacent nucleotide, whereas those in complementary strand go vice versa.

A

If both assertion and reason are true and reason is the correct explanation of assertion

B

If both assertion and reason are true but reason is not the correct explanation of assertion

C

If assertion is true but reason is false

D

if both assertion and reason are false.

Text Solution

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The correct Answer is:
### Step-by-Step Solution: 1. **Understanding the Assertion**: The assertion states that the sugar-phosphate backbone of the two chains in the DNA double helix shows anti-parallel polarity. This means that the two strands of DNA run in opposite directions. 2. **Understanding the Reason**: The reason given explains how the phosphodiester bonds are formed in the DNA strands. It states that in one strand, the phosphodiester bonds connect the 3' carbon of one nucleotide to the 5' carbon of the adjacent nucleotide. In the complementary strand, the bonds go in the opposite direction, connecting the 5' carbon of one nucleotide to the 3' carbon of the adjacent nucleotide. 3. **Analyzing the Structure of DNA**: The backbone of DNA is composed of alternating deoxyribose sugars and phosphate groups. The phosphate group is attached to the 5' carbon of one sugar and the 3' carbon of the next sugar, forming a phosphodiester bond. 4. **Identifying the Directionality**: In one strand, the directionality is from the 5' end to the 3' end, while in the complementary strand, the directionality is from the 3' end to the 5' end. This is what is meant by anti-parallel. 5. **Conclusion**: Both the assertion and the reason are correct. The reason correctly explains why the sugar-phosphate backbone of the DNA strands is anti-parallel. Therefore, the correct answer is that both the assertion and the reason are true, and the reason is the correct explanation for the assertion. ### Final Answer: Both the assertion and the reason are correct, and the reason is the correct explanation for the assertion. ---
### Step-by-Step Solution: 1. **Understanding the Assertion**: The assertion states that the sugar-phosphate backbone of the two chains in the DNA double helix shows anti-parallel polarity. This means that the two strands of DNA run in opposite directions. 2. **Understanding the Reason**: The reason given explains how the phosphodiester bonds are formed in the DNA strands. It states that in one strand, the phosphodiester bonds connect the 3' carbon of one nucleotide to the 5' carbon of the adjacent nucleotide. In the complementary strand, the bonds go in the opposite direction, connecting the 5' carbon of one nucleotide to the 3' carbon of the adjacent nucleotide. 3. **Analyzing the Structure of DNA**: The backbone of DNA is composed of alternating deoxyribose sugars and phosphate groups. The phosphate group is attached to the 5' carbon of one sugar and the 3' carbon of the next sugar, forming a phosphodiester bond. ...
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Assertion: The two strands in double strand helix structure of DNA are complementary to each other Reason: Disulphide bonds are formed between SQPecific pairs of bases

In a double standed DNA, the sequence of nucleotides in one strand is 3' ATTCGCTAT 5'. What will be the complementary squence on the other strand ?

Knowledge Check

  • The chemical formula of deoxyribonucleic acid (DNA) is now well established. The molecule is a very long chain, the backbone of which consists of a regular alternation of sugar and phosphate groups. 5 To each sugar is attached a nitrogenous base, which can be of four different types. Two of the possible bases—adenine and guanine—are purines, and the other two—thymine and cytosine—are pyrimidines. So far as is known, the sequence of bases along the 10 chain is irregular. The monomer unit, consisting of phosphate, sugar and base, is known as a nucleotide. The first feature of our structure which is of biological interest is that it consists not of one chain, but of two. These two chains are both coiled around 15 a common fiber axis. It has often been assumed that since there was only one chain in the chemical formula there would only be one in the structural unit. However, the density, taken with the X-ray evidence, suggests very strongly that there are two. 20. The other biologically important feature is the manner in which the two chains are held together. This is done by hydrogen bonds between the bases. The bases are joined together in pairs, a single base from one chain being hydrogen-bonded to a single 25 base from the other. The important point is that only certain pairs of bases will fit into the structure. One member of a pair must be a purine and the other a pyrimidine in order to bridge between the two chains. If a pair consisted of two purines, for 30 example, there would not be room for it. We believe that the bases will be present almost entirely in their most probable forms. If this is true, the conditions for forming hydrogen bonds are more restrictive, and the only pairs of bases possible are: 35 adenine with thymine, and guanine with cytosine. Adenine, for example, can occur on either chain, but when it does, its partner on the other chain must always be thymine. The phosphate-sugar backbone of our model is 40 completely regular, but any sequence of the pairs of bases can fit into the structure. It follows that in a long molecule many different permutations are possible, and it therefore seems likely that the precise sequence of bases is the code which carries the 45 genetical information. If the actual order of the bases on one of the pair of chains were given, one could write down the exact order of the bases on the other one, because of the specific pairing. Thus one chain is, as it were, the complement of the other, and it is 50 this feature which suggests how the deoxyribonucleic acid molecule might duplicate itself. The table shows, for various organisms, the percentage of each of the four types of nitrogenous bases in that organism’s DNA. Adapted from Manju Bansal, “DNA Structure: Revisiting the Watson-Crick Double Helix.” ©2003 by Current Science Association, Bangalor 27. The authors’ use of the words “exact,” “specific,” and “complement” in lines 47-49 in the final paragraph functions mainly to

    A
    confirm that the nucleotide sequences are known for most molecules of DNA.
    B
    counter the claim that the sequences of bases along a chain can occur in any order.
    C
    support the claim that the phosphate sugar backbone of the authors’ model is completely regular.
    D
    emphasize how one chain of DNA may serve as a template to be copied during DNA replication

  • The chemical formula of deoxyribonucleic acid (DNA) is now well established. The molecule is a very long chain, the backbone of which consists of a regular alternation of sugar and phosphate groups. 5 To each sugar is attached a nitrogenous base, which can be of four different types. Two of the possible bases—adenine and guanine—are purines, and the other two—thymine and cytosine—are pyrimidines. So far as is known, the sequence of bases along the 10 chain is irregular. The monomer unit, consisting of phosphate, sugar and base, is known as a nucleotide. The first feature of our structure which is of biological interest is that it consists not of one chain, but of two. These two chains are both coiled around 15 a common fiber axis. It has often been assumed that since there was only one chain in the chemical formula there would only be one in the structural unit. However, the density, taken with the X-ray evidence, suggests very strongly that there are two. 20. The other biologically important feature is the manner in which the two chains are held together. This is done by hydrogen bonds between the bases. The bases are joined together in pairs, a single base from one chain being hydrogen-bonded to a single 25 base from the other. The important point is that only certain pairs of bases will fit into the structure. One member of a pair must be a purine and the other a pyrimidine in order to bridge between the two chains. If a pair consisted of two purines, for 30 example, there would not be room for it. We believe that the bases will be present almost entirely in their most probable forms. If this is true, the conditions for forming hydrogen bonds are more restrictive, and the only pairs of bases possible are: 35 adenine with thymine, and guanine with cytosine. Adenine, for example, can occur on either chain, but when it does, its partner on the other chain must always be thymine. The phosphate-sugar backbone of our model is 40 completely regular, but any sequence of the pairs of bases can fit into the structure. It follows that in a long molecule many different permutations are possible, and it therefore seems likely that the precise sequence of bases is the code which carries the 45 genetical information. If the actual order of the bases on one of the pair of chains were given, one could write down the exact order of the bases on the other one, because of the specific pairing. Thus one chain is, as it were, the complement of the other, and it is 50 this feature which suggests how the deoxyribonucleic acid molecule might duplicate itself. The table shows, for various organisms, the percentage of each of the four types of nitrogenous bases in that organism’s DNA. Adapted from Manju Bansal, “DNA Structure: Revisiting the Watson-Crick Double Helix.” ©2003 by Current Science Association, Bangalore 30. According to the table, which of the following pairs of base percentages in sea urchin DNA provides evidence in support of the answer to the previous question?

    A
    17.3% and 17.7%
    B
    17.3% and 32.1%
    C
    17.3% and 32.8%
    D
    17.7% and 32.8%

  • The chemical formula of deoxyribonucleic acid (DNA) is now well established. The molecule is a very long chain, the backbone of which consists of a regular alternation of sugar and phosphate groups. 5 To each sugar is attached a nitrogenous base, which can be of four different types. Two of the possible bases—adenine and guanine—are purines, and the other two—thymine and cytosine—are pyrimidines. So far as is known, the sequence of bases along the 10 chain is irregular. The monomer unit, consisting of phosphate, sugar and base, is known as a nucleotide. The first feature of our structure which is of biological interest is that it consists not of one chain, but of two. These two chains are both coiled around 15 a common fiber axis. It has often been assumed that since there was only one chain in the chemical formula there would only be one in the structural unit. However, the density, taken with the X-ray evidence, suggests very strongly that there are two. 20. The other biologically important feature is the manner in which the two chains are held together. This is done by hydrogen bonds between the bases. The bases are joined together in pairs, a single base from one chain being hydrogen-bonded to a single 25 base from the other. The important point is that only certain pairs of bases will fit into the structure. One member of a pair must be a purine and the other a pyrimidine in order to bridge between the two chains. If a pair consisted of two purines, for 30 example, there would not be room for it. We believe that the bases will be present almost entirely in their most probable forms. If this is true, the conditions for forming hydrogen bonds are more restrictive, and the only pairs of bases possible are: 35 adenine with thymine, and guanine with cytosine. Adenine, for example, can occur on either chain, but when it does, its partner on the other chain must always be thymine. The phosphate-sugar backbone of our model is 40 completely regular, but any sequence of the pairs of bases can fit into the structure. It follows that in a long molecule many different permutations are possible, and it therefore seems likely that the precise sequence of bases is the code which carries the 45 genetical information. If the actual order of the bases on one of the pair of chains were given, one could write down the exact order of the bases on the other one, because of the specific pairing. Thus one chain is, as it were, the complement of the other, and it is 50 this feature which suggests how the deoxyribonucleic acid molecule might duplicate itself. The table shows, for various organisms, the percentage of each of the four types of nitrogenous bases in that organism’s DNA. Adapted from Manju Bansal, “DNA Structure: Revisiting the Watson-Crick Double Helix.” ©2003 by Current Science Association, Bangalore 31. Based on the table, is the percentage of adenine in each organism’s DNA the same or does it vary, and which statement made by the authors is most consistent with that data?

    A
    The same, “Two of . . . pyrimidines” (lines 6-8)
    B
    The same, “The important . . . structure” (lines 25-26)
    C
    It varies, “Adenine . . . thymine” (lines 36-38)
    D
    It varies, “It follows . . . information” (lines 41-45)

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    Which of these statements about protein synthesis are NOT correct ? I. During transcription, mRNA synthesized from DNA nucleotides to have the same sequence of nucleotides as the DNA strand on which it was made. II. During transcription , tRNA is synthesized from RNA nucleotides and carries codons that are complementary to the sequence of nucleotides on the DNA strand on which it was made. III. During translation, mRNA is synthesized from RNA nucleotides to have the complementary sequence of nucleotides to that. Of the DNA strand on which it was made . IV. During translation ribosomes move on mRNA from '5' and '3' one codon at a time .This is called translocation

    The chemical formula of deoxyribonucleic acid (DNA) is now well established. The molecule is a very long chain, the backbone of which consists of a regular alternation of sugar and phosphate groups. 5 To each sugar is attached a nitrogenous base, which can be of four different types. Two of the possible bases—adenine and guanine—are purines, and the other two—thymine and cytosine—are pyrimidines. So far as is known, the sequence of bases along the 10 chain is irregular. The monomer unit, consisting of phosphate, sugar and base, is known as a nucleotide. The first feature of our structure which is of biological interest is that it consists not of one chain, but of two. These two chains are both coiled around 15 a common fiber axis. It has often been assumed that since there was only one chain in the chemical formula there would only be one in the structural unit. However, the density, taken with the X-ray evidence, suggests very strongly that there are two. 20. The other biologically important feature is the manner in which the two chains are held together. This is done by hydrogen bonds between the bases. The bases are joined together in pairs, a single base from one chain being hydrogen-bonded to a single 25 base from the other. The important point is that only certain pairs of bases will fit into the structure. One member of a pair must be a purine and the other a pyrimidine in order to bridge between the two chains. If a pair consisted of two purines, for 30 example, there would not be room for it. We believe that the bases will be present almost entirely in their most probable forms. If this is true, the conditions for forming hydrogen bonds are more restrictive, and the only pairs of bases possible are: 35 adenine with thymine, and guanine with cytosine. Adenine, for example, can occur on either chain, but when it does, its partner on the other chain must always be thymine. The phosphate-sugar backbone of our model is 40 completely regular, but any sequence of the pairs of bases can fit into the structure. It follows that in a long molecule many different permutations are possible, and it therefore seems likely that the precise sequence of bases is the code which carries the 45 genetical information. If the actual order of the bases on one of the pair of chains were given, one could write down the exact order of the bases on the other one, because of the specific pairing. Thus one chain is, as it were, the complement of the other, and it is 50 this feature which suggests how the deoxyribonucleic acid molecule might duplicate itself. The table shows, for various organisms, the percentage of each of the four types of nitrogenous bases in that organism’s DNA. Adapted from Manju Bansal, “DNA Structure: Revisiting the Watson-Crick Double Helix.” ©2003 by Current Science Association, Bangalore 28. Based on the table and passage, which choice gives the correct percentages of the purines in yeast DNA?

    The chemical formula of deoxyribonucleic acid (DNA) is now well established. The molecule is a very long chain, the backbone of which consists of a regular alternation of sugar and phosphate groups. 5 To each sugar is attached a nitrogenous base, which can be of four different types. Two of the possible bases—adenine and guanine—are purines, and the other two—thymine and cytosine—are pyrimidines. So far as is known, the sequence of bases along the 10 chain is irregular. The monomer unit, consisting of phosphate, sugar and base, is known as a nucleotide. The first feature of our structure which is of biological interest is that it consists not of one chain, but of two. These two chains are both coiled around 15 a common fiber axis. It has often been assumed that since there was only one chain in the chemical formula there would only be one in the structural unit. However, the density, taken with the X-ray evidence, suggests very strongly that there are two. 20. The other biologically important feature is the manner in which the two chains are held together. This is done by hydrogen bonds between the bases. The bases are joined together in pairs, a single base from one chain being hydrogen-bonded to a single 25 base from the other. The important point is that only certain pairs of bases will fit into the structure. One member of a pair must be a purine and the other a pyrimidine in order to bridge between the two chains. If a pair consisted of two purines, for 30 example, there would not be room for it. We believe that the bases will be present almost entirely in their most probable forms. If this is true, the conditions for forming hydrogen bonds are more restrictive, and the only pairs of bases possible are: 35 adenine with thymine, and guanine with cytosine. Adenine, for example, can occur on either chain, but when it does, its partner on the other chain must always be thymine. The phosphate-sugar backbone of our model is 40 completely regular, but any sequence of the pairs of bases can fit into the structure. It follows that in a long molecule many different permutations are possible, and it therefore seems likely that the precise sequence of bases is the code which carries the 45 genetical information. If the actual order of the bases on one of the pair of chains were given, one could write down the exact order of the bases on the other one, because of the specific pairing. Thus one chain is, as it were, the complement of the other, and it is 50 this feature which suggests how the deoxyribonucleic acid molecule might duplicate itself. The table shows, for various organisms, the percentage of each of the four types of nitrogenous bases in that organism’s DNA. Adapted from Manju Bansal, “DNA Structure: Revisiting the Watson-Crick Double Helix.” ©2003 by Current Science Association, Bangalore 24. In the second paragraph (lines 12-19), what do the authors claim to be a feature of biological interest?

    The chemical formula of deoxyribonucleic acid (DNA) is now well established. The molecule is a very long chain, the backbone of which consists of a regular alternation of sugar and phosphate groups. 5 To each sugar is attached a nitrogenous base, which can be of four different types. Two of the possible bases—adenine and guanine—are purines, and the other two—thymine and cytosine—are pyrimidines. So far as is known, the sequence of bases along the 10 chain is irregular. The monomer unit, consisting of phosphate, sugar and base, is known as a nucleotide. The first feature of our structure which is of biological interest is that it consists not of one chain, but of two. These two chains are both coiled around 15 a common fiber axis. It has often been assumed that since there was only one chain in the chemical formula there would only be one in the structural unit. However, the density, taken with the X-ray evidence, suggests very strongly that there are two. 20. The other biologically important feature is the manner in which the two chains are held together. This is done by hydrogen bonds between the bases. The bases are joined together in pairs, a single base from one chain being hydrogen-bonded to a single 25 base from the other. The important point is that only certain pairs of bases will fit into the structure. One member of a pair must be a purine and the other a pyrimidine in order to bridge between the two chains. If a pair consisted of two purines, for 30 example, there would not be room for it. We believe that the bases will be present almost entirely in their most probable forms. If this is true, the conditions for forming hydrogen bonds are more restrictive, and the only pairs of bases possible are: 35 adenine with thymine, and guanine with cytosine. Adenine, for example, can occur on either chain, but when it does, its partner on the other chain must always be thymine. The phosphate-sugar backbone of our model is 40 completely regular, but any sequence of the pairs of bases can fit into the structure. It follows that in a long molecule many different permutations are possible, and it therefore seems likely that the precise sequence of bases is the code which carries the 45 genetical information. If the actual order of the bases on one of the pair of chains were given, one could write down the exact order of the bases on the other one, because of the specific pairing. Thus one chain is, as it were, the complement of the other, and it is 50 this feature which suggests how the deoxyribonucleic acid molecule might duplicate itself. The table shows, for various organisms, the percentage of each of the four types of nitrogenous bases in that organism’s DNA. Adapted from Manju Bansal, “DNA Structure: Revisiting the Watson-Crick Double Helix.” ©2003 by Current Science Association, Bangalore 23. A student claims that nitrogenous bases pair randomly with one another. Which of the following statements in the passage contradicts the student’s claim?

    The chemical formula of deoxyribonucleic acid (DNA) is now well established. The molecule is a very long chain, the backbone of which consists of a regular alternation of sugar and phosphate groups. 5 To each sugar is attached a nitrogenous base, which can be of four different types. Two of the possible bases—adenine and guanine—are purines, and the other two—thymine and cytosine—are pyrimidines. So far as is known, the sequence of bases along the 10 chain is irregular. The monomer unit, consisting of phosphate, sugar and base, is known as a nucleotide. The first feature of our structure which is of biological interest is that it consists not of one chain, but of two. These two chains are both coiled around 15 a common fiber axis. It has often been assumed that since there was only one chain in the chemical formula there would only be one in the structural unit. However, the density, taken with the X-ray evidence, suggests very strongly that there are two. 20. The other biologically important feature is the manner in which the two chains are held together. This is done by hydrogen bonds between the bases. The bases are joined together in pairs, a single base from one chain being hydrogen-bonded to a single 25 base from the other. The important point is that only certain pairs of bases will fit into the structure. One member of a pair must be a purine and the other a pyrimidine in order to bridge between the two chains. If a pair consisted of two purines, for 30 example, there would not be room for it. We believe that the bases will be present almost entirely in their most probable forms. If this is true, the conditions for forming hydrogen bonds are more restrictive, and the only pairs of bases possible are: 35 adenine with thymine, and guanine with cytosine. Adenine, for example, can occur on either chain, but when it does, its partner on the other chain must always be thymine. The phosphate-sugar backbone of our model is 40 completely regular, but any sequence of the pairs of bases can fit into the structure. It follows that in a long molecule many different permutations are possible, and it therefore seems likely that the precise sequence of bases is the code which carries the 45 genetical information. If the actual order of the bases on one of the pair of chains were given, one could write down the exact order of the bases on the other one, because of the specific pairing. Thus one chain is, as it were, the complement of the other, and it is 50 this feature which suggests how the deoxyribonucleic acid molecule might duplicate itself. The table shows, for various organisms, the percentage of each of the four types of nitrogenous bases in that organism’s DNA. Adapted from Manju Bansal, “DNA Structure: Revisiting the Watson-Crick Double Helix.” ©2003 by Current Science Association, Bangalore 26. Based on the passage, the authors’ statement “If a pair consisted of two purines, for example, there would not be room for it” (lines 29-30) implies that a pair

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