Architecture

Why Do Purines Bond With Pyrimidines In The Dna Ladder ? Why Do Purines Pair With Pyrimidines

Explanation:

Within a DNA molecule, there are specific nucleotide binding patterns, a phenomenon called “complementary base pairing.” Specific pyrimidine nucleotides can only bind to specific purine bases: cytosine binds to guanine via three hydrogen bonds and adenine binds to thymine via hydrogen bonds. Normally, within a DNA molecule, no other base pair combinations exist. These specific complementary base pairs allow DNA to take the form of a double helix. The double helix can be most simply described as a twisted ladder; the base pairs and their hydrogen bonds represent the rungs, and the sugar-phosphate backbone represents the sides of the ladder.

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Example Question #42 : Dna And Rna Structure

*

The given diagrams depict which of the following?

Possible Answers:

Ribose and deoxyribose

Purines

Pyrimidines

Thymine and cytosine

Amino acids

Correct answer:

Purines

Explanation:

The diagram depicts two purines (adenine and guanine), identifiable by their pyrimidine-imidazole double-ring structure. Pyrimidines (such at thymine and cytosine) have only one ring, amino acids have both amine and carboxylic acid groups, and ribose and deoxyribose are pentameric sugars (and contain no nitrogen).

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Example Question #43 : Dna And Rna Structure

What type of bonding occurs between the two parallel strands of nucleic acids in DNA?

Possible Answers:

Hydrogen bonding

Covalent bonding

Ionic bonding

Single bond

Double bond

Correct answer:

Hydrogen bonding

Explanation:

The bonding that occurs between two parallel strands of nucleic acids in DNA is hydrogen bonding. As you know, hydrogen bonding occurs between molecules containing fluorine, nitrogen and oxygen with other fluorine, nitrogen and oxygen atoms. This is a fairly weak bond but there are so many hydrogen bonds along a strand of DNA making the attachment between the two quite strong, but the two strands can still be separated as needed (during replication and transcription). Adenine and thymine form two hydrogen bonds, while cytosine and guanine form three hydrogen bonds.

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Example Question #44 : Dna And Rna Structure

There are 4 types of bases in DNA: Guanine (G), Cytosine (C), Adenine (A), and Thymine (T). The complimentary pairing of these bases forms the double helix of DNA 

Which bases are complimentary (bond together) to form the spiral staircase of the double helix present in DNA?

Possible Answers:

Adenine with thymine and guanine with cytosine

Adenine with guanine and cytosine with thymine

Adenine with cytosine and guanine with thymine

Adenine with uracil and cytosine with guanine

Thymine with uracil and cytosine with guanine

Correct answer:

Adenine with thymine and guanine with cytosine

Explanation:

There are two types of bases in DNA: purines and pyrimidines. The purines are adenine and guanine. The pyrimidines are cytosine and thymine (note that uracil is also a pyrimidine, but is only found in RNA). Adenine forms two hydrogen bonds with thymine, and guanine forms three bonds with cytosine. As a result, cytosine/guanine-rich regions in DNA require more energy to denature. One was to remember which bases are purines is through the use of the mnemonic “Pure As Gold”. Another mnemonic to help you remember which nitrogenous bases are pyrimidines are that: pyrimidines, like pyramids, are sharp, and sharp things CUT (Cytosine, Uracil, and Thymine).

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Example Question #21 : Understanding Nucleotides And Base Pairs

If a strand of DNA is ten percent adenine, then what percentage of guanine will it possess?

Possible Answers:

*

None of these

*

*

Correct answer:

Explanation:

If the imaginary DNA is ten percent adenine, then that means there must be ten percent thymine because they are complementary to one another. The rest of the eighty percent of the DNA strand must be made up of guanine and cytosine. Because they are complementary to each other, half will be guanine and half will be cytosine. This means that there will be forty percent guanine present in the DNA strand.

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Example Question #22 : Understanding Nucleotides And Base Pairs

A sample of double-stranded RNA is composed of thirty percent guanine. How much uracil is present in this sample?

Possible Answers:

None of these

Correct answer:

*

Explanation:

If the RNA is thirty percent guanine, then that means it must be composed of thirty percent cytosine because they are complementary to each other. The other forty percent of the RNA strand is made up of adenine and uracil. Because they are complementary to each other, half will be adenine and the other half will be uracil. This means that there will be twenty percent uracil present in the RNA strand.

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Example Question #23 : Understanding Nucleotides And Base Pairs

There are __________ hydrogen bonds between the nucleotides adenine and thymine and __________ hydrogen bonds between the nucleotides cytosine and guanine. 

Possible Answers:

two . . . three

three . . . three

three . . . two

two . . . two

one . . . three

Correct answer:

two . . . three

Explanation:

Hydrogen bonds between nucleotides of different strands are crucial for the stability of DNA. Adenine and thymine pair up with two hydrogen bonds between the nucleotides. On the other hand, cytosine and guanine pair up with three hydrogen bonds between the nucleotides.

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Example Question #24 : Understanding Nucleotides And Base Pairs

What would be the nucleotide sequence of the mRNA strand from the DNA strand below?

3″-ATCCCAGGTACC-5″

Possible Answers:

3″-UAGGGUCCAUGG-5″

5″-UAGGGUCCAUGG-3″

3″-TAGGGTCCATGG-5″

5″-TAGGGTCCATGG-3″

3″-ATCCCAGGTACC-5″

Correct answer:

5″-UAGGGUCCAUGG-3″

Explanation:

In order to solve this problem, it is imperative that you remember that RNA replaces thymine with uracil. This automatically eliminates three of the answer choices. Next, the RNA strand must have nucleotides that pair up with the DNA nucleotides (adenine pairs with thymine and cytosine pairs with guanine). For example, if DNA has a nucleotide of G, the RNA would have a nucleotide of C. Finally, since the strands must be antiparallel to one another, the mRNA must start with a 5″ and end with a 3″. Thus, our answer is 5″-UAGGGUCCAUGG-3″. 

Below is a side by side comparison:

3″-ATCCCAGGTACC-5″ (DNA)

5″-UAGGGUCCAUGG-3 (mRNA)

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Example Question #25 : Understanding Nucleotides And Base Pairs

What are four possible chromosome structure abnormalities?

Possible Answers:

Nondisjunction, deletion, duplication, inversion

Deletion, independent assortment, inversion, duplication

Polyploidy, deletion, inversion, translocation

Deletion, duplication, inversion, translocation

Synapsis, duplication, inversion, translocation

Correct answer:

Deletion, duplication, inversion, translocation

Explanation:

Chromosomal related mutations include deletion, duplication, inversion, or translocation. Nondisjunction is a faulty separation event of homologous chromosomes but does not necessarily involve improper chromosome structures. Independent assortment is a mendelian inheritance principle which states chromosomes are divided randomly into two daughter cells. Synapsis is a normal pairing up event of homologous chromosomes in prophase I. Polyploidy is a condition of having more than two sets of chromosomes and is typically a characteristic of a species, not an abnormality.

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Example Question #26 : Understanding Nucleotides And Base Pairs

During DNA synthesis, DNA polymerase mistakenly substitutes a purine (adenine or guanine) for a pyrimidine (cytosine or thymine). This is known as what type of mutation?

Possible Answers:

Silent mutation

Transversion

Inversion

Transition

Replacement substitution

Correct answer:

Transversion

Explanation:

The substitution of a purine for a pyrimidine, or vice versa, is called a transversion. The substitution of one purine for another or one pyrimidine for another is called a transition. Either of these can be referred to as a point mutation, but transversion is the most specific answer to this question.

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