1. Chargaff found that the amount of adenine present in DNA always equals the am
ID: 53700 • Letter: 1
Question
1.
Chargaff found that the amount of adenine present in DNA always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine. The Watson-Crick model, explains this because adenine will only properly hydrogen bond with thymine and guanine with cytosine.
True
False
2.
When deoxyribose molecules bind in DNA, a phosphodiester bond is formed.
True
False
3.
The 2-nanometer diameter is maintained because a small pyrimidine always pairs with a larger pyrimidine.
True
False
4.
The two strands of DNA found in a double helix are:
semidiscontinuous.
antiparallel.
identical.
topoisomers.
linked by a phosphodiester bond.
5.
What functional group is found at the 5 end of a DNA strand?
a phosphate group
a hydroxyl group
a carbonyl group
a deoxyribose sugar
a carboxyl group
6.
The nitrogenous bases are always attached to what carbon of the sugar in a nucleic acid?
5
4
3
2
1
7.
The free hydroxyl group is attached to what carbon of the sugar in nucleic acids?
5
4
3
2
1
8.
According to Chargaff's rules, if the DNA of a species contains 20% thymine, what percent of guanine will it contain?
80%
30%
60%
20%
40%
9.
Which is true of standard Watson-Crick base-pairing in a molecule of DNA?
Purines base pair with purines.
Pyrimidines base pair with pyrimidines.
Purines base pair with pyrimidines.
All bases can potentially base pair.
More than one of the above are correct.
10.
Which feature of the DNA helix contributes to its stability?
hydrogen bonding between bases
the presence of a 3-OH group
the presence of a 2-OH group
proportion of the nitrogenous bases
phosphodiester backbone
11.
Match the following
1. The proportion of adenine always equals thymine; the proportion of guanine always equals cytosine.
2. A two-ringed nitrogenous base, such as adenine or guanine.
3. Linkage of a phosphate group to two sugars by means of a pair of ester bonds allowing DNA to form long chains.
4. Each strand of a DNA molecule can be used to specify the other by base-pairing.
5. A white, slightly acidic material extracted from nuclei, discovered by Miescher, known as DNA or RNA today.
6. A single-ringed nitrogenous base, such as thymine or cytosine in DNA, or uracil or cytosine in RNA.
A. Chargaff's rules
B. phosphodiester bond
C. complimentary
D. pyrimidine
E. nucleic acid
F. purine
12.
A nucleotide is a subunit of DNA consisting of a five-carbon sugar, a PO4 group, a nitrogenous base.
True
False
Explanation / Answer
1. Answer is True
DNA is made up of nucleotides (purines and pyrimidines). Purines are Adenine (A) and Guanine (G), which form complementary base pair with pyrimidines (Cytosine and Thymine) always. Adenine (A) always pairs with T and G with C.
2. Answer is True
In DNA, the phosphodiester bond is formed by the linkage of 3’ carbon atom of one sugar molecule and the 5’ carbon atom of another molecule.
3.Answer is False
In order to maintain 2nm of diameter across the DNA, it is necessary that smaller pyrimidines bind with larger purines.
4. Answer is Antiparallel
The two strands of DNA run in opposite directions complementary to each other, thus antiparallel. Adenine binds Thymine with double hydrogen bond and Guanine binds triple hydrogen bond with Cytosine.
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