Question 1Easy
The nitrogenous base that pairs with adenine (A) is:
- Acytosine
- Badenine
- Cguanine
- Dthymine
Show answer and explanation
Correct answer: (D) thymine
Explanation: Adenine always pairs with thymine (A with T) by two hydrogen bonds.
Chapter 5 — DNA and Genetic Information · Biology. These are 10 questions from the Magmo3 bank on this lesson, from easy to hard. Solve each one, then open "Show answer and explanation". Magmo3 has 38 questions on this lesson, each with an explanation.
The nitrogenous base that pairs with adenine (A) is:
Correct answer: (D) thymine
Explanation: Adenine always pairs with thymine (A with T) by two hydrogen bonds.
The number of hydrogen bonds between adenine and thymine is:
Correct answer: (C) two bonds
Explanation: A and T have two hydrogen bonds between them, while G and C have three.
The nitrogenous bases classified as purines (two rings) are:
Correct answer: (D) adenine and guanine
Explanation: The purines (two rings) are adenine and guanine; the pyrimidines (one ring) are cytosine and thymine.
The nitrogenous bases always pair such that a purine goes with a:
Correct answer: (B) pyrimidine
Explanation: A purine (two rings) pairs with a pyrimidine (one ring) so that the width of the helix stays constant.
The backbone (framework) of the DNA molecule is composed of:
Correct answer: (A) alternating sugar and phosphate
Explanation: The two sides of the ladder are made of alternating sugar and phosphate, while the nitrogenous bases lie in the middle.
In a nucleotide, the nitrogenous base attaches to:
Correct answer: (D) the pentose sugar
Explanation: The nitrogenous base bonds to the pentose sugar, and the sugar bonds to the phosphate.
In the twisted-ladder analogy of DNA, the rungs of the ladder represent:
Correct answer: (A) the paired nitrogenous bases
Explanation: The rungs = the pairs of complementary nitrogenous bases, and the sides = the sugar and phosphate.
Which ratio is expected to differ between the double-stranded DNA of a human and that of a wheat plant?
Correct answer: (D) (A + T) / (G + C)
Explanation: In any double-stranded DNA, A = T and G = C, so A/T and purines/pyrimidines are always 1. The proportion of A–T pairs to G–C pairs depends on the base sequence, so it differs between species.
How many free 5' phosphate ends are there in the DNA of one human chromosome before replication, and in the main DNA molecule of the bacterium E. coli?
Correct answer: (C) 2 and 0
Explanation: A chromosome contains a single linear double helix, and each of its two strands has one free 5' phosphate end (lying at opposite ends of the molecule, since the strands are antiparallel), giving 2. The main DNA of a prokaryote such as E. coli is a double helix whose ends are joined to form a circle, so it has no free ends.
Which base pair gives greater stability to the DNA molecule?
Correct answer: (D) G with C because there are three hydrogen bonds between them
Explanation: G and C have three hydrogen bonds between them, stronger and more stable than the two bonds of A with T.
The first 10 questions in every subject are free, each with an explanation.