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Question 1
In DNA, which base pairs with Guanine?
Correct Answer:
Cytosine
Explanation:
Base pairing in DNA is based on complementary geometry and hydrogen bonding. Guanine pairs with Cytosine because they form three hydrogen bonds and fit together as a purine-pyrimidine pair, helping maintain the consistent width of the double helix. This differs from Adenine, which pairs with Thymine through two hydrogen bonds, and Uracil, which pairs with Adenine in RNA. So, Guanine's partner in DNA is Cytosine.
Question 2
Compared to covalent bonds in the DNA backbone, how do hydrogen bonds between base pairs compare in strength?
Correct Answer:
They are weaker than covalent bonds.
Explanation:
The main concept is that bond strength depends on bond type: covalent bonds form the DNA backbone and are very strong, while hydrogen bonds between base pairs are non-covalent attractions and are much weaker. Each base pair is held together by several hydrogen bonds—two for A–T and three for G–C—but even collectively these are far weaker than the covalent phosphodiester bonds that make up the sugar–phosphate backbone. This weaker, reversible nature of hydrogen bonds explains why the two strands can be separated during replication and transcription, while the backbone remains intact. So, hydrogen bonds between base pairs are weaker than the covalent bonds in the DNA backbone.
Question 3
Which molecules make up the sides of the DNA ladder?
Correct Answer:
Ribose, Phosphate
Explanation:
DNA’s ladder sides are the sugar–phosphate backbone. In DNA, the sugar is deoxyribose, a five‑carbon sugar missing an oxygen at the 2′ position, and each sugar is connected to a phosphate group. These alternating deoxyrose and phosphate units form the phosphodiester backbone that runs along the length of the molecule, providing the structural rails for the double helix while the bases pair and form the rungs in the middle. So the sides are made from deoxyribose and phosphate. Ribose would be in RNA, not DNA, which is why it doesn’t fit DNA’s backbone.
Question 4
What type of bond is found between all components of the DNA molecule except the nitrogen bases?
Correct Answer:
Covalent bonds
Explanation:
DNA’s structure is built from nucleotides joined into long polymers. The sugar–phosphate backbone is connected by covalent phosphodiester bonds, which form a strong, continuous chain along each strand. Between the two strands, the nitrogenous bases pair via hydrogen bonds, which are weaker and sit between strands rather than forming the backbone. While the sugar–base linkage (glycosidic bond) is also covalent, the phrase “except the nitrogen bases” focuses on the backbone connections, which are covalent. Ionic bonds aren’t the main stabilizing links in DNA, and peptide bonds occur in proteins, not DNA. So the bonds that connect the components of the DNA molecule, aside from the bases, are covalent.
Question 5
Which base is present in RNA but not in DNA?
Correct Answer:
Uracil
Explanation:
Uracil is the base found in RNA but not in DNA. In RNA, uracil pairs with adenine, taking the place of thymine, which is the base used in DNA to pair with adenine. The other bases—adenine, cytosine, and guanine—are present in both RNA and DNA. Using thymine in DNA helps protect the genetic material from certain types of mutations that can arise if uracil were present.
Question 1
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About this Exam

Prepare with the Genetics and Molecular Biology Practice Exam practice quiz. This question bank includes 10 questions covering base, pairs, bonds, components, and transcription. Use it to review important concepts, identify knowledge gaps, and build confidence for the related exam, course, or assessment.

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Genetics and Molecular Biology Practice Exam

This practice set contains 10 questions from the matching question bank and focuses on base, pairs, bonds, components, and transcription. Work through each question carefully, review the provided solutions, and revisit topics that need more study before your next attempt.

This is an independent study resource intended for practice and review; it is not an official examination or an endorsement by any organization named in the title.

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