High School Biology : DNA

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #1 : Understanding Nucleotides

 Which of these molecules could not be found in a nucleotide?

Possible Answers:

Arginine

Phosphate group

Pentose sugar

Thymine

Correct answer:

Arginine

Explanation:

A nucleotide is the building block of nucleic acids (a type of macromolecule). It is made up of three main parts: phosphate group(s), pentose sugar, and a nitrogenous base (adenine, thymine, guanine, cytosine, or uracil). The amount of phosphate groups, the type of pentose sugar, and the type of nitrogenous base varies based on the nucleotide. For example, RNA contains ribose sugar whereas DNA contains deoxyribose sugar.

Arginine is a type of amino acid. Recall that amino acids are found in polypeptide chains that make up proteins (another type of macromolecule); therefore, arginine is found in proteins rather than nucleic acids.

Example Question #51 : Dna

Which of the following is true regarding a nucleotide and a nucleoside?

Possible Answers:

A nucleotide contains at least one more nitrogenous base than a nucleoside

A nucleoside contains at least one more nitrogenous base than a nucleotide

A nucleoside contains at least one more phosphate group than a nucleotide

A nucleotide contains at least one more phosphate group than a nucleoside

Correct answer:

A nucleotide contains at least one more phosphate group than a nucleoside

Explanation:

The main difference between a nucleotide and a nucleoside is the presence or absence of phosphate group(s). A nucleotide contains one or more phosphate groups, a pentose sugar, and a nitrogenous base. A nucleoside, on the other hand, contains only a pentose sugar and a nitrogenous base; therefore, a nucleotide always contains more phosphate groups than a nucleoside.

Example Question #1 : Understanding Nucleotides

Which of the following does not contain a nucleotide or nucleotide derivative?

I. NADH

II. cAMP

III. Acetylcholine

Possible Answers:

I, II, and III

III only

II and III

II only

Correct answer:

III only

Explanation:

NADH is a coenzyme that functions to carry electrons during metabolism. It is made up of adenine (a nitrogenous base), nicotinamide (a modified nitrogenous base), two phosphate groups, and two pentose sugars. Since it contains nitrogenous bases, phosphate groups, and pentose sugars it is a type of nucleotide.

cAMP, or cyclic adenosine monophosphate, is a second messenger molecule that facilitates signal transduction inside the cell. It is made up of adenine, a phosphate group, and a pentose sugar (ribose); therefore, it is also a type of nucleotide.

Acetylcholine is a type of neurotransmitter that plays a key role in signal transmission between neurons. Acetylcholine does not contain the three essential groups for a nucleotide; therefore, acetylcholine is not a nucleotide.

Example Question #2 : Understanding Nucleotides

A nucleotide molecule contains more __________ than the DNA backbone.

Possible Answers:

pentose sugars

nitrogenous bases

phosphate groups

hexose sugars

Correct answer:

nitrogenous bases

Explanation:

To answer this question you need to know the difference between a nucleotide and a DNA backbone. A nucleotide is the monomer of nucleic acids and is made up of phosphate group(s), a pentose sugar, and a nitrogenous base. A DNA molecule is a type of nucleic acid and is made up of several nucleotides.

DNA has two different structural divisions: the DNA backbone and the nitrogenous bases. The DNA backbone consists of the phosphate groups and pentose sugars, whereas the bases consist of only the nitrogenous bases. This means that the DNA backbone does not contain any nitrogenous bases; therefore, nucleotide contains more nitrogenous bases than the DNA backbone.

Since the full DNA molecules has several nucleotides, the DNA backbone contains multiple phosphate groups and pentose sugars; therefore, the DNA backbone always contains more phosphate groups and pentose sugars than a nucleotide molecule.

Example Question #1 : Understanding Nucleotides

Nucleotides in DNA consist of a sugar (deoxyribose), a phosphate group, and one of four nitrogenous bases. Which of the following is not a nitrogenous base found in DNA?

Possible Answers:

Adenine

Thymine

Cytosine

Uracil

Correct answer:

Uracil

Explanation:

The four nitrogenous bases found in DNA are: thymine, cytosine, adenine, and guanine. Uracil is a nitrogenous base that takes the place of thymine in RNA. Note that uracil only base pairs with adenine, forming two hydrogen bonds.

Example Question #3 : Understanding Nucleotides

Guanine, the DNA nitrogen base, binds with which of the following?

Possible Answers:

Thymine

Guanine

Uracil

Adenine 

Cytosine

Correct answer:

Cytosine

Explanation:

DNA contains four nitrogen bases: adenine, thiamine, guanine and cytosine. Adenine and thymine pair, and guanine and cytosine pair. Adenine and thiamine form two hydrogen bonds, and guanine and cytosine form three hydrogen bonds. In RNA, uracil takes thiamine's and binds with adenine.

Example Question #391 : High School Biology

When separating strands of DNA, little ‘bubbles’ will often form due to certain portions of the molecule separating before others. Which portion of DNA will separate first under high heat?

Possible Answers:

Portions with a low ratio of adenine-thymine bonds

Portions with a high ratio of adenine-uracil bonds

Portions with a high ratio of guanine-cytosine bonds

Portions with a high ratio of adenine-thymine bonds

Correct answer:

Portions with a high ratio of adenine-thymine bonds

Explanation:

Bonds between A-T (adenine and thymine) are held together by 2 hydrogen bonds, while G-C (guanine and cytosine) are held together by 3 hydrogen bonds. Therefore, A-T bonds are weaker, and will separate first when exposed to heat stress. DNA does not contain uracil.

Example Question #51 : Dna

In regard to DNA, which nucleotide only binds to guanine?

Possible Answers:

Adenine

Thymine

Uracil

Cytosine

Correct answer:

Cytosine

Explanation:

Guanine always binds to cytosine in DNA and RNA. Thymine always bonds to adenine in DNA. Uracil replaces thymine in RNA, and uracil bonds to adenine.

Example Question #59 : Dna, Rna, And Proteins

Which of the following sets of nitrogenous bases are classified as purines? 

Possible Answers:

Adenine and cytosine

Thymine and guanine

Cytosine and thymine

Adenine and guanine

Correct answer:

Adenine and guanine

Explanation:

Adenine and guanine are the purines that bond to the pyrimidines. Cytosine and thymine are the pyrimidines. The purines consist of two carbon rings, and the pyrimidines consist of one carbon ring.

Example Question #401 : High School Biology

Which of the following is not a nucleotide found in DNA?

Possible Answers:

Guanine

Uracil 

Cytosine

Adenine

Correct answer:

Uracil 

Explanation:

DNA is the hereditary material found in virtually all organisms; however, some viruses use RNA. DNA consists of several components. It has a phosphate-sugar (deoxyribose) backbone and is composed of two strands made from purine-pyrimidine hydrogen bonds in a double helix confirmation. The purines associated with DNA include adenine and guanine and the pyrimidines include cytosine and thymine. Adenine bonds with thymine and cytosine bonds with guanine. 

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