High School Biology : Understanding Nucleotides

Study concepts, example questions & explanations for High School Biology

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Example Questions

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Example Question #1 : Understanding Nucleotides

DNA polymerase is used to crate a new DNA strand based on the following template strand.

5'-GCCTCATGA-3'

Which of the following shows the correct complementary strand?

Possible Answers:

5'-TCATGAGGC-3'

5'-AGTACTCCG-3'

5'-CGGAGTACT-3'

5'-UCAUGAGGC-3'

Correct answer:

5'-TCATGAGGC-3'

Explanation:

When determining the complementary strand, remember that it will be written in the opposite direction of the template strand. This means that the new strand's 5' end will begin at the 3' end of the template strand. The complementary strand will also be composed of the nucleotides that complete the base pairs found in DNA (A-T and C-G).

Template: 5'-GCCTCATGA-3'

Answer:     5'-TCATGAGGC-3'

To see these pairs match up, the 3' end of the answer must align with the 5' end of the template.

Template:       5'-GCCTCATGA-3'

Answer (3'-5'): 3'-CGGAGTACT-5'

Example Question #2 : Understanding Nucleotides

Which of the following bases are purines?

Possible Answers:

Adenine and guanine

Cytosine, thymine, and uracil

Adenine, thymine, and uracil

Guanine and cytosine

Adenine and thymine

Correct answer:

Adenine and guanine

Explanation:

There are two classes of bases in DNA and RNA: purines and pyrimidines. The difference between these classes is the structure of the base. Purines have two rings in their structure, while pyrimidines have only one. Purines will pair with pyrimidines.

The purines are adenine and guanine, and the pyrimidines are thymine, cytosine, and uracil. You can remember that the bases that contain a "y" are pyrimidines (thymine and cytosine).

Example Question #3 : Understanding Nucleotides

What is a common feature of all the nucleotides in DNA?

Possible Answers:

Each of the nucleotides can bind to any of the other ones

They are bound to a sugar backbone

They are the same nucleotides used in RNA

They are all used in equal amounts in a strand of DNA

They contain the same atoms in different structures

Correct answer:

They are bound to a sugar backbone

Explanation:

There are four nitrogenous bases in DNA: adenine, guanine, cytosine, and thymine. A nucleotide is composed of one of these bases bound to a deoxyribose sugar and a phosphate group. Polymers of nucleotides form strands of DNA, which adhere to one another by hydrogen bonding between the bases.

Each strand of DNA is unique and may contain any ratio of the nitrogenous bases, but strands of DNA will always be complementary to one another. The structure of the bases requires that adenine bind to thymine and cytosine bind to guanine to maintain the structural integrity of the DNA molecule. RNA does not contain thymine, and instead uses uracil.

Example Question #4 : Understanding Nucleotides

The DNA of a eukaryotic cell is found to contain 30% cytosine. The DNA also contains __________.

Possible Answers:

20% guanine

30% thymine

30% adenine

20% adenine

Correct answer:

20% adenine

Explanation:

There are four bases in DNA: adenine, thymine, guanine, and cytosine. Adenine always pairs with thymine, so the number of adenine residues always equals the number of thymine residues. Guanine always pairs with cytosine, which means they are always present in equal amounts as well. If one strand contains three cytosine bases and five thymine bases, then the opposite strand must contain three guanine bases and five adenine bases.

The trick to this problem is remembering that the sum of all four bases by percentage must be 100%.

We know that 30% of the bases are cytosine. Since cytosine pairs with guanine, there is also 30% guanine.

That leave us with 40% of the bases being thymine and adenine.

Since adenine and thymine will be equal, each will represent 20% of the DNA composition.

Example Question #5 : Understanding Nucleotides

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

Possible Answers:

Thymine

Arginine

Pentose sugar

Phosphate group

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 #6 : Understanding Nucleotides

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 nucleotide contains at least one more phosphate group than a nucleoside

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

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

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 #7 : Understanding Nucleotides

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

I. NADH

II. cAMP

III. Acetylcholine

Possible Answers:

II only

III only

II and III

I, II, and III

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 #395 : High School Biology

A nucleotide molecule contains more __________ than the DNA backbone.

Possible Answers:

phosphate groups

nitrogenous bases

hexose sugars

pentose 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 #8 : 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:

Cytosine

Thymine

Uracil

Adenine

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 #9 : Understanding Nucleotides

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

Possible Answers:

Adenine 

Uracil

Guanine

Cytosine

Thymine

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.

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