Biochemistry : Nucleic Acid Structures and Functions

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #18 : Dna And Rna

In eukaryotes, the TATA box and/or Hogness box found on DNA are __________.

Possible Answers:

primer sites

promoter sites

transcription stop sites

DNA replication origin sites

degradation sites

Correct answer:

promoter sites

Explanation:

The TATA box and/or the Hogness box are regions on DNA that function as promoter sites. RNA polymerase scans DNA for these regions and when it sees one, it recognizes that it should begin transcription of the following gene.

Example Question #31 : Nucleic Acid Structures

Which of the following statements about B DNA structure is incorrect?

Possible Answers:

It has a pitch of 10 base pairs per helical turn.

Its glycosidic bonds are in the syn conformation.

It is a right handed helix with a diameter of 20 A.

Its minor groove is narrow and deep.

Correct answer:

Its glycosidic bonds are in the syn conformation.

Explanation:

The glycosidic bonds of B DNA are in the anti conformation. This means that the nucleotide and sugar are on opposite sides of the N-glycosidic bond.

Example Question #32 : Nucleic Acid Structures

Which of the following is not a feature of both DNA and RNA?

Possible Answers:

Guanine can pair with cytosine.

Read from the 5' to 3' direction.

Uses a ribose sugar.

Uses adenine nitrogenous bases.

Correct answer:

Uses a ribose sugar.

Explanation:

DNA and RNA share many common characteristics, as they are both nucleic acids. One of the key differences is that DNA use a deoxyribose sugar while RNA uses a ribose sugar. It should be noted that while RNA is typically assumed to be single stranded, it can still exhibit complementary base pairing. As a result, the guanine and cytosine base pairing can still take place.

Example Question #33 : Nucleic Acid Structures

A histone is mutated so all lysine residues are changed to glutamate. What effect will this mutation have?

Possible Answers:

The histone will introduce more negative supercoils in the DNA.

The histone will be tagged with ubiquitin.

The histone will have a reduced binding affinity for DNA.

The histone will have an increased binding affinity for DNA.

Correct answer:

The histone will have a reduced binding affinity for DNA.

Explanation:

DNA is negatively charged because of the sugar-phosphate backbone. Histones are rich in lysine residues because they are positively charged and are ideal for DNA to wrap around. If the lysines became glutamates, the histone would overall have a negative charge, causing the DNA to bind weakly to each histone. The function of introducing negative supercoils would be reduced, and ubiquitination would not be affected.

Example Question #34 : Nucleic Acid Structures

Primase is needed for which of the following?

Possible Answers:

Suppling a DNA primer with a free 3' end

Reliving supercoiling stress on DNA

Supplying a DNA primer with a free 5' end

Suppling and RNA primer with a free 3' end

Supplying an RNA primer with a free 5' end

Correct answer:

Suppling and RNA primer with a free 3' end

Explanation:

Primase is an enzyme used in the replication of DNA. DNA polymerase synthesizes DNA in a 5' to 3' direction, so it needs a free 3' end to begin its replication from. The primase constructs an RNA substrate with a free 3' end, that binds complementary to the unwound and single-stranded DNA template that is about to be replicated. 

Example Question #35 : Nucleic Acid Structures

Starting with the first start codon, what is the third codon in the following mRNA sequence?

5'AAUGUUAGCGUGCGCUA3'

Possible Answers:

UAC

CGC

GCG

CUA

AUG

Correct answer:

GCG

Explanation:

A codon is a set of three nucleic acids on the messenger RNA that codes for an amino acid. The start codon is AUG. In this strand, AUG is the first codon, the second is UUA, and the third is GCG.

Example Question #36 : Nucleic Acid Structures

During bacterial DNA replication, what is required for sealing the Okazaki fragments of DNA together after the RNA primers have been replaced with DNA?

Possible Answers:

Primase and free nucleic acids

DNA ligase and ATP

DNA polymerase 1

DNA polymerase 3

DNA ligase and AMP

Correct answer:

DNA ligase and ATP

Explanation:

After DNA Polymerase 1 replaces the RNA primers with DNA. DNA ligase then comes along and uses an ATP for energy as it connects the 3' and 5' ends of the DNA gap, completing the replication of the template strand. 

Example Question #37 : Nucleic Acid Structures

Which of the following statements is true about the B and Z forms of the DNA helix?

I. Z-DNA is a left-handed helix; B-DNA is a right-handed helix.

II. Z-DNA has 12 base pairs per turn of the helix; B-DNA has 10 base pairs per turn of helix.

III. B-DNA is present in chromosomal DNA.

IV. Z-DNA can occur in sequences with many guanine (G), cytosine(C) residues (polyGC sequence).

Possible Answers:

I and IV

II and III

I and II

III and IV

I, II, III, and IV

Correct answer:

I, II, III, and IV

Explanation:

There are 3 conformations of the DNA molecule. The B form is in chromosomal DNA, the A form is representative of DNA-RNA hybrids. The Z form of DNA appears in poly GC (poly guanine, cytosine) sequences.

Example Question #38 : Nucleic Acid Structures

How are base pairs positioned and what is the number of base pairs per complete helical turn in the B form of DNA helix (predicted by Watson and Crick)? 

Possible Answers:

Base pairs are towards the inside of the helix; there are 10 base pairs per complete turn of the helix.

Base pairs are towards the outside of the helix; there are 8 base pairs per complete turn of the helix.

Base pairs are towards the outside of helix; there are 6 base pairs per complete turn of the helix.

Base pairs are towards the inside of the helix; there are 8 base pairs per complete turn of the helix.

None of these

Correct answer:

Base pairs are towards the inside of the helix; there are 10 base pairs per complete turn of the helix.

Explanation:

The deoxyribose–phosphate backbone of DNA is on the outside (hydrophylic) of the helix while the hydrophobic bases are inside. The classical B form, found in chromosomal DNA, and predicted by Watson and Crick, is a right-handed helix with 10 bases per turn of helix. The number of bases is different in Z and A DNA helix conformations.

Example Question #152 : Biochemistry

What is the name of a deoxynucleotide in which the base is thymine?

I. Deoxythymidine monophosphate

II. Deoxythymidine diphosphate 

III. Deoxythymine monophosphate

IV. Deoxythymine diphosphate 

Possible Answers:

I, II, III, and IV

I, II, and III

I and II

III and IV

II, III, and IV

Correct answer:

I and II

Explanation:

Phosphate groups attach to the 5' carbon of the nucleosides forming nucleotides. Phosphodiester bonds of DNA form between the 3'-hydroxyl group of the deoxy pentose of one nucleotide and the 5'-hydroxyl group of the deoxy pentose of another nucleotide.Deoxythymidine is the deoxynucleotide with thymine as its base. It can be mono-, di, or tri- phosphorylated as deoxythymidine mono-, di- or triphosphate.

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