Biochemistry : DNA and RNA

Study concepts, example questions & explanations for Biochemistry

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Example Questions

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Example Question #11 : Nucleic Acid Structures And Functions

Which molecule contains an anticodon region?

Possible Answers:

DNA

rRNA

mRNA

htRNA

tRNA

Correct answer:

tRNA

Explanation:

tRNA carries the anticodon. tRNA is a transfer ribonucleic acid; it is a type of RNA molecule that decodes the mRNA sequence to form a protein. The anticodon is the part of the tRNA structure that complements the mRNA codon, dictating the identity of the amino acid carried by the tRNA and required to build the proper polypeptide chain.

Example Question #12 : Nucleic Acid Structures And Functions

Which of the following statements about RNA is false?

Possible Answers:

Hairpin turn structures are composed of two RNA molecules in a parallel configuration

None of the other answers is false

mRNA has a half-life shorter than the cell division cycle

A hydroxyl group on the 2’ of riboses makes RNA phosphodiester bonds fragile

RNA forms intramolecular double helices

Correct answer:

Hairpin turn structures are composed of two RNA molecules in a parallel configuration

Explanation:

The presence of an  group on the 2’ carbon if ribose does indeed make any phosphodiester bonds at this site subject to hydrolysis. RNA can sometimes form double-helices, such as in tRNA. mRNA is constantly being degraded in the cytoplasm, and so it has a very short half-life relative to the life of the cell. RNA’s hairpin turn structures are composed of only one molecule which has doubled back on itself, rather than two separate molecules.

Example Question #11 : Nucleic Acid Structures

Which of the following statements about B DNA are incorrect?

Possible Answers:

B DNA is right handed with 10 base pairs per turn

B DNA has a wide and deep major groove and a narrow and shallow minor groove

B DNA is the most commonly found double helical structure

B DNA has a diameter of 

All of these are correct

Correct answer:

B DNA has a wide and deep major groove and a narrow and shallow minor groove

Explanation:

B DNA has a wide and deep major groove and a narrow and deep minor groove. All other statements regarding B DNA are true.

Example Question #14 : Nucleic Acid Structures And Functions

1. chromosome

2. solenoid

3. nucleosome

4. radial loop

5. base pair

6. nucleotide

Place the above structures in order from smallest to largest.

Possible Answers:

Correct answer:

Explanation:

The correct order is base pair, nucleotide, nucleosome ("bead on a string"), solenoid, radial loop, chromosome. A solenoid is created by the packing of DNA with multiple nucleosomes, and a radial loop is compacted even further in chromatin.

Example Question #15 : Nucleic Acid Structures And Functions

Two strands of DNA were isolated from a solution, named DNA-1 and DNA-2. DNA-2 was found to have a higher melting point (temperature at which the two strands break apart). What can we conclude about the two strands' nucleotide composition? 

Possible Answers:

DNA-1 has a higher guanine and cytosine concentration

DNA-2 has a higher adenine and thymine concentration

DNA-1 has a higher adenine and thymine concentration

DNA-2 has a higher guanine and cytosine concentration

Correct answer:

DNA-2 has a higher guanine and cytosine concentration

Explanation:

Recall that guanine and cytosine form three hydrogen bonds to one another in DNA, while adenine and thymine only form two hydrogen bonds to one another. This means that DNA strands with higher concentrations of guanine and cytosine will be more stable, and thus require greater energy to break apart. In this case, since DNA-2 required more energy (higher temperature) to denature, it has a higher concentration of guanine and cytosine. 

Example Question #15 : Nucleic Acid Structures

Transcription is initiated when RNA polymerase binds to the DNA at the __________. (In humans, this is known as the TATA box). 

Possible Answers:

operator

poly-A tail

promoter region

initiator

start codon

Correct answer:

promoter region

Explanation:

The promoter region is a short segment of DNA that is recognized and bound to by RNA polymerase prior to transcription. The promoter region is usually upstream of the operator and will not be transcribed into mRNA. 

Example Question #16 : Nucleic Acid Structures And Functions

Which of the following statements concerning DNA packing is incorrect?

Possible Answers:

A nucleosome is a histone with DNA coiled around it, allowing for extremely efficient DNA packing

Nucleosomes appear as "beads on a string" when viewed under a microscope

Joining two units of H2A, H2B, H3, and H4 all together forms a histone octamer

More than one of these are incorrect

Histones are rich in the amino acids Asp and Glu, giving them a net negative charge

Correct answer:

Histones are rich in the amino acids Asp and Glu, giving them a net negative charge

Explanation:

Histones are rich in the amino acids Asp Lys and Glu Arg, giving an overall net negative positive charge. (Because DNA is negatively charged, this allows for tighter binding between the histones and coiled DNA).

Example Question #17 : Nucleic Acid Structures And Functions

Which of the following is a difference between DNA and RNA?

Possible Answers:

DNA is only found in prokaryotes and RNA is found in eukaryotes

DNA has a  as opposed to a  on carbon two

RNA contains sulfur and DNA contains phosphate

The sugar of DNA is glucose and the sugar of RNA is fructose

Correct answer:

DNA has a  as opposed to a  on carbon two

Explanation:

DNA's sugar is deoxyribose, which involves the lack of a hydroxyl group on the second cabon. RNA's sugar is ribose. DNA and RNA is found in both prokaryotes and eukaryotes and both contain phosphate and neither contain sulfur.

Example Question #16 : Nucleic Acid Structures

What enzyme involved DNA replication has a 3'-5' proofreading exonuclease activity to help ensure fidelity in replication of DNA?

Possible Answers:

DNA ligase

Primase

DNA polymerase III

Helicase

DNA polymerase I

Correct answer:

DNA polymerase III

Explanation:

DNA polymerase III is the only DNA replication enzyme with proofreading (3'-5' exonuclease) capabilities. Ligase links Okazaki fragments. Helicase unwinds the two DNA strands. DNA polymerase I contains 5'-3' exonuclease activity, but this is involved in primer removal, not proofreading. Primase is a type of RNA polymerase.

Example Question #21 : Nucleic Acid Structures And Functions

The primosome remains that are associated with the lagging strand in DNA replication are known as which of the following?

Possible Answers:

Okazaki fragments

DNA polymerase III

Primase fragments

DNA polymerase I

DNA ligase

Correct answer:

Okazaki fragments

Explanation:

Okazaki fragments are found in the lagging strand, and are linked by DNA ligase. These short fragments of DNA are formed because DNA polymerase III (the main polymerizing enzyme complex) can only add nucleotides the the 3' end of a DNA strand. Since DNA strands are antiparallel, this is unavoidable. 

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