Biochemistry : Macromolecule Structures and Functions

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #12 : Nucleic Acid Structures And Functions

Which of the following statements about RNA is false?

Possible Answers:

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

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

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

RNA forms intramolecular double helices

None of the other answers is false

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 #1 : Dna And Rna

Which of the following statements about B DNA are incorrect?

Possible Answers:

All of these are correct

B DNA is right handed with 10 base pairs per turn

B DNA is the most commonly found double helical structure

B DNA has a diameter of 

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

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 #2 : Dna And Rna

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 #2 : Dna And Rna

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-2 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-1 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 #3 : Dna And Rna

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

Possible Answers:

start codon

initiator

operator

poly-A tail

promoter region

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 #4 : Dna And Rna

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

More than one of these are incorrect

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

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

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

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 #2 : Dna And Rna

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

Possible Answers:

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

DNA has a  as opposed to a  on carbon two

RNA contains sulfur and DNA contains phosphate

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

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 #131 : Biochemistry

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

Possible Answers:

DNA polymerase III

DNA polymerase I

DNA ligase

Primase

Helicase

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 #1 : Dna And Rna

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

Possible Answers:

Primase fragments

DNA polymerase I

DNA polymerase III

Okazaki fragments

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. 

Example Question #21 : Nucleic Acid Structures

Meselson and Stahl described DNA replication as __________.

Possible Answers:

dependent

independent

conservative

dispersive

semiconservative

Correct answer:

semiconservative

Explanation:

The semiconservative model of DNA replication describes the daughter strand containing one new and one old strand. Dispersive and conservative models were both rejected from their experiment. Independet and dependent do not pertain to any of the scientist's theories of replication.

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