Practice Exam On Biochemistry: Quiz!

In E. coli, the replication fork copies DNA continuously and segmented in a 360^o direction. 

• True

• False

Stacked base pairs absorb less light in native DNA.

• True

• False

In E.coli, only one replication fork is needed to replicate a new DNA strand. 

• True

• False

The component(s) of DNA which is responsible for the absorbance band at 250-270 nm is:

• Bases, pentoses, and phosphates all contribute

• Only bases

• Only bases and pentoses

• Only pentoses and phosphates

The oligonucleotide, AUGGp, has all these properties except:

• Composed of ribonucleotides

• Contains a 3' phosphate

• Composed of deoxyribonucleotides

• Contains three phosphodiester bonds

Eukaryotic DNA can contain more than 2 replication forks. 

• True

• False

The rate of DNA renaturation is an index of its homology. 

• True

• False

The separation of a double-stranded DNA will form two template strands. 

• True

• False

RNA can form an unstable hybrid structure with DNA. 

• True

• False

The Klenow fragment of E. coli DNA polymerase I can be used to add nucleotides to a DNA with staggered ends if the ends

• Are recessed with 5'-phosphates

• Are recessed with 3'-OHs

• Are extended with 5'-phosphates

• Are extended with 3'-OHs

Due to nitrogenous bases, UV abs. of DNA increases when heated above body temperature. 

• True

• False

DNA is unwound by gyrase without breaking it. 

• True

• False

 The shorter the primer, the more specific the DNA. 

• True

• False

 Z-DNA can be stable in A:T-rich regions allowing its transition from B-DNA form. 

• True

• False

DNA replication mainly occurs in a conservative manner. 

• True

• False

Template strands are only copied continuously. 

• True

• False

Which of the following is not a characteristic for DNA synthesis?

• DNA polymerase adds nucleotides in a 5'--> 3' direction

• A primer strand of DNA must contain a free 3'-OH end

• The primer strand of DNA determines which nucleotides are added next

• The correct complementary hydrogen bonding between base pairs is the primary check on the fidelity of the newly synthesized DNA

The linking number of a highly supercoiled plasmid can be readily changed without producing a relaxed DNA by

• Changing the temperature

• Increasing salt concentration

• The action of topoisomerase

• The action of a nuclease such as pancreatic DNase

Replication occurs mainly during the G2 and G1 phases where cell growth occurs. 

• True

• False

The polymerase which plays a similar role as that of Prokaryotic polII in eukaryotic replication is?

• DNA polymerase alpha

• DNA polymerase delta

• DNA polymerase gamma

• DNA polymerase kappa

Which is not a property of E. coli DNA polymerase III?

• It is responsible for incorporating most of the nucleotides in the lagging strand.

• It synthesizes most of the leading strand prior to aiding in the synthesis of the lagging strand.

• It contains a 3¨ to 5¨ exonuclease activity.

• It synthesizes the leading strand and the lagging strand at the same time

Bidirectional replication starts at the_______________, moving replication forks in opposite direction.

Which E. coli enzyme has the greatest frequency of incorporating the incorrect nucleotide into its nucleic acid polymer?

• RNA polymerase

• DNA polymerase I

• DNA polymerase III

• Klenow fragment from DNA polymerase I

An individual heterogeneous nuclear RNA (hnRNA)

• Contains intron sequences not found in the final mature mRNA.

• Contains exon sequences which are removed prior to translation.

• Encodes more than one protein.

• Can be found in the cytoplasm.

What statement is incorrect about the different RNA molecules?

• TRNAs contain numerous intramolecular hydrogen bonds between bases.

• There are more distinct tRNA molecules than there are rRNA molecules.

• RRNAs are complexed to proteins in the ribosome.

• The most abundant RNA molecule in the cell is mRNA.

E. coli replication on the lagging strand

• Is primarily carried out by DNA polymerase I

• Is synthesized continuously

• This DNA strand is synthesized in a 3'-5'direction of synthesis

• Is initially synthesized as Okazaki fragments

Which of the following double-stranded DNAs may convert to a cruciform structure?

• ATGCATGCATGCATGC / TACGTACGTACGTACG

• CATTAAGCAGTGCTTAAGA / GTAATTCGTCACGAATTCT

• ATATATATGCGCGCGCGC / TATATATACGCGCGCGCG

• AAAAAAAAACCCCCCCCC / TTTTTTTTTGGGGGGGG

Which statement is incorrect about the structure of native E. coli chromosomal DNA?

• The DNA is primarily in the B-helix.

• The DNA is circular and supercoiled

• The DNA exists as a right-handed double helix.

• The DNA is one large linear piece about 4000 kb in length.

____________is a topoisomerase II that introduces ______________ supercoiling and promote  ________________. (answer, answer, answer)

A _______________ region is the same DNA sequence read either 5’ to 3’ or viceversa. 

When supercoiled, the _____________number increases when there are more twists.

Part 2. Determine W, T and L respectively if DNA gyrase puts 4 negative supercoils into the 200-bp circular DNA. If relaxed, what would the value of L be?

A_______________ is bound to Ter locus to prevent helicase activity.

High_______________means a high number of successive cycles of nucleotide addition.

A primer needed for replication is formed by a_________________.

The process in which an RNA template is transcribed to cDNA is executed by _______________.

Reverse transcriptase

• Can be a telomerase that uses its own RNA as template.

• Is contained in all RNA tumor viruses.

• Allows the transcription of cDNA from an RNA template to form a DNA:RNA hybrid.

• Can be inhibited by HIV therapy.

• All of the above

Which one of the following characteristics is not associated with E. coli primase?  

• It synthesizes the RNA primer in DNA replication.

• It is a specific RNA polymerase.

• It is essential for DNA replication.

• It is also a gyrase

DNA-dependent RNA polymerase acts on the DNA template in eukaryotic cells in the synthesis of

• A 5'-3' hnRNA transcript as the RNA polymerase moves in the 3'-5' direction on the DNA template

• A mature RNA transcript as the RNA polymerase moves in the 5'-3' direction

• An RNA transcript, with the sigma subunit of polymerase dissociating after the initiation event

• An RNA transcript, which is complementary to the sense strand of the DNA, except for the replacement of uridines for the thymidines

The RNA molecules which are involved in processing the hnRNA are:

• MRNA

• TRNA

• RRNA

• SnRNA

A DNA is found to exhibit a melting temperature of 75 C in 0.1 M NaCl. Under what experimental conditions would the Tm be increased?

• Decreasing the concentration of DNA.

• Increasing the concentration of NaCl in the solution.

• Adding 1% urea (an organic denaturant).

• All of the above.

A feature which is distinctive to Z-DNA is

• A left-handed helix

• It has 12 bases per turn

• It is found in vivo

• All of the above

E. coli DNA polymerase I has all the following characteristics except

• A 5'-3' exonuclease activity on a second subunit in the polymerase

• A 3'-5' exonuclease activity

• A 5'-3' DNA polymerase activity

• Modest processivity (ca. 20 nucleotides)

In the repair of DNA, the E. coli DNA polymerase involved performs which function in addition to its polymerase activity?

• It recognizes the abnormality in the duplex DNA structure.

• It nicks the DNA to provide a 3'-OH.

• It removes the damaged section of DNA with its 5'-3' exonuclease activity.

• It ligates the DNA after the repair synthesis.

Which of the following is not a characteristic of replication of the E. coli circular chromosome?

• Replication is bidirectional.

• It initiates at a unique position called oriC.

• Torsional stress introduced in the duplex DNA is relieved by DNA gyrase.

• The unwinding of the duplex DNA is driven by the translocation of the DNA polymerase.

Which statement is incorrect about E. coli DNA polymerase I?

• The cell contains more molecules of DNA pol I than DNA pol III.

• DNA pol I is a single polypeptide with three domains.

• DNA pol I is involved in the repair of UV damaged DNA.

• DNA pol I has a larger turnover number than DNA pol III.

________studies the way genes express, determining the differences between vertebrates. 

In a duplex circular DNA, the _____________ state has around ____________ per turn. (answer, answer)