Bio Sci 99 quizzes

Which of the following is not a component of a ribonucleotide?

Thymine

One step of the Hershey/Chase experiment involved blending the virus/cell mixtrue before centrifugation and probing the pellet for radioactivity. Why was the blending step necessary?

To separate the bacteria from the bacteriophages.

The human genome is mostly composed of: (270)

Transposons and retrotransposons that are mostly inactive.

T/F: For each strand of the DNA double helix: One end has a free phosphate (5' end) and one a free OH (3' end).

True because antiparallel double helix

T/F: High pH (basic) breaks Hydrogen bonding pairing in DNA helix

True because more OH- = less interaction = deprotonation = decrease in Tm

Which of the following is not a feature of the DNA helix proposed by Watson and Crick?

Two grooves of equal dimensions

Which of the following cells are more protected from the end replication problem? Select all that apply.

germ, cancer, stem

DNA partially unwinds as the hydrogen bonds between complementary bases are broken. The enzyme responsible for this is:

helicase

Of the proteins associated with chromatin, which of the following represents the largest component?

histones

In the following pathway, mutation of enzyme II would result in the accumulation of __________ and the mutant would require __________ in the media in order to grow.

ornithine, citrulline

Watson and Crick proposed that during DNA replication, the double strand is unwound and each parental strand is used as a template to generate a new daughter strand. The new and old strands then form a new DNA helix. What is this mode of replication called?

semi-conservative replication

Which of the following is not directly affected by supercoiling of DNA?

translation

This question is based on the experiment that identified the role of the origin of replication using bacteria and a plasmid. The group starts with a plasmid where the oriC is removed. What result would we expect to see if we transferred this plasmid into E. coli?

- No growth on media containing ampicillin. - Growth on media lacking ampicillin.

The human genome consists mostly of non-coding DNA. Which of the following are benefits of this?

- Random DNA mutations generally won't affect RNA and protein function. - The existence of introns can lead to multiple variations of proteins encoded by a single gene.

Which of the following types of RNA associate with the ribosome?

- mRNA - rRNA - tRNA

Which of the following are examples of auxotrophs? (46)

-A yeast cell that is unable to synthesize the amino acid leucine. -A neurospora strain that requires lysine from the environment in order to grow.

Why does each replication fork require both leading and lagging strand synthesis? Select the 2 reasons below.

-Because the DNA templates are antiparallel. -Because DNA polymerase only synthesizes DNA in one direction.

The function of DNA ligase is to (select all that apply):

-Catalyze the formation of covalent bonds between adjacent nucleotides. -Join Okazaki fragments with other pieces of DNA.

Genomics is the field dedicated to the study of: (260)

-DNA on a cellular scale.

The genomes of many organisms have been sequenced. What benefits or uses could result from this information?

-Genome-based personalized medicine. -Trace our evolutionary history. -Elucidate genetic patterns related to diseases. -Identify genes that can improve agricultural yield.

Which of the following is the correct order of the enzymes used during replication?

-Helicase, Primase, DNA polymerase, Ribonuclease H, DNA ligase

Which of the following are true regarding nucleic acid hybridization?

-It is possible to visualize a region of genomic DNA using a fluorescent probe. - It is possible to hybridize a DNA strand to an RNA strand. - It is possible for DNA from different species to hybridize.

The contacts between the DNA and the histones of the nucleosome are:

-Mainly between the conserved histone folds and the phosphate backbone of the DNA helix

Which of the following does not describe an aspect of the Human Genome Project?

-Overlapping clones from YAC and BAC libraries were identified by hybridization and organized into long contiguous stretches called contigs. -Landmark sequences on the contig called sequence tagged sites (STS) were used to aid in ordering the contigs. -The contigs were sequenced using a shotgun method, and the resulting sequences were assembled by computer.

Which of the following are reasons why the "one gene, one enzyme" hypothesis is not completely accurate? Select all that apply. (269)

-Some enzymes are encoded by more than one gene to be functional, function as a multiprotein complex. -Some genes synthesize RNAs that do not produce proteins, non-coding RNAs. -Some genes are capable of making multiple different enzymes by alternative splicing.

Which of the following is necessary for a DNA synthesis reaction catalyzed by DNA polymerase? Select all that apply.

-Template DNA -RNA primer -dNTPs

Which of the following is/are part of the mechanism of the Type I topoisomerase reaction? Select all that apply.

-The 3' OH of the broken strand attacks the link between active site tyrosine and the 5' end of the broken strand, resulting in re-ligation of the broken strand. -The active site tyrosine acts as a nucleophile and attacks one strand to form an enzyme-linked intermediate.

Which of the following is not true of histone tails?

-They have enzymatic properties that can covalently modify DNA.

Chromatin consists of: (332)

DNA and protein

Because replication takes place in the 5' to 3' direction only, the lagging strand consists of short 5' to 3' segments called Okazaki fragments. The Okazaki fragments are joined together by the enzyme:

DNA ligase

An appropriate dNTP forms a hydrogen bond with an exposed base on the template strand. The next dNTP forms a bond between the 3' OH group of the 1st nucleotide and the 5' phosphate of the 2nd nucleotide. The enzyme responsible for catalyzing formation of this bond is:

DNA polymerase

DNA/RNA is the less stable molecule because:

DNA, because it has a 2' H group

Cystic fibrosis is caused by nonsense and missense mutations in the CFTR gene, which encodes for a chloride channel. You are studying cystic fibrosis patients to determine what mutation they possess in the CFTR gene. The difference between the mutant and wild type CFTR genes can be uncovered by examining the CFTR:

DNA, mRNA, and protein

Choose the answer that has the information flow of the central dogma in the correct order.

DNA, transcription, RNA, translation, protein

Which of the following will lower the Tm of a given DNA strand? Select all that apply.

Decreasing the buffer concentration from 50mM NaCl to 5mM NaCl.

What is the difference between exonucleases and endonucleases?

Exo cuts the ends of DNA strands, endo cuts internally.

Griffith and Avery's transformation experiments allowed us to identify that DNA is our genetic information. Which of the following scenarios would result in bacterial cells that are capable of killing mice upon injection? Select all that apply.

Heat killed non-virulent bacteria is added to a live virulent bacteria strain.

Which of the following is not true regarding protein coding DNA in humans?

Human protein coding genes are mostly exon sequences.

Which of the following is not a reason why proteins were thought to be the cell's carrier of genetic information?

Protein synthesis only requires proteins.

Which of the following is the best evidence that supercoiling is an intrinsic property of double-stranded DNA molecules?

Purified plasmid DNAs are supercoiled even when all proteins are removed.

Hershey and Chase's experiment demonstrated that DNA is the hereditary information. Which experimental result allowed them to conclude this?

Radioactive phosphorus was found in the bacterial pellets.

Observing replication of circular plasmid DNAs by electron microscopy show that:

Replication initiates from a single origin, creating two replication forks that move in opposite directions.

Arthur Kornberg's group found that in vitro DNA replication required all four dNTPs. What conclusion did they arrive at based on this result?

The DNA synthesis enzyme must be using a DNA strand as a template for synthesis.

Nucleotides are added to the 3' end of a growing DNA chain via nucleophilic attack. In the first step of this reaction:

The OH group of the last nucleotide attached to the DNA strand attacks the 5' triphosphate of the incoming nucleotide.

Which of the following correctly describes the roles of Mg2+ ions in the polymerase reaction?

The first Mg2+ deprotonates the 3' OH of the last nucleotide in the DNA strand.

Which of the following is not a reason why H. influenzae was chosen to be the first genome sequenced.

The genome sequence had already been partially uncovered.

Why is there a problem replicating the ends of linear DNA?

The primer used for lagging strand synthesis can't be replaced because there is no available 3' OH to add the replacement DNA on to.

Why does the presence of telomeres protect the ends of linear chromosomes?

The telomeres represent large buffer zones of DNA sequence that do not code for biomolecules.

You would like to ensure that this experiment (to determine whether patients have a specific CFTR gene truncation using hybridization) is properly controlled. Which of the following samples must you test?

- The genome of a healthy individual who does not have CFTR (has wild-type WT CFTR) - The genome of a CFTR patient known to have the specific truncation you are trying to identify.

You decide to identify the CFTR mutation by analyzing the genomic DNA of your patients compared to healthy individuals. You specifically are looking to see whether a specific 3' gene truncation has occurred in the patients. You will determine this using hybridization techniques with samples from healthy and CF patients. Which of the following would allow you to accomplish this?

- Using an RNA probe complementary to the region removed by the truncation. - Using an DNA probe complementary to the region removed by the truncation.

Which base is found in both DNA and RNA?

A. Uracil B. Thymine C. Guanine Answer: C. Guanine

Which of the following is true of the trombone model of replication?

?

To conduct the hybridization experiment, you are trying to decide between using a DNA or RNA probe. Which would be ideal to use and why? Select the best answer.

A DNA probe because it is more stable than RNA.

Nucleotides are added to the 3' end of a growing DNA chain via nucleophilic attack. In the second step of this reaction:

A diphosphate is removed from the newly attached nucleotide.

Bidirectional synthesis was demonstrated by an experiment involving radiolabeled dTTP in a pulse chase experiment. Which result told the researchers that replication is bi-directional?

A gradient of radioactivity, with increased density at the forks.

Each nucleosome contains: (334)

A histone octamer composed of two copies of each of the following proteins: H2A, H2B, H3 and H4.

The first evidence for nucleosome formation came from digesting chromosomal DNA with a non-specific nuclease. Gel electrophoresis of the DNA after the reaction revealed:

A ladder of protected fragments about 200 bp apart.

Which of the following is not a feature of the DNA helix proposed by Watson and Crick ?

A. Double stranded B. Right-handed C. Anti-parallel D. Complimentary base pairing E. Two grooves of equal dimensions Answer = E

Which of the following forces STABILIZE DNA double helix (keeps strands together)? Check all that apply. Hint: imagine interacting molecules and their impact on the double helix

A. Hydrogen bonding B. Phosphate-Phosphate interactions C. Ring Stacking D. Endo Pucker E. Phosphate Cation interactions Answer = H bonding because it keeps bases together, Ring stacking because it keeps it compact, and Phosphate cation interactions to stabilize the backbone

A deoxyribonucleotide is composed of:

A. Nitrogenous Base B. Ribose C. Phosphate group D. Pentose with 3' OH Answer = Nitrogenous Base, Phosphate Group, Pentose with 3' OH

Successive nucleotides of a DNA chain are joined by:

A. Phosphodiester binds between the 5' carbon of one nucleotide and the 2 carbon of the next B. Glycosidic bond between the 5' carbon of one nucleotide and the 3' carbon of the next C. Hydrogen bonds between the complementary bases D. Ionic bonds between the phosphate group of one nucleotide and the sugar group of the next E. Phosphodiester bond between the 3' carbon of one nucleotide and the 5' carbon of the next Answer = E

The carbons of the pentose group of DNA and RNA nucleotides are identical except for:

A. The functional group attached to C1 B. The functional group attached to C2 C. The functional group attached to C3 D. The functional group attached to C4 E. The functional group attached to C5 Answer = B because RNA has an OH on C2 while DNA does not have an OH on C2

How did Meselson and Stahl distinguish between semi-conservative and conservative replication in their experiment?

After one round of replication, only mixed DNA helices were present in the gradient.

Which of the following is a reason why primase is required?

Because RNA polymerase is capable of initiating strand synthesis while DNA polymerase is not.

Which of the following is not a way nucleosome formation affects DNA?

Binding of H1 destabilizes the nucleosome, alleviating the transcriptional repression exerted by the binding of nucleosome histones.

Imagine Hershey/Chase had used an RNA virus (genome composed of RNA) instead of a DNA virus in their experiment. Would radioactivity still have been found in the pellet?

Yes, because DNA and RNA nucleotides are similar.

Choose the answer that has the information flow of the central dogma in the correct order:

[DNA]-- replication --> [RNA] -- transcription --> [protein] -- translation -->

Avery found that DNA was necessary and sufficient for bacterial transformation. Which of the following experimental results support this statement? Select all that apply.

b) DNA alone can cause bacterial transformation to occur c) Removal of DNA from virulent Streptococcus pneumoniae cell extracts eliminated transformation

DNA polymerases also have nuclease activities. Which of the following is not a use for the nuclease activity of DNA polymerase I?

degradation of viral DNA