Deck 5: Fundamental Molecular Genetic Mechanisms

Question 1

Which of the following is not a constituent of deoxyribonucleotides?

A)phosphate moieties
B)deoxyribose
C)ribose
D)organic bases

Answer 1

C

Question 2

When the circular double-stranded DNA of certain viruses is underwound,the DNA can twist back on itself and form:

A)supercoils
B)pseudoknots
C)relaxed coils
D)hairpins

Answer 2

A

Question 3

Nucleotide bases within a single strand of DNA are held together by which of the following bonds?

A)phosphodiester
B)pentose-phosphate
C)polynucleotide
D)phosphoester

Answer 3

A

Question 4

In the laboratory,which of the following two factors are most useful in manipulating DNA?

A)magnesium ions and sugar concentrations
B)UV light and calcium ions
C)formaldehyde and iron ions
D)temperature and pH

Question 5

In humans,the ribosome responsible for translating proteins consists of which of following two subunits?

A)60S and 30S
B)40S and 50S
C)18S and 40S
D)60S and 40S

Question 6

Which of the following is seen when a single mRNA is simultaneously translated to form multiple copies of a polypeptide chain?

A)phagosome
B)multisome
C)nucleosome
D)polysome

Question 7

In DNA,which of the following base pairing normally occurs between two strands of DNA?

A)A to C
B)T to A
C)G to T
D)C to T

Question 8

There are four basic molecular processes in a cell,three of which lead to the production of protein.Which of the following shows the correct order?

A)translation,RNA processing,transcription
B)RNA processing,translation,transcription
C)transcription,RNA processing,translation
D)transcription,translation,RNA processing

Question 9

You are studying polysomes and want to see if their numbers are actually increased in cells translating protein from an expressed retroviral oncogene.Which of the following methods are used to visualize these structures?

A)sedimentation analyses
B)electron microscopy
C)PCR
D)sedimentation analyses and electron microscopy

Question 10

In biology the central dogma refers to:

A)protein to DNA to RNA.
B)RNA to DNA to protein.
C)DNA to RNA to protein.
D)RNA to protein to DNA.

Question 11

The first stage of protein translation occurs when Met-tRNAᵢᴹᵉᵗ base pairs with the mRNA being translated in the ribosomal:

A)P site.
B)A site.
C)E site.
D)T site.

Question 12

The base in the wobble position of a codon

A)is the 5´ (first)base.
B)is the 3´ (third)base.
C)is the second base.
D)often contains adenine.

Question 13

The genetic code is said to be "degenerate" because:

A)amino acid sequences are always read in the 3'→5' direction of the mRNA.
B)amino acids are encoded only by DNA sequences found in introns.
C)a particular amino acid can be specified by more than one codon.
D)tryptophan is the first amino acid in all polypeptide chains.

Question 14

Approximately what percent of all human genes are expressed as alternatively spliced mRNAs?

A)2
B)25
C)50
D)90

Question 15

Which base pair(s)typically occur(s)in double-stranded DNA?

A)G·C
B)G·T
C)G·A
D)G·G

Question 16

In eukaryotic cells,protein synthesis in the cytoplasm utilizes three types of RNA molecules.Which of the following contains a three nucleotide sequence called the anticodon?

A)mRNA
B)tRNA
C)rRNA
D)all of the above

Question 17

Which of the following are removed from mRNAs during processing?

A)exons
B)noncoding sequences
C)RNA cap structure
D)poly(A)tail

Question 18

The ability of DNA to denature is important for which process?

A)DNA synthesis
B)nucleic acid hybridization experiments
C)RNA synthesis
D)all of the above

Question 19

The most common arrangement of protein-coding genes in bacteria are those where the genes encoding proteins that work together are arranged in a contiguous array of DNA called:

A)an operon.
B)a terminator.
C)a promoter.
D)an operator.

Question 20

Which of the following techniques would you need to use in order to determine the size of the large and small ribosomal subunits in E.coli?

A)X-ray crystallography
B)plaque assay
C)centrifugation
D)hybridization

Question 21

Viruses that use the lytic cycle of growth generally proceed through five general stages.Which one of the following shows the correct order of three of these stages?

A)replication,assembly,adsorption
B)penetration,adsorption,release
C)replication,assembly,release
D)assembly,replication,penetration

Question 22

Which of the following lead(s)to a point mutation?

A)deamination of a cytosine base into a uracil base
B)benzo(a)pyrene conversion of guanine to a thymine base
C)deamination of 5-methyl cytosine into thymine
D)all of the above

Question 23

Which codon serves as the start codon in mRNA for translation?

A)AGU
B)AUG
C)UGA
D)UGG

Question 24

You have received a saliva sample from a group of veterinarians who think one of the dogs they are treating has rabies.Which of the following techniques would you use to determine not only if this sample contains viral particles,but how many viral particles are in the sample?

A)centrifugation
B)nucleic acid hybridization
C)plaque assay
D)all of the above

Question 25

In eukaryotes,the circular structure of mRNA molecules undergoing translation serves to

A)increase translation efficiency.
B)target the mRNA for destruction.
C)prevent the formation of polysomes.
D)promote the termination step in protein synthesis.

Question 26

In which of these polymers are the monomers added one at a time?

A)DNA
B)rRNA
C)protein
D)all of the above

Question 27

Which of the following are enzymes that play a key role in the base excision repair of nucleotide mismatches and damaged bases?

A)glycosamines
B)glycosidases
C)glycosylases
D)none of the above

Question 28

Which of the following structures interacts with ribosomes?

A)tRNA
B)mRNA
C)rRNA
D)all of the above

Question 29

Which of the following factors recognizes the UAG,UAA,and UGA codons?

A)RNA polymerase
B)DNA polymerase
C)termination factors
D)elongation factors

Question 30

Thymine-thymine dimers are chemical adducts that develop in the DNA as a result of damage caused by which of the following?

A)UV light
B)X-rays
C)RNA polymerase reading errors
D)gamma radiation

Question 31

A double-stranded piece of DNA containing the sequence GCATGGCCACTACCG has a higher Tm than one containing the sequence GAATGGTAACAACTG.Describe the properties of DNA that make this true.

Question 32

Silent mutations that occur under a variety of conditions in DNA results in which of the following?

A)a stop codon
B)a change of an amino acid to another
C)the formation of an anticodon
D)no change in the amino acid

Question 33

A Holliday structure is a(n)

A)intermediate in genetic recombination.
B)double-stranded DNA break.
C)collapsed replication fork.
D)thymine-thymine dimer.

Question 34

Which of the following is not a recognized stage of protein synthesis in either prokaryotes or eukaryotes?

A)elongation
B)initiation
C)translation
D)termination

Question 35

Which of the following is a protein that is involved in translation?

A)topoisomerase
B)ribosomal RNA
C)RNA polymerase
D)aminoacyl-tRNA synthetase

Question 36

Cellular protein synthesis proceeds in which direction?

A)carboxyl to amino terminus
B)amino to carboxyl terminus
C)3´' to 5´
D)5´ to 3´

Question 37

An enzyme that breaks DNA,dispels the tension,and reseals the strand ahead of a DNA replication growing fork is called a(n)

A)topoisomerase.
B)DNA polymerase.
C)phosphodiesterase.
D)aminoacyl-tRNA synthetase.

Question 38

This type of assay can be used to count the number of viral particles in a sample.

A)plaque assay
B)pap smear
C)lytic cycle
D)transformation assay

Question 39

Okazaki fragments are small fragments of DNA that eventually are ligated to form which of the following strands of DNA?

A)lagging
B)parent
C)leading
D)joining

Question 40

DNA replication begins at sequences called

A)promoters.
B)initiators.
C)origins.
D)Okazaki fragments.

Question 41

Why is the enzyme reverse transcriptase found within retroviral virions?

Question 42

What is the difference between lytic and lysogenic bacteriophages?

Question 43

Many antibiotics,most of which have been isolated from fungi,act by inhibiting initiation,elongation,or termination of peptides during protein synthesis.These compounds have been very useful in the study of protein synthesis,mainly because an individual antibiotic usually interferes with protein synthesis at a single well-defined step in the complex process of translation.Assume that you have isolated a novel antibiotic from the fungus Pilobolus.This antibiotic inhibits bacterial growth and bacterial protein synthesis but does not affect growth or protein synthesis in eukaryotic cells.How could you identify the component of the translational machinery that is affected by this novel antibiotic?

Question 44

To incorporate radiolabeled nucleotides into newly synthesized DNA,researchers use α-phosphorus32-labeled nucleotides,in a DNA synthesis reaction,where the α denotes the position of the radioactive phosphate moiety.Explain why the α position and not the β or γposition is the best position for the radioactive group in these experiments.

Question 45

The replication of DNA is quite complicated and requires the participation of many different enzymatic activities.These include an RNA polymerase (DNA primase)that synthesizes short segments of RNA,called primers,which are base paired to the DNA template.The 3´-OH ends of these RNA primers serve as initiation sites for the actual DNA polymerase activity.Obviously,DNA primase can synthesize polynucleotides without the benefit of a 3´-OH primer;indeed,it can catalyze the hydrolysis and subsequent linkage of two nucleoside triphosphates without the need for a complementary strand whatsoever.The short segments of RNA must be eliminated and replaced with DNA before replication can be completed.Why do you think that RNA,rather than DNA,primers are employed in the DNA replication process?

Question 46

Which parts of the newly synthesized mRNA molecule do not transmit information for the synthesis of protein?

Question 47

When the CAU anticodon of a tRNAᴹᵉᵗ was modified to UAC,the anticodon for tRNAⱽᵃˡ,valine aminoacyl-tRNA synthetase recognized the altered tRNAᴹᵉᵗ and added valine rather than methionine to it.When the converse modification was made,the altered tRNAⱽᵃˡ containing a CAU anticodon (rather than UAC)was recognized and activated by methionine aminoacyl-tRNA synthetase.What do these data suggest about the mechanism by which aminoacyl-tRNA synthetases recognize their cognate tRNAs?

Question 48

What is the difference between a nucleoside and a nucleotide?

Question 49

If perfect Watson-Crick base pairing were demanded between codons and anticodons,cells would need 61 different tRNAs.If there are only 20 amino acids used in protein synthesis,how would you explain this excess number of tRNAs compared to amino acids? Conversely,how would you explain the fact that some cells contain fewer than 61 tRNAs?

Question 50

Polio virus affects only intestinal cells and motor neurons.By analogy to HIV,explain why only these particular cell types are susceptible to polio infection.