Biology Test 3

Front 1

In which model of DNA replication does the parent DNA molecule break into fragments that are copied?

Back 1

dispersive .


Correct This answer choice is correct because according to the dispersive model of DNA replication, each parent molecule is broken into pieces that are then copied, and the daughter molecules are constructed from a combination of original and newly synthesized fragments.

Front 2

Why did Meselson and Stahl transfer E. coli from media containing 15N to media containing 14N?

Back 2

They needed to ensure that all newly synthesized DNA would contain the same marker. .


Correct This answer choice is correct because E. coli would incorporate nitrogen isotopes as the cells replicated their DNA. If Meselson and Stahl had not transferred the cells to new media, they would have continued to incorporate 15N into newly replicated DNA.

Front 3

Which protein is responsible for synthesizing the new DNA strand during replication in prokaryotes?

Back 3

None of the answers are correct. .


Correct This answer choice is correct because DNA polymerase III synthesizes the new DNA strand during replication.

Front 4

What is the role of DNA polymerase I in the replication of E. coli DNA?

Back 4

It replaces RNA nucleotides with DNA nucleotides. .


Correct This answer choice is correct because one of the functions of DNA polymerase I is to replace RNA primers with DNA nucleotides.

Front 5

What happens at the origin of replication?

Back 5

Helicase separates the strands of DNA. .


Correct This answer choice is correct because helicase separates the double helix at the origin of replication

Front 6

What is one way that the replication of eukaryotic DNA generally differs from the replication of prokaryotic DNA?

Back 6

Replication shortens the lagging strand in eukaryotic DNA. .


Correct This answer choice is correct because replication of the lagging strand leads to shortening of linear DNA, which is found in eukaryotes.

Front 7

Complete the following sentence: Mutation can be described as...

Back 7

changes in the genetic code. .


Correct This answer choice is correct because mutations result in changes in the genetic code.

Front 8

Which of the following is NOT a type of chromosomal mutation?

Back 8

nondisjunction .


Correct This answer choice is correct because nondisjunction is a mechanism by which chromosomal mutations can occur, but it is not itself a type of chromosomal mutation.

Front 9

Complete the following sentence: A frameshift mutation is one of the most severe types of mutations because...

Back 9

frameshift mutations often result in stopping translation. .


Correct This answer choice is correct because frameshift mutations affect the entire reading frame after the mutated site, which often results in a stop codon prematurely ending translation.

Front 10

Which of the following would NOT be expected as a result of a point mutation?

Back 10

a duplicated chromosome .


Correct This answer choice is correct because all of the other examples occur in single nucleotides, but a duplicated chromosome is a large-scale mutation.

Front 11

Compete the following sentence: The role of tautomerism in causing mutations relates to the fact that the process ultimately affects the...

Back 11

hydrogen bonding affinities of the base. .


Correct This answer choice is correct because tautomerism changes the base pairing properties of affected bases. For example, the normal keto form of thymine base pairs to adenine, but the tautomerized enol form base pairs to guanine instead.

Front 12

Which of the following is NOT true of a tautomeric shift?

Back 12

Shifts involve damage to bases by free radicals. .


Correct This answer choice is correct because tautomeric shifts do not cause damage to bases by free radicals.

Front 13

Which of the following is the best definition of genetic fitness as applied to a mammal?

Back 13

the ability of the animal to survive and reproduce with changes to the environment that may kill or reduce the reproductive ability of other members of the population .


Correct This answer choice is correct because survival and reproductive ability are the key parameters to measuring genetic fitness.

Front 14

Who first observed chromatin?

Back 14

Walther Flemming .


Correct This answer choice is correct. Walther Flemming was the first to observe chromatin.

Front 15

Thomas Hunt Morgan and his students at Columbia University were the first to demonstrate that the units of heredity were carried on chromosomes. Which of the following pieces of data was NOT important to their studies?

Back 15

X-linked mutations may be dominant. .


Correct This answer choice is correct because the researchers would not have been able to reach their conclusions if the white-eyed mutation had been dominant.

Front 16

How many different types of histone subunits are present in a nucleosome?

Back 16

4 .


Correct This answer choice is correct. There are eight subunits but only four different ones: H2A, H2B, H3 and H4.

Front 17

Which of the following is NOT a process that may provide an adaptive advantage to eukaryotic chromosomes?

Back 17

rapid cell division .


Correct This answer choice is correct because rapid cell division is a process more often seen in prokaryotes.

Front 18

Which of these sentences most accurately describes heterochromatin?

Back 18

It consists mainly of DNA that is more densely packed and that is actively being repressed. .


Correct This answer choice is correct because heterochromatin consists mainly of densely packed DNA that is also actively being repressed.

Front 19

Why do histones and DNA bind together?

Back 19

Histones are positively charged and the phosphate groups in the DNA backbone are negatively charged. .


Correct This answer choice is correct because histones are positively charged and the phosphate groups in the DNA backbone are negatively charged.

Front 20

Which scientist's research first showed that parents were able to pass heritable factors to their offspring?

Back 20

Gregor Mendel .


Correct This answer choice is correct because Gregor Mendel was the first to demonstrate heritable factors.

Front 21

Which sequence is required for the initiation of transcription in eukaryotes?

Back 21

TATA box .


Correct This answer is correct because the TATA box, an AT-rich region upstream of the gene to be transcribed, is required for eukaryotic transcription.

Front 22

Complete the following sentence: The genes that are passed from generation to generation are stored in...

Back 22

DNA. .


Correct This answer choice is correct because DNA passes genetic material from generation to generation.

Front 23

One of the differences between RNA and DNA is the nucleotides each contains. What nucleotide does RNA have that DNA does not?

Back 23

uracil .


Correct This answer choice is correct because uracil is normally only found in RNA.

Front 24

Complete the following sentence: The monomers that make up a protein are called...

Back 24

amino acids. .


Correct This answer choice is correct because amino acids are the monomers that make up proteins.

Front 25

What is accomplished during transcription?

Back 25

DNA transfers information to RNA. .


Correct This answer choice is correct because transcription transfers the genetic information in DNA to RNA.

Front 26

Which specific sequence is important for termination in eukaryotes?

Back 26

a polyadenylation signal .


Correct This answer choice is correct because the polyadenylation signal causes RNA polymerase and the mRNA transcript to dissociate from the DNA template.

Front 27

Which of the following does NOT occur during transcription in bacteria?

Back 27

RNA splicing .


Correct This answer choice is correct because in prokaryotes the mRNA generated by transcription does not include introns, so RNA splicing does not occur.

Front 28

Which of the following is important for transcription in prokaryotes?

Back 28

sigma .


Correct This answer choice is correct because sigma is important for initiation of transcription in prokaryotes. Sigma is the part of the holoenzyme that binds to the promoter.

Front 29

If the template strand of DNA has the sequence 3′-TCTAGGACT-5′, what will the sequence of the transcribed RNA be?

Back 29

5′-AGAUCCUGA-3′ .


Correct This answer choice is correct because the template strand of DNA and the mRNA have complementary sequences except that thymine (T) is replaced by uracil (U).

Front 30

Other than the core RNA polymerase, what proteins are required for the initiation of transcription in bacteria?

Back 30

sigma .


Correct This answer choice is correct because RNA polymerase and sigma associate to form the holoenzyme that binds to the DNA to initiate transcription.

Front 31

Mutation of which of these sequences would have no effect on the initiation of transcription?

Back 31

Polyadenylation signal .


Correct This answer choice is correct because mutating it would affect termination, not initiation of transcription.

Front 32

If the coding strand of DNA has the sequence 5′-CGAGACTTCTGA-3′, what will the sequence of the transcribed RNA be?

Back 32

5′-CGAGACUUCUGA-3′ .


Correct This answer choice is correct because the coding strand of DNA and the RNA have the same sequence except that thymine (T) is replaced by uracil (U).

Front 33

One codon for asparagine has the sequence AAC. What is the sequence of the anticodon on the aminoacyl-tRNA (in the 5′ to 3′ direction)?

Back 33

GUU .


Correct This answer choice is correct because the anticodon is complementary to the codon nucleotide sequence.

Front 34

All polypeptides in eukaryotes have which of the following in common?

Back 34

All polypeptides start with the same amino acid. .


Correct This answer choice is correct because the start codon for all polypeptides is the same. The start codon codes for the amino acid methionine.

Front 35

Which of the following are post-translational modifications?

Back 35

All answers are correct. .


Correct This answer choice is correct because glycosylation, phosphorylation, cleavage, and multi-protein binding are all examples of post-translational modification.

Front 36

Which of the following first binds to the mRNA at the translation initiation site?

Back 36

small ribosomal subunit .


Correct This answer choice is correct because the first factor to bind to the mRNA is the small ribosomal subunit. Then the aminoacyl-tRNA binds, followed by the large ribosomal subunit.

Front 37

How many different aminoacyl-tRNA synthetases exist?

Back 37

20 .


Correct This answer choice is correct because there are 20 aminoacyl-tRNA synthetases, one for each amino acid. The same aminoacyl-tRNA synthetase can bind to all of the tRNA molecules that code for a particular amino acid.

Front 38

Complete the following sentence: Prokaryotes differ from eukaryotes by...

Back 38

lacking a nucleus. .


Correct This answer choice is correct because prokaryotes lack a nucleus, while eukaryotes have a nucleus.

Front 39

How would a mutation in the operator of the lac operon that prevented the LacI repressor from binding affect the expression of the genes in the lac operon?

Back 39

The lac operon genes would be expressed continuously. .


Correct This answer choice is correct because a mutation in the operator blocking the LacI repressor from binding would cause the lac operon genes to be expressed continuously because RNA polymerase would have unlimited access to the promoter.

Front 40

Complete the following sentence: The lac repressor is an allosteric molecule because...

Back 40

it interacts with another molecule to change the repressor's active site. .


Correct This answer choice is correct because the lac repressor is an allosteric molecule that interacts with another molecule — allolactose — to change the DNA-binding site so that it can no longer bind to the operator.

Front 41

What is the function of the sigma factor in transcription?

Back 41

to enable specific binding of RNA polymerase to promoters .


Correct This answer choice is correct because sigma factors enable specific binding of RNA polymerase to promoters.

Front 42

Which environmental condition results in maximal expression levels of the lac operon genes?

Back 42

low glucose, high lactose .


Correct This answer choice is correct because low glucose activates the CAP-cAMP positive regulatory system, while high lactose disables the repression of the lac operon by the LacI repressor.

Front 43

Which mutation is expected to have a similar effect to a mutation in which the LacI repressor is no longer able to bind to the operator?

Back 43

a mutation in the operator that prevents recognition by the LacI repressor .


Correct This answer choice is correct because a mutation in the operator that causes it to be unrecognizable by the LacI repressor would have the same effect as a mutation in LacI that causes it to be unable to bind to the operator. In both cases, the lac operon genes would be continuously expressed.

Front 44

How do eukaryotes and prokaryotes differ?

Back 44

Eukaryotes contain a nucleus, while prokaryotes do not. .


Correct This answer choice is correct because prokaryotes lack a nucleus, while eukaryotes have a nucleus.

Front 45

Which of the following reduces the net positive charge of a histone?

Back 45

acetylation .


Correct This answer choice is correct because acetylation decreases the net positive charge of a histone, which causes reduced binding of DNA to the histone.

Front 46

Which of the following statements is true of an enhancer?

Back 46

Enhancers may be thousands of nucleotides from the gene they are associated with. .


Correct This answer choice is correct because enhancers may be thousands of nucleotides from the gene they are associated with.

Front 47

Which of these is NOT a process that may be involved in post-transcriptional regulation?

Back 47

methylation .


Correct This answer choice is correct because this is not a process that may be involved in post-transcriptional regulation. Methylation occurs to chromatin and would affect the initiation of transcription.

Front 48

What is a transcription factory?

Back 48

a physical grouping of genes on different chromosomes that come together to coordinate transcription .


Correct This answer choice is correct because a physical grouping of genes on different chromosomes that come together to coordinate transcription is called a transcription factory.

Front 49

What is the function of the proteasome?

Back 49

protein degradation .


Correct This answer choice is correct because a proteasome degrades proteins.

Front 50

How do maternal effect genes determine cell differentiation?

Back 50

They can create an mRNA gradient that determines body layout. .


Correct This answer choice is correct because an mRNA gradient produced by maternal effect genes in fruit flies establishes the anterior-posterior axis of the embryo.

Front 51

How does expression of the bicoid gene in fruit flies control differentiation of the early fruit fly embryo?

Back 51

Bicoid protein determines the polarity of the developing embryo. .


Correct This answer choice is correct because Bicoid protein is necessary to establish the anterior-posterior axis in fruit fly embryos.

Front 52

How do homeotic genes contribute to pattern formation in the early embryo?

Back 52

Homeotic gene products are necessary for proper morphogenesis of an embryo. .


Correct This answer choice is correct because homeotic genes, which are master control genes, establish the location and patterning of certain body regions.

Front 53

What characteristic of stem cells gives them the ability to differentiate into multiple cell types?

Back 53

Stem cells have few permanent changes in their ability to express genes. .


Correct This answer choice is correct because alterations to stem cell gene expression are flexible to allow for changes in gene expression during differentiation.

Front 54

How does a single embryonic stem cell give rise to daughter cells that are liver cells and other daughter cells that are skin cells?

Back 54

through division and differentiation .


Correct This answer choice is correct because stem cells must differentiate and divide to become multiple cell types.

Front 55

How does cell-to-cell induction affect cell differentiation?

Back 55

Induction affects gene expression in targeted cells. .


Correct This answer choice is correct because induction signals both increase and decrease gene expression in their target cells.

Front 56

What is the purpose of a viral envelope?

Back 56

Viral envelopes contain proteins that identify and bind to cellular receptor sites. .


Correct This answer choice is correct. The viral envelope contains glycoproteins, often in the form of spikes, that identify cell hosts and help the virus bind to the cell surface.

Front 57

Which of the following do virtually all viruses possess?

Back 57

capsids and nucleic acids .


Correct This answer choice is correct. Virtually all viruses are made of nucleic acids — either DNA or RNA — enclosed in a protein covering called a capsid.

Front 58

Which of these cellular locations do viruses use to construct a viral envelope?

Back 58

cell membrane .


Correct This answer choice is correct because the lipids in the viral envelope are primarily derived from the cell membrane.

Front 59

How do most animal viruses differ from bacteriophages?

Back 59

All answers are correct. .


Correct This answer choice is correct. Unlike bacteriophages, most animal viruses contain single-stranded RNA, have envelopes, enter cells with their capsids intact, and exit by budding.

Front 60

Which is true about a lysogenic cycle?

Back 60

A lysogenic cycle is a replication cycle used by bacteriophages that delays the lytic cycle. .


Correct This answer choice is correct. Bacteriophages use lysogenic cycles to delay the lytic cycle (which results in immediate cell death). In the lysogenic cycle, the phage's genetic material incorporates itself into the bacterial genome for an indefinite amount of time.

Front 61

How do viral drug therapies generally work?

Back 61

They are made to target viral products. .


Correct This answer choice is correct. Because viruses and host cells use the same cellular machinery, drug therapies mostly target viral products so as not to disrupt the host cell's metabolism.

Front 62

In the process of using bacteria for gene cloning, what is the target DNA sequence inserted into?

Back 62

a plasmid .


Correct This answer choice is correct because plasmids are one type of vector used for delivering target DNA sequences to bacteria. Bacteria may take up the recombinant plasmids and produce more of the sequence of interest as they reproduce.

Front 63

Which of the following is a reason that a prokaryotic gene expression system might not be compatible for expressing eukaryotic genes?

Back 63

All answers are correct. .


Correct This answer choice is correct because each of the answers is a reason that prokaryote expression systems might be incompatible for expressing a eukaryotic gene.

Front 64

In constructing an expression vector, what characteristic of the promoter is important?

Back 64

highly active in the bacteria .


Correct This answer choice is correct because expression vectors link highly active bacterial promoters to the gene sequence of interest, resulting in high expression levels of genes inserted into the vector and an abundance of protein product.

Front 65

Why do scientists try to use the same restriction enzyme to excise the target DNA sequence and to cut the plasmid?

Back 65

The plasmid and the insert will have compatible sticky ends. .


Correct This answer choice is correct because using the same restriction enzyme results in each DNA component (plasmid and target sequence) having compatible sticky ends and enhances the probability that they will stick to each other.

Front 66

In screening for bacterial colonies containing recombinant plasmids, which color indicates that the recombinant plasmid is present?

Back 66

white .


Correct This answer choice is correct because the usual color choices in a screening are blue and white, and white indicates the presence of a recombinant plasmid. White indicates that the lacZ gene was interrupted by insertion of the gene of interest.

Front 67

Which enzyme is required in the first step of constructing a cDNA library?

Back 67

reverse transcriptase .


Correct This answer choice is correct because reverse transcriptase is required to reverse-transcribe the mRNAs in a sample into a cDNA library before anything else can be done to them.

Front 68

Which of the following is NOT a required component for PCR?

Back 68

green fluorescent protein (GFP) .


Correct This answer is correct because GFP is used in promoter fusions, not for basic PCR.

Front 69

Which of the following would be identified from genome-wide association studies and used to determine disease risk?

Back 69

single nucleotide polymorphisms (SNPs) .


Correct This answer choice is correct because genome-wide association studies can identify single base-pair changes, called single nucleotide polymorphisms, and associate them with specific diseases or disease risk in populations.

Front 70

Scientists identified a SNP site associated with an increased risk of hypertension. How is this information used to diagnose people with a potential risk of hypertension?

Back 70

DNA samples from a patient could be sequenced and analyzed for the presence of the SNP. .


Correct This answer choice is correct because DNA may be analyzed for the presence of certain SNP sequences associated with diseases.

Front 71

Would identical twins be expected to have very similar patterns of short tandem repeats (STRs)? Why or why not?

Back 71

Yes. Because barring any recombination after conception, their repeats will reflect their identical inheritance from the first zygotic division. .


Correct This answer choice is correct because while recombination can sporadically increase a repeat, the identical twins will have very similar STR patterns overall.

Front 72

Which of the following techniques is a way to create a recombinant bacterial strain that can break down heavy metals, possibly for use in bioremediation?

Back 72

transformation with a recombinant plasmid .


Correct This answer choice is correct because a recombinant strain is usually made by mixing the bacteria with a recombinant plasmid containing the gene of interest. The uptake and incorporation of this plasmid is called transformation, and the resulting transformed bacteria are recombinants.

Front 73

What is the purpose of creating genetically modified superfoods?

Back 73

to enhance the nutritional or therapeutic value of components of food .


Correct This answer choice is correct. Foods such as snapdragon tomatoes or Golden Rice have been created with the goal of enhancing their nutritional or therapeutic effects.