A molecule of bacterial DNA introduced into a yeast cell is imported into the nucleus but fails to replicate with the yeast DNA. Where do you think the block to replication arises? Choose the protein or protein complex below that is most probably responsible for the failure to replicate bacterial DNA. Give an explanation for your answer.

A molecule of bacterial DNA introduced into a yeast cell is imported into the nucleus but fails to replicate with the yeast DNA. Where do you think the block to replication arises? Choose the protein or protein complex below that is most probably responsible for the failure to replicate bacterial DNA. Give an explanation for your answer.

(a) primase
(b) helicase
(c) DNA polymerase
(d) initiator proteins

Answer: 

You have discovered an "Exo-" mutant form of DNA polymerase in which the 3'-to-5' exonuclease function has been destroyed but the ability to join nucleotides together is unchanged. Which of the following properties do you expect the mutant polymerase to have?

You have discovered an "Exo-" mutant form of DNA polymerase in which the 3'-to-5' exonuclease function has been destroyed but the ability to join nucleotides together is unchanged. Which of the following properties do you expect the mutant polymerase to have?

(a) It will polymerize in both the 5'-to-3' direction and the 3'-to-5' direction.
(b) It will polymerize more slowly than the normal Exo+ polymerase.
(c) It will fall off the template more frequently than the normal Exo+ polymerase.
(d) It will be more likely to generate mismatched base pairs.

Answer: 

Which of the following statements about the newly synthesized strand of a human chromosome is true?

Which of the following statements about the newly synthesized strand of a human chromosome is true?

(a) It was synthesized from a single origin solely by continuous DNA synthesis.
(b) It was synthesized from a single origin by a mixture of continuous and discontinuous DNA synthesis.
(c) It was synthesized from multiple origins solely by discontinuous DNA synthesis.
(d) It was synthesized from multiple origins by a mixture of continuous and discontinuous DNA synthesis.

Answer: 

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking DNA ligase were used to make the cell extracts?

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking DNA ligase were used to make the cell extracts?

(a) initiation of DNA synthesis
(b) Okazaki fragment synthesis
(c) leading-strand elongation
(d) lagging-strand completion

Answer: 

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking single-strand binding protein were used to make the cell extracts?

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking single-strand binding protein were used to make the cell extracts?

(a) initiation of DNA synthesis
(b) Okazaki fragment synthesis
(c) leading-strand elongation
(d) lagging-strand completion

Answer: 

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking helicase were used to make the cell extracts?

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking helicase were used to make the cell extracts?

(a) initiation of DNA synthesis
(b) Okazaki fragment synthesis
(c) leading-strand elongation
(d) lagging-strand completion

Answer: 

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking the exonuclease activity of DNA polymerase were used to make the cell extracts?

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking the exonuclease activity of DNA polymerase were used to make the cell extracts?

(a) initiation of DNA synthesis
(b) Okazaki fragment synthesis
(c) leading-strand elongation
(d) lagging-strand completion

Answer: 

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking primase were used to make the cell extracts?

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking primase were used to make the cell extracts?

(a) initiation of DNA synthesis
(b) Okazaki fragment synthesis
(c) leading-strand elongation
(d) lagging-strand completion

Answer: 

Which of the following statements is true with respect to this in vitro replication system?

Which of the following statements is true with respect to this in vitro replication system?

(a) There will be only one leading strand and one lagging strand produced using this template.
(b) The leading and lagging strands compose one half of each newly synthesized DNA strand.
(c) The DNA replication machinery can assemble at multiple places on this plasmid.
(d) One daughter DNA molecule will be slightly shorter than the other.

Answer: 

DNA polymerase catalyzes the joining of a nucleotide to a growing DNA strand. What prevents this enzyme from catalyzing the reverse reaction?

DNA polymerase catalyzes the joining of a nucleotide to a growing DNA strand. What prevents this enzyme from catalyzing the reverse reaction?

(a) hydrolysis of pyrophosphate (PPi) to inorganic phosphate (Pi) + Pi
(b) release of PPi from the nucleotide
(c) hybridization of the new strand to the template
(d) loss of ATP as an energy source

Answer: 

The chromatin structure in eukaryotic cells is much more complicated than that observed in prokaryotic cells. This is thought to be the reason that DNA replication occurs much faster in prokaryotes. How much faster is it?

The chromatin structure in eukaryotic cells is much more complicated than that observed in prokaryotic cells. This is thought to be the reason that DNA replication occurs much faster in prokaryotes. How much faster is it?

(a) 2×
(b) 5×
(c) 10×
(d) 100×

Answer: 

Which of the following statements correctly explains what it means for DNA replication to be bidirectional?

Which of the following statements correctly explains what it means for DNA replication to be bidirectional? 

(a) The replication fork can open or close, depending on the conditions.
(b) The DNA replication machinery can move in either direction on the template strand.
(c) Replication-fork movement can switch directions when the fork converges on another replication fork.
(d) The replication forks formed at the origin move in opposite directions.

Answer: 

How does the total number of replication origins in bacterial cells compare with the number of origins in human cells?

How does the total number of replication origins in bacterial cells compare with the number of origins in human cells?

(a) 1 versus 100
(b) 5 versus 500
(c) 10 versus 1000
(d) 1 versus 10,000

Answer: 

How many replication forks are formed when an origin of replication is opened?

How many replication forks are formed when an origin of replication is opened?

(a) 1
(b) 2
(c) 3
(d) 4


Answer: 

If the genome of the bacterium E. coli requires about 20 minutes to replicate itself, how can the genome of the fruit fly Drosophila be replicated in only 3 minutes?

If the genome of the bacterium E. coli requires about 20 minutes to replicate itself, how can the genome of the fruit fly Drosophila be replicated in only 3 minutes?

(a) The Drosophila genome is smaller than the E. coli genome.
(b) Eukaryotic DNA polymerase synthesizes DNA at a much faster rate than prokaryotic DNA polymerase.
(c) The nuclear membrane keeps the Drosophila DNA concentrated in one place in the cell, which increases the rate of polymerization.
(d) Drosophila DNA contains more origins of replication than E. coli DNA.

Answer: 

Initiator proteins bind to replication origins and disrupt hydrogen bonds between the two DNA strands being copied. Which of the factors below does not contribute to the relative ease of strand separation by initiator proteins?

Initiator proteins bind to replication origins and disrupt hydrogen bonds between the two DNA strands being copied. Which of the factors below does not contribute to the relative ease of strand separation by initiator proteins?

(a) replication origins are rich in A-T base pairs
(b) the reaction can occur at room temperature
(c) they only separate a few base pairs at a time
(d) once opened, other proteins of the DNA replication machinery bind to the origin

Answer: 

The classic experiments conducted by Meselson and Stahl demonstrated that DNA replication is accomplished by employing a _____ mechanism.

The classic experiments conducted by Meselson and Stahl demonstrated that DNA replication is accomplished by employing a _____ mechanism.

(a) continuous
(b) semiconservative
(c) dispersive
(d) conservative

Answer: 

DNA replication is considered semiconservative because _________________.

DNA replication is considered semiconservative because _________________.

(a) after many rounds of DNA replication, the original DNA double helix is still intact.
(b) each daughter DNA molecule consists of two new strands copied from the parent DNA molecule.
(c) each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand.
(d) new DNA strands must be copied from a DNA template.

Answer: 

The process of DNA replication requires that each of the parental DNA strands be used as a ________ to produce a duplicate of the opposing strand.

The process of DNA replication requires that each of the parental DNA strands be used as a ________ to produce a duplicate of the opposing strand.

(a) catalyst
(b) competitor
(c) template
(d) copy

Answer: 

APC is a tumor suppressor and acts in the Wnt signaling pathway to prevent the TCF complex from turning on Wnt-responsive genes. Mice that lack the gene encoding TCF4 do not have the ability to maintain the pool of proliferating gut stem cells needed to renew the gut lining. What do you predict will happen in mice that lack the APC gene?

APC is a tumor suppressor and acts in the Wnt signaling pathway to prevent the TCF complex from turning on Wnt-responsive genes. Mice that lack the gene encoding TCF4 do not have the ability to maintain the pool of proliferating gut stem cells needed to renew the gut lining. What do you predict will happen in mice that lack the APC gene?

(a) Mice lacking the APC gene will be like the mice lacking TCF4 and not be able to renew the gut lining.
(b) Mice lacking the APC gene will have inappropriate proliferation of gut stem cells.
(c) Mice lacking the APC gene will have a hyperactive Wnt receptor even though there is no Wnt signal.
(d) Mice lacking the APC gene will be like normal healthy mice, since APC is a tumor suppressor and thus not needed unless there is a tumor present.

Answer: 

Ras is a GTP-binding protein that is often defective in cancer cells. A common mutation found in cancer cells causes Ras to behave as though it were bound to GTP all the time, which will cause cells to divide inappropriately. From this description, the normal Ras gene is _______.

Ras is a GTP-binding protein that is often defective in cancer cells. A common mutation found in cancer cells causes Ras to behave as though it were bound to GTP all the time, which will cause cells to divide inappropriately. From this description, the normal Ras gene is _______.

(a) a tumor suppressor.
(b) an oncogene.
(c) a proto-oncogene.
(d) a gain-of-function mutation.

Answer: 

Which of the following statements about tumor suppressor genes is false?

Which of the following statements about tumor suppressor genes is false?

(a) Gene amplification of a tumor suppressor gene is less dangerous than gene amplification of a proto-oncogene.
(b) Cells with one functional copy of a tumor suppressor gene will usually proliferate faster than normal cells.
(c) Inactivation of tumor suppressor genes leads to enhanced cell survival and proliferation.
(d) Individuals with only one functional copy of a tumor suppressor gene are more prone to cancer than individuals with two functional copies of a tumor suppressor gene.

Answer: 

Which of the following genetic changes cannot convert a proto-oncogene into an oncogene?

Which of the following genetic changes cannot convert a proto-oncogene into an oncogene?

(a) A mutation that introduces a stop codon immediately after the codon for the initiator methionine.
(b) A mutation within the coding sequence that makes the protein hyperactive.
(c) An amplification of the number of copies of the proto-oncogene, causing overproduction of the normal protein.
(d) A mutation in the promoter of the proto-oncogene, causing the normal protein to be transcribed and translated at an abnormally high level.

Answer: 

Which of the following statements about cancer is false?

Which of the following statements about cancer is false?

(a) Viruses cause some cancers.
(b) Tobacco use is responsible for more than 20% of all cancer deaths.
(c) A mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell.
(d) Chemical carcinogens cause cancer by changing the nucleotide sequence of DNA.

Answer: 

A metastasis is _________.

A metastasis is _________.

(a) a secondary tumor in a different part of the body that arises from a cell from the primary tumor.
(b) a cell that is dividing in defiance of normal constraints.
(c) a part of the primary tumor that has invaded the surrounding tissue.
(d) the portion of the cancerous tumor that displays genetic instability.

Answer: 

A malignant tumor is more dangerous than a benign tumor because ___________.

A malignant tumor is more dangerous than a benign tumor because ___________.

(a) its cells are proliferating faster.
(b) it causes neighboring cells to mutate.
(c) its cells attack and phagocytose neighboring normal tissue cells.
(d) its cells invade other tissues.

Answer: 

The artificial introduction of three key ______________ into an adult cell can convert the adult cell into a cell with the properties of ES cells.

The artificial introduction of three key ______________ into an adult cell can convert the adult cell into a cell with the properties of ES cells.

(a) chromosomes
(b) viruses
(c) hormones
(d) transcription factors

Answer: 

Induced pluripotent stem (iPS) cells ___________.

Induced pluripotent stem (iPS) cells ___________.

(a) are created by the expression of a set of key genes in cells derived from adult tissues so that these cells can differentiate into a variety of cell types.
(b) require a supply of donor egg cells, such as embryonic stem cells.
(c) can differentiate into a greater variety of adult tissues than embryonic stem cells.
(d) are created by nuclear transplantation.

Answer: 

An individual that arises by reproductive cloning has a nuclear genome that is identical to __________.

An individual that arises by reproductive cloning has a nuclear genome that is identical to __________.

(a) the female who donated the egg.
(b) the adult who donated the cell for nuclear transplantation.
(c) both the female who donated the egg and the adult who donated the cell for nuclear transplantation.
(d) the foster mother in which the embryo is placed.

Answer: 

How do reproductive cloning and therapeutic cloning differ?

How do reproductive cloning and therapeutic cloning differ?

(a) The DNA in the nucleus of cells produced for therapeutic cloning is genetically identical to the donor genome, whereas in cells produced for reproductive cloning it is not.
(b) Reproductive cloning requires a supply of fertilized donor egg cells, whereas therapeutic cloning requires unfertilized egg cells.
(c) Therapeutic cloning requires nuclear transplantation, whereas reproductive cloning does not.
(d) Embryos are placed into foster mothers during reproductive cloning but not during therapeutic cloning.

Answer: 

Mouse embryonic stem (ES) cells ___________.

Mouse embryonic stem (ES) cells ___________.

(a) can only be produced through therapeutic cloning.
(b) can give rise to all tissues and cell types in the body except germ cells.
(c) can be implanted in foster mothers to produce cloned cows and other animals.
(d) come from the inner cell mass of early embryos.

Answer: 

A pluripotent cell _________.

A pluripotent cell _________.

(a) can only be produced in the laboratory.
(b) can give rise to all the tissues and cell types in the body.
(c) can only give rise to stem cells.
(d) is considered to be terminally differentiated.

Answer: 

An adult hematopoietic stem cell found in the bone marrow ___________.

An adult hematopoietic stem cell found in the bone marrow ___________.

(a) will occasionally produce epidermal cells when necessary.
(b) can produce only red blood cells.
(c) can undergo self-renewing divisions for the lifetime of a healthy animal.
(d) will express all the same transcription factors as those found in an unfertilized egg.

Answer: 

When a terminally differentiated cell in an adult body dies, it can typically be replaced in the body by a stock of ________.

When a terminally differentiated cell in an adult body dies, it can typically be replaced in the body by a stock of ________.

(a) proliferating precursor cells.
(b) cells more apically located than the terminally differentiated cells.
(c) Wnt proteins.
(d) induced pluripotent cells.


Answer: 

Cells that are terminally differentiated ___________.

Cells that are terminally differentiated ___________.

(a) will undergo apoptosis within a few days.
(b) can no longer undergo cell division.
(c) are unable to move.
(d) no longer produce RNAs.

Answer: 

The plasmodesmata in plants are functionally most similar to which animal cell junction?

The plasmodesmata in plants are functionally most similar to which animal cell junction?

(a) tight junction
(b) adherens junction
(c) gap junction
(d) desmosome


Answer: 

Plasmodesmata ___________.

Plasmodesmata ___________.

(a) permit small molecules to pass from one cell to another.
(b) are found only in animal cells.
(c) are closed by the neurotransmitter dopamine.
(d) provide tensile strength.


Answer: 

Cadherins ___________.

Cadherins ___________.

(a) are used to transfer proteins from one cell to another.
(b) mediate cell-cell attachments through homophilic interactions.
(c) are abundant in the plant cell wall.
(d) bind to collagen fibrils.

Answer: 

Which type of junction contributes the most to the polarization of epithelial cells?

Which type of junction contributes the most to the polarization of epithelial cells?

(a) adherens junctions
(b) desmosomes
(c) tight junctions
(d) gap junctions

Answer: 

Which type of junction involves a connection to the actin cytoskeleton?

Which type of junction involves a connection to the actin cytoskeleton?

(a) adherens junctions
(b) desmosomes
(c) tight junctions
(d) gap junctions

Answer: 

Which of the following statements about gap junctions is false?

Which of the following statements about gap junctions is false?

(a) Gap junctions are made of connexons.
(b) Molecules up to 1000 daltons in molecular mass can move across gap junctions.
(c) Because gap junctions do not allow ions to pass through, they are not used for electrically coupling cells.
(d) Gap junctions can close in response to extracellular signals.

Answer: 

A major distinction between the connective tissues in an animal and other main tissue types such as epithelium, nervous tissue, or muscle is _______________.

A major distinction between the connective tissues in an animal and other main tissue types such as epithelium, nervous tissue, or muscle is _______________.

(a) the ability of connective-tissue cells such as fibroblasts to change shape.
(b) the amount of extracellular matrix in connective tissues.
(c) the ability of connective tissues to withstand mechanical stresses.
(d) the numerous connections that connective-tissue cells make with each other.

Answer: 

Hemidesmosomes are important for ___________.

Hemidesmosomes are important for ___________.

(a) tubulation of epithelial sheets.
(b) linkages to glycosaminoglycans.
(c) forming the basal lamina.
(d) attaching epithelial cells to the extracellular matrix.

Answer: 

At desmosomes, cadherin molecules are connected to _____.

At desmosomes, cadherin molecules are connected to _____.

(a) actin filaments.
(b) intermediate filaments.
(c) microtubules.
(d) gap junctions.

Answer: 

Adherens junctions _______.

Adherens junctions _______.

(a) can be used to bend epithelial sheets into tubes.
(b) are most often found at the basal surface of cells.
(c) are found only in adult tissues.
(d) involve fibronectin and integrin interactions.

Answer: 

Tight junctions __________.

Tight junctions __________.

(a) allow small, water-soluble molecules to pass from cell to cell.
(b) interact with the intermediate filaments inside the cell.
(c) are formed from claudins and occludins.
(d) are found in cells in connective tissues.

Answer: 

A basal lamina ________.

A basal lamina ________.

(a) is a thin layer of connective-tissue cells and matrix underlying an epithelium.
(b) is a thin layer of extracellular matrix underlying an epithelium.
(c) is attached to the apical surface of an epithelium.
(d) separates epithelial cells from each other.

Answer: 

Which of the following statements is false?

Which of the following statements is false?

(a) Proteoglycans can act as filters to regulate which molecules pass through the extracellular medium.
(b) The negative charge associated with proteoglycans attracts cations, which cause water to be sucked into the extracellular matrix.
(c) Proteoglycans are a major component of compact connective tissues but are relatively unimportant in watery tissues such as the jellylike substance in the interior of the eye.
(d) Glycosaminoglycans are components of proteoglycan.

Answer: 

Proteoglycans in the extracellular matrix of animal tissues ________________.

Proteoglycans in the extracellular matrix of animal tissues ________________.

(a) chiefly provide tensile strength.
(b) allow cartilage to resist compression.
(c) are linked to microtubules through the plasma membrane.
(d) are polysaccharides composed of glucose subunits.

Answer: 

Which of the following statements about integrins is false?

Which of the following statements about integrins is false?

(a) Integrins use adaptor proteins to interact with the microtubule cytoskeleton.
(b) Integrins can switch to an activated state by binding to an extracellular matrix molecule.
(c) Integrins can switch to an activated state by binding to an intracellular protein.
(d) An activated integrin molecule takes on an extended conformation.

Answer: 

A cell can crawl through a tissue because of the transmembrane ______________ proteins that can bind to fibronectin outside of the cell.

A cell can crawl through a tissue because of the transmembrane ______________ proteins that can bind to fibronectin outside of the cell.

(a) integrin
(b) collagen
(c) gap junction
(d) claudin

Answer: 

Fibroblasts organize the collagen of the extracellular matrix by ______________.

Fibroblasts organize the collagen of the extracellular matrix by ______________.

(a) cutting and rejoining the fibrils.
(b) processing procollagen into collagen.
(c) twisting fibrils together to make ropelike fibers.
(d) pulling the collagen into sheets or cables after it has been secreted.

Answer: 

Which of the following statements about collagen is false?

Which of the following statements about collagen is false?

(a) Collagen synthase organizes the mature collagen molecules into ordered collagen fibrils.
(b) Collagen is synthesized as procollagen and secreted to the outside of the cell in a secretory vesicle.
(c) The terminal procollagen domains are cleaved by a protease in the extracellular space.
(d) Cells can break down a collagen matrix using matrix proteases.

Answer: 

Which of the following statements about animal connective tissues is true?

Which of the following statements about animal connective tissues is true?

(a) Enzymes embedded in the plasma membrane synthesize the collagen in the extracellular matrix extracellularly.
(b) In connective tissue, the intermediate filaments within the cells are important for carrying the mechanical load.
(c) Cells can attach to a collagen matrix by using fibronectin, an integral membrane protein.
(d) Proteoglycans can resist compression in the extracellular matrix.

Answer: 

Which of the following is not an example of a connective tissue?

Which of the following is not an example of a connective tissue?

(a) bone
(b) the layer of photoreceptors in the eye
(c) the jellylike interior of an eye
(d) cartilage

Answer: 

Which of the following statements about cellulose is false?

Which of the following statements about cellulose is false?

(a) Cellulose synthase enzyme complexes are integral membrane proteins.
(b) An array of microtubules guides the cellulose synthase complex as it moves in the membrane.
(c) The sugar monomers necessary for the synthesis of a cellulose polymer are transported across the plasma membrane.
(d) Microtubules are directly attached to the outside surface of the plasma membrane to form tracks that help orient the cellulose polymers.

Answer: