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DNA replication is a process solely dedicated to repairing damaged DNA strands.
Answer: False
DNA replication is the fundamental biological process by which a cell creates exact copies of its DNA, essential for cell division and inheritance, not solely for DNA repair.
In semiconservative DNA replication, each new DNA molecule consists of two newly synthesized strands.
Answer: False
Semiconservative replication means each new DNA molecule comprises one original (parental) strand and one newly synthesized strand.
The double-stranded helical structure of DNA facilitates replication by allowing each strand to serve as a template for the other.
Answer: True
The complementary base pairing within the double helix enables each strand to act as a template for the synthesis of a new complementary strand.
What is the fundamental biological process by which a cell creates exact copies of its DNA?
Answer: DNA replication
DNA replication is the biological process by which a cell creates exact copies of its DNA, essential for cell division and inheritance.
Which statement accurately describes semiconservative DNA replication?
Answer: Each new DNA molecule contains one original strand and one newly synthesized strand.
Semiconservative replication means each new DNA molecule comprises one original (parental) strand and one newly synthesized strand, ensuring accurate genetic information transfer.
How does the double-stranded structure of DNA facilitate its replication?
Answer: The complementary base pairing allows each strand to serve as a template for a new strand.
The complementary base pairing within the double helix enables each strand to act as a template for the synthesis of a new complementary strand.
A DNA nucleotide is composed of a deoxyribose sugar, a phosphate group, and a nitrogenous base.
Answer: True
The source material indicates that a DNA nucleotide comprises a deoxyribose sugar, a phosphate group, and a nitrogenous base. The presence of ribose sugar characterizes RNA nucleotides.
Adenine and guanine are classified as pyrimidine bases in DNA.
Answer: False
Adenine and guanine are purines, while cytosine and thymine are classified as pyrimidines in DNA.
Adenine pairs with guanine via three hydrogen bonds during DNA replication.
Answer: False
Adenine pairs with thymine via two hydrogen bonds, while guanine pairs with cytosine through three hydrogen bonds.
Which of the following is NOT a component of a DNA nucleotide?
Answer: Ribose sugar
A DNA nucleotide consists of deoxyribose sugar, a phosphate group, and a nitrogenous base. Ribose sugar is found in RNA nucleotides.
In DNA, which base pairs with Guanine (G)?
Answer: Cytosine (C)
Guanine (G) specifically pairs with Cytosine (C) through three hydrogen bonds in DNA.
DNA polymerase can initiate DNA synthesis without a pre-existing strand.
Answer: False
DNA polymerases cannot initiate DNA synthesis from scratch; they require a pre-existing strand with a free 3'-hydroxyl group, typically provided by an RNA primer.
DNA helicase unwinds the DNA double helix by breaking hydrogen bonds between base pairs.
Answer: True
DNA helicase functions by disrupting the hydrogen bonds that hold the two DNA strands together, thereby unwinding the double helix at the replication fork.
Okazaki fragments are joined together by the enzyme DNA ligase.
Answer: True
Following the removal of RNA primers and replacement with DNA, Okazaki fragments are covalently linked by DNA ligase, which forms the phosphodiester bonds necessary to complete the lagging strand.
Topoisomerases prevent DNA tangling by relieving torsional stress ahead of the replication fork.
Answer: True
Topoisomerases function to alleviate the torsional strain that accumulates ahead of the replication fork as the DNA unwinds. They achieve this by transiently cleaving and rejoining the DNA backbone.
Single-strand binding proteins (SSBs) stabilize separated DNA strands to prevent them from re-annealing.
Answer: True
Single-strand binding proteins bind to the separated DNA strands, preventing them from re-annealing or forming secondary structures that could impede the progress of DNA polymerase. They stabilize the single-stranded DNA templates.
In E. coli, DNA polymerase I removes RNA primers using its 5' to 3' exonuclease activity.
Answer: True
DNA polymerase I in E. coli possesses 5' to 3' exonuclease activity, which it utilizes to excise RNA primers during DNA synthesis. It subsequently fills the gap with DNA via its polymerase activity.
The Minichromosome Maintenance (Mcm) complex functions as the primary DNA helicase in eukaryotes.
Answer: True
The Mcm complex serves as the principal DNA helicase in eukaryotic cells, responsible for unwinding the DNA double helix at the replication fork.
The replisome is a complex molecular machine composed of numerous replication enzymes.
Answer: True
The replisome is not a single enzyme but rather a multi-protein complex that orchestrates the various enzymatic activities required for DNA replication at the replication fork.
In eukaryotes, DNA polymerase epsilon (Pol ε) is primarily responsible for leading strand synthesis.
Answer: True
In eukaryotic DNA replication, DNA polymerase epsilon (Pol ε) is primarily responsible for the synthesis of the leading strand, while DNA polymerase delta (Pol δ) is predominantly involved in lagging strand synthesis.
DNA ligase seals breaks in the DNA backbone by forming phosphodiester bonds.
Answer: True
DNA ligase functions to catalyze the formation of phosphodiester bonds, thereby sealing nicks in the DNA backbone and joining DNA fragments.
Primase synthesizes short RNA primers to initiate DNA synthesis.
Answer: True
Primase is an enzyme that synthesizes short RNA primers, which are essential for initiating DNA synthesis as DNA polymerases require a pre-existing 3'-OH group.
DNA polymerase alpha (Pol α) in eukaryotes synthesizes the initial RNA-DNA primers.
Answer: True
DNA polymerase alpha (Pol α), in complex with primase, is responsible for synthesizing the initial RNA primers and a short stretch of DNA, thereby initiating DNA synthesis on both leading and lagging strands.
Which enzyme is primarily responsible for unwinding the DNA double helix at the replication fork?
Answer: DNA helicase
DNA helicase is the enzyme that unwinds the DNA double helix by breaking the hydrogen bonds between complementary base pairs, creating the replication fork.
What is the function of primase in DNA replication?
Answer: To synthesize short RNA primers that initiate DNA synthesis.
Primase is an enzyme that synthesizes short RNA primers, which are essential for initiating DNA synthesis as DNA polymerases require a pre-existing 3'-OH group.
Which enzyme seals the nicks in the DNA backbone, particularly joining Okazaki fragments?
Answer: DNA ligase
DNA ligase functions to catalyze the formation of phosphodiester bonds, thereby sealing nicks in the DNA backbone and joining DNA fragments, including Okazaki fragments.
Which of the following enzymes is responsible for relieving torsional stress ahead of the replication fork?
Answer: Topoisomerase
Topoisomerases function to alleviate the torsional strain that accumulates ahead of the replication fork as the DNA unwinds. They achieve this by transiently cleaving and rejoining the DNA backbone.
What is the primary role of DNA polymerase I in E. coli replication?
Answer: Removing RNA primers and filling the resulting gaps with DNA.
DNA polymerase I in E. coli plays a key role in removing RNA primers using its 5' to 3' exonuclease activity and filling the resulting gap with DNA via its polymerase activity.
What is the 'replisome'?
Answer: A complex molecular machine of replication enzymes.
The replisome is not a single enzyme but rather a multi-protein complex that orchestrates the various enzymatic activities required for DNA replication at the replication fork.
What is the function of the Mcm complex in eukaryotic DNA replication?
Answer: To act as the primary DNA helicase.
The Mcm complex serves as the principal DNA helicase in eukaryotic cells, responsible for unwinding the DNA double helix at the replication fork.
Which eukaryotic DNA polymerases are primarily responsible for synthesizing the leading and lagging strands, respectively?
Answer: Pol ε (leading), Pol δ (lagging)
In eukaryotic DNA replication, DNA polymerase epsilon (Pol ε) is primarily responsible for the synthesis of the leading strand, while DNA polymerase delta (Pol δ) is predominantly involved in lagging strand synthesis.
DNA strands possess directionality, denoted as 5' and 3' ends, which dictates the direction of DNA synthesis.
Answer: True
DNA strands have directionality, referred to as the 5' (five-prime) and 3' (three-prime) ends, based on the numbering of carbon atoms in the deoxyribose sugar. DNA polymerase can only add new nucleotides to the 3' end, meaning DNA synthesis always proceeds in the 5' to 3' direction.
The leading strand is synthesized discontinuously in short fragments known as Okazaki fragments.
Answer: False
The leading strand is synthesized continuously, whereas the lagging strand is synthesized discontinuously in short fragments known as Okazaki fragments.
DNA replication initiation involves the unwinding of DNA at origins of replication.
Answer: True
The initiation of DNA replication begins at specific sequences known as origins of replication, where the DNA double helix is unwound to form a replication bubble.
Origins of replication often contain sequences rich in Adenine (A) and Thymine (T) bases because they are easier to separate.
Answer: True
Origins of replication frequently feature sequences with a high proportion of adenine and thymine bases, as the two hydrogen bonds between A-T pairs require less energy to break compared to the three hydrogen bonds in G-C pairs, facilitating DNA unwinding.
Prokaryotes typically initiate DNA replication from a single origin on their circular chromosomes.
Answer: True
Prokaryotic DNA replication typically commences from a singular origin of replication on the circular chromosome, contrasting with the multiple origins found in eukaryotic chromosomes.
The replication factory model proposes that DNA template moves through stationary replication enzymes.
Answer: True
The replication factory model posits that DNA replication occurs at fixed nuclear sites, with the DNA molecule itself translocating through these stationary enzymatic complexes.
Termination of replication in eukaryotes occurs when forks meet or reach the ends of linear chromosomes.
Answer: True
In eukaryotes, DNA replication termination occurs when replication forks converge or reach the termini of linear chromosomes.
What is the directionality of DNA synthesis, meaning the direction in which DNA polymerase adds new nucleotides?
Answer: 5' to 3'
DNA synthesis proceeds exclusively in the 5' to 3' direction because DNA polymerase adds incoming nucleotides to the 3'-hydroxyl group of the growing strand.
Which of the following is a key characteristic of DNA replication origins in eukaryotes?
Answer: They are often rich in Adenine (A) and Thymine (T) bases.
Origins of replication frequently feature sequences with a high proportion of adenine and thymine bases, as the two hydrogen bonds between A-T pairs require less energy to break compared to the three hydrogen bonds in G-C pairs, facilitating DNA unwinding.
How does DNA replication differ significantly between prokaryotes and eukaryotes regarding initiation?
Answer: Eukaryotes use multiple origins, while prokaryotes typically use a single origin.
Prokaryotic DNA replication typically commences from a singular origin of replication on the circular chromosome, contrasting with the multiple origins found in eukaryotic chromosomes.
Which statement best describes the 'replication factory' model?
Answer: DNA replication occurs at fixed sites, with DNA moving through these sites.
The replication factory model posits that DNA replication occurs at fixed nuclear sites, with the DNA molecule itself translocating through these stationary enzymatic complexes.
Which of the following is a key difference in termination of DNA replication between bacteria and eukaryotes?
Answer: Eukaryotes terminate replication when forks meet or reach chromosome ends, while bacteria terminate at specific sites.
In eukaryotes, DNA replication termination occurs when replication forks converge or reach the termini of linear chromosomes, whereas bacteria typically terminate at specific sites on their circular chromosomes.
The energy required for DNA synthesis is derived from the hydrolysis of ATP molecules.
Answer: False
The energy for DNA synthesis originates from the hydrolysis of high-energy phosphate bonds within incoming nucleoside triphosphates (dNTPs), releasing pyrophosphate.
Telomerase adds repetitive DNA sequences to the ends of eukaryotic chromosomes, known as telomeres.
Answer: True
Telomerase is an enzyme that extends the repetitive DNA sequences found at the termini of eukaryotic chromosomes, termed telomeres, thereby counteracting the shortening that occurs during replication.
The Hayflick limit refers to the finite number of cell divisions a normal cell population can undergo.
Answer: True
The Hayflick limit denotes the limited number of times a normal somatic cell population can divide before entering senescence, a phenomenon linked to telomere shortening.
The pre-replication complex (pre-RC) in eukaryotes licenses origins for DNA replication during the G1 phase.
Answer: True
The pre-replication complex (pre-RC) assembles at origins of replication during the G1 phase, a process known as licensing, which permits DNA replication to commence during the subsequent S phase.
DnaA protein is the key initiator of DNA replication in prokaryotic cells like E. coli.
Answer: True
The DnaA protein is recognized as the primary initiator of DNA replication in prokaryotic organisms such as E. coli, binding to the origin of replication to commence the process.
SeqA protein in E. coli prevents replication initiation by binding to hemimethylated DNA sequences at the origin.
Answer: True
The SeqA protein in E. coli functions to inhibit replication initiation by binding to hemimethylated DNA at the origin, thereby sequestering it until full methylation occurs.
Replication stress occurs when the DNA replication process is disrupted or slowed down.
Answer: True
Replication stress is defined as a condition where the normal progression of DNA replication is impeded or decelerated due to various cellular challenges.
The Polymerase Chain Reaction (PCR) amplifies specific DNA sequences in vitro using cycles of heating and cooling.
Answer: True
PCR amplifies specific DNA sequences in vitro through repeated cycles of denaturation, annealing, and extension, utilizing a thermostable DNA polymerase.
The G1/S checkpoint controls the cell's entry into the S phase, preventing replication if conditions are unfavorable.
Answer: True
The G1/S checkpoint serves as a critical regulatory point that governs the cell's transition into the S phase, ensuring that cellular conditions are conducive for DNA replication before it commences.
Cdt1 is a licensing factor that helps load the Mcm helicase onto origins during the G1 phase.
Answer: True
Cdt1 functions as a key licensing factor in eukaryotes, facilitating the loading of the Mcm helicase onto origins of replication during the G1 phase of the cell cycle.
Geminin prevents DNA re-replication by binding to Cdt1, thereby inhibiting Mcm helicase loading.
Answer: True
Geminin acts as an inhibitor of DNA re-replication by binding to Cdt1, thereby preventing the loading of the Mcm helicase complex onto origins. This mechanism ensures that DNA is replicated only once per cell cycle.
The proofreading function of DNA polymerase increases the rate of mutations during replication.
Answer: False
The proofreading function of DNA polymerase serves to remove incorrectly incorporated nucleotides, thereby decreasing the rate of mutations.
What provides the energy required for the addition of new nucleotides during DNA synthesis?
Answer: The release of pyrophosphate from incoming nucleoside triphosphates (dNTPs)
The energy for DNA synthesis originates from the hydrolysis of high-energy phosphate bonds within incoming nucleoside triphosphates (dNTPs), releasing pyrophosphate.
The 'Hayflick limit' is related to which phenomenon in cell biology?
Answer: The number of cell divisions a normal cell population can undergo
The Hayflick limit denotes the limited number of times a normal somatic cell population can divide before entering senescence, a phenomenon linked to telomere shortening.
What is the role of the G1/S checkpoint in the eukaryotic cell cycle concerning DNA replication?
Answer: It prevents the cell from entering the S phase if conditions are unfavorable for replication.
The G1/S checkpoint serves as a critical regulatory point that governs the cell's transition into the S phase, ensuring that cellular conditions are conducive for DNA replication before it commences.
How does geminin regulate DNA replication in eukaryotes?
Answer: By inhibiting Cdt1, thus preventing Mcm helicase loading.
Geminin acts as an inhibitor of DNA re-replication by binding to Cdt1, thereby preventing the loading of the Mcm helicase complex onto origins. This mechanism ensures that DNA is replicated only once per cell cycle.
What is replication stress?
Answer: A state where DNA replication is disrupted or slowed down.
Replication stress is defined as a condition where the normal progression of DNA replication is impeded or decelerated due to various cellular challenges.
What is the purpose of the Polymerase Chain Reaction (PCR)?
Answer: To amplify specific DNA sequences in a laboratory setting.
PCR amplifies specific DNA sequences in vitro through repeated cycles of denaturation, annealing, and extension, utilizing a thermostable DNA polymerase.
In E. coli, how does the SeqA protein regulate the initiation of DNA replication?
Answer: By binding to hemimethylated DNA at the origin, sequestering it.
The SeqA protein in E. coli functions to inhibit replication initiation by binding to hemimethylated DNA at the origin, thereby sequestering it until full methylation occurs.
What is the function of the pre-replication complex (pre-RC) in eukaryotes?
Answer: To license origins of replication for initiation.
The pre-replication complex (pre-RC) assembles at origins of replication during the G1 phase, a process known as licensing, which permits DNA replication to commence during the subsequent S phase.
What is the purpose of proofreading by DNA polymerase?
Answer: To remove incorrectly incorporated nucleotides and reduce mutation rates.
The proofreading function of DNA polymerase serves to remove incorrectly incorporated nucleotides, thereby decreasing the rate of mutations and increasing replication fidelity.