Biology Cell Cycle and DNA Replication

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Questions and Answers

What is a major limitation of DNA polymerase accuracy?

Incorporation of ribonucleotides at high rates

Inability to initiate DNA synthesis

Flickering of bases into wrong tautomeric forms (correct)

Degradation of the DNA at the 5' end

How does DNA polymerase ensure the removal of incorrectly paired nucleotides?

By elongating the DNA from the 5' end

By incorporating ribonucleotides into the chain

By utilizing a proofreading exonuclease activity (correct)

By altering the nucleotide-binding site

What is the primary reason DNA polymerases do not incorporate rNTPs efficiently?

The lack of a 3'-OH group on rNTPs

Incompatibility with the template strand

Higher concentration of rNTPs in the cell

Steric exclusion due to active site size (correct)

Which change would likely weaken the discrimination between dNTPs and rNTPs in DNA polymerase?

Changing amino acids to smaller side chain variants Signup and view all the answers

What role does the 3' end of an existing nucleotide play in DNA synthesis?

It provides a free -OH group for adding nucleotides Signup and view all the answers

Which of the following statements about DNA polymerase is true?

It requires an RNA primer to initiate synthesis Signup and view all the answers

What class of compounds can inhibit DNA synthesis effectively?

Nucleotides that fail to meet all requirements for use Signup and view all the answers

Which of the following best describes a property of DNA polymerases?

They can discriminate between rNTPs and dNTPs Signup and view all the answers

What role do telomeres play in somatic cells of aging individuals?

They shorten, potentially contributing to aging. Signup and view all the answers

How can steady shortening of telomeres be beneficial in preventing cancer?

By limiting the number of divisions in somatic cells. Signup and view all the answers

What correlation exists between telomere length and tumor cells?

Tumor cells frequently have short telomeres due to high divisions. Signup and view all the answers

Which outcome has been observed with telomerase reactivation in studies on mice?

Extension of telomeres and reversal of neurodegeneration. Signup and view all the answers

What happens if the DNA repair mechanisms fail to correct nucleotide pairing?

Mutations arise and can be passed to daughter cells. Signup and view all the answers

What can be a potential consequence of mutations in genes?

They can lead to both deleterious and advantageous effects. Signup and view all the answers

Which statement is true regarding the central dogma of molecular biology?

It explains how genes encode proteins. Signup and view all the answers

What is one proposed effect of telomere shortening on overall organism aging?

It may contribute to the aging process of certain tissues. Signup and view all the answers

What is a potential consequence of insertion or deletion mutations during DNA replication?

Frameshift mutations or changes in amino acids Signup and view all the answers

Which regions in DNA are more prone to replication slippage?

Regions with repetitive sequences Signup and view all the answers

What spontaneous reaction leads to the daily loss of approximately 18,000 purine bases in human DNA?

Depurination Signup and view all the answers

How often does spontaneous deamination of cytosine to uracil occur in DNA per cell per day?

About 100 bases per cell Signup and view all the answers

What type of damage can ultraviolet radiation cause to DNA?

Covalent linkages between adjacent pyrimidine bases Signup and view all the answers

What is a possible effect if DNA mutations are not repaired during replication?

Propagation of mutations in daughter DNA Signup and view all the answers

What is the relationship between reactive metabolites and DNA damage?

They can damage DNA bases Signup and view all the answers

What can frequent random changes in DNA sequences lead to?

Disastrous genetic consequences Signup and view all the answers

What is the primary requirement for homologous recombination repair (HR) to function effectively?

Availability of a homologous intact DNA strand Signup and view all the answers

During which phase of the cell cycle does double-strand break repair primarily occur?

Late S phase or early G2 phase Signup and view all the answers

Which step initiates the homologous recombination repair process?

Enzyme recognition of the double-strand break Signup and view all the answers

In homologous recombination repair, what role do overhanging 3′ ends play?

They aid in aligning complementary sequences on the sister chromatid. Signup and view all the answers

How does nonhomologous end joining (NHEJ) differ from homologous recombination repair?

It does not require a homologous DNA template. Signup and view all the answers

What is a potential consequence of defects in double-strand break repair mechanisms?

Increased susceptibility to breast and ovarian cancer Signup and view all the answers

What happens to the resulting heteroduplex molecule after DNA repair synthesis in homologous recombination?

It is resolved and the chromatids separate. Signup and view all the answers

Which of the following syndromes is associated with defects in double-strand break repair?

Fanconi anemia Signup and view all the answers

What is the primary reason that DNA polymerase can only synthesize RNA primers at the lagging strand?

DNA polymerase requires an existing DNA strand to extend from. Signup and view all the answers

What is the consequence of DNA polymerase I not being able to replace the final RNA primer on the lagging strand?

A short stretch of DNA remains unreplicated. Signup and view all the answers

Why is it that prokaryotic DNA does not experience the shortening problem seen in eukaryotic DNA?

Prokaryotic DNA has no free ends due to its circular structure. Signup and view all the answers

What structure at the ends of linear eukaryotic chromosomes helps to prevent DNA shortening?

Telomeres Signup and view all the answers

What happens to the DNA strands after replication if there is no mechanism to prevent shortening?

Each daughter DNA becomes shorter after each round of replication. Signup and view all the answers

What underlying reason causes the lagging strand to be synthesized in short fragments?

DNA polymerase synthesizes DNA in the opposite direction to the template reading. Signup and view all the answers

Which statement accurately describes the function of RNA primers during DNA replication?

RNA primers initiate the synthesis of Okazaki fragments on the lagging strand. Signup and view all the answers

What is the fate of the final RNA primer synthesized during DNA replication at the 5' end of the lagging strand?

It is removed and cannot be replaced with DNA. Signup and view all the answers

What is the primary function of DNA polymerase III in prokaryotic cells?

It monitors base pairing during DNA synthesis. Signup and view all the answers

What is the consequence of incorrect base pairing by DNA polymerase III?

It dramatically slows down the rate of nucleotide addition. Signup and view all the answers

How does DNA polymerase III ensure high precision during DNA replication?

By possessing 3' → 5' exonuclease activity. Signup and view all the answers

What happens when a mismatched base pair is formed in the DNA polymerase active site?

The exonuclease activity removes the incorrect nucleotide. Signup and view all the answers

What is the average error rate of DNA synthesis by DNA polymerase III without proofreading?

1 incorrect nucleotide per 105 nucleotides added. Signup and view all the answers

What effect does the proof-reading function of DNA polymerase III have on the error rate?

It decreases the error rate to 1 in 10 million nucleotides. Signup and view all the answers

What process provides an additional level of accuracy in DNA synthesis beyond proofreading?

Post-replication mismatch repair. Signup and view all the answers

What term describes nucleases that degrade DNA from its ends?

Exonucleases Signup and view all the answers

Study Notes

The Cell Cycle

Living organisms reproduce to create more of their own kind. Cell division is essential for growth and replacing damaged cells. Daughter cells must be genetically identical to the parent cell.
Cell division is crucial in all biological functions.
Cell division plays a role in the reproduction of prokaryotic cells, unicellular eukaryotes, and the growth and repair of multicellular eukaryotes. Renewal and repair of cells occur in fully grown multicellular organisms.

DNA Replication, Damage, and Repair

DNA replication is essential for the transmission of genetic information to daughter cells.
DNA replication involves accurate copying of DNA, distribution of the copies, and then cell division into daughter cells.
The genome is a cell's total genetic information.
Eukaryotic genomes typically consist of multiple DNA molecules, and human cells have approximately 2 meters of DNA.
The replication and distribution of a large amount of DNA is a complex process, which is possible due to the manageable organization of the DNA.

DNA Replication

DNA replication requires a template, enzymes, and building blocks.
Replication starts at an origin of replication.
DNA replication happens in a semiconservative way.
Replication proceeds in both directions from the origin of replication at a replication fork.
Many replication bubbles can begin from many origins and eventually fuse together, thus increasing replication speed in eukaryotes.

DNA Replication Requires

Template: The parental DNA molecule.
Enzymes: Enzymes that copy the template.
Building blocks: Nucleotides to assemble into the new copy.
DNA polymerase: This enzyme matches existing DNA bases with complementary nucleotides, linking the nucleotides together to form new strands.

Semiconservative DNA Replication

DNA polymerase monitors if a correct base pair forms.
DNA polymerase will have a significantly slower rate of incorrect base pairing.
The rate of incorrect nucleotide incorporation is much slower than the correct.
DNA polymerase contains a 3' to 5' exonuclease activity that checks new nucleotides continuously.
Nucleases are enzymes that can degrade a DNA end or cut within a strand.
DNA Polymerase is highly accurate, and DNA polymerase insertions one incorrect nucleotide for every 10^5 nucleotides.
Proofreading exonucleases reduce incorrect pairing to 1 per 10^7 nucleotides.

DNA Replication Begins

Replication begins at specific sites called origins of replication.
Special proteins recognize the origin sequences and separate the two strands, creating a replication "bubble."
Replication proceeds on both strands simultaneously.
E. coli chromosomes have one origin of replication; whereas eukaryotic chromosomes have multiple origins.

DNA Replication of Two Strands

Leading strand is synthesized continuously.
Lagging strand is synthesized discontinuously in short segments called Okazaki fragments.
RNA primers are required to initiate replication on the lagging strand.
DNA polymerase I replaces the RNA primers with DNA.

Replicating the Ends of DNA Molecules

Linear chromosomes have ends called telomeres to prevent shortening during replication.
Telomerases catalyze the lengthening of telomeres in germ cells and some stem cells to maintain the chromosome's length.

DNA Damage and Repair

DNA is vulnerable to damage from reactive oxygen species, reactive chemicals, and physical agents (e.g., radiation).
Mutations can be deleterious or advantageous.
Cells have evolved multiple repair mechanisms to correct DNA damage.
Base-excision repair and nucleotide-excision repair are common DNA repair pathways.
Double-strand break repair utilizes homologous recombination repair or non-homologous end joining.

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Description

This quiz covers important processes in the cell cycle, including cell division and DNA replication. Understand how these processes are essential for growth, repair, and reproduction in both prokaryotic and eukaryotic organisms. Explore the complexities involved in accurately copying and distributing genetic information in cells.