DNA Replication and Repair

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Questions and Answers

What distinguishes type II topoisomerases from type I topoisomerases?

Type II topoisomerases hydrolyze ATP to reset after each cycle. (correct)

Type II topoisomerases are more common in eukaryotic cells.

Type II topoisomerases operate only on single-stranded DNA.

Type II topoisomerases do not require ATP.

What role do the initiator proteins play in bacterial DNA replication?

They recruit DNA polymerases for synthesis.

They repair DNA damage during replication.

They synthesize the leading strand of DNA.

They promote the unwinding of the double helix. (correct)

During DNA replication in E. coli, what happens to the hemimethylated origin of replication?

It becomes active immediately for replication.

It allows all initiator proteins to bind freely.

It facilitates rapid synthesis of Okazaki fragments.

It is blocked by the Seq A protein. (correct)

How does DNA methylation affect the initiation of replication in E. coli?

It creates a refractory period for DNA initiation. Signup and view all the answers

What is the significance of the replication fork in DNA replication?

It marks the location where the leading and lagging strands are synthesized. Signup and view all the answers

What role do helicases play during DNA replication?

They separate the DNA strands for replication. Signup and view all the answers

What is the consequence of a fully methylated GATC sequence in the replication origin?

It activates the origin for initiation of replication. Signup and view all the answers

Which protein is responsible for loading the helicase in bacterial DNA replication?

DnaC Signup and view all the answers

What is the primary function of germ-line cells in sexually reproducing organisms?

To propagate genetic information to the next generation Signup and view all the answers

How many chromosomes do gametes contain compared to somatic cells?

Half the number of chromosomes as somatic cells Signup and view all the answers

What direction is DNA synthesized during replication?

5'-to-3' direction Signup and view all the answers

What is the role of DNA polymerase during DNA synthesis?

To add nucleotides to the growing DNA strand Signup and view all the answers

What occurs when a deoxynucleoside triphosphate pairs with a template strand?

It creates a hydrogen bond with its complementary base Signup and view all the answers

What is the result of the hydrolysis of a high-energy phosphate bond during DNA synthesis?

It provides energy for the formation of pyrophosphate Signup and view all the answers

What ensures the precision of DNA replication?

The complementary nature of base pairing Signup and view all the answers

What is released during the addition of a deoxynucleotide to a growing DNA strand?

A molecule of pyrophosphate Signup and view all the answers

What is the primary role of the CMG helicase during eukaryotic DNA replication?

To move unidirectionally along the leading-strand template Signup and view all the answers

Which of the following correctly describes the process of strand-directed mismatch repair in eukaryotes?

MutL, in conjunction with a nuclease, removes DNA starting from the mismatch Signup and view all the answers

What is one consequence of the 'winding problem' that occurs during DNA replication?

Tension buildup that can halt the replication fork Signup and view all the answers

How do DNA topoisomerases alleviate the tension created during DNA replication?

By allowing rotation of the DNA around the covalent backbone bonds Signup and view all the answers

In the context of DNA replication, what does the term 'supercoiling' refer to?

The twisting of the DNA double helix around itself due to tension Signup and view all the answers

What action does DNA polymerase d perform in the mismatch repair process?

It fills in the gap left after the excision of nucleotides Signup and view all the answers

What is the main function of the MutS protein during DNA repair?

To bind and kink the DNA at mismatched base pairs Signup and view all the answers

What can effectively stop the progression of the replication fork?

Excessive tension that exceeds the helicase's energy provision Signup and view all the answers

Study Notes

DNA Replication, Repair, and Recombination

Germ-line cells propagate genetic information to the next generation.
Gametes (e.g., eggs and sperm) have half the number of chromosomes as other body cells.
Zygotes form after fertilization, containing a full set of chromosomes.
Somatic cells form the organism's body and do not contribute their DNA to the next generation.

DNA Replication as a Template

DNA acts as a template for its own replication.
Nucleotides A pairs with T, and G pairs with C.
Each strand of a DNA double helix can serve as a template for a complementary strand.
Two exact copies of the original double helix are produced.

DNA Synthesis Chemistry

Nucleotides enter as deoxyribonucleoside triphosphates.
Addition of a deoxyribonucleotide to the 3' end of a polynucleotide chain is the fundamental DNA synthesis reaction.
Base pairing between incoming and existing strands guides new strand formation.
Ensuring complementary nucleotide sequence.

DNA Polymerase's Role

DNA polymerase adds deoxyribonucleotides to the 3' end of a growing DNA strand.
This occurs in the 5'-to-3' direction.
Energy for polymerization comes from hydrolysis of high-energy phosphate bonds in incoming nucleotides.
DNA polymerase guides the incoming nucleoside triphosphate to the template strand.
DNA polymerase proofreads its work.
If an incorrect nucleotide is added, DNA polymerase removes it and replaces it with the correct one.
This process maintains high fidelity of DNA replication.

DNA Polymerases Contain Separate Sites

DNA polymerases have separate sites for synthesis and proofreading.
Polymerization activity is distinct from editing activity.
Incorrect nucleotides are removed in the editing site.
This process ensures nucleotide sequence accuracy.

Different Enzymes for Lagging Strand Synthesis

RNA primers are synthesized by primase, using a DNA template.
Primase synthesizes 5' to 3'.
Primase can start a new polynucleotide chain without a base-paired 3' end.
Eukaryotic RNA primers are made at intervals, typically 10 nucleotides long.
These primers are extended by DNA polymerases.
Primers are removed by nucleases.
Gaps are filled in by repair DNA polymerase, with proofreading ability.
Fragments are joined by DNA ligase.

DNA Helicase Enzymes and Strand Separation

DNA helicases separate DNA strands.
Their movement is powered by ATP hydrolysis.
Most DNA helicases consist of a ring of 6 subunits.

Single-Stranded DNA-Binding Proteins (SSB)

SSB proteins bind to single-stranded DNA.
They prevent re-annealing of DNA strands.
Cooperative binding helps straighten DNA, improving the process of DNA polymerization.
Prevents hairpin helices from forming.

Eukaryotic Mismatch Repair

In eukaryotes, MutS proteins bind to mismatched base pairs.
They recruit MutL and the complex scans for a gap and a sliding clamp.
MutL and another nuclease removes the mismatched portion of DNA.
This is followed by DNA polymerase to fill in the gaps.
Sealed by DNA Ligase.

DNA Topoisomerase I and II

Type I DNA topoisomerases create a transient single covalent bond with DNA.
This allows free rotation of the DNA around the covalent backbone.
Type II DNA topoisomerases hydrolyze ATP to release and reset the enzyme.
They are essential during rapidly dividing cells.

Replication Fork Initiation

DNA replication starts at specific origin sites.
Origin-recognition complex (ORC) binds to origins in eukaryotes.
Initiator proteins destabilize DNA.
Additional proteins participate in loading helicases.
Primers are required and then synthesized.

Bacterial Replication Fork

Bacterial chromosomes are circular.
Two replication forks move in opposite directions.
DNA is unwound and separated.
New strands are synthesized.

Eukaryotic Replication Fork

Unlike bacteria, eukaryotic replication forks can function independently.
CMG (Cdc45-MCM-GINS) helicase moves unidirectionally along the leading strand template during replication.
Eukaryotic DNA replication is more complicated.

Telomere Replication

Telomeres are repetitive sequences at the ends of linear eukaryotic chromosomes.
Telomerase synthesizes new telomere DNA by using its RNA molecule as a template.
DNA polymerase then extends the strand.

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Description

Explore the fundamentals of DNA replication, repair, and recombination in this quiz. Learn about germ-line and somatic cells, the role of gametes, and the chemistry of DNA synthesis. Test your understanding of these crucial biological processes.