19 Questions
What is the rate of elongation in bacteria?
500 nucleotides per second
How many RNA primers are required for the leading strand?
One
Which enzyme is responsible for joining RNA nucleotides into a primer?
Primase
What does DNA polymerase III do after reaching the next RNA primer to the right?
Detaches
Which DNA polymerase replaces RNA nucleotides with DNA nucleotides in adjacent primers?
DNA polymerase I
What enzyme joins the sugar-phosphate backbones of Okazaki fragments into a continuous DNA strand?
DNA ligase
Which enzyme cannot join the final nucleotide of a replacement DNA segment to the adjacent Okazaki fragment?
DNA polymerase I
What is the role of DNA pol III in bacterial DNA replication?
Joining Okazaki fragments
What happens when DNA pol I adds DNA nucleotides to the 3' end of fragment 1?
It detaches from the fragment
What is the function of DNA ligase in DNA replication?
Links Okazaki fragments of newly synthesized DNA
How are Okazaki fragments synthesized during DNA replication?
Discontinuously on the lagging strand
What is the main role of DNA polymerase I in DNA replication?
Joins Okazaki fragments
Which enzyme is responsible for unwinding the double helix during DNA replication?
DNA helicase
In which direction does DNA synthesis proceed during replication?
5' → 3'
What happens at the end of each cycle of DNA replication?
Telomeres are snipped off, leading to shorter strands
Which enzyme is NOT involved in the process of joining Okazaki fragments?
DNA primase
What is the role of topoisomerases during DNA replication?
Prevent tangling and knotting of DNA strands
How many origins of replication may a eukaryotic chromosome have?
2
What is the purpose of synthesizing short RNA primers on the lagging strand during DNA replication?
To provide a starting point for DNA synthesis
Study Notes
- Helicase unwinds the parental double helix during DNA replication.
- Single strand binding proteins stabilize the unwound template strands to assist in replication.
- Leading strand synthesis occurs continuously in the 5′ to 3′ direction by DNA Polymerase III (Pol III).
- Primase initiates RNA primer synthesis for the Okazaki fragments in the lagging strand.
- DNA Pol III completes synthesis of a fragment before detaching to add DNA nucleotides to the next fragment.
- DNA Pol I removes RNA primers and replaces them with DNA nucleotides, leaving a free 3’ end.
- DNA ligase joins Okazaki fragments together to form a continuous DNA strand.
- Cells are exposed to DNA-damaging agents, which can lead to mutations if not repaired.
- DNA repair mechanisms include proofreading by DNA polymerases, mismatch repair, and nucleotide excision repair.
- Semiconservative DNA replication was demonstrated by Meselson and Stahl.
- Bacterial DNA replication involves several proteins like helicase, single-strand binding proteins, and topoisomerase.
- Replication forks are where new DNA strands elongate during replication.
- DNA polymerases require primers for nucleotide addition, with a rate of about 500 nucleotides per second in bacteria.
- Leading and lagging strands are synthesized differently, with the lagging strand requiring multiple primers.
- Eukaryotic chromosomes have multiple origins of replication and replicate bidirectionally.
- DNA synthesis always proceeds in the 5′ to 3′ direction.
- Telomeres are snipped off at the end of each replication cycle, leading to shorter DNA strands.
- DNA polymerases proofread newly synthesized DNA to correct any errors.
Test your knowledge on the steps involved in DNA replication, from unwinding the parental double helix to the synthesis of leading and lagging strands. Identify the correct sequence of events in DNA replication.
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