26 Questions
Which enzyme is central to DNA replication?
DNA polymerase
What is the term for replication in which each daughter double helix contains one parental and one newly synthesized strand?
Semiconservative replication
During which phase of the cell cycle does DNA replication occur?
S phase
What are the building blocks of the DNA backbone?
Nucleotides
What is the role of DNA ligase in DNA replication?
Joining Okazaki fragments
Which enzyme is responsible for removing RNA primers and filling the gaps between Okazaki fragments with DNA?
DNA polymerase
What is the major role of topoisomerases in DNA replication?
Preventing DNA tangling
Which type of topoisomerase produces transient double-strand breaks in DNA?
Type II
What is the function of the DNA Polymerase/primase complex in eukaryotic replication?
Producing RNA-DNA oligonucleotides
What is the 'end-replication problem' in DNA replication?
Lagging strand shorter than its template
When does replication begin at some origins earlier in S phase than at others?
Early S phase
What is the bidirectional nature of DNA replication?
Replication in both directions from the origin
What happens to chromosomal histone and nonhistone proteins during DNA replication?
They are duplicated
When do genes in active segments of the chromosomes replicate?
Early in S phase
What happens as replication nears completion in eukaryotic cells?
Formation of new molecules
What is the function of DNA polymerase?
Joining nucleotides to form the growing DNA chain
How are replication origins identified?
By the replication apparatus and sequence-specific binding proteins
What is the role of DNA helicase in replication fork formation?
Unwinding the two strands of parental DNA
How does DNA polymerase 1 synthesize DNA?
In the 5' to 3' direction without a primer strand
What is the function of primase in DNA replication?
Synthesizing RNA primers for DNA synthesis initiation
Which structure is involved in DNA replication and consists of DNA helicase, SSBs, DNA polymerase, and Primase?
Replication fork
What is the significance of repeated 11 nucleotide sequences in Saccoromyces cerevisiae replication origins?
They are recognized by the replication apparatus
In which direction is one strand synthesized during DNA synthesis?
5' to 3'
What is the role of single-stranded DNA-binding proteins (SSBs) in replication fork formation?
Stabilizing single-stranded DNA strands
What is the spacing interval between replication origins in higher eukaryotes?
30,000 to 300,000 bp
What is the function of Okazaki fragments in DNA replication?
Joining nucleotides to form the growing DNA chain
Study Notes
- Isolation of coli by Körnberg was a significant discovery in molecular biology
- DNA polymerase is an enzyme that catalyzes the joining of nucleotides to form the growing DNA chain
- The free nucleotides (dNTPs) serve as substrates for this enzyme
- Replication requires a single-stranded DNA template and DNA polymerase
- Replication in genomes of prokaryotes and eukaryotes begins from specific nucleotide sequences called origins of replication
- Identification of origins of replication:
- Recognized by the replication apparatus (sequence-specific dsDNA binding proteins = initiator proteins)
- In Saccoromyces cerevisiae, replication origins contain repeated 11 nucleotide sequences (A/T)TTTAT(A/G)TTT(A/T) (100 bp in length)
- Prokaryotes have a single replication origin
- Higher eukaryotes have many replication origins (30,000 ORC in human genome)
- Replication origins are spaced at intervals of 30,000 to 300,000 bp
- Replication fork formation:
- A critical step is provided by a DNA helicase, which helps open up the double helix DNA
- Helicases unwind the two strands of parental DNA ahead of the replication fork
- The unwound DNA strands are then stabilized by single-stranded DNA-binding proteins
- DNA replication takes place at a Y-shaped structure called a replication fork
- A replication fork consists of four components: 1-DNA helicase, 2-SSBs (single-strand binding proteins), 3-DNA polymerase, 4-Primase
- DNA polymerases join nucleotides by formation of phosphodiester bonds
- DNA polymerase 1 synthesizes DNA in the 5' to 3' direction and only requires a primer strand
- Primase synthesizes RNA primers, which are essential for the initiation of DNA synthesis
- During DNA synthesis, one strand is synthesized in a continuous manner (the leading strand), while the other is formed from small discontinuous DNA fragments (Okazaki fragments) that are synthesized in the opposite direction (lagging strand)
- Primer synthesis for lagging strand is ongoing as replication fork moves, with primase synthesizing numerous RNA primers to trigger the growth of each Okazaki fragment.
Test your knowledge of DNA replication in medical biology with this quiz. Learn about how genetic material is duplicated before each mitotic division and passed on to daughter cells.
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