L03: DNA replication Flashcards
Why do cells replicate?
For growth, development, repair (replacement of damaged cells), and for reproduction in bacterias
How do bacteria reproduce and divide their DNA?
Through binary fission, where a single circular chromosome of the bacteria replciates and the cell divides into two daughter cells
What is the primary function of helicase enzyme in DNA replciation?
The enzyme unwinds the DNA double helix by breaking the hydrogen bonds holding the nitrogenous bases together into two single strands at the replication fork.
What role does topoisomerase play in DNA replication?
Topoisomerases plays a crucial role by relieving the tension to prevent supercoiling of DNA molecules by cutting and rejoining DNA strands to ensure smooth replication.
Why are RNA primers necessary?
RNA primers provide a starting point for DNA polymerase III to add nucleotides to replicate DNA, they are synthesized by Primase.
In which direction does DNA polymerase III add nucleotides to the growing DNA strand.
DNA polymerase III adds nucleotides from the 5’ end to the 3’ direction.
What is the difference between the leading and lagging strands in DNA replication?
The leading strand is synthesized continously, while the .agging strand is synthesized in short fragments called okazaki fragments.
What is the function of DNA polymerase I in the replication process?
DNA polymerase I removes the RNA primers and fills in the gap with nucleotides.
How are okazaki fragments joined together?
The enzyme DNA ligase helps seal the fragments between the two fragments by forming phosphodiester bonds, creating a continuous DNA strand.
Describe semi-conservative replication
In semi-conservative replication, each new DNA molecule consists of one original strand and one newly synthesized strand.
What cellular phase comes before DNA replication and what occurs during it?
The G1 phase, where the cell grows and synthesizes proteins and organelles.
During which phase of the cell cycle does DNA replication occur?
During the S-phase (synthesis phase)
How do prokaryotic and eukaryotic DNA replication origins differ?
Prokaryotes have a single origin of replication on their circular DNA while eukaryotes have multiplay DNA origins along the linear chromosomes.
Which enzymes ensure that newly formed DNA strands are kept stable during replication?
Single-Stranded Binding Proteins (SSBPs). They prevent the reannealing of the separated DNA
What must a cell have before it can successfully divide?
A cell requires adequate ATP reserves for sufficient energy to bring forth division, sufficient nutrients, copies of DNA to ensure each daughter cell has the full amount of DNA, proteins and organelles for cellular activities
Why do cells replciate DNA
For growth, development, replacement of damaged cells (repair) and reproduction in bacteria
What are the types of cell division for reproduction in eukaryotes
Mitosis, for somatic cells and Meiosis for gametes/sex cells
What is the replication fork
Point in which two DNA strands are separated during replicaiton
What is semi-conservative replication?
Is a process where each of the two DNA strands acts as a template for a new strand, resulting in two DNA molecules, each with one original and one new strand.
How many origins of replication do humans and proaryotes have?
Humans: Multiple, on linear DNA
Prokaryotes: Singular on circular DNA
What happens during G2 phase of interphase
Cell continues to grow and prepares for cell division and correction/checking of errors.
significance of 3’–OH end in DNA replication?
DNA poly III requires the free 3’ -OH end provided by RNA primers to initiate DNA synthesis and addition of nucleotides.
What is the final step of DNA replication
DNA ligase seals the nicks between the okazaki fragments, creating continuous DNA strand.
why is Okazaki fragments formed?
DNA has antiparallel strands, one strand rusn from 5’ to 3’ and the other 3’ to 5’. DNA polymerase III can only synthesize new DNA from a 5’ to 3’ direction, oakazai fragments allow DNA synthesis to proceed in short manageable sections that can be joined to form a complete strand.
