Answer:
All of these choices are correct.
Explanation:
Cell cycle is the process of growth and division of cell. It comprises of interphase and mitosis. In interphase the cell grows, replicates its genomic content and prepares itself for division. In mitosis the division occurs.
Cell cycle is controlled by a group of kinases called as Cyclin dependent Kinases (CDKs). They act by phosphorylating their substrates. They are of various types like Cdk1, Cdk2, Cdk4 etc. They become active when they bind to a regulatory protein called cyclin. They are also of various types like Cyclin A, Cyclin B, Cyclin C etc. Level of cyclin and corresponding CDK increases and decreases according to the stage of cell cycle. For example in S phase of cell cycle concentration of cyclin A and E shoots up. CDK2 is able to bind to these cyclin molecules and hence it becomes active.
Cell cycle has major checkpoints where the condition of cell is analysed before it proceeds to the next stage of cycle. If any abnormality is detected, repair mechanism is activated or the cell is killed. Checkpoints do not allow cell cycle to proceed in damaged cells.
p53 is a tumor suppressor protein which can halt cell cycle when it detects some abnormality in cell. It usually acts in G1/S checkpoint (before the DNA replication starts in cell) and G2/M checkpoint (before the cell division begins). Hence, all of the above statements are true.
Answer:
a. Ligase
b. Ligase (
it's repeated)
Explanation:
DNA synthesis begins, therefore, by synthesizing a short segment of RNA called a primer, which primer is synthesized by an enzyme called Primasa. Primasa is an RNA polymerase that uses DNA as a template. All fragments of Okazaki begin with a Primer. Subsequently, the DNA polymerase III Holoenzyme performs the synthesis of the corresponding DNA fragment until it reaches the next primer. At that time, DNA polymerase Ia replaces the DNA polymerase Holoenzyme III. The DNA polymerase I is responsible for removing the RNA primer through its 5'P-3'OH exonueotic activity and at the same time fills the hole by synthesizing DNA.
Finally, the two Okazaki fragments have to be joined, it is necessary to link the 3'OH end of a fragment with the 5'P of the next fragment. This work of sealing and joining the successive fragments is done by Ligase.
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