Timeline by Anju Gani

Interphase

anjanasowmiganesh — 2024-12-09 13:57:05 UTC

Interphase is the preparatory phase before mitosis. This phase contains the G1 phase, S phase, and G2 phase.

During the G1 phase, the cell grows and its plasma membrane expands as its cytoplasm increases. Cyclins build up to activate cyclin-dependent kinases which drive progression into the next phase.

The S phase is known for DNA replication, which occurs by doubling the chromosomes into two sister chromatids that are joined together by a centromere.

Lastly, the G2 phase. During this phase, the cell checks for DNA errors and produces microtubules and other structures that are needed for mitosis.

Prophase

anjanasowmiganesh — 2024-12-09 14:10:59 UTC

Prophase is the first phase of mitosis. During this phase, chromatin condenses into visible chromosomes, each chromosome is made up of two sister chromatids. During this phase, the nuclear envelope breaks down and centrioles move to opposite poles causing spindle fibers to begin to form. Nucleolus disappears as well during this phase.

Prometaphase

During prometaphase, the chromosomes continue to condense, Kinetochores appear at the centromeres, mitotic spindle microtubules attach to kinetochores, and centrosomes move toward opposite poles.

Anaphase

anjanasowmiganesh — 2024-12-09 22:25:36 UTC

checkpoint - Before anaphase begins, the metaphase to anaphase checkpoint ensures that all chromosomes are properly attached to spindle fibers at the kinetochores. If this checkpoint is passed, the cyclin-dependent kinases help trigger the transition into anaphase.

During anaphase, centromeres holding the sister chromatids together split, allowing them to become an independent chromosome. These chromosomes are pulled toward opposite poles of the cell by the shortening of spindle fibers, which are attached to the kinetochore of each chromosome.

The microtubules that make up the spindle fibers bread down to shorten and pull chromosomes.

The cytoplasm elongate as the spindle fibers push the poles of the cell apart creating a clear separation between the two sets of chromosomes.

Telophase

anjanasowmiganesh — 2024-12-09 22:39:25 UTC

During telophase, the chromosomes, which were pulled to opposite poles during anaphase, begin to decondense into loose chromatin. A nuclear envelope reforms around each set of chromosomes, creating two separate nuclei within the same cell.

The nucleoli, which disappeared during prophase, reappear which signals the reformation of the nucleus. The spindle fibers and microtubules disassemble s they are no longer needed to separate chromosomes. At this stage, the plasma membrane starts to show signs of division as the cell prepares for cytokinesis.

checkpoint - The telophase to cytokinesis checkpoint ensures that the nuclei have reformed correctly and that the chromosomes have completely separated.

Cytokinesis

anjanasowmiganesh — 2024-12-09 22:43:48 UTC

Cytokinesis is the physical division of the cytoplasm resulting in two separate daughter cells.

In animal cells...

A cleavage furrow forms as the plasma membrane pinches inward, driven by a ring of actin and myosin proteins. The furrow deepens until the two cells are completely separated.

In plant cells...

A cell plate forms in the middle of the cell, constructed from vesicles produced by the golgi apparatus. This plate becomes the plasma membrane and cell wall that separates the two daughter cells.

Metaphase

anjanasowmiganesh — 2024-12-12 01:56:36 UTC

In metaphase, the spindle has captured all the chromosomes and lined them up at the middle of the cell, ready to divide. All the chromosomes align at the metaphase plate (not a physical structure, just a term for the plane where the chromosomes line up). At this stage, the two kinetochores of each chromosome should be attached to microtubules from opposite spindle poles.

Before proceeding to anaphase, the cell will check to make sure that all the chromosomes are at the metaphase plate with their kinetochores correctly attached to microtubules. This is called the spindle checkpoint and helps ensure that the sister chromatids will split evenly between the two daughter cells when they separate in the next step. If a chromosome is not properly aligned or attached, the cell will halt division until the problem is fixed.