Jose Peña

The Cell Cycle

The cell cycle is a series of events from the time a cell forms until its cytoplasm divides. Most of the lifespan of a cell is spent in interphase and only a small fraction at the end of its lifespan is spent in the process of mitosis

The most basic function of the cell cycle is to duplicate accurately the vast amount of DNA in the chromosomes and then segregate the copies precisely into two genetically identical daughter cells. These processes define the two major phases of the cell cycle. DNA duplication occurs during S phase (S for synthesis), which requires 10–12 hours and occupies about half of the cell-cycle time in a typical mammalian cell. After S phase, chromosome segregation and cell division occur in M phase (M for mitosis), which requires much less time (less than an hour in a mammalian cell). M phase involves a series of dramatic events that begin with nuclear division, or mitosis.

Interphase

This is where a normal cell spends most of its lifespan. Interphase is the interval between mitotic division when a cell grows. During this time, roughly doubles the number of its cytoplasmic components, and replicates its DNA.

G1: metabolic activities –

S: Creation of DNA

G2: creation of protein needed for cell division

Prophase: The first step of mitosis

-Chromosomes further condense

-One of the two centrosomes move to the opposite end of cell

-Microtubules assemble and lengthen, forming a spindle (functions to move chromosomes)

-Sister chromatids are attached to opposite centrosomes

Nuclear envelope breaks up

Metaphase: Second stage of mitosis

All chromosomes are aligned midway between spindle poles

Anaphase: third stage of mitosis

Sister chromatids separate and move toward opposite spindle poles

Telophase: Final stage of mitosis

Step in which the chromatids or chromosomes move to opposite ends of the cell and two nuclei are formed.

Telomeres

This is a region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes.

Cancer

Cancer can be defined as a disease in which a group of abnormal cells grow uncontrollably by disregarding the normal rules of cell division. Normal cells are constantly subject to signals that dictate whether the cell should divide, differentiate into another cell or die.

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