The Cell

Most cell division results in genetically identical daughter cells.

cell cycle: the life of a cell from the time its first formed from a dividing parent cell until its own division into two cells.

genome: cells genetic info, & before a cell can divide, the genome must be copied

somatic cells: have 46 chromosomes

-humans are haploid (23 chromosomes)

-diploid (46 chromosomes)

-When chromosomes are replicated, each duplicated chromosome consists of two sister chromatids, that are attached by centromere

The meiotic phase alternates with interphase in the cell

-the primary events of interphase which accounts for 90% of the cell cycle

G1 phase: the cell grows while carrying out cell functions unique to its cell type

S phase: the cell continues to carry out its unique functions but also duplicates its chromosomes

G2 phase: cell continues to grow and prepare for mitosis

Phases of Mitosis (PMAT)

Prophase:

1. The chromatin become more tightly coiled into discrete chromosomes

2. The nucleoli disappear

3. The mitotic spindle (consisting of microtubules) begins to form in the cytoplasm

Prometaphase:

1. The nuclear envelope begins to fragment, allowing the microtubules to attach to the chromosomes

2. The two chromatids of each chromosome are held together by the centromere. The centromere contains protein kinetochores no each chromatid, which is where the microtubules will attach.

Metaphase:

1. The microtubules move the chromosomes to the metaphase plate at the equator of the cell. The microtubule complex is referred to as the spindle

2. The centrioles have migrated to opposite poles in the cell, riding along on the developing spindle

Anaphase:

1. Sister chromatids begin to separate pulled apart by motor molecules interacting with kinetochore microtubules

2. The cell elongates, as the nonkinetochore microtubules ratchet apart again with the help of motor molecules

3. By the end opposite ends of the cell contain complete and equal sets of chromosomes

Telophase:

1. The nuclear envelopes re-form around the sets of chromosomes located at opposite ends of the cell

2. The chromatin fiber of the chromosomes becomes less condensed

cytokinesis:

1. The cytoplasm of the cell is divided in animal cells, a cleavage furrow forms that eventually divides the cytoplasm, in plant cells a cell plate forms that divides the cytoplasm

2. This process is NOT included in cytokinesis, making mitosis 5 phases

The eukaryotic cell cycle is regulated by a molecular control system

cell control system: moves the cell through its stages by a series of checkpoints, places where signals to continue or stop dividing

G1 phase checkpoint: the most important, if a cell passes this point, it usually completes the whole cell cycle and divides, if not it enters the non dividing phase called the G0 phase

-most mature human cells remain in G0 and never get the signal to divide

Kinases: protein enzymes that control the cell cycle and are only active when connected to cyclin proteins, hence the name of cyclin- dependent kinases

-these kinases give the go- ahead signals at the G1 and G2 checkpoints

Normal cell division Characteristics:

density dependent inhibition: the phenomenon in which crowded cells stop dividing

Anchorage dependency: normal cells must be attached to a substratum, like the extracellular matrix of a tissue, to divide

-Cancer cells form due to a lack of density dependent inhibition or anchorage dependency

transformation: the process that converts a normal cell to a cancer cell

tumor: mass of abnormal cells, they can be malignant or benign

metastasis: when cells separate from a malignant tumor and enter the blood or lymph vessels and travel to other parts of the body