The cell cycle consists of the events in a cell's life from birth to division. Interphase consists of three growth stages: gap phase 1; S phase, when DNA replication occurs; gap phase 2, when the cell synthesizes proteins.
Cell Division (00:45)
In mitosis, the cell divides the nucleus; centromeres break off, and duplicated chromosomes separate. In cytokinesis, remaining cell materials, the organelles, divide.
Histones help keep chromosomes, with long DNA strands in tight space, structurally stable. The cell makes spindle fibers to pull on opposite sides of chromosomes.
The nucleus gets the signal to begin chromosome separation and division and undergoes chromosome condensation. Centrosomes make spindle fibers. Loose DNA triggers lysosomes.
Metaphase, Anaphase and Telophase (01:34)
Metaphase attaches chromosomes to spindles and lines them up to the equator. Anaphase pulls chromosomes apart. In telophase, the nuclear envelope is reformed and spindle fibers are attached.
Cytokinesis completes cell division by separating cell components. Spindle fibers squeeze the plasma membrane toward the equator. Technically, cytokinesis occurs throughout mitosis.
Meiosis is the cell division in sexual reproduction. Male and female produce gametes, which fuse to form a new cell, while each losing half their chromosomes, creating genetic variability.
Meiosis One and Two (01:34)
Meiosis creates four new cells. Meiosis one in females creates a functional cell and a polar body. The functional cell produces a haploid gamete in meiosis two.
Definitions of Chromosome Types (00:57)
Diploid cells contain the normal number of chromosomes; haploid cells contain half the normal number. Homologous chromosomes come half from the mother, half from the father.
Meiosis One (02:04)
In Meiosis One, chromosome rearrangement creates genetic diversity in gametes. In prophase one, homologous chromosomes touch each other in genetically similar regions. Recombination can occur.
Metaphase One and Anaphase One (01:04)
In metaphase one, tetrads are lined up randomly -- independent assortment. In anaphase one, homologous chromosomes separate, creating new combinations of maternal and paternal cells.
Telophase One and Cytokinesis One (00:55)
In Telophase one, daughter cells enter interkinesis. In Cytokinesis one, each cell divides into haploids.
Meiosis Two (01:43)
In prophase two, similar genetic sequences are attracted and can form a break, allowing recombination. The narrator briefly describes metaphase two, anaphase two, and telophase two.
Gametes Fuse (00:42)
Cytokinesis two produces gametes, which have haploid chromosomes and fuse with a gamete of the opposite sex. Crossing over and independent assortment produces genetic variation.
Reason for Apoptosis (01:27)
Apoptosis is programmed cell death; death and regeneration is necessary due to exposure of cells to their environment. It is thought that particular proteins begin the process when activated.
Process of Apoptosis (01:52)
Nucleases destroy DNA and also serve a protective function. Chromosome shortening triggers apoptosis. Homeostatic imbalance kills the cell. Macrophages clean up remnants.
Apoptosis and Cancer (01:16)
Apoptosis prevents old or damaged cells from dividing. When apoptosis breaks down, cells from uncontrolled growth form a tumor.
Credits: Cell Division and Growth (00:44)
Credits: Cell Division and Growth
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