Cell Division

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What is a cell?


Cells are the structural and functional units of all living organisms. Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms, such as humans, are multicellular, or have many cells—an estimated 100,000,000,000,000 cells! Each cell is an amazing world unto itself: it can take in nutrients, convert these nutrients into energy, carry out specialized functions, and reproduce as necessary. Even more amazing is that each cell stores its own set of instructions for carrying out each of these activities.


Spindle Fiber -One of a network of achromatic filaments that extend inward from the poles of a dividing cell, forming a spindle-shaped figure.
Centromere -The most condensed and constricted region of a chromosome, to which the spindle fiber is attached during mitosis.
Chromatin-A complex of nucleic acids and proteins, primarily histones, in the cell nucleus that stains readily with basic dyes and condenses to form chromosomes during cell division.
Chromatid -Either of the two daughter strands of a replicated chromosome that are joined by a single centromere and separate during cell division to become individual chromosomes.
Chromosome-thread-like, gene-carrying bodies in the nucleus of a cell.  Chromosomes are composed primarily of DNA and protein.  They are visible only under magnification during certain stages of cell division.  Humans have 46 chromosomes in each somatic cell and 23 in each sex cell.


Definitions
Gene- units of inheritance usually occurring at specific locations, or loci, on a chromosome.  Physically, a gene is a sequence of DNA bases that specify the order of amino acids in an entire protein or, in some cases, a portion of a protein.  A gene may be made up of hundreds of thousands of DNA bases.  Genes are responsible for the hereditary traits in plants and animals.
Alleles-alternate forms or varieties of a gene


Cell Cycle


The cell cycle is the event that makes new cells, by cell division, through six processes. They are; interphase,mitosis(prophase), mitosis(metaphase), mitosis(anaphase), mitosis(telophase), and cytokinesis


Mitosis, in general


Mitosis is the mechanism that allows the nuclei of cells to split and provide each daughter cell with a complete set of chromosomes during cellular division. This, coupled with cytokinesis (division of the cytoplasm), occurs in all multicellular plants and animals to permit growth of the organism.

Mitosis:Metaphase


Next, the nuclear envelope breaks down, and a large protein network, called the spindle, attaches to each sister chromatid. The chromosomes are now aligned perpendicular to the spindle in a process called metaphase.