Mitosis cell division somatic cellThe form of cell division by which a eukaryotic somatic cell duplicates. Mitosisasexual reproduction.Mitosis is asexual reproduction. Cell divisionCell division is the continuation of life based on the reproduction of cells.

Somatic Reproduction Somatic Reproduction mitosisMost eukaryotic cells reproduce asexually by mitosis. Somatic cells body cells(like nerve, liver, etc...)Somatic cells are all body cells (like nerve, liver, etc...) except sperm and ova (egg). chromosomesAll Somatic cells have the same number of chromosomes.

Cell Division Cell Division: All cells are derived from preexisting cells (Cell Theory) Cell division is the process by which cells produce new cells Cell division differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals) Some tissues must be repaired often such as the lining of gut, white blood cells, skin cells with a short lifespan Other cells do not divide at all after birth such as muscle & nerve Reasons for Cell Division: Cell growth Repair & replacement of damaged cell parts Reproduction of the species

Copying DNA Since the instructions for making cell parts are encoded in the DNA, each new cell must get a complete set of the DNA molecules This requires that the DNA be copied (replicated, duplicated) before cell division

Chromosomes & Their Structure The plans for making cells are coded in DNA DNA is a long thin molecule that stores genetic information DNA is organized into giant molecules called chromosomes Chromosomes are made of protein & a long, single, tightly- coiled DNA molecule visible only when the cell divides When a cell is not dividing the DNA is less visible & is called chromatin DNA in eukaryotic cells wraps tightly around proteins called histones to help pack the DNA during cell division Centromeres hold duplicated chromosomes together before they are separated in mitosis When DNA makes copies of itself before cell division, each half of the chromosome is called a sister chromatid

Chromosome Numbers Humans somatic or body cells have 23 pairs of chromosomes or 46 chromosomes (diploid or 2n number) The 2 chromatids of a chromosome pair are called homologues (have genes for the same trait at the same location) Human reproductive cells or gametes (sperms & eggs) have one set or 23 chromosomes (haploid or n number) Every organism has a specific chromosome number OrganismChromosome Number (2n) Human46 Fruit fly8 Lettuce14 Goldfish94

Fertilization, is the joining of the egg & sperm cell Sex chromosomes, either X or Y, determine the sex of the organism Two X chromosomes, XX, will be female and XY will be male All other chromosomes, except X & Y, are called autosomes Chromosomes from a cell may be arranged in pairs by size starting with the longest pair and ending with the sex chromosomes to make a karyotype A human karyotype has 22 pairs of autosomes and 1 pair of sex chromosomes (23 total) Human Male Karyotype

Cell division in Prokaryotes DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane Prokaryotes divide into two identical new cells by the process of binary fission Binary fission is an asexual method of reproduction Occurs in 3 steps:  The chromosome, attached to cell membrane, makes a copy of itself  The cell grows to about twice its normal size  Next, a cell wall forms between the chromosomes & the parent cell splits into 2 new identical daughter cells (clones)

Binary Fission binary fissionBacteria, cyanobacteria, and most single celled organisms reproduce by binary fission. Asexual Reproduction chromosome plasma membrane bacteria

Cell Cycle Mitosis -prophase -metaphase -anaphase -telophase G1G1 G2G2 S phase interphase

Cell Cycle: The phases of life of a cell are called THE CELL CYCLE The cell cycle includes 2 main parts --- interphase and cell division Cell division includes mitosis (nuclear division) and cytokinesis (division of the cytoplasm) Interphase is the longest part of a cell's life cycle and is called the "resting stage" because the cell isn't dividing Interphase consists of 3 parts: G1, S, & G2 phases

Interphase 1. G 1 (gap) phase:  First growth stage  Cell increases in size  Cell prepares to copy its DNA 2. S phase:  Copying of all of DNA’s instructions  Chromosomes duplicated 3. G 2 (gap) phase:  Time between DNA synthesis & mitosis  Cell continues growing  Needed proteins produced

Cell Cycle  Stages in growth & division  G1 Phase  S Phase  G2 Phase  M Phase  Cytokinesis

Cell Division in Eukaryotes: Eukaryotes have a nucleus & membrane-bound organelles which must be copied exactly so the 2 new cells formed from division will be exactly alike The original parent cell & 2 new daughter cells must have identical chromosomes Both the nucleus (mitosis) and the cytoplasm (cytokinesis) must be divided during cell division in eukaryotes Stages of Mitosis: Division of the nucleus or mitosis occurs first Mitosis is an asexual method of reproduction Mitosis consists of 4 stages --- Prophase, Metaphase, anaphase, & Telophase

Prophase Longest phaseLongest phase Nucleolus disappears chromosomes sister chromatidsChromatin material condenses into chromosomes, consisting of two sister chromatids. CentriolesCentrioles move apart (not found in plants). Spindle fibers centriolescentromeres by kinetochores.Spindle fibers form and attach from centrioles to centromeres by kinetochores. Nuclear envelope fragments and disappears.

Prophase late prophase early prophase centrioles spindle fibers centromere nuclear envelope disappearing aster fibers

Metaphase Shortest phase Centrioles aster fibersCentrioles are at opposite ends of the cell and attached with aster fibers. Chromosomesmetaphase plate equatorial plateChromosomes move to the metaphase plate (equatorial plate - center of cell).

Metaphase metaphase plate centrioles spindle fibers aster fibers

Anaphase Sister chromatidsSister chromatids separate and move apart. chromatids chromosomesAfter separation, chromatids are now considered chromosomes. chromosomesDuring this phase, the cell contains twice the normal number of chromosomes. elongateCell begins to elongate. chromosomesAt the end, there are equal numbers of chromosomes at the poles.

Anaphase sister chromatidschromosomes No longer sister chromatids, now chromosomes centrioles spindle fibers aster fibers

Telophase Nuclear membrane & nucleolus reappears. ChromosomesChromosomes uncoil. In the end, two genetically identical nuclei are present.

Telophase cleavage furrow (cytokinesis) nuclear membrane reforming nucleolus reappears

Cytokinesis Cytoplasmic division furrow CytokinesisCleavage furrow develops in animal cells (Cytokinesis begins). plantsCell plate develops in plants (no cleavage furrows in plants). Nucleolus reappears. cell plate

2 daughter cells identical to original Parent cell Chromosomes are copied and double in number Chromosomes now split

Question: chromosomes eachA cell containing 20 chromosomes at the beginning of mitosis would, at its completion, produce cells containing how many chromosomes each?

Answer: 20 chromosomes20 chromosomes

Cancer is Uncontrolled Mitosis: Mitosis must be controlled, otherwise growth will occur without limit (cancer) Control is by special proteins produced by oncogenes