Cell Division Suzanne DAnna 1 Cell Division process

Cell Division Suzanne D'Anna 1

Cell Division process by which cells reproduce themselves n Includes: - nuclear division - cytoplasmic division n Two types: - somatic cell division - reproductive cell division n Suzanne D'Anna 2

Transcription process by which genetic information encoded in DNA is copied onto a strand of RNA n when strands divide, one strand (the sense strand) acts as the template for m. RNA synthesis n the other strand is called the antisense strand n Suzanne D'Anna 3

What is DNA? composed of building blocks called nucleotides n double strand of nucleotides n ladder-like molecule n coiled into a spiral n double helix n Suzanne D'Anna 4

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DNA Replication DNA helix uncoils n gradually separates into two nucleotide chains n template for next strand n each nucleotide joins in a complementary sequence n Suzanne D'Anna 6

Nucleotide Structure n Composed of: - nitrogenous base - pentose monosaccharide - phosphate groups Suzanne D'Anna 7

Nucleotide Structure n (cont. ) nitrogenous base - purines (adenine and guanine) - pyrimidines (cytosine, thymine, and uracil Suzanne D'Anna 8

DNA n DNA bases: - adenine (A) - guanine (G) - cytosine (C) - thymine (T) adenine (A) bonds with thymine(T) n guanine (G) bonds with cytosine (C) n Suzanne D'Anna 9

RNA n RNA bases: - adenine (A) - guanine (G) - cytosine (C) - uracil (U) Suzanne D'Anna 10

Messenger RNA n carries genetic information from DNA to cytosol where it serves as template for protein synthesis Suzanne D'Anna 11

Translation process by which nucleotide sequence on a strand of m. RNA is used as a template for protein synthesis n generates a corresponding amino acid sequence in a polypeptide chain n three consecutive nucleotides are called a codon, which specifies one amino acid n Suzanne D'Anna 12

Somatic Cell Division n results in an increase in number of cells in body (growth, repair) n Cell life cycle has two major periods: - interphase (resting stage) - mitotic phase (cell division reproduction occurs) Suzanne D'Anna 13

Interphase series of activities before reproduction n between divisions n each chromosome makes copy of self n two identical chromosomes n chromatids are united by centromere n metabolic activities continue n longest phase of the cell cycle n very active n Suzanne D'Anna 14

Cell Division n Process includes: - mitosis nuclear division formation of two daughter nuclei - cytokinesis division of cytoplasm begins once mitosis is nearly complete Suzanne D'Anna 15

Stages of Mitosis prophase n metaphase n anaphase n telophase n Suzanne D'Anna 16

Prophase (pro = before) chromosomes become visible as chromatids n nucleolus disappears n mitotic spindle appears n Suzanne D'Anna 17

Prophase (cont. ) chromatin threads coil and shorten into chromosomes - double stranded (chromatids) n each chromatid is held together by small median body called a centromere n centrosome and its centrioles each move to opposite sides of cell n Suzanne D'Anna 18

Prophase (cont. ) mitotic spindle between centrioles (responsible for attachment and movement of chromosomes) n end of stage - nuclear membrane and nucleoli have broken down and disappeared n chromosomes are randomly attached to centromeres by spindle fibers n Suzanne D'Anna 19

Prophase 1 Suzanne D'Anna Prophase 2 20

Metaphase (meta = after) short n chromosome pairs line up on the metaphase plate (exact midpoint or center of the mitotic spindle) n straight line of chromosomes n Suzanne D'Anna 21

Metaphase Suzanne D'Anna 22

Anaphase (ana=upward) centromeres divide and separate n identical chromosomes move to opposite poles with centromeres n Suzanne D'Anna 23

Anaphase Suzanne D'Anna 24

Telophase (telo = far or end) begins as soon as chromosomal movement stops n chromosomes at poles uncoil n resume chromatin form (threadlike) n nuclear membrane forms around each chromatin mass n nucleoli reappear n mitotic spindle disappears n Suzanne D'Anna 25

Telophase Suzanne D'Anna 26

Cytokinesis (kinesis = motion) division of cytoplasm and organelles n occurs in late anaphase n furrow develops and progresses inward dividing cell into two separate portions of cytoplasm n Suzanne D'Anna 27

Conclusion two daughter cells genetically identical to the original mother cell n each cell diploid in number n Suzanne D'Anna 28

Meiosis cell division n restricted to sex cell (gametes) production n involves two successive nuclear divisions n results in daughter cells with haploid (1/2) number of chromosomes n Suzanne D'Anna 29

Haploid n one half the normal number of chromosomes (23 in humans) Diploid n number of chromosomes characteristically found in somatic cells of an organism (46 in humans) Suzanne D'Anna 30