CELL DIVISION

Think about it… How many different cells make up our body?

CELL DIVISION Some cells divide frequently (some human skin cells divide once/hour) Some cells divide occasionally (liver cells divide about once/year) Some cells don’t divide once they form (nerve cells)

Asexual Reproduction Production of genetically identical offspring from a single parent cell (CLONES) Bacteria (binary fission), some multicellular organisms (budding) We do it too! (mitosis) PRO: Fast, simple CON: Same DNA, no diversity

Sexual Reproduction Fusion of two gametes genetic info PRO: Diverse DNA CON: Takes longer, 2 gametes needed

95% of the time DNA is loosely coiled in nucleus(CHROMATIN) Chromatin condenses into tight complex of visible chromosomes during cell division (5% of time)

Duplicated Chromosome: A closer look… Chromatid Protein DNA is coiled around

Cell Division Process in which a parent cell divides to produce daughter cells Process in which a parent cell divides to produce daughter cells It is estimated that more than 25 million cells undergo division each second in an adult human It is estimated that more than 25 million cells undergo division each second in an adult human

Eukaryotic Cell Cycle

CELL CYCLE INTERPHASE Phase in preparation for cell division Phase in preparation for cell division Cell spends about 90% of its life in interphase Divided into 3 phases: Divided into 3 phases: G1 – gap phase 1 - Cell growth, performs cell duties, DNA in form of chromatin S – synthesis - DNA synthesis (replication) G2 – gap phase 2 -Prepares to undergo mitosis

Cell Cycle checkpoints Cell Cycle checkpoints Checkpoints in G 1 and G 2 ensure the cell is prepared to enter into the next phase of the cell cycle (adequate nutrition, size, not damaged…)

CELL CYCLE M phase = Mitosis and Cytokinesis Mitosis Parent cell nucleus undergoes cell division Parent cell nucleus undergoes cell division 4 Phases 4 Phases – Prophase – Metaphase – Anaphase – Telophase Cytokinesis Process in which the cell finally splits into two daughter cells Process in which the cell finally splits into two daughter cells

Mitotic spindle Cells contain centrioles made of microtubules and produce long fibers called spindle fibers Cells contain centrioles made of microtubules and produce long fibers called spindle fibers

MITOSIS

Mitosis: PROPHASE Chromatin fibers condense into visible chromosomes Nuclear envelope breaks down Mitotic Spindles form; microtubules attach to centromere to direct their movement (like puppet strings)

microtubules

Mitosis: Metaphase Chromosomes gather in middle of cell between the two ends of spindles Form a line at “equator” of cell

Mitosis: Anaphase Sister chromatids separate from “partner” Spindle microtubules shorten, bringing chromosomes closer to opposite poles (reeling them in)

Sister Chromatids

Mitosis: Telophase (and cytokinesis) Chromosomes reach opposite poles of spindle 2 new nuclear envelopes reform around each new set of daughter chromosomes Chromosomes uncoil (prophase….in reverse) Cytokinesis completes cell division by dividing cytoplasm in 2, each with a nucleus

Mitosis in action!

Cancer A disorder where body cells lose the ability to control cell growth (defective gene) Don’t respond to regulatory signals Tumor- a mass of cells benign (not cancer, doesn’t spread) Malignant (invade and destroy surrounding tissue  metastasis)

Cancer Smoking, chewing tobacco, radiation, genes Treatments – Remove tumor – Radiation – Chemotherapy uses chemicals that target rapidly dividing cells (downside, affects normal cells also undergoing cell division)

Embryonic Stem Cells Have the ability to differentiate into almost any cell in body Possibly treat damaged tissue (heart attacks, stroke brain tissue, spinal cord)

Apoptosis- Cells die or it is “programmed” to die. Important in development

Eukaryotes have two different types of cells – Somatic - include skin, internal organs, bones, blood, etc. (cells produced thru MITOSIS) – Gametes - egg or sperm (cells produced thru MEIOSIS)

–Somatic cells have 46 chromosomes or 23 pairs of chromosomes, 1 set of 23 from Mom and 1 set of 23 from Dad = DIPLOID cell (2N) –Gametes have 23 chromosomes; HAPLOID (1N) when gametes meet during conception they “fuse” together

HOMOLOGOUS pairs of chromosomes- Pair of corresponding chromosomes (1 from mom, 1 from dad) Pairs 1-22 are autosomal 23 rd pair of chromosomes are sex chromosomes (XX or XY)

A Karyotype is an Arranged Picture of Chromosomes At Their Most Condensed State A normal human karyotye Boy or girl? Note that almost all chromosomes come in homologous pairs.

Mitosis – process in which a eukaryotic somatic cell divides into 2 identical daughter cells Mitosis – process in which a eukaryotic somatic cell divides into 2 identical daughter cells Diploid cells  Diploid cells Diploid cells  Diploid cells Meiosis – process in which the number of chromosomes is halved to produce gametes (ie eggs and sperm) Meiosis – process in which the number of chromosomes is halved to produce gametes (ie eggs and sperm) Diploid cells  haploid cells Diploid cells  haploid cells

Meiosis-Prophase 1 Homologous chromosomes pair up (TETRAD) Chromosomes swap genetic information called Crossing over Tetrad

MEIOSIS- METAPHASE I Tetrads line up in center of cell

MEIOSIS- ANAPHASE I Homologous chromosomes separate and move to the opposite poles IMPORTANT: CHROMATIDS DO NOT SEPERATE

MEIOSIS- TELOPHASE I Nuclear membrane reforms around each cluster of chromosomes Cytokinesis follows, forming two new cells

MEIOSIS- PROPHASE II New spindle forms around the chromosomes

MEIOSIS- METAPHASE II Chromosomes line up at the equator

MEIOSIS- ANAPHASE II Chromatids move to the opposite poles

MEIOSIS- TELOPHASE II Nuclear envelope forms around each new set of chromosomes, cytokinesis. 4 haploid sex cells

Haploid cells to Sperm and Eggs Spermatogenesis – Each of the 4 haploid cells become spermatozoa Spermatogenesis – Each of the 4 haploid cells become spermatozoa Oogenesis – Only 1 of the 4 haploid cells become an ovum (egg cell) Oogenesis – Only 1 of the 4 haploid cells become an ovum (egg cell)

But its just a little more complicated than that… What happens next?! Spermatogenesis Oogenesis Meiosis I begins before birth Meiosis I begins before birth Puberty elicits continuation of Meiosis Puberty elicits continuation of Meiosis Hormones play major role Hormones play major role Get Excited....Meiosis Animation!! Get Excited....Meiosis Animation!! Get Excited....Meiosis Animation!! Get Excited....Meiosis Animation!!

Meiosis Contributes to Genetic Variation 3 Main Ways lead to genetic variation – 1. Independent Assortment – 2. Crossing Over – 3. Random Fertilization