Mitosis / The Cell Cycle

Mitosis / The Cell Cycle Cells division types Brain Skin A special type of division produces nonidentical daughter cells A cell divisions result in daughter cells with identical genetic information DNA Blood have half as many chromosomes as somatic cells (meiosis) have two sets of chromosomes (mitosis) Before Growth 46 The continuity of life is based on the reproduction of cells, or cell division 46 ✓ 46 46 23 23 Fertilized egg ( zygote) > with the genetic material (DNA) copied precisely. Mitosis: ( the division of the genetic material ) 23 material to the two daughter cells other and moved to opposite ends of the cell. Cell division is remarkably accurate in passing DNA from one generation to the next Cytokinesis: ( the division of the cytoplasm ) Egg ( gamete cell ) 23 Sperm ( gamete cell ) > new organisms through cell division Division Multicellular eukaryotes undergo embryonic > development through cell division identical to each other and to the parent cell. Phases of the Cell Cycle 2 new bacteria genome I www.# All the DNA ( genetic material ) in a cell is called the cell’s genome A genome can consist of a single DNA molecule ( common in prokaryotic cells) interphase Chromosomes or a number of DNA molecules (common in eukaryotic cells) mitotic (M) phase DNA molecules DNA molecules in a cell are packaged into chromosomes The DNA molecule of a chromosome carries (cell growth and copying of chromosomes in preparation for cell division) : Interphase (about 90% of the cell cycle) can be divided into three phases: - > Repair The cell divides into two daughter cells, genetically 23 23 46 Somatic cell Single-celled organisms give rise to The chromosome copies are separated from each A crucial function of most cell division is the distribution of identical genetic After Development cell division, the chromosomes are duplicated, distinguishes living things from nonliving matter Gametes (reproductive cells: sperms and eggs) Somatic cells (nonreproductive cells) Multicellular organisms Interphase: The cell grows; in preparation for The ability of organisms to produce more of their own kind is the one characteristic that called gamete cells or Sperm and eggs “ germ cells “ Somatic cells ( Most body cells ) Heart Unicellular organisms Meiosis Mitosis Mitosis: Distribution of chromosomes into two daughter nuclei Mitosis is divided to 5 stages interphase is divided to 3 stages duplication and protein that condenses during cell division Cytokinesis: Division of cytoplasm, producing two daughter cells. Each daughter cell can start a new cell cycle. ÷ Chromosome Eukaryotic chromosomes consist of chromatin, a complex of DNA the division of the cytoplasm the division of the genetic material in the nucleus The cell grows during all three phases, but chromosomes are duplicated only during the S phase several hundred to a few thousand genes Cytokinesis Mitosis In animal cells, cytokinesis occurs by a proces known as cleavage Centromere In preparation for cell division, DNA is replicated Sister chromatids and the chromosomes condense The first sign of cleavage is the appearance of a cleavage furrow, a shallow groove in the cell surface near the old metaphase plate In plant cells, a cell plate forms during cytokinesis Each duplicated chromosome has two sister chromatids (joined copies of the original chromosome) , attached along their lengths by cohesins Separation of sister chromatids The centromere is the narrow “waist”of the duplicated chromosome, where the two chromatids are most closely attached G1 phase S phase (“first gap”) (“synthesis”) (“second gap”) chromosomes 2 Centrosomes duplication microtubules start (duplicated, uncondensed) Nonkinetochore The nuclear envelope is degraded microtubules Centromere > chromosome separate and move into two nuclei Once separate, the chromatids are called chromosomes attached to them Aster forming Centromere During cell division ,the two sister chromatids of each duplicated telophase Separation of sisters chromatids chromosomes have microtubules chromosomes start condensing Chromosomes (with centriole pairs) anaphase metaphase prometaphase prophase G2 phase > - - - - - - - - > . . . - • . . - - - - - - - - - - - Nucleolus forming furrow Metaphase plate - Duplicated Cleavage chromosomes Unduplicated chromosomes J S Spindle Centrosome move to Nucleolus Plasma membrane Daughter chromosomes different poles Kinetochore Kinetochore • Two sister chromatids of Nuclear envelope :*. one chromosome Centrosome at one microtubules spindle pole Nuclear envelope forming cell cycle control system The sequential events of the cell cycle are directed by a distinct cell cycle control system The frequency of cell division varies with the type of cell Internal The cell cycle control system is regulated by both internal and external controls Two types of regulatory proteins are involved in cell cycle control: Many signals registered at check points come from cellular surveillance mechanisms within the cell Check points also register signals from outside the cell cyclins The clock has specific check points where the cell cycle stops cyclin-dependent kinases (Cdks) Loss of Cell Cycle Controls in Cancer Cells until a go-ahead signal is received Cyclins are named for their cyclically Three important check points are those in the G1, G2, and M phases - For many cells, the G1 checkpoint seems to be the most important @ If a cell receives a go-ahead signal at the G1 checkpoint, it will usually cyclins complete the S, G2, and M phases and divide If the cell does not receive the go-ahead signal, it will exit the cycle, switching The activity of a Cdk rises and falls with changes in concentration of its cyclin partner fluctuating concentrations in the cell Cdks must be attached to a cyclin to be active + Cdks = MPF - e : Cancer cells do not need growth factors to grow and divide: External factors Peaks of MPF activity correspond to the peaks of cyclin concentration Cancer cells form tumors masses of a bnormal cells within otherwise normal tissue benign tumor Abnormal cells remain only at the original site Most benign tumors do not cause serious problems – They may make their own growth factor – They may convey a growth factor’s signal without the presence of the growth factor (depending on their location) – They may have an abnormal cell cycle control system MPF acts both as a kinase and indirectly through activating other kinases Internal factors Cancer cells do not respond normally to the body’s control mechanisms They do not stop dividing when growth factorsare depleted MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase into a nondividing state called the G0 phase Cancer cells manage to escape the usual controls on the cell cycle I Cells that acquire the ability to divide indefinitely have undergone transformation both chemical and physical influence cell division Growth factors are released by certain cells Apoptosis is programmed or controlled cell suicide and stimulate other cells to divide l cells will not begin anaphase until all chromosomes are properly attached to the spindle at the metaphase plate This mechanism ensures that daughter cells have the correct number of chromosomes : necrosis is an accidental cell death A cell is chopped and packaged into vesicles that are digested by scavenger cells Apoptosis prevents enzymes from leaking out of a dying cell and damaging neighboring cells Malignant tumors invade surrounding tissues and can metastasize exporting cancer cells to other parts of the body, where they may form secondary tumors