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Cellular Division

Cellular Division. I. Introduction. According to the CELL THEORY, new cells are only produced by existing cells… THUS, cell division is essential for the continuation of life!. Why do cells DIVIDE?. Maintain Homeostasis Reproduction: create new,independent

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Cellular Division

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  1. Cellular Division

  2. I. Introduction • According to the CELL THEORY, new cells • are only produced by existing cells… • THUS, cell division is essential for the • continuation of life! • Why do cells DIVIDE? • Maintain Homeostasis • Reproduction: create new,independent • organisms (i.e. prokaryotes) •  divide by binary fission • 3. Growth and repair of damage cells • (e.g. next slide)

  3. About 2 trillion cells are produced by an • adult human body every day. • These new cells are formed when • older cells REPRODUCE (i.e. divide), • which is known as CELL DIVISION.  When cells divide, the DNA is: 1. replicated (i.e. copied) 2. distributed - each new cell receives a complete set (copy) of parent DNA

  4. Cell Division involves DIFFERENTIATION • Differentiation is the process by which • cells grow into specialized tissues When cells differentiate, they develop specific structures or contain more of a certain organelle that allow them to perform particular functions in the body Example: - RBC’s have large amount of hemoglobin enabling them to carry large amts of O2 - Nerve cells have special receptors to react to stimuli and conduct impulses - Muscle cells have large amounts of mitochondria for extra ATP production

  5. Cell Differentiation

  6.  Differentiation involves SPECIALIZATION • - Due to the complexity of multicellular • organisms, cells must become highly • organized, in which their cells perform • specific functions • - It means that every cell doesn’t perform • the exact same function all of the time, • this would waste NRG • Thus, cells can shut off certain genes: • lung cells don’t need proteins used by liver • hair cells don’t need dental enamel

  7. Cell Specialization

  8. There are two phases of cell division: • 1. Nuclear Division • a. division of the genetic material • (i.e. nucleus) • b. two types: • Mitosis – produces two • genetically identical nuclei 2. Meiosis – produces 4 nuclei w/ half the genetic material as the original cell 2. Cytoplasmic Division (Cytokinesis)  divides the cytoplasmic contents

  9. II. VOCABULARY!!!!! The “uncoiled” complex of DNA wrapped around proteins (similar to plate of tangled spaghetti) • Chromatin – • Histones – 8 proteins that form • a core that DNA wraps itself • around. Why does DNA do this? • It’s too large, needs to be wound up to fit into nucleus 2. Nucleosome – the complex of DNA wrapped around histones  strung together like a thin strand of beads

  10. B. Chromatid – 1. A single strand of tightly coiled up chromatin

  11. C. Chromosome - • 1. A tightly coiled structure of DNA • and proteins which contains genes • 2. When DNA replicates; chromosomes • consist of 2 chromatid strands • (i.e. sister chromatids, exact copies)  centromere – the region on a chromosome where sister chromatids are attached

  12. III. Chromosome # A. Humans contain two types of cells: 1. SEX CELLS (a.k.a. gametes)  the egg and sperm 2. SOMATIC CELLS (a.k.a. body cells)  Any cell that is not egg or sperm B. Humans have 2 types of chromosomes: 1. sex chromosomes (i.e. X and Y) 2. autosomes – all other chromosomes

  13. C. Sets of chromosomes • Every human somatic cell has 2 SETS • (i.e. copies, 1 from MOM & 1 from DAD) • of 23 different chromosomes •  23 pairs of Homologous chromosomes • (identical in size, shape, genetic info, • genes found in same location) • - 22 pairs of autosomes • - 1 pair of sex chromosomes •  TOTAL = 46 CHROMOSOMES

  14. 2. Every human sex cell has only ONE SET of chromosomes (i.e. 23 TOTAL)  Sex cells fuse together during FERTILIZATION to form a ZYGOTE, which now has 46 chromosomes.

  15. 3. PLOIDY Levels  represents the number of complete sets of chromosomes present in an organism’s cells. • Sex cells (i.e. gametes) are: •  HAPLOID (n) = • b. Somatic cells are: •  DIPLOID (2n) = • What about strawberries? 23 chromosomes 46 chromosomes • Octoploid (8n)

  16. 4. KARYOTYPE – a photograph that shows the 23 sets of chromosomes arranged by size 22 pairs autosomes 1 pair sex-chrom.

  17. D. Changes to chromosomes (Disorders) • Disorders can result from STRUCTURAL • mutations (discuss this later…genetics) 2. Disorders can result from mutations in NUMBER (i.e. extra chromosomes). Ex…

  18. IV. The Cell Cycle • Background •  Cells are not always engaged • in division; cells go thru • different stages of life… •  some cells’ division is ongoing • (e.g. stem cells – skin, bone, • bone marrow) •  some cells lose ability to divide • (e.g. muscle, neurons, RBC’s)

  19. B. Overview of Cell Cycle 1. Definition – the orderly events in the lifetime of a cell 2. One cycle is the period b/n a cells creation by mitosis and its subsequent division into two new daughter cells. 3. Broken into two phases: a. INTERPHASE – the longer period b/n divisions 1. G1 phase – Growth; normal activity 2. S phase – DNA synthesis 3. G2 phase – Preparation for division b. MITOSIS & CYTOKINESIS – nuclear & cytoplasmic division

  20. C. Two main stages: 1. Interphase a. cells are NOT dividing b. eukaryotic cells spend most of their life in this stage c. the cell does normal tasks associated w/ its specialized fxns and maintenance d. DNA in the form of chromatin e. three phases: G1, S, G2

  21. * the three phases of interphase: G1 (gap/growth 1):  DNA is relaxed & unreplicated (chromatin) in order to direct normal cell activity (e.g. protein synthesis)  organelles are duplicated  G1 checkpoint – ensures that everything is ready for synthesis  S-cyclins – proteins that help activate a protein complex called MPF. An active MPF then activates multiple other enzymes in a cascade effect. This essentially signals DNA to move into the next phase (synthesis/replication)

  22. S phase (DNA Synthesis)  all 46 chromosomes and the DNA they contain will be replicated  each chromosome is now composed of sister chromatids  MPF will begin to degrade the S-cyclins and once again becomes inactive

  23. G2 (gap/growth 2)  the cell “double checks” the duplicated chromosomes and other contents & repairs any errors  G2 checkpoint – ensures the cell is ready for mitosis  M-cyclins will activate a different MPF complex, creating another cascade which tells the cell to move into the final phase (i.e. mitosis)

  24. 2. Mitosis  the contents of the nucleus will be divided into 2 genetically identical daughter cells  M checkpoint – ensures that cell is ready to complete division  MPF will degrade the M-cyclins and become inactive  cells re-enter G1 phase after finish dividing

  25. G0 (gap/growth 0)  Cells that cease cell division will enter this phase and remain there until cell death (e.g. RBC)

  26. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.html

  27. SOMATIC V. Mitosis (nuclear division of ________ cells)  Definition – the replication & division of ONE PARENT NUCLEUS into 2 IDENTICAL DAUGHTER NUCLEI, each receiving an EXACT COPY of parent’s chromosomes.

  28. A. Preparation for mitosis  Interphase 1. nuclear envelope & nucleolus intact 2. “uncoiled” chromatin 3. centrosomes w/ centrioles form (this will direct chromosome mov’t)

  29. B. Phases of Mitosis (5 total) 1. Prophase: longest * centrosomes move toward opposite poles * spindle fibers begin to form * chromatin coils tightly (chromosomes now visible; 2 sister chromatids) Early prophase

  30. Late Prophase: * kinetochores develop on centromeres (this is where spindle fibers will attach)

  31. 2. Prometaphase * nuclear envelope & nucleolus dismantle * spindle fibers attach to kinetochores and begin moving chromosomes toward center of cell

  32. 3. Metaphase * all chromosomes are aligned in the in the center of the cell (equatorial plate)

  33. 4. Anaphase * centromeres divide * spindles shorten & pull chromatids apart * each chromatid, now a daughter chromosome, moves to opposite poles * “V-shaped” (centromeres being pulled) (20 ATP)

  34. 5. Telophase * chromosomes reach poles & spindles break down * chromosomes “uncoil” to form chromatin * nuclear envelope & nucleolus reform

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