Cell Growth and Division

1. Cell Growth and Division

2. Cell Size • 8 micrometers in diameter to 1 meter with small diameters. • Most cells are between 2 and 200 micrometers in diameter. • Human Body: • Smallest: sperm cells • Largest: ovum • Longest: nerve cells • Largest Living Cell- Ostrich Egg (unfertilized)

3. Comparison of Cell sizes

4. Cell Size Limitations • Cell must be small • Large need more food • Must export waste • Rate of Diffusion • Size :diffusion slower and less efficient. • DNA (molecule where critical information stored) Too large “Information Crisis” • Cell cannot survive unless • enough DNA to support protein needs • cell activities are carried out quickly and efficiently

5. Cell Size Increase Not enough cell membrane to adequately supply the cell interior with enough oxygen, water, and food. Result: Cell Death

6. Surface area-to-volume ratio As cell’s size increases, its volume increases much faster than its surface area.

7. Surface Area and Volume Surface Area: 6 (# of sides) x A x A Volume: A x A X A Cube doubled Outside Grows by 4 x Inside grows by 8 x

10. Cell Growth and Reproduction

11. Asexual Versus Sexual Reproduction Asexual Sexual Offspring inherit genetic information from each parent. Most plants and animals, some single celled organisms. • Genetically identical offspring • Single Cell • ex. Bacteria • Multi Cellular-Break off and new organism produced • ex. Hydra

12. Asexual Versus Sexual Reproduction Asexual Sexual Different survival strategy Finding a mate, growth and development take more time. Genetic diversity; better tolerate change • Survival Strategy • Better the conditions the faster reproduce, better chance of survival, • As long as conditions favorable; genetically identical has advantages • Lack of diversity a disadvantage when conditions change and are not favorable.

13. Both Sexual and Asexual • Ex. Yeast • Mostly asexual, however, may under certain conditions reproduce sexually.

14. Cell TheoryAll cells come from pre-existing cells!Cell division results in two cells that are identical to the original parent cell.

15. Prokaryotic Cells • Lack nucleus & many organelles • DNA molecule found in cytoplasm • Most contain single, circular DNA with all genetic information

16. ChromosomesChroma (Greek) “colored”Soma “body”Genetic information is bundled into packages of DNA

17. Structure of the Eukaryotic Chromosome • Exist as CHROMATIN—Long strands of DNA wrapped around proteins. • Microscope—Plate of spaghetti

19. Components • Sugar-Deoxy-ribose –derived from ribose sugar-one less oxygen • Phosphate Group -backbone • 4 Nitrogen Bases-In complementary base pairs held by hydrogen bonds • Adenine & Thymine • Cytosine &Guanine

20. Make it possible to separate DNA precisely during cell division Chromosomes

21. A series of events the cells go through as they grow and divide During cell cycle, a cell grows, prepares for division, and divides to form two daughter cells. Cell Cycle

22. Prokaryotic Cell Cycle • Regular pattern of growth, DNA replication, and cell division that can take place under ideal conditions • Just beginning to understand process • Form of reproduction called Binary Fission. • Result-two genetically identical cells.

24. Cell Cycle • Interphase-Period of cell cycle b/w cell division • most of the cell’s metabolic functions are carried out • chromosomes are replicated • LONGEST of Cell Cycle • Cell Division (M Phase) • Mitosis when nuclear division occurs, leading to the formation of two daughter cells. • The division of the cytoplasm, called cytokinesis, follows mitosis. • Length of cell cycle depend on the type of cell

25. Eukaryotic Cell Cycle

26. Interphase: Cell prepares for Mitosis • Cell grows in size • Carry on metabolism • Chromosomes are duplicated for cell division.

27. Interphase • G1 Phase: Cell Growth • Most cell growth • Increase in size • Synthesize new proteins and organelles

28. Interphase Continued S Phase G2 Phase: Preparing for Cell Division Shortest phase of Interphase Organelles and molecules required for cell division are produced. Result: Cell ready for division • “S” Synthesis • DNA is synthesized when chromosomes replicated. • Result: Cell has 2x as much DNA

29. Helicase-(Enzyme) unzips/breaks hydrogen bonds b/w base pairs Nitrogen Bases

31. M Phase • Produces 2 daughter cells • “M” comes from Mitosis • Cell division relatively quick • Includes Mitosis and Cytokinesis • Mitosis-division of the cell nucleus • 2 daughter cells produced with genetic information • Cytokinesis-division of the cytoplasm

32. Mitosis: A period of nuclear division

33. Mitosis Interphase • Prophase • Metaphase • Anaphase • Telophase Mitosis Cytokinesis

34. Prophase • 1st / longest phase of mitosis. • Chromatin coils up (condenses)-chromosomes. • Duplicate chromosomes become visible • Two halves of the double structure are called sister chromatids. (Exact Copies of each other) • Centromere—holds together sister chromatids.

35. Prophase continued… • Nucleus disappears • Nuclear envelope and nucleolus disintegrate. • Animals—centrioles migrate to opposite end of the cell. • Centriole—Small, dark, cylindrical structures that are made of microtubules and are located just outside the nucleus.(animal cells only)

36. Prophase continued… • Spindle—A football shaped, cage-like structure consisting of thin fibers made of microtubules.

37. Metaphase: Second stage of mitosis • Chromosomes • Line up at center of cell • Attach to the spindle fibers via centromeres. • Pulled by spindle fibers and line up on the midline (equator). • One sister chromatid’s spindle fiber extends to one pole, and the other extends to the opposite poles (ensures a complete set of chromosomes)

38. Anaphase: Third Phase of Mitosis • Separation of sister chromosomes • Centromeres split apart and chromatid pair separate • Pulled apart by the shortening of the microtubules in the spindle fiber.

39. Telophase: 4th phase of mitosis • Chromosomes reach opposite poles of cell. • Prophase changes are reversed (independent existence). • Chromosomes unwind; Spindle breaks down; nucleolus reappears; new nuclear envelope forms each set of chromosomes; new double membrane begins to form.

40. Cytokinesis • Cytoplasm division • Animal Cells—Membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts. • Plant Cells—(cell membrane not flexible enough to draw inward because of rigid cell wall) Cell plate forms b/w the divided nuclei. Gradually, cell plate develops into cell membrane that separates two daughter cells.

41. Result of Mitosis • Two new cells with chromosome sets identical to those of the parents; Carry out same function of parent cells; Grow and divide like parent cells. • Tissues: group of cells that work together to do a specific function. • Organs: group of two or more tissues organized to perform complex activities within an organism. • Organ Systems: Multiple organs that work together to perform specific life function.

43. Cell Cycle

44. Purpose of Cell Division and Mitosis • Keep total cell number in a mature organism relatively constant, • Replace worn-out or damaged cells, • Enable a multicellular organism to grow to adult size.

46. Control of Cell Cycle Cell cycle 24 to 48 hours less then an hour never divide only mature Most muscle and nerve never divide A mistake in the cell cycle can lead to cancer.

47. Cell Regulation • Injury occurs-cells divide rapidly, healing process begins, as near completion, slows down, everything returns to normal • Cyclin-a protein that regulates timing of cell cycle • Regulatory Proteins-Proteins that control cell cycle (both inside and outside cell) • Functions: slow down or stop cell division, start cell division, etc • Internal Regulators- allow cell to proceed only when certain events have occurred • External Regulators-Respond to events outside cell. • Growth factors-stimulate growth and division of cells.

48. Control of the Cell Cycle • Enzymes • Begin and drive the cell cycle • Control the cycle through its phases. • Cell can lose control (uncontrolled dividing) • failure to produce certain enzymes • production of other enzymes at the wrong time. • Cancer is the result of uncontrolled cell division.

49. Cell Death • Death due to injury • Apoptosis-Cell may be programmed to die (self-destruction) • Controlled steps to death • Cell and its chromosomes shrink • Parts of cell membrane break off • Neighboring cells clean up cell’s remains

50. Causes of loss of control of cell cycle • Environmental Factors • Changes in enzyme production • Enzyme production is directed by genes located on the chromosome. • A gene is a segment of DNA that controls the production of a protein. • Many studies point to portion of interphase just before DNA replication as being a key control period.