1 / 54

Cell Reproduction

Cell Reproduction. Chapter 8. Chapter overview. 3 SECTIONS: SECTION 1 CHROMOSOMES SECTION 2 CELL DIVISION SECTION 3 MEIOSIS. CHROMOSOMES. SECTION 1 P. 151-153. CHROMOSOME STRUCTURE. CHROMOSOMES …. ARE MADE OF DNA AND PROTEIN ARE LINEAR

ursa
Télécharger la présentation

Cell Reproduction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cell Reproduction Chapter 8

  2. Chapter overview • 3 SECTIONS: • SECTION 1 CHROMOSOMES • SECTION 2 CELL DIVISION • SECTION 3 MEIOSIS

  3. CHROMOSOMES • SECTION 1 • P. 151-153

  4. CHROMOSOME STRUCTURE • CHROMOSOMES…. • ARE MADE OF DNA AND PROTEIN • ARE LINEAR • HAVE A SYSTEM OF COILING TO COMPACT DNA TO FIT IN EUKARYOTIC NUCLEUS • HISTONES = proteins around which the chromosome wraps to compact its length • ARE TECHNICALLY MOLECULES OF DNA • Each chromosome = 1 molecule of DNA

  5. Chromosome structure (con’t) • Are controlled by NONHISTONE proteins • Activate/deactivate areas on DNA molecules • Consist of 2 parts in a dividing cell • CHROMATIDS = chromosome + its exact copy • CENTROMERE = protein disk which connects chromatids in center • Exists as CHROMATIN in a nondividing cell • Long and thin DNA • Not as tightly coiled • Enables DNA’s code to be read and used as needed

  6. Chromosome structure (con’t) • PROKARYOTIC CELLS AND CHROMOSOMES • Usually have 1 chromosome in each cell • Are circular DNA molecules • Are compacted • Found in nucleoid region • Attached to inside of cell membrane

  7. Chromosome numbers • Number of chromosomes found in each species is a distinguishing characteristic • Number of chromosomes in each species is not unique • Number of chromosomes in each species is not reflective of intelligence, social skills, etc….

  8. Chromosome numbers • SEX CHROMOSOMES AND AUTOSOMES • Sex chromosomes determine if an organism is male or female • Each organism has 2 sex chromosomes (XX or XY) • Sex chromosomes can also carry GENES = section of DNA which code for a certain trait • All chromosomes other than the sex chromosomes are called AUTOSOMES • 1 set of autosomes is received from each parent • Therefore each organism has 2 sets of chromosomes • The same number pair of chromosome from each parent is called a HOMOLOGOUS PAIR • Same size, shape, + carry same genes • The chromosomes are referred to as HOMOLOGUES

  9. Chromosome numbers • Pictures of chromosomes can be made by taking the DNA out of cells (blood) • Cells are stimulated to divide • At METAPHASE (foreshadow SECTION 2!) the cells are photographed • Homologous chromosomes are paired and the picture of the chromosomes are analyzed for genetic defects + sex of organism can be determined • Picture is called a KARYOTYPE

  10. Karyotype

  11. Chromosome number • DIPLOID AND HAPLOID CELLS • Cells with 2 sets of chromosomes=DIPLOID CELLS • Includes SOMATIC cells (regular body cells) • Referred to as 2n • Human diploid = 46 • Cells with 1 set of chromosomes = HAPLOID CELLS • Includes SEX cells (egg and sperm) • Referred to a 1n or n • Human haploid = 23 WHY ARE SEX CELLS HAPLOID? • So when egg + sperm combine, their combined chromosome number = the correct diploid number • Cells without exact diploid # may be dysfunctional • The pairing of sex cells created homologous chromosome pairs!

  12. Cell division Section 2 p. 154-159

  13. Cell division in prokaryotes • Each prokaryotic cell…. • Has onesinglecircularDNA molecule which is attached to cell membrane • Is not coiled around histones • Reproduces through BINARY FISSION • Splitting into 2 cells • Occurs in a series of steps…

  14. CELL DIVISION IN PROKARYOTES • The steps of BINARYFISSION… • Step 1: DNA is copied • Step 2: Cell membrane grows between the 2 copies of DNA • Step 3: Cell grows • Step 4: New cell wall forms • Step 5: 2 new IDENTICAL CELLS!

  15. Binary fission

  16. Binary fission

  17. CELL DIVISION IN EUKARYOTES • 2 STAGES TO CELL DIVISION IN EUKARYOTES • MITOSIS • Division of the nucleus in a series of steps • CYTOKINESIS • Division of the cytoplasm in series of steps • Varies in animal and plant cells

  18. Cell reproduction • Mitosis occurs in organisms undergoing growth, development, repair, or asexual reproduction • Asexual reproduction • Production of offspring from one parent • Sexual reproduction • Production of offspring from 2 parents • Creates geneticvariety • Requires GAMETES or sex cells which are created through the process of MEIOSIS

  19. THE CELL CYCLE • Defined: • Repeating set of events in cell’s life • Divided into: • Interphase : time between divisions • Includes G1, S, and G2 • Mitosis: division of the nucleus • Includes prophase, metaphase, anaphase, telophase • Creates haploid cells from haploid cells • Creates diploid cells from diploid cells • Occurs in SOMATIC (body) cells • Cytokinesis: division of the cytoplasm

  20. Cell cycle

  21. interphase • Majority of cell’s life spent in this… • Includes: • G1(~90%) • “first gap” - cell grows following a division • S • “synthesis” - DNA is copied- replication • Each chromosome connected to its copy by a protein disk called a centromere and are now called sister chromatids • G2 • “second gap” - cell prepares for division • G0 • can follow G1 for certain cells which do NOT divide (EXAMPLES– NERVE + IMMUNECELLS)

  22. Stages of mitosis • Divided into 4 stages • Flows like a movie: 1 stage leads into next • Each stage can be divided into early, mid, and late • Cytokinesis usually occurs simultaneously with the last phase: telophase

  23. Stages of mitosis

  24. prophase • Shortening & coiling of DNA into chromosomes • Nuclear membrane & nucleolus disappear • 2 centrosomes containing a pair of centrioles each appear & move to opposite poles of cell • Plant cells lack centrioles • Mitotic spindle forms (microtubules) • POLAR fibers connect centrosome to centrosome • KINETOCHORE fibers connect from centrosome to the kinetochore located on the centromere of sister chromatids

  25. prophase

  26. metaphase • Sister chromatids are moved to center of cell by spindle fibers • Side note: karyotypes typically use cells from metaphase

  27. metaphase

  28. anaphase • Centromeres are broken as sister chromatids are pulled to opposite poles • Sister chromatids are now individual CHROMOSOMES again

  29. anaphase

  30. telophase • Chromosomes reach opposite sides of cell • Spindle fibers break apart • Chromosomes loosen and become chromatin • Nuclear envelope reforms • Nucleolus forms

  31. telophase

  32. cytokinesis • Division of the cytoplasm • In animal cells, the cell membrane pinches in and forms a cleavage furrow through the use of microfilaments • In plant cells, vesicles from the Golgi body fuse to form a cell plate, which becomes the cell wall • Newly formed cells are ½ the size of the original (why we need the “first gap” of interphase!) • New cells are IDENTICAL to original cell

  33. cytokinesis

  34. A look @ mitosis…

  35. Control of cell division • There are 3 places where a cell “decides” if it is going to divide • Cell growth checkpoint • Proteins check size of cell • DNA synthesis checkpoint • DNA copying process is checked for accuracy by enzymes • Cell cycle continues if passed • Mitosis checkpoint • If passed, cell finishes mitosis

  36. Cell division control

  37. When cell control is lost • In the genes of DNA, there are codes for the proteins which control cell division • Mutations (change in DNA’s code) can lead to abnormal or missing proteins • If cell growth is uncontrollable, cancercan result

  38. meiosis Section 3 p.161-164

  39. meiosis • Purpose: • To create haploid cells from a diploid cell • Result: • 4 cells with half the number of chromosomes as in the original cell • Reason: • When sexual reproduction occurs and gametes (sex cells) join, they have the correct number of chromosomes

  40. meiosis

  41. Formation of haploid cells • Cell cycle begins and includes all the phases of interphase • DNA IS COPIED DURING S PHASE! • Cell division occurs TWICE • MEIOSIS I: prophase I, metaphase I, anaphase I and telophase I • MEIOSIS II: prophase II, metaphase II, anaphase II and telophase II • The chromosome number is reduced to half during the first division

  42. Formation of haploid cells

  43. MEIOSIS I – “Separate the Homologues” • PROPHASE I • DNA coils into chromosomes • Spindle fibers appear • Homologous chromosomes pair in SYNAPSIS forming TETRADS • Crossing over may occur • Increases genetic variety • Each organism receives one set of chromosomes from each parent. During this stage, the chromosome from the mother pairs with the SAME chromosome from the father • SAME= has same GENES in same order, but not necessarily the same TRAITS (characteristics)

  44. Meiosis I: prophase I

  45. Meiosis I • Metaphase I • Tetrads line up in middle of cell • Spindle fibers attach to centromere of homologous chromosome • Spindle fibers from opposite pole attach to other centromere of homologous pair • FYI: • Due to random orientation of chromosomes, you will never look exactly like your parents….. • There are 8, 388, 608 possible combinations for our chromosomes!

  46. Meiosis I: metaphase I

  47. Meiosis I • Anaphase I • Homologous pairs are separated randomly • INDEPENDENT ASSORTMENT

  48. MEIOSIS I • Telophase I and Cytokinesis I • Chromosomes reach opposite poles • Sister chromatids are still attached at centromere • 2 new cells result • Each cell has half the original number of chromosomes, but still have copies attached • In other words, are still SISTERCHROMATIDS

  49. MEIOSIS II – “Separate the Chromatids” • ******Not preceded by copying of DNA****** • Can occur immediately after meiosis I • Can be delayed for considerable time

  50. Meiosis II (similar to mitosis) • Prophase II • Spindle fibers reform • Metaphase II • Sister chromatids moved to center of cell • Anaphase II • Sister chromatids separated at centromere and move to opposite poles of cell • Telophase II • Nuclear membrane reforms • Cytokinesis II • 4 new HAPLOID cells created

More Related