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Cell Division

Cell Division

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Cell Division

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  1. Cell Division

  2. Nucleic Acids Deoxyribonucleic Acid - DNA   • Found primarily in the nucleus in chromosomes - stores and transmit information to make proteins.   • Structure   Consists of two strands of nucleotide monomers   Parts of a nucleotide   Deoxyribose - 5-carbon sugar   Phosphate group   Nitrogen base  

  3. Nucleic Acids

  4. Nucleic Acids

  5. Nucleic Acids Nitrogen base   • Purine- nitrogen base with a double ring of carbon and nitrogen atoms.   Adenine Guanine   • Pyrimidine- nitrogen base having a single ring of carbon and nitrogen atoms.   Thymine Cytosine  

  6. Nucleic Acids

  7. Nucleic Acids Two strands of nucleotides twist around a central axis to form a double helix First described by Watson and Crick in 1953.   Similar to a twisted ladder   Sides of alternating sugar and phosphate Rungs consist of pairs of nitrogen bases - equal in length.   Purine always pairs with a pyrimidine -have hydrogen bonds.   Adenine bonds with thymine   Guanine bonds with cytosine

  8. Nucleic Acids

  9. Nucleic Acids

  10. Nucleic Acids

  11. Nucleic Acids • Base sequence one strand is exact complement of base sequence in second strand.   1st Strand Sequence A - G - C - T - T - A - G - C   2nd Strand Sequence T - C - G - A - A - T - C - G  

  12. Nucleic Acids

  13. Nucleic Acids Replication Process of duplicating the DNA molecule Each strand serves as a template or mold for new complementary strand to be built.

  14. Nucleic Acids Process of Replication • DNA helicase attaches to DNA molecule - "unzips" the 2 strands - breaks hydrogen bonds between bases.   • Unpaired bases of strands react with complementary bases of nucleotides in nucleus - hydrogen bonds form.   • DNA polymerase catalyzes formation of sugar to phosphate bonds - connect one nucleotide to the next.   • Result - two new DNA molecules - each consists of 1 "old" strand and 1 "new" strand.   • Process doesn't begin at one end and proceed to the other - may occur simultaneously at many points.

  15. Nucleic Acids

  16. Nucleic Acids DNA may be damaged by body heat, radiation, chemicals, etc.   Cell can "proofread" for mistakes Can be repaired and corrected

  17. Nucleic Acids Ribonucleic Acid – RNA • Nucleic acid that uses information stored in DNA to synthesize proteins. • Structure Consists of a single strand of nucleotide monomers. Parts of nucleotide Ribose - 5-carbon sugar Phosphate group Nitrogen base

  18. Nucleic Acids Nitrogen bases of RNA • Purines Adenine Guanine • Pyrimidines Uracil Cytosine

  19. Nucleic Acids RNA differs from DNA in 3 ways • RNA consists of only one strand of nucleotides instead of the 2 strands of DNA.   • RNA contains the 5-carbon sugar, ribose, instead of deoxyribose   • RNA contains the nitrogen base, uracil, instead of thymine.  

  20. Nucleic Acids

  21. Nucleic Acids

  22. Nucleic Acids Types of RNA   • Messenger RNA (mRNA) - single, uncoiled strand, transmits information from DNA for protein synthesis; acts as template for amino acid assembly during protein synthesis at ribosomes.  • Transfer (tRNA) - single strand of RNA folded back on itself in hairpin fashion; allows some bases pairing; exists in 20 or more varieties each for only 1 specific type of amino acid.   • Ribosomal RNA (rRNA) - globular form of RNA; major constituent of ribosomes.

  23. Nucleic Acids Transcription • Process where mRNA is produced from the DNA - transcribed according to the information coded in the base sequence of DNA.   Base sequence of mRNA complementary to sequence of DNA from which it was transcribed.   Directed by enzyme, RNA polymerase   • Process   Enzyme binds to DNA causing strands to separate.   Hydrogen bonds to form between DNA template and complementary RNA nucleotide bases.   Enzyme moves to next section of DNA, bonds form between phosphate groups and ribose. RNA molecule released when enzyme reaches DNA sequence that acts as a termination signal.  

  24. Nucleic Acids

  25. Nucleic Acids Protein Synthesis • Structural and functional characteristics of proteins are determined by the sequence of amino acids in the protein   • Sequence of amino acids in a protein encoded in DNA   • Genetic Code - System that contains information needed by cells for proper functioning; built into the arrangement of nitrogen bases in a particular sequence of DNA.   Codon- series of three bases in mRNA that codes for a specific amino acid.   Anticodon- series of three bases in tRNA, complementary to a codon; pairs with the codon during translation  

  26. Nucleic Acids Translation- process where protein molecules are made from information encoded in mRNA. • mRNA moves out of nucleus through a nuclear pore   • mRNA migrates to a group of ribosomes   • Amino acids in the cytoplasm are transported to the ribosomes by tRNA - each specific for an amino acid.   • Assembly of polypeptide begins when A - U - G codon attaches to the ribosome.   • Codon pairs with its anticodon adding specific amino acid to the growing polypeptide chain.   • Process continues until a "stop" codon reaches the ribosome.   • mRNA is released and polypeptide is complete and released

  27. Nucleic Acids

  28. Nucleic Acids Gene- region of DNA that directs the formation of a polypeptide. • Proteins usually consist of more than one polypeptide.   • Several genes may direct protein synthesis

  29. Cell Division Process by which cells reproduce.   • Cell Theory   Cell is basic unit of life   Living things are made of cells or cell fragments.   All cells come form existing cells.   • Reasons Cells Divide   Maintenance   Repair   Growth   Reproduction  

  30. Cell Division Nucleus • Organelle that directs the everyday metabolic activities of the cell.   • Composed of Chromatin Normally - grainy mass of material   During cell division appear as bodies called chromosomes.   Composed of DNA and protein   Carries the "genetic code"   Individual heredity units are genes - determine cell characteristics and how cell functions - by proteins that are synthesized.   • Each time the cell divides the genetic material must be replicated– makes exact copy   Must then be distributed to the new cell.   Replication occurs during interphase.

  31. Cell Division

  32. Cell Division Chromosome Number   • The number of chromosomes found in the nucleus.   Varies from one organism to another.   Man - 46   Fruit Fly - 8   Bullfrog - 26   • All cells of an organism will have the same number of chromosomes.   Exception is the sex cells or Gametes Egg - female   Sperm - male   • Body cells called Somatic Cells or Somates.

  33. Cell Division Humans 23 pairs of chromosomes - total of 46 chromosomes. • Pairs of chromosomes are known as being Homologous.   Individual members of the pair are called Homologs.   Get one homolog of each pair from each parent   Each homolog of pair has same size and shape.   • Number of pairs of chromosomes in a somate is expressed as "n" - total number of chromosomes expressed as "2n"   Humans: n = 23; 2n = 46   • Total number of chromosomes is Diploid Number = 2n   • Total number of different pairs in cell is its Haploid Number (Monoploid) = n   • Features of the cell's chromosomes including size and number make up cell's Karyotype- arranged by size and shape.  

  34. Cell Division Actually talking about division of nuclear material   • Two types of nuclear division   Mitosis Meiosis • Cytokinesis- division of the cytoplasm  

  35. Mitosis Process by which the nucleus divides to produce 2 new nuclei, each with the same number of chromosomes as the parent nucleus.   From the Greek - Mitos - Thread   Occurs in somatic cells.   • Requirements   Precise replication of the genetic material   Distribution of a complete set of chromosomes to each new cell - called Daughter Cells   • Five Phases of Cell Cycle - continuous   Interphase   Prophase   Metaphase   Anaphase   Telophase  

  36. Mitosis Interphase– not really a part of mitosis • Once called the "resting" stage   • Cell performing various metabolic activities  • Occupies about 2/3 of cell's life cycle   • Genetic material replicates during phase.   • Nucleus clearly defined by membrane   • Chromosomes not visible - chromatin appears grainy.   • Consists of 3 subphases   G1 Phase - first phase of interphase; cell doubles in size; enzymes and organelles,roughly double in size.   S Phase - DNA in the chromatin replicates   G2 Phase - Cell undergoes rapid growth that prepares it for mitosis, synthesizing necessary enzymes and structures.  

  37. Cell Division

  38. Mitosis Prophase • Early prophase - chromatin coils; forms chromosomes.   • Chromosomes appear as rod-like structures.   • Nucleolus and nuclear membrane breakdown and disappear.   • Centrioles appear next to the disappearing nucleus - move to opposite ends or poles of cell (not plants).   • Spindle fibers form - asters radiate from centrioles in animal cells.   • Chromosomes appear as double stranded structure   Each strand is a Chromatid Two chromatids are joined at a Centromere.

  39. Mitosis

  40. Mitosis Metaphase • Chromosomes arrange themselves on equator of spindle   • Chromosomes attach to spindle fibers at the centromere.   • Centromeres aligned on the equator.

  41. Mitosis

  42. Mitosis Anaphase • Centromere divides - one chromatid moves toward 1 pole of spindle while other chromatid moves to the opposite pole.  

  43. Mitosis

  44. Mitosis Telophase • Two identical sets of chromatids are clustered at opposite ends of the cell.   • Centrioles and spindle fibers disappear.   • Chromatids unwind and elongate into chromatin - chromosomes disappear • Nuclear membrane and nucleolus reappear.  

  45. Mitosis

  46. Mitosis • Process completed with cytokinesis - get two distinct cells   Animals – Cleavage Furrowforms from outside toward the center – pinches cell in two.   Plants – Cell Plate forms from center and grows to the outside.   • No reduction in chromosome number   Parent Cell = 2n ----> Each Daughter Cell = 2n  

  47. Mitosis

  48. Meiosis Process by which the cell nucleus divides resulting in a reduction of chromosome number from the diploid number (2n) to the haploid number (n) • Involves 2 divisions   Chromosome number reduced in first division - Meiosis I   Second division - mitotic - Meiosis II   • Cell division that results in formation of gametes or sex cells.   Occurs in the Gonads (sex organs)   Ovary- female Testes- male   Process in males - called Spermatogenesis Process in females - called Oogenesis

  49. Meiosis Phases   • Interphase   • Prophase I   • Metaphase I   • Anaphase I   • Telophase I   • Prophase II • Metaphase II • Anaphase II • Telophase II

  50. Meiosis Interphase- same as in mitosis   • Chromosomes replicate