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 3.a.2 – In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis, or meiosis plus.

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Presentation on theme: " 3.a.2 – In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis, or meiosis plus."— Presentation transcript:


2  3.a.2 – In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis, or meiosis plus fertilization (12.1-12.3).

3 1. Reproduction (uni vs. multi) 2. Growth 3. Repair/replace old or damaged cells 4. To distribute identical genetic material to two new daughter cells  Goal: To split the sister chromatids and give one to each new cell – to make two new cells with the correct amount of genetic info

4 1. Somatic  Non-sex cells (all body cells EXCEPT sex)  Ex: red blood, skin, muscle 2. Sex  Otherwise known as gametes  Ex: sperm, egg

5  The cell's hereditary endowment of DNA  Usually packaged into chromosomes (easier to manage during the cell cycle)  Prokaryotes:  Single stranded, in cytoplasm, circular in shape  Eukaryotes:  Double stranded, in nucleus, helix/spiral in shape

6 chromatin  Made of a DNA and protein complex called chromatin  During cell division, the chromatin becomes highly condensed into the chromosomes  # of chromosomes:  Sex cell (haploid cell) ▪ 23 (no pairs)—only contains one set of chromosomes  Somatic cell (diploid cell) ▪ 46 (in 23 pairs)—contain two sets of chromosomes

7  Chromatin  Long, thin fiber  Uncondensed  Before/after cell division  Genetic material usually in this form  Chromosome  Characteristic “X” shape  Condensed into this shape  Only during cell division

8  At cell division, each chromosome has been duplicated sister chromatids  The duplicated chromosome consists of two sister chromatids  Centromere – the point where two sister chromatids are connected


10 Interphase 1. Interphase - (90% of cycle) - when the cell grows and duplicates the chromosomes Mitotic Phase 2. Mitotic Phase (M) - when the chromosomes are split into separate cells


12  In order:  G1  G1 - first gap  S  S - synthesis  G2  G2 - second gap

13  G1:  Cell grows and carries out regular biochemical functions  S:  DNA is replicated or synthesized - chromosomes are replicated  G2:  Cell completes preparations  Comment:  Comment: A cell can complete S, but fail to enter G2.

14 Mitosis 1. Mitosis - division of replicated chromosomes Cytokinesis 2. Cytokinesis - division of the cell’s cytoplasm

15  To divide the 2 copies of the DNA equally  To separate the sister chromatids into separate cells

16 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase  Mitosis Video #1 Mitosis Video #1  Mitosis Video #2 Mitosis Video #2


18  Nucleoli disappear  Chromatin condenses into chromosomes  Centrioles separate to opposite ends of the cell  Mitotic spindle begins to form


20  Nuclear envelope dissolves  Spindle fibers join with the kinetochore of the centromeres


22  Centrioles now at opposite ends of the cell  Chromosomes line up on the metaphase plate  Spindle apparatus fully developed


24  Centromeres break and the duplicate chromosomes are pulled away from each other toward opposite ends of the cell  Cell elongates; poles move slightly further apart

25  Specialized regions of the centromeres where spindle microtubules attach  Appear to “ratchet” the chromosome down the spindle fiber microtubule using a motor protein  Microtubules dissolve behind the kinetochore



28  Chromosomes uncoil back to chromatin  Nuclear envelope reforms  Nucleoli reappear  Spindle fibers disappear  Cytokinesis usually starts


30  Animal  Cleavage furrow forms  Microfilaments contracts and divides the cytoplasm into two parts  Plant  Cell plate develops in between the two new daughter cells (from Golgi vesicles)  New cell wall developed around the cell plate


32 Plant Cell - Mitosis


34  Hypothesis  Hypothesis: Mitosis has origins in prokaryotic cells  How do we know this? ▪ Proteins involved are identical ▪ Ex: kinetochores, protein kinase checkpoints, etc.

35  Must be controlled  Rate of cell division depends on the cell type  Ex  Ex - skin: frequently  liver - as needed  brain - rarely or never

36  A critical control point in the cell cycle  Several are known  Cells must receive a “go-ahead” signal before proceeding to the next phase

37  Also called the “restriction point” in mammalian cells G o phase  Places cells in a non-dividing phase called the G o phase


39  Non-dividing state  Most cells are in this state  Some cells can be reactivated back into M phase from the G o phase

40  Uses protein kinases to signal “go- ahead” for the G2 phase  Activated by a protein complex whose concentration changes over the cell cycle

41 GOGO Protein Kinase

42  M-phase Promoting Factor  Protein complex required for a cell to progress from G2 to Mitosis  Role of MPF - to trigger a chain of protein kinase activations  Active MPF has: cdk and cyclin

43 GOGO Protein Kinase MPF

44  CDK:  Protein Kinase  Amount remains constant during cycle  Inactive unless bound with cyclin  Cyclin:  Protein whose concentration builds up over G1, S and G2  When enough cyclin is present, active MPF is formed

45  Triggers Mitosis  Activates a cyclin-degrading enzyme, which lowers the amount of cyclin in the cell  Result - no active MPF to trigger another mitosis until the cycle is repeated

46  External signals that affect mitosis  Examples:  PDGF  Density-dependent inhibition  Anchorage dependence

47  Platelet- Derived Growth Factor  Stimulates cell division to heal injuries

48  The number of cells in an area force competition for nutrients, space, and growth factors  When density is high -  no cell division  When density is low -  cells divide


50  Inhibition of cell division unless the cell is attached to a substratum  Prevents cells from dividing and floating off in the body

51  Do not stop dividing.  The control mechanisms for cell division have failed

52  Regulation of cell division is a balance between: Mitosis Mitosis - making new cells Apoptosis Apoptosis - cell suicide  Cancer can result if either process doesn’t work

53  Identify the roles of cell division  Identify the composition of a chromosome.  Recognize the phases of the cell cycle.  Identify the stages and characteristics of Interphase.  Identify the stages and characteristics of Mitosis.  Recognize the mechanisms of Cytokinesis.  Recognize factors that control cell division.  Recognize the results when the regulation of cell division goes wrong.

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