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Chapter 12 The Cell Cycle.

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Presentation on theme: "Chapter 12 The Cell Cycle."— Presentation transcript:

1 Chapter The Cell Cycle

2 Essential Knowledge 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 ( ).

3 Roles of Cell Division Reproduction (uni vs. multi) Growth
Repair/replace old or damaged cells 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 Two cell types Somatic Sex Non-sex cells (all body cells EXCEPT sex)
Ex: red blood, skin, muscle Sex Otherwise known as gametes Ex: sperm, egg

5 Genome 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 Chromosomes 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 Chromosomes vs. 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 Chromosomes - Structure
At cell division, each chromosome has been duplicated The duplicated chromosome consists of two sister chromatids Centromere – the point where two sister chromatids are connected


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


12 Interphase - parts In order: G1 - first gap S - synthesis
G2 - second gap

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

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

15 Mitosis - Purpose To divide the 2 copies of the DNA equally
To separate the sister chromatids into separate cells

16 Mitosis Steps Prophase Prometaphase Metaphase Anaphase Telophase
Mitosis Video #1 Mitosis Video #2

17 Prophase

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

19 Prometaphase

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

21 Metaphase

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

23 Anaphase

24 Anaphase 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 Kinetochores 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


27 Telophase

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

29 Cytokinesis

30 Cytokinesis – Animal vs. Plant
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

31 Animal Cell - Mitosis

32 Plant Cell - Mitosis

33 Evolution of Mitosis

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

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

36 Checkpoints 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 G1 Checkpoint Also called the “restriction point” in mammalian cells
Places cells in a non-dividing phase called the Go phase

38 GO

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

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

41 GO Protein Kinase

42 MPF 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 GO Protein Kinase MPF

44 CDK and Cyclin CDK: Cyclin: 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 Active MPF 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 Growth Factors External signals that affect mitosis Examples: PDGF
Density-dependent inhibition Anchorage dependence

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

48 Density-Dependent Inhibition
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 Anchorage Dependence Inhibition of cell division unless the cell is attached to a substratum Prevents cells from dividing and floating off in the body

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

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

53 Summary 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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