The Cell Cycle: Cell Growth, Cell Division

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The Cell Cycle Cell Growth, Cell Division
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Where it all began

• You started as a cell smaller than a period at
  the end of a sentence

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And now look at you
How did you get from there to here?
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Why do cells divide?

• Reproduction
• asexual reproduction
• one-celled organisms
• Growth and Development
• from fertilized egg to multi-celled organism
• Repair and Replacement
• replace cells that die from normal wear tear or
  from injury

amoeba
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Cell Cycle
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Cell cycle

• Cell has a life cycle

cell is formed from a mitotic division
cell grows matures to divide again
cell grows matures to never divide again
G1, S, G2, M
G1?G0
liver cells
epithelial cells,blood cells, stem cells
brain / nerve cells muscle cells
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Interphase

• 90 of cell life cycle
• cell doing its everyday job
• produce RNA, synthesize proteins/enzymes
• prepares for duplication if triggered

Im working here!
Time to divide multiply!
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Interphase

• Divided into 3 phases
• G1 1st Gap
• cell doing its everyday job
• cell grows
• A few hours to indefinitely
• S DNA Synthesis
• copies chromosomes
• 3-6 hours
• G2 2nd Gap
• prepares for division
• cell grows (more)
• produces organelles,proteins, membranes
• 2-5 hours

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Interphase
green key features

• Longest phase of the cell cycle
• Consists of G1, S, G2
• Cell prepares for mitosis
• replicates chromosome
• DNA proteins
• produces proteins organelles

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Organizing DNA
ACTGGTCAGGCAATGTC
DNA

• DNA is organized in Nucleosomes
• double helix DNA molecule
• wrapped around Histones
• like thread on spools
• DNA-protein complex Chromatin
• organized into long thin fiber
• condensed further during mitosis

histones
chromatin
double stranded chromosome
duplicated mitotic chromosome
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Copying DNA packaging it

• After DNA duplication, chromatin condenses
• coiling folding to make a smaller package

mitotic chromosome
DNA
chromatin
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double-strandedmitotic humanchromosomes
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Mitotic Chromosome

• Duplicated chromosome
• 2 chromatids
• narrow at centromere
• contain identical copies of original DNA

single-stranded
homologous same information
double-stranded
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Mitosis

• Dividing cells DNA between 2 daughter nuclei
• dance of the chromosomes
• 4 phases
• Prophase
• Metaphase
• Anaphase
• Telophase

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Mitosis
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Overview of mitosis
I.P.M.A.T.
interphase
prophase
(pro-metaphase)
cytokinesis
metaphase
anaphase
telophase
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Prophase
green key features

• Chromatin condenses
• Becomes chromosomes
• chromatids
• Centrioles move to opposite poles of cell
• animal cell
• Protein fibers cross cell to form mitotic spindle
• microtubules
• actin, myosin
• coordinates movement of chromosomes
• Nucleolus disappears

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Transition to Metaphase
green key features

• Prometaphase
• Special proteins attach to the centromeres
• creating kinetochores
• microtubules attach at kinetochores
• connect centromeres to centrioles
• Nuclear envelope fragments

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Anaphase
green key features

• Sister chromatids separate
• move to opposite poles
• pulled at centromeres
• pulled by motor proteins walkingalong
  microtubules
• actin, myosin
• increased production of ATP by mitochondria
• Poles move farther apart
• polar microtubules lengthen

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Telophase
green key features

• Chromosomes arrive at opposite poles
• Nuclear envelop starts to reappear
• nucleoli form
• Chromosomes uncoil
• no longer visible under light microscope
• Spindle fibers disperse
• Cytokinesis
• cell division

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Cytokinesis

• Animals
• constriction belt of actin microfilaments around
  equator of cell
• cleavage furrow forms
• splits cell in two
• like tightening a draw string

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Mitosis in whitefish blastula
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Cytokinesis in Plants

• Plants
• Cell Plate
• vesicles line up at equator
• derived from Golgi
• vesicles fuse to form 2 cell membranes
• new cell wall laid down between membranes
• new cell wall fuses with existing cell wall

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Cytokinesis in plant cell
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onion root tip
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G1/S checkpoint

• G1/S checkpoint is most critical
• primary decision point
• Go Ahead signal
• if cell receives GO signal, it divides
• internal signals cell growth (size), cell
  nutrition
• external signals growth factors
• if cell does not receive signal, it exits cycle
  switches to G0 phase
• non-dividing, working state

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What about Stem cells?

• What are stem cells?
• How can they be used?
• What are concerns about using stem cells?
• What are the types of stem cells?

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Multicellular organisms depend on interactions
among different cell types.

• Tissues are groups of cells that perform a
  similar function.
• Organs are groups of tissues that perform a
  specific or related function.
• Organ systems are groups of organs that carry out
  similar functions.

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Specialized cells perform specific functions.

• Cells develop into their mature forms through the
  process of cell differentiation.
• Cells differ because different combinations of
  genes are expressed.
• A cells location in an embryo helps determine
  how it will differentiate.

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Stem cells can develop into different cell types.

• Stem cells have the ability to
• divide and renew themselves
• remain undifferentiated in form
• develop into a variety of specialized cell types

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• Stem cells are classified into three types.

• totipotent, or growing into any other cell type
• pluripotent, or growing into any cell type but a
  totipotent cell
• multipotent, or growing into cells of a closely
  related cell family

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• Stem cells come from adults and embryos.

• Adult stem cells can be hard to isolate and grow.
• The use of adult stem cells may prevent
  transplant rejection.
• The use of embryonicstem cells raisesethical
  issues.
• Embryonic stem cellsare pluripotent andcan be
  grown indefinitelyin culture.

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• The use of stem cells offers many current and
  potential benefits.

• Stem cells are used to treat leukemia and
  lymphoma.
• Stem cells may cure disease or replace damaged
  organs.
• Stem cells Blindness
• Stem cells may revolutionize the drug development
  process.

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Cell cycle signals
inactivated Cdk

• Cell cycle controls
• Cyclin
• regulatory proteins
• levels cycle in the cell
• CDK
• cyclin-dependent kinases
• phosphorylates cellular proteins
• activates or inactivates proteins
• MPF
• triggers passage through different stages of cell
  cycle

activated Cdk