BISC 101 Lecture Notes - Lecture 4: G2 Phase, Hydrophile, Golgi Apparatus

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BISC 101 – Lecture 4 – A Tour of the Cell: Part II
Cell Systems: The Dynamic Cytoskeleton
Cytoskeleton: Dense and complex network of fibers that help maintain cell shape
by providing structural support
oWhole network of fibers that organizes structures and activities in the cell
oNot a permanent structure and is dynamic
oFibrous proteins move to change the cells shape, contents and move the
entire structure
oCellular scaffolding or skeleton within a cell’s cytoplasm that is made of
oThe cytoskeleton helps to support the cell and maintain its shape
oIt interacts with motor proteins (cilia and flagella) to produce motility
oVesicles can travel along monorails provided by the cytoskeleton
Three distinct cytoskeletal elements in eukaryotic cells:
oActin filaments
oIntermediate filaments
Actin Filaments or Microfilaments
Microfilaments or Actin Filaments: Thinnest fibrous structure component of the
cytoskeleton made of actin protein
Protein Subunits
oActin: Most abundant of all proteins that represents 5 -10% of the total
protein in a cell
Actin Filament Structure
oTwo intertwined strands of actin
Actin Filament Function
oMaintenance and changes of cell shape
oMuscle contraction
oCytoplasmic streaming
oCell motility
oCell division
Localized contraction from actin and myosin also causes amoeboid to move
oPseudopodia (Cellular extensions) extend and contract through the
reversible assembly and contraction of actin subunits into microfilaments
Cytoplasmic Streaming: Circular flow of cytoplasm within cells to allow for rapid
distribution of materials within the cell
Intermediate Filaments
Intermediate Filaments: Component of the cytoskeleton with fibers in a middle
diameter range
Protein Subunits
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oOne of several different proteins of the keratin family
oEx: Keratin: Cells that make up your skin and line surfaces inside the
body. Also make nails and hair
Intermediate Filament Structure
oFibrous proteins supercoiled into thicker cables
Intermediate Filament Functions
oMaintenance of cell shape
oAnchorage of nucleus and chromosomes and certain other organelles
oFormation of nuclear lamina
oNuclear lamins: Dense mesh under the nuclear envelope, aka
intermediate filaments involved in the breakup and reassembly of the
nuclear envelope when cells divide
Intermediate filaments form a flexible skeleton that helps shape the cell surface
and hold the nucleus in place
oIntermediate fibers reach out from the nucleus and stab through the
cytoplasm to the plasma membrane where they link with other
intermediate filaments that run parallel to the cell surface
Microtubules or Tubulin Polymers
Microtubules or Tubulin Polymers: The thickest of the three components of the
Protein Subunits
Microtubule Structure
oHollow tubes
Microtubule Function
oMaintenance of cell shape
oCell motility
oChromosome movements in cell division
oOrganelle movements
oTubulin dimers polymerize to form microtubules
Microtubules control the beating of cilia and flagella
Flagella and Cilia: Moving the Entire Cell
Flagella: Long, hair – like projections from the cell surface that function in
oBoth bacteria and eukaryotes have flagella, but the structure is
completely different in the two groups
Eukaryotic flagella are closely related to structures called cilia
Cilia: Short – filament – like projections
Flagella are longer than cilia
A typical cell will have one or two flagella but many cilia
Common structures between cilia and flagella:
oCore of microtubules sheathed by the plasma membrane
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