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AP Bio- Cells 3: Structure & Support

Original By David Knuffke.
by

Jennifer Harvey

on 9 January 2013

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Transcript of AP Bio- Cells 3: Structure & Support

"Open" Junctions A Tour of The Cell (Part 3) If you recall... The Life of the Cell All cells must do the following things to stay alive:
Process matter: Molecules need to be acquired, synthesized and digested
Process energy: In order to process matter, energy must be provided. This energy usually comes from one of two places (where?)
Process information: The instructions that enable the cell to process matter and energy must be interpreted by the cellular system. Signals from the environment must also be interpreted.

Many cells will also do the following :
Reproduce: The information that runs the cell must be passed on to new generations of cells.
Communicate: Cells respond to/direct other cells. Cells have systems to do all of these things! Big Questions: What does the internal structure of a cell look like?

How do cells separate themselves from their environments?

How do cells communicate with the environment?

How do cells communicate with other cells? Explain why cells need to have internal structural organization and support.

Explain the structure and function of the cytoskeleton.

Compare the components of the cytoskeleton.

Explain the structure and function of the cell membrane.

Describe the roles of phospholipids, cholesterol, and membrane proteins in cell membrane function.

Explain the structure and function of the cell wall.

Compare the structures of plant-like, fungal, and bacterial cell walls.

Explain the structure and function of the extracellular matrix.

Compare the structure and function of different types of intercellular junctions. Make Sure You Can: Inside the Cell: At the Boundary: Outside the Cell: Between Cells: The Cytoskeleton Structure: A network of structural proteins that extends throughout the cytoplasm. Functions: Structural support
Maintaining cell shape
Anchorage of organelles
Regulation of cell & organelle motility
Movement of chromosomes during cell division Cilia & Flagella Structure: Motility related extensions of cytoskeletal proteins Centrosome Function: Motion of the cell through space Structure: Animal-like cell only microtubule-organizing center Function: Origin of all microtubules in cell. Major role in animal-like cell division Cell Wall Intercellular Junctions ECM (Extracellular Matrix") Structure: A cross-linked network of structural polysaccharides. Function: Structural support only! Cell walls are non-living Cellulose: Plant-like cells Chitin: Fungal cells Bacterial Cells Peptidoglycan: No Cell Walls in Animal-like Cells! ...Why? Structure: A network of connective proteins and "proteoglycan" molecules outside of the cell membrane of animal cells Function: Cell anchorage. Cell communication. Only animal cells have any major ECM... ...Why? Structure: Proteins that connect cells to other cells.
Depending on the junction, a channel between cells may exist "Closed" Junctions Functions: Anchorage & Transport ("open" junctions only) The Cell Membrane Structure: Functions: The "Fluid Mosaic Model": A phospholipid bi-layer with associated proteins Boundary of cell
Transport of materials in and out of the cell
Communication between cell and environment Cytoskeletal elements stained green & orange Motor proteins connect vesicles to microtubules intermediate actin filaments play a large role in cell motility green = microtubules
red = microfilaments The cytoskeleton is a dynamic regulator of cellular structure and function Cholesterol: Structure: a steroid lipid Function: acts as a "temperature buffer" to help maintain membrane fluidity over a range of temperatures Membrane Proteins: Structure: Various, depending on the role they play:
Integral proteins: penetrate one or both layers of the bi-layer.
Peripheral proteins: associated with the membrane, but don't penetrate the bi-layer.
The polarity of different regions of a membrane protein vary according to the role of that protein. Functions: Many and more. Here's brief overview: Spotlight: Membrane Receptors Structure: Integral proteins that span the bi-layer with regions ("domains") that extend extra- and intra-cellularly. Function: Signal Transduction: The receipt of chemical messages from the environment and the relay (transduction") of those messages into the cell for response. Spotlight: Glycoproteins Structure: Integral proteins that span the bi-layer with short polysaccharide residues projecting extra-cellularly into the environment Function: Cell-Cell Recognition: Glycoproteins serve as an identifying marker in cellular populations (like your body). Membrane receptors are exploited by viruses (how?) Glycoproteins are a complication for organ transplants (why?) lipids with a phosphate attached to glycerol in place of a fatty acid tail.
polar (hydrophilic) phosphate "head", nonpolar (hydrophobic) fatty acid tails. This type of polar/non-polar molecule is called "amphipathic"
Spontaneously organizes in the presence of water to form a bi-layer
fluid: phospholipids are constantly moving Structure: Function: Membrane Phospholipids: Makes a "selectively permeable" membrane. Only small, non-polar molecules can easily move through the phosopholipid bi-layer (Why?) membrane proteins are mobile in the cell membrane: Each component of the cytoskeleton is assembled from protein subunits Structure of chitin: Structure of peptidoglycan: Structure of cellulose: Plasmodesmata:
Open channels in plant cell walls Gap Junctions:
Open channels between animal cells Desmosomes:
Cellular "rivets" that anchor cells to basement mebranes in tissues Tight Junctions:
Cell-cell connections that make a waterproof seal. Plants: Animals: Any Questions? Now, let's put it all together:
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