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Structure and Support

If you recall...

Inside the Cell:

At the Boundary:

Outside the Cell:

Between Cells:

Any Questions?

Make Sure You Can:

Big Questions:

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.

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?

Now, let's put it all together:

Cilia & Flagella

The Life of the Cell

The Cytoskeleton

Structure:

Motility related extensions of cytoskeletal proteins

Structure:

A network of structural proteins that extends throughout the cytoplasm.

Cytoskeletal elements stained green & orange

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.

Function:

Motion of the cell through space

Functions:

Centrosome

Each component of the cytoskeleton is assembled from protein subunits

  • Structural support
  • Maintaining cell shape
  • Anchorage of organelles
  • Regulation of cell & organelle motility
  • Movement of chromosomes during cell division

Structure:

Animal-like cell only microtubule-organizing center

Cells have systems to do all of these things!

Motor proteins connect vesicles to microtubules

The cytoskeleton is a dynamic regulator of cellular structure and function

intermediate actin filaments play a large role in cell motility

green = microtubules

red = microfilaments

Function:

Origin of all microtubules in cell. Major role in animal-like cell division

Membrane Proteins:

Structure:

The Cell Membrane

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.

Structure:

membrane proteins are mobile in the cell membrane:

The "Fluid Mosaic Model": A phospholipid bi-layer with associated proteins

Functions:

Spotlight: Membrane Receptors

Spotlight: Glycoproteins

Many and more. Here's brief overview:

Structure:

Integral proteins that span the bi-layer with regions ("domains") that extend extra- and intra-cellularly.

Integral proteins that span the bi-layer with short polysaccharide residues projecting extra-cellularly into the environment

Function:

Signal Transduction: The receipt of chemical messages from the environment and the relay (transduction") of those messages into the cell for response.

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?)

Functions:

Membrane Phospholipids:

Cholesterol:

Structure:

  • a steroid lipid
  • 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
  • Boundary of cell
  • Transport of materials in and out of the cell
  • Communication between cell and environment

Function:

  • acts as a "temperature buffer" to help maintain membrane fluidity over a range of temperatures
  • Makes a "selectively permeable" membrane. Only small, non-polar molecules can easily move through the phosopholipid bi-layer (Why?)

Intercellular Junctions

("Extracellular Matrix")

Cell Wall

ECM

Structure:

A cross-linked network of structural polysaccharides.

Proteins that connect cells to other cells.

Depending on the junction, a channel between cells may exist

A network of connective proteins and "proteoglycan" molecules outside of the cell membrane of animal cells

Cellulose:

Chitin:

Plant-like cells

Fungal cells

Structure of chitin:

Functions:

Anchorage & Transport ("open" junctions only)

Structure of cellulose:

Peptidoglycan:

Structure of peptidoglycan:

Bacterial Cells

"Open" Junctions

"Closed" Junctions

Plants:

Animals:

Function:

Cell anchorage. Cell communication.

Structural support only! Cell walls are non-living

No Cell Walls in Animal-like Cells!

Only animal cells have any major ECM...

Plasmodesmata:

Open channels in plant cell walls

Tight Junctions:

Cell-cell connections that make a waterproof seal.

Gap Junctions:

Open channels between animal cells

Desmosomes:

Cellular "rivets" that anchor cells to basement mebranes in tissues

...Why?

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