ANATOMY OF THE CELL

THE CELL

The cell is the basic unit of life. Some organisms consist only of one cell. These unicellular organisms are capable of performing all life functions within this one cell.
Life Functions: .............................
Below is the structure of a typical animal cell.

Identify all parts of the cell, including parts not indicated by arrows, and provide a description and the function of each part.

Structure of a typical animal cell

animalcell.jpg



The Cell membrane

The cell membrane is a double unit membrane. A unit membrane is composed a layer of protein with a layer of phospholipid. The second membrane will be inverted i.e a layer of phospholipid with a layer of protein. Summed up: a double layer of phospholipid sandwiched between a double layer of protein.
The molecules have microscopic spaces between them. At some places along the cell membrane, a guarded gap - pore - is created where specific proteins are on either side of the gap. This pore is utilised when substances have to enter or exit the cell. Since protein is a polar molecule with other unique properties, entrance and exit through this ‘guarded’ pore is not easy.
Immediately above the outer protein layer there is a layer of surface protein, some attached to the protein layer by weak bonds. Other proteins extend through the spaces between the protein molecules and attach to the lipids = lipid anchored proteins. These look like ‘umbrellas’ over the underlying microscopic spaces, partially obscuring the space, thus making approach by any foreign particle difficult. Thus, we see that the cell membrane can be very difficult to penetrate if all the structures are in place.

CellSurface.jpg

Vitamins play a major role in cellular activities. Protein synthesis is enhanced by the presence of Vitamin C. Thus, with enough Vit C in the body the cells are able to maintain a healthy cell membrane and retard or prevent invasion by foreign bodies/particles.
All animals, whether unicellular or multicellular, have cells surrounded by a double unit membrane, which curves into the cell forming the ER which provides a passage for substance from the outside to the innermost parts of the cell.

The cell plasma is the medium in which cellular reactions occur. The sum total or activities of the cells is known as metabolism. Metabolic reactions can be either

anabolic (building up) eg. protein synthesis, synthesis of fats etc.

or catabolic (breaking down) eg. hydrolysis of substances, cellular respiration etc.

Many anabolic reactions are reversible reactions i.e. the products formed can be broken down again into its constituent molecules:
glycerol + 3 fatty acids <-----------> Lipid + H2O

Special CELLULAR STRUCTURES, ACTIVITIES and MECHANISMS



Homeostasis: Definition:

Feedback mechanisms: examples:

Secretory mechanisms:
Golgi Apparatus -

GolgiSecretory.jpg


ER -
Secretory vesicles -

Ribosomes and Protein synthesis:




Endocytosis:

endocytosisParticle.jpgendocytosisMolecule.jpg




Exocytosis:

exocytosis.jpg




Phagocytosis:

phagocytosis.jpg



Pinocytosis:

pinocytosis.jpg





Entry of Lipid soluble substances:: Enlarged lipid layer - easy for fat soluble substances to enter cells.


Liposomes:
Liposome.jpg


[from Wikipedia]
A liposome is an artificially-prepared vesicle primarily composed of a lipid bilayer. The liposome is a vehicle for administration of nutrients and pharmaceutical drugs. Liposomes can be prepared by disrupting biological membranes.

Liposomes are composed of natural phospholipids, and may also contain mixed lipid chains with surfactant properties (e.g., egg phosphatidylethanolamine). A liposome design may employ surface ligands for attaching to unhealthy tissue.

The major types of liposomes are the multilamellar vesicle (MLV), the small unilamellar vesicle (SUV), and the large unilamellar vesicle (LUV).

Liposomes should not be confused with micelles and reverse micelles composed of monolayers. [From Wikipedia


Entry of Lipid soluble substances: Enlarged lipid layer - easy for fat soluble substances to

enter cells.

Cytoskeletal structures


Microfilaments: strands of actin - a protein prevalent mostly at edge of cells.

Shape/support, movement, cell division, muscle contraction
Intermediate filaments: - strands of different proteins thicker than microfilaments - helps to keep organelles in place. Helps to attach cells to one another.
Microtubules: larger than above. Proteins (tubulin) from tubule. Help to determine the cell shape


Microvilli - minutest cell extensions supported by microfilaments.
Cilium - 20 microtubules surrounded by plasma & membrane forming a hair-like outgrowth of the cell
Flagellum - a whip-like similar in structure to cilium - much longer. Used for locomotion.
From: Tortora & Derickson 12th Ed Vol I
Liposomes From Wikipedia



How cells are held together

Tight Junctions - weblike stands of transmembrane proteins - particularly in organs that contain liquid or semi-liquid to prevent lesion.
Adherens Junctions - thickened area at membrane in regions of microfilaments -plaque - connecting glycoprotein cadherin anchors into plaque of both cells
forming a ‘bond’ between the cells - regions = adhesion zones
Desmosomes: similar to above but anchorage in intermediate filaments in plasma - stabilizes tissue structure considerably eg. in skin, cardiac muscle and other tissue
subject to stress
Hemidesmosomes: anchorage to basement membrane - proteins : integrin (transmembrane glycoprotein anchored within cell) laminin (in basement membrane)
Gap Junctions: protein- connexin - narrow tubules between cells for rapid chemical communication eg. nerve cells, spreading nutrients within tissues, removal of waste, etc.

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