Chapter 3a Overview of the cell, and structure of the plasma membrane

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 The cell is the basic structural and functional unit of life  Amoebas are single-cellular  Humans, dogs, trees are multi-cellular

 Human body has 50 to 100 Trillion cells  200 types

 First to observe cells – Robert Hooke in 1600s (1665) (he observed cork)  Anton van Leeuwenhoek observes single cell organisms in pond water 1674

1838 Matthias Schleiden concludes all plants are made up of cells

1839 Theodor Schwann concludes all animals are made up of cells

 1855 Rudolph Virchow proposed all cells come from existing cells

 These discoveries were very important, before ‘cell theory’ which includes all these discoveries, people accepted the theory of spontaneous generation

 Four concepts that are known as the Cell Theory

 1. A cell is the basic structural and functional unit of life.  2. The activity of an organism depends on the individual and collective activities of its cells

 3. Principle of complementarity, (its function depends on its form)  4. Continuity of life has a cellular basis

 Cubelike  Tilelike  Disk-shaped  Spherical  Branching  Cylindrical

Figure 3.2

 All cells are composed chiefly of carbon, hydrogen, nitrogen, oxygen, and trace amounts of several other elements  All cells have the same basic parts and some common functions

 Human cells have 3 Main Parts  1. Plasma membrane  Outer boundary of the cell  2. Cytoplasm  Intracellular fluid packed with organelles  3. Nucleus  Controls cellular activities

 Separates intracellular fluids from extracellular fluids  Plays a dynamic role in cellular activity

 You can picture the plasma membrane using the Fluid Mosaic Model

 Thin, Double layer (bilayer) of lipids with imbedded, dispersed proteins  Bilayer consists of phospholipids, cholesterol, and glycolipids

 Phospholipids have hydrophobic and hydrophilic bipoles  Each phospholipid molecule has a polar ‘head’ that is charged and is hydrophilic  Each phospholipid molecule has a nonpolar ‘tail’ made of 2 fatty acid chains and is hydrophobic

 Hydro = water  Philic = loving  Phobia = hating  Polar heads are attracted to water so they lie on the inner and outer surfaces of the membrane  Nonpolar tails avoid water and line up in the center of the membrane

 Plasma membranes also have proteins, glycolipids, glycoproteins, and cholesterol  20% of all membrane lipid is cholesterol  Cells recognize one another by markers made out of glycoproteins called Glycocalyx

 Membranes differ in the kind and amount of lipids they contain  Glycolipids are lipids with bound carbohydrate  Glycolipids are found only in the outer membrane surface  20% of all membrane lipid is cholesterol

 Less fluid and more stable than the rest of the lipid bilayer  Make up 20% of the outer membrane surface  Composed of sphingolipids (lipids that can pack tightly together) and cholesterol  Are concentrating platforms for cell-signaling molecules

 Plasma membranes lipid bilayers are imbedded with protein groups  Cells recognize one another by markers made out of glycoproteins called Glycocalyx

 Glycocalyx is a glycoprotein  Sugar coating on cells  Every cell type has a different pattern of sugars in its glycocalyx  Biological markers that approaching cells recognize

Figure 3.4.2

 Integral proteins  Peripheral proteins

 Firmly inserted into the lipid bilayer  Some protrude on just one side of the membrane  Most are transmembrane proteins  span the entire width of the membrane and protrude on both sides

 Attached loosely to integral proteins or membrane lipids  Easily removed without disrupting the membrane

 Glycoproteins in the glycocalyx act as an adhesive  Wavy contours of the membranes of adjacent cells fit together in a tongue & groove fashion  Special membrane junctions are formed  Tight junctions, desmosomes, and gap junctions

 Tight junction – impermeable junction that encircles the cell Figure 3.5a

 Desmosome – anchoring junction scattered along the sides of cells Figure 3.5b

 Gap junction – a nexus that allows chemical substances to pass between cells Figure 3.5c

 Small extensions of the plasma membrane that project from a free, or exposed cell surface  Increases surface area

 Most often found on the surface of cells that function in absorption like intestinal and kidney cells

Next time! Study guide check pages 53 – 55 after next lecture.

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