cells: The living units

cells: The living units Chapter 3a Overview of the cell, and structure of the plasma membrane

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

Cells • Human body has 50 to 100 Trillion cells • 200 types

Cells • 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

Cells • 1855 Rudolph Virchow proposed all cells come from existing cells

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

Cell Theory • Four concepts that are known as the Cell Theory

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

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

Cell Shapes • Cubelike • Tilelike • Disk-shaped • Spherical • Branching • Cylindrical

Structure of a Generalized Cell Figure 3.2

Generalized Cell • 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

Structure of a Generalized Cell • 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

The structure of the Plasma Membrane

Plasma Membrane • Separates intracellular fluids from extracellular fluids • Plays a dynamic role in cellular activity

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

Plasma Membrane • 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

Plasma Membrane • 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 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

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

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

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

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cells: The living units