Chapter 6 Introduction Bozeman Tutorial: Tour of the Cell (14:16) A Tour of the Cell Chapter 6 Introduction Bozeman Tutorial: Tour of the Cell (14:16)

Overview of Cells Cell Theory – Several statements assembled in the 1800’s to explain cells: a. All living things are made of cells. b. Cells are alike in structure and function. c. Cells are the basic unit of life. d. New cells come from pre-existing cells Two reasons that cells are small: a. Efficiency: Smaller cells have increased surface area to volume. If the cell is too big, it’s difficult to move nutrients/wastes across the membrane and throughout the cell. b. Specialization: Having numerous small cells permits cells to have different functions.

Two Types of Cells 1. EUKARYOTIC – Kingdoms Animalia, Plantae, Fungi, Protista. Eukaryotes contain a membrane-bound nucleus and other structures, called organelles, that have specific functions. The organelles are found in a jelly-like medium called cytosol. Plant cells have three more organelles than the animal cells (cell wall, chloroplasts, and a large central vacuole). 2. PROKARYOTIC – Kingdoms Archaebacteria and Eubacteria. Prokaryotes are the simplest of all cells and were probably the first life forms, containing only cell wall, cell membrane, DNA, and ribosomes.

Intercellular Junctions Cells of a complex organisms are integrated into one functional organism. Cells interact through direct physical contact. Cell walls of plants have perforations called plasmodesmata through which the living contents of adjacent cells are connected. In animals there are three main types of junctions: tight junctions, desmosomes, and gap junctions.

Tight Junctions Membranes of neighboring cells are fused together forming a seal.

Desmosomes Cells are fastened together (spot weld) and reinforced with keratin filaments.

Gap Junctions Channels between cells provide for chemical communication.

Fig. 6-32 Tight junction Tight junctions prevent fluid from moving across a layer of cells 0.5 µm Tight junction Intermediate filaments Desmosome Desmosome Gap junctions 1 µm Extracellular matrix Space between cells Gap junction Plasma membranes of adjacent cells 0.1 µm