Tour of the Cell 11/19/2018

I. Why do cells have organelles (little organs)? mitochondria I. Why do cells have organelles (little organs)? Specialized structures specialized functions cilia or flagella for locomotion Containers partition cell into compartments create different local environments separate pH, or concentration of materials distinct & incompatible functions lysosome & its digestive enzymes Membranes as sites for chemical reactions unique combinations of lipids & proteins embedded enzymes & reaction centers chloroplasts & mitochondria chloroplast Golgi Why organelles? There are several reasons why cells evolved organelles. First, organelles can perform specialized functions. Second, membrane bound organelles can act as containers, separating parts of the cell from other parts of the cell. Third, the membranes of organelles can act as sites for chemical reactions. Organelles as specialized structures An example of the first type of organelle is cilia, these short filaments act as "paddles" to help some cells move. Organelles as Containers Nothing ever invented by man is as complex as a living cell. At any one time hundreds of incompatible chemical reactions may be occurring in a cell. If the cell contained a uniform mixture of all the chemicals it would not be able to survive. Organelles surrounded by membranes act as individual compartments for these chemical reactions. An example of the second type of organelle is the lysosome. This structure contains digestive enzymes, these enzymes if allowed to float free in the cell would kill it. Organelle membranes as sites for chemical reactions An example of the third type of organelle is the chloroplast. The molecules that conduct the light reactions of photosynthesis are found embedded in the membranes of the chloroplast. ER

II. Isolation of organelles A. Occurs by process of cell fractionation II. Isolation of organelles A. Occurs by process of cell fractionation. B. Based on various densities of organelles. C. Begins with breaking open cell membranes without damaging organelles; Called homogenization.

Homogenate is spun in a centrifuge to separate the pellet of organelles from the liquid (supernatant). Pellet is removed, and the supernatant is spun again at higher speed to cause heaviest of remaining organelles to settle out.

Heaviest to lightest cell fractions are nuclei, mitochondria/chloroplasts, parts of membranes, then ribosomes. G. Specific metabolic processes are identified with certain cell fractions, and then tied to specific organelles.

Types of cells Eukaryote animal cells Eukaryote plant cells Prokaryote bacteria cells Eukaryote animal cells Eukaryote plant cells

II. General Types of cells Basic cell structures 1. Plasma membrane 2. Cytosol (jelly-like substance) 3. Ribosomes 4. DNA B. Prokaryotic cells have DNA in nucleiod region; No membrane around DNA.

C. Eukaryotic cells have DNA in membrane-bound nucleus. D. Eukaryotes also have membrane-bound organelles floating in cytoplasm (region between nucleus and cell membrane). E. Eukaryotes are bigger than prokaryotes.

F. Eukaryotes have many internal membranes that divide internal space into compartments. G. Compartmentalization allows for multiple metabolic processes to occur at the same time.