Introduction to Cell Structure and Function 08/2007 Lecture By Dr. Dirk M. Lang Dept. of Human Biology Faculty of Health Sciences University of Cape Town South Africa Phone:
Cellular Structures and Their Functions are Complex…
I. Definition of a Cell: Basic structural and functional units of life The smallest units that display the characteristics of life, i.e. reproduction, metabolism, response to stimuli
Prototypes of Cells:
II. Cell Structure Detail
III. General Subdivisions of a Cell A. Nucleus (regulatory center of the cell) B. Plasma Membrane (selectively permeable boundary between the cell and the environ- ment) C. Cytoplasm (everything between the plasma membrane and the nuclear compartment) Organelles are individual compartments in the cytoplasm
(Chromosomes with DNA that regulate all cell activities) (Ribosome synthesis) (Phospholipid bilayer with nuclear pores = membrane barrier to control what enters/leaves nucleus) (Proteins embedded in the nuclear envelope; most substances must pass through the pores to enter or leave the nucleus) A. B. D. C. The Nucleus
The Plasma Membrane Structure: phospholipd bilayer with proteins embedded in and attached to the inner (intracellular) and outer (extracellular) surfaces
The Plasma Membrane Function: “selectively permeable” barrier; main responsibility is to ensure that the composition of extracellular fluid is not the same as the composition of the intracellular fluid Most substances must use proteins to gain access to cell; proteins are selective Lipids move freely through bilayer
The Plasma Membrane Function (continued): phospholipids are liquid at body temperature so membrane functions as a “fluid mosaic” Serves as attachment site for the cytoskeleton
The Plasma Membrane (continued) Glycocalyx: protein and carbohydrate coat covering the extracellular surface of the plasma membrane Allows attachment to other cells Allows the cell to interact with the environment
The Cytoplasm Cytoplasm: water with dissolved salts, nutrients, enzymes; site of many chemical reactions Cytoskeleton: network of protein fibers extending throughout the cytoplasm Flagellum Organelles: “little organs”found throughout cytoplasm
Functions of the Cytoskeleton Provides support and structure for the cell Very dynamic, always remodelled Important in cellular reproduction
Functions of the Cytoskeleton (continued) Important in cell movement: Cilia - short and numerous Flagella - long, single (Moveable portions of the cytoskeleton that project from the surface of the cell)
Organelles Separate compartments within the cytoplasm formed by membranes Each organelle has a specific function in the cell
The Mitochondrion “Thread granule”; contained by double membrane
Function of Mitochondrion Major source of cell’s energy: Energy is taken from sugar, stored in molecule called ATP (adenosine triphosphate) Requires oxygen to make this exchange (aerobic metabolism)
The Ribosomes Sites of protein synthesis; function in the cytoplasm, but are assembled in the nucleolus Free: unbound in the cytoplasm; produce proteins for use inside the cell Bound: attached to the endoplasmic reticulum; produce proteins for export and for the plasma membrane
The Cytomembrane System System of tubes and chambers formed by membranes Extensively distributed throughout the fluid cytoplasm Involved in synthesis, modification, processing and packaging of cellular lipids and proteins
1. Endoplasmic Reticulum (ER) “within the cytoplasm network”, system of tubes and sacs formed by membranes
Endoplasmic Reticulum (ER) a)Rough: with bound ribosomes modifies proteins produced by the ribosomes b)Smooth: without bound ribosomes doesn’t modify proteins functions in lipid synthesis, drug detoxification, carbohydrate metabolism
2. The Golgi Apparatus A series of flattened sacs formed by membranes, functions in final lipid and protein processing prior to use by the cell
The Golgi Apparatus Proteins get shuttled from the ER to one end of the Golgi In each sac, different modifications are made (proteins get individually tailored) Proteins get sorted and shipped off to their destination (like the post office of the cell)
3. Vesicles Small membrane-bound structures that transport proteins and lipids around the cell Little transporters that shuttle their contents from one organelle to another When they contact the appropriate organelle, they fuse with its outer membrane and release their contents inside Same for plasma membrane, allowing the export of materials from the cell (exocytosis)
4. The Lysosome Membrane-bound vesicle that contains digestive enzymes or toxic chemicals Merges with vesicles containing food particles, invading bacteria Harsh chemicals and enzymes degrade the food or bacteria, without harming rest of cell
Interaction of ER and Golgi: Vesicle trafficking