Biology 107Cell III September 26, 2005
Cell III Student Objectives: As a result of this lecture and the assigned reading, you should understand the following: 1. The mitochondria carry out cellular respiration in which the chemical energy of foods, such as sugars, is converted to “useful” chemical energy in the form of the molecule ATP. Mitochondria are double membrane containing structures. a. The inner membrane encloses a fluid-filled space called the mitochondrial matrix. b. The space between the inner and outer membrane is the intermembrane space.
Cell III c. The intermembrane space contains one set of enzymes, while the mitochondrial matrix contains a different set of enzymes. Also, the inner cell membrane is highly folded and contains enzymes that are responsible for ATP production. Each fold is called a crista (plural, cristae) and the folding increase the membrane surface area for the enzymes. d. Mitochondria contain circular DNA and prokaryote-like ribosomes, suggesting they arose from symbiotic association between aerobic organisms (the precursors of mitochondria) and anaerobic organisms (the precursors of the cell in which the mitochondria reside).
Cell III 2. Like mitochondria, chloroplasts are double membrane structures with their own DNA and ribosomes. Like mitochondria, chloroplasts are fuel processors, but they convert solar energy into chemical energy, while mitochondria convert one form of chemical energy into another form of chemical energy. The membranes partition the chloroplast into three major compartments involved in photosynthesis. a. The intermembrane space is between the outer and inner chloroplast membranes. b. The space enclosed by the inner membrane, the stroma, contains the thylakoid membranes, a the network of tubules and hollow discs. c. The space inside thylakoid membranes.
Cell III • The cytoskeleton is a supportive network of intracellular linear polymers. These cytoskeletal elements are important in maintaining cell shape and motility of cells and their organelles. a. Microfilaments are long polar filaments composed of actin. These filaments are involved in cell shape changes; through interaction with other proteins (e.g., myosin), they participate in cellular contractility. b. Intermediate filaments constitute a class of proteins rather than a single protein species. Intermediate filaments are very stable linear, rope-like structures that help to anchor structures. c. Microtubules are composed of tubulin that forms long straight polymers that are easily assembled and disassembled. These dynamic structures are involved in the movement of organelles around the cell.
Cell III • Cells are dynamic structures - they are continually moving components around and transferring substances between compartments and regions. Examples of how cells segregate materials include protein sorting and vesicular transport. a. Protein sorting relates to the different regions specific proteins must localize to provide proper functioning in the cell. Some proteins must enter the nucleus, others enter membranous organelles such as mitochondria, lysosomes, or chloroplasts, and still others become integral membrane proteins or secreted proteins. b. Vesicular transport carries vesicle contents and membrane to intracellular sites or to sites on the plasma membrane for release to the outside of the cell. The various vesicular transport and secretion pathways use molecular signals or "tags" to designate the proper sorting.
Micrographs of Microfilaments and Intermediate Filaments Intermediate filaments
Microtubule Organizing Centers (MTOCs) Actin MTOC
Microtubules and Accessory Proteins are Involved with Intracellular Movement of Organelles