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University of British Columbia
BIOL 153
Robert Harris

Biology 153/155 Subcellular Organization and Function Based on lecture and text material, you should be able to do the following: Membranes define selective permeability and indicate its importance in biological membranes list the major constituents of cell membranes and indicate the general membrane function of each discuss the hydrophilic and hydrophobic nature of membrane phospholipids and discuss why this is important in forming a lipid bilayer distinguish between intrinsic and extrinsic membrane proteins and state the reason why they exist in these different locations discuss the concept of membrane fluidity illustrate how some proteins move freely within the membrane while others are anchored in stationary positions within the membrane define diffusion (without having to use the phrase "all other things being equal") and list the physical factors that determine the rate of diffusion describe which types of molecules can diffuse through cell membranes and the routes through which they diffuse describe the different types of membrane transport proteins and how it is believed they assist the movement of molecules across the membrane describe how these proteins can be so specific with regards to which molecules they will transport describe the process of active transport by membrane transport proteins illustrate the manner in which facilitated diffusion differs from active transport define osmosis (in terms of water molecules, not solute particles) and describe the physical factors which determine the direction and rate of osmosis compare the structure and function of tight junctions, desmosomes, and gap junctions Organelles list the primary functions served by membranes in cells define organelle describe the structure, composition and function of the cell nucleus describe the structure and function of ribosomes describe the structure and function of mitochondria define the endomembrane system distinguish between the structure and function of smooth and rough endoplasmic reticulum describe the structure and function of the Golgi apparatus and lysosome define endocytosis and exocytosis, and distinguish between pinocytosis and phagocytosis describe how new cell membranes are formed describe the concept of membrane flow and use it to show how new cell membrane is transported from its site of synthesis to the plasma membrane. define cytoskeleton and provide examples of cytoskeletal components define glycocalyx and discuss its function Cell Growth and Reproduction list the phases of the cell cycle and describe the events of each phase describe DNA replication define gene and explain the function of genes define transcription distinguish between mRNA, tRNA, and rRNA define translation describe the process of protein synthesis 1 I. COMMON CHARACTERISTICS of CELLS (pp 65-67) A. CELL THEORY The cell theory assumes the following: 1) The cell is the basic unit of life 2) The activity of an organism is dependent on the individual and collective activities of its cells 3) The biochemical activities of cells are determined by subcellular structures 4) All cells arise from pre-existing cells Most cells are small, depend on external energy sources, selectively regulate exchange of material with their environments and use information in their DNA to regulate their chemistry. B. TOTIPOTENCY Each cell contains the genetic information necessary to produce an entire organism. Thus: There are many examples where an entire plant can be produced from only a small part of a plant Organelles can be sustained in culture but none can reproduce an entire cell, not even the nucleus. There is tremendous diversity in diameter, length and shape of different cells. II. PLASMA MEMBRANE A. STRUCTURE (pp 68-70) The Fluid Mosaic Model Biological membranes have two components: 1. Phospholipid bilayer and 2. Proteins Phospholipid bilayer: 6592. Polar phosphate heads and non-polar lipid tails orient initially through hydrophilic and hydrophobic interactions. 6593. Weak bonds between the non-polar lipid tails stabilize the membrane - this produces a highly organized and oriented structure dictated by polarity. 6594. Cholesterol has a polar and a short non-polar region. It binds with the phospholipid head and stabilizes the outer portion of the membrane. Proteins: Proteins are incorporated into the membrane in the following ways: 10208. Extrinsic or peripheral proteins are attached to either the external or internal surface of the membrane. 10209. Intrinsic or integral proteins project through both surfaces (span the bilayer). All these proteins act as one or more of the following: transport proteins enzymes cell recognition markers receptors (e.g. for hormones or neurotransmitters) cell adhesion molecules attachement sites for cytoskeleton The structure of the plasma membrane is not static, as the lipid molecules are held together byweak bonds or simple hydrophobic interactions and, therefore, they can and do move around. They move laterally almost continually and can even flip flop from internal to external surfaces although this does not occur very often. It is this "fluidity" that gives the fluid mosaic model part of its name. Proteins can also move to some extent. Many, however, are anchored in place by binding within the membrane as well as binding to the internal cytoskeleton of the cell. It is the fact that the proteins are scattered throughout the membrane that gives rise to the mosaic part of the name. Glycocalyx (Cell Coat) Animal cells have carbohydrates covalently bonded to the proteins (glycoprotein) and lipids (glycolipid) of the cell membrane (glycocalyx). All these components do not form a rigid structure but serve primarily as recognition sites. As a result, cells can recognize other cells of the same type, as in tissue culture, or cells of a different type, as during development (e.g. outgrowth of nerves and blood vessels to different tissues).Certain components of glycocalyx are also important regulators of cell growth and division. Contact on all sides with other cells usually leads to cessation of growth (contact inhibition), both in tissue culture and in vivo. There is also strong scientific evidence suggesting that in certain types of cancer some abnormality of glycocalyx leads to uncontrolled proliferation of such cells.Glycocalyx is important in antibody-antigen interactions, which may take place as a result of im
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