Biology 243 Chapter 3 Notes
Biology 243 Chapter 3 Notes BIOL 243
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This 7 page Class Notes was uploaded by Karla Kristo on Wednesday September 7, 2016. The Class Notes belongs to BIOL 243 at University of South Carolina taught by Lewis Bowman in Fall 2016. Since its upload, it has received 38 views. For similar materials see Human Anatomy and Physiology I in Biology at University of South Carolina.
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Date Created: 09/07/16
Chapter 3: The Living Units Cell à structural and functional unit of life o Structure depends on function o Cells only form preexisting cells Cell Diversity o Over +200 types o Differ in size, shape, subcellular components (lead to difference in functions) Macrophages White blood cells Function: Cell that fight disease Fat cell Nerve cell Function: Gathers information and controls body functions Generalized cell All cells have common structures and functions o Human cells have three basic parts 1. Plasma membrane: flexible outer boundary 2. Cytoplasm: intracellular fluid containing organelles 3. Nucleus: DNA containing control center Extracellular Materials Substances found outside cells Classes of extracellular materials include: o Extracellular fluids (body fluids) such as: Interstitial fluid: cells are submersed (bathed) in this fluid Blood plasma: fluid of the blood Cerebrospinal fluid: fluid surrounding nervous system organs o Cellular secretions (e.g., saliva, mucus) o Extracellular matrix: substance that acts as glue to hold cells together in tissues I. Plasma/ cell membranes: Acts as an active barrier separating intracellular fluid from extracellular fluid Controls what enters and leave cell “selective permeability” Consists of membrane lipids that form a flexible lipid bilayer Specialized membrane proteins float through this fluid membrane, resulting in constantly changing patterns o Reffered to as fluid mosaic Surface sugars form glycocalyx (“sugary coat”) Membrane structures help to hold cells together through cell junctions a. All cellular membranes have similar structure b. Backbone consists of bilayer of phospholipids c. Center of membrane = fatty acid tails of phospholipids and is nonpolar or hydrophobic (water fearing) d. Hydrophobic region is the major barrier for the movement of polar or charged molecules through the membrane e. Surface of the membrane = charged head of the phospholipid molecules – this region is hydriphillic (water loving) and interacts with aqueous environment found inside and outside the cell II. Cholesterol a. Inserted into the hydrophobic center of the membrane b. Stabilizes the membrane III. Proteins a. Found in membranes Membrane proteins Allow cell communication w environment Make up half the mass of plasma membrane o Two Types: 1) Integral proteins 2) Peripheral proteins IV. Intergral membrane proteins a. Inserted in hydrophobic region of the membrane V. Transmembrane protein goes from one side to the other of the membrane Function as transport proteins (channels and carriers), enzymes, or receptors VI. Peripheral membrane proteins Do not interact with the hydrophobic core of the membrane but are associated with charged (hydrophilic) heads of phospholipids Function as enzymes, motor proteins for shape change during cell division and muscle contraction, cell to cell connections Functions of the membrane protein I. Transport spans the membrane may prove a hydrophilic channel across the membrane that is selective for a particular solute a. Some hydrolyze ATP as an energy source to actively pump substances across the membrane II. Receptors for signal transduction a. Exposed to the outside of the cell may have binding site with a specific shape that fits the shape of the chemical messenger (ex. Hormone) b. External signal may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell III. Attachement to the cytoskeleteon and extracellular matric (ECM) a. Elements of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may be anchored to membrane proteins b. Helps maintain cell shape and fix the location of a certain membrane protein c. Others play role in cell movement or bind adjacent cells together IV. Enzymatic activity a. Protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution b. Most cases, several enzymes in a membrane act as a team that catalyzes sequential steps of a metabolic patherway as indicated (left to right) here V. Intercellular joining a. Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions b. Some (CAMs) of this group provide temp. bonding sites that guide cell migration and other cell to cell interactions VI. Cell-cell recognition a. Some glycoproteins (proteins bonded to short chains of sugars) serve as identification tags that are specifically recognized by other cells In addition, carbohydrate groups are attached to some of the membrane lipids to form glycolipids. Carbohydrates are also attached to some membrane proteins to form glycoproteins. These glycolipids and glycoproteins are primarily associated with outer surface of the plasma membrane. Carrier mediated facilitated via a protein carrier specific for one chemical; binding of substrate causes shape change in transport protein Channel mediated facilitated diffusion through a channel protein, mostly ions selected on basis of size and charge Membrane Junctions 1) Tight Junctions impermeable junctions prevent molecules from passing through the intercellular space; found in the intestine a. Used to prevent leakage b. Ex. Urine from urinary bladder and microorganisms from the digestive tract 2) Desmosomes Anchoring junctions bind adjacent cells together and help form an internal tension- reducing network of fibers. Found in many epithelia tissues, especially the skin. a. Used to counteract mechanical stress b. ex. Skeletal muscle and heart 3) Gap Junctions Communication junctions allow ions and small molecules to pass from one cell to the next for intercellular communication; found in smooth muscle a. Used to spread ions, simple sugars, or other small molecules between cells b. Allow electrical signals to be passed quickly from one cell to next cell i. Used in cardiac and smooth muscle cells ii. More effective in communication than in binding together Two ways substances cross membrane: 1) Passive processes NO ENERGY REQUIRED Do not require the cells to expand energy and is for net movement of molecules from a region of high concentration to a region of lower concentration, ie down the concentration gradient Diffusion = refers to the random movement of molecules o Simple diffusion o Carrier and channel mediated facilitated diffusion o Osmosis Special case of diffusion; diffusion of a solvent through a semipermeable membrane. Filtration o Type of transport that usually occurs across capillary walls ** Smaller molecules diffuse more rapidly and occurs faster in higher temperatures End result: molecules are randomly distributed Active processes requires expenditure of energy by the cell Two active processes: a. Active transport Moves molecules up their concentration gradient and concentrates molecules (less randomly distributed) b. Vesicular transport employs membrane vesicles to transport larger molecules/ particles Simple Diffusion of fat soluable molecules directly through the phospholipid bilyar Osmosis diffusion of a solvent such as water through a s pecific channel protein (aquaporin) or through a lipid bilayer Active transport requires a carrier protein to facilitate movement of molecules up a concentration gradient. Example: Sodium Potassium Pump Na+ is present in a much higher concentration OUTSIDE the cell where K+ is found much higher INSIDE the cell. Sodium potassium pump moves Na+ out of the cell and K+ into the cell Can not occur with faciliatated diffusion or simple Process requires the expenditure of energy in the form of the hydrolysis of ATP to ADP + P Simple Diffusion: Result in net movement of these molecules down their concentration gradient Nonpolars molecules such as O2, CO2, fats and steroid hormones readily pass through the membrane because they are nonpolar Osmosis: Special case of diffusion; diffusion of a solvent through a semipermeable membrane. In living systems the solvent is water 1) Hypotonic solutions Cells take on water by osmosis until they become bloated and burst (lyse) in a hypotonic solution (contains a lower conc. Of solutes than are present in cells. 2) Hypertonic solutions Cells lose water by osmosis and shrink in hypertonic solution (contain a higher conc. of solutes than are present inside the cell) 3) Isotonic solutions Cells retain their normal size and shape in isotonic solutions (same solute/water conc. inside cells’ water moves in and out) Facilitated diffusion: where charged or polar molecules are transported down their concentration gradient Facilitated transport: a passive transport process for net movement down a concentration gradient and does not require the expenditure of energy by the cell Examples: Ions, amino acids and carbohydrates like glucose Endocytosis = Phagocytosis cell engulfs a large particle by forming projecting pseudopods (‘false feet”) around it and enclosing it within a membrane sac called a phagosome o Phagosome is combined with a lysosome o Undigested contents remain in the vesicle (now called a residual body) or are ejected by exocytosis o Vesicle may or may not be protein coated but has receptors capable o binding to microorganisms or solid particles Pinocytosis cell gulps drops of extracellular fluid containing solutes into tiny vesicles o No receptors are used – process is nonspecific o Most vesicles are protein coated Receptor- mediated endocytosis extracellular substances bind to specific receptor proteins in regions of coated pits, enabling the cell to ingest and concentrate specific substances (ligands) in protein coated vesicles. o Ligands may simply be released inside the cell or combines with a lysosome to digest contents o Receptors are recycled to the plasma membrane in vesicles
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