PLASMA MEMBRANE (all cells have a plasma membrane)

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1 Biol Human Anatomy CELL STRUCTURE & FUNCTION REVIEW Atoms are the building blocks of molecules, cells are the building blocks of living organisms. They are the basic unit of life! PLASMA MEMBRANE (all cells have a plasma membrane) 1. FUNCTIONS: gives shape to a cell; encloses & protects the cell some membrane proteins & carbohydrates provide receptor sites or binding sites (functions described below) some membrane proteins function as enzymes that catalyze chemical reactions some membrane proteins help change membrane shape during processes such as cell division, locomotion, & endocytosis regulates the entrance & exit of materials (it is very selective about what it lets in & out; this is called selective permeability) 2. STRUCTURE: Fluid Mosaic Model (what does this mean? why is this important?) Some Membrane Lipids: phospholipid bilayer - hydrophobic fatty acid tails & hydrophilic phosphate heads - review chemistry handout on phospholipids. cholesterol - its ring structure keeps the phospholipid fatty acid tails from packing together to keep the membrane more fluid; in other words, cholesterol molecules create space. Some Membrane Proteins: (proteins float in the fluid lipid bilayer) Integral proteins - inserted in the bilayer (they span the entire width of the cell membrane; mainly involved in transport; channel proteins - proteins with a channel through which water and small, polar substances move across the membrane; carrier proteins - bind to specific substances & transport them across the membrane Peripheral proteins - usually appended to exposed parts of integral proteins on the outside of the membrane; some are enzymes; others are involved in the changes in cell shape that occur during cell division & contraction of muscle cells. Membrane Carbohydrates: Glycoproteins & Glycolipids - branching chains of sugars are attached to proteins and lipids in the membrane; these carbohydrate chains form a glycocalyx on the outside of the membrane (cells are "sugar coated" and sticky or gummy on the outside); some of the functions of the glycocalyx: determine the ABO blood groups recognition of the egg by sperm can serve as receptors for hormones can serve as receptors to trigger endocytosis act as markers - id. a cell as being a certain type; also id the cell as belonging to self (not a foreigner like a bacterium) help anchor the cell in place MICROVILLI - minute, fingerlike projections of the cell membrane; their function is to increase the surface area of the cell membrane; most often found on the surface of absorptive cells such as columnar epithelial cells in the intestine; different from cilia, which are hair-like projections made of protein.

2 MEMBRANE TRANSPORT A. PASSIVE TYPES OF TRANSPORT ACROSS THE PLASMA MEMBRANE 1. Most passive transport processes depend on the process of DIFFUSION Definition - the net movement of particles from a greater concentration to a lower concentration (down a concentration gradient) to distribute the particles uniformly; it's a passive process - molecules move by their own kinetic energy - requires no energy expenditure in the form of ATP by the cell. Diffusion through the cell membrane - The lipid interior of the cell membrane is a barrier to simple diffusion; most polar molecules (polar molecules get "stuck" in the nonpolar fatty acid tails). Small, nonpolar, lipid soluble molecules like fats, carbon dioxide, oxygen, & alcohol move easily through the cell membrane by simple diffusion. 2. OSMOSIS - a special case of diffusion; the movement of water across a semipermeable membrane water moves from a high water concentration to a low water concentration (or from a low solute concentration to a high solute concentration); water moves across cellular membranes through pores in channel proteins or through momentary openings in the membrane. Tonicity: describes the relative concentrations of solute in two fluids, such as the fluid inside & outside a cell; you can then describe the relative concentrations of water in the two fluids; 3 cases: 1.) isotonic solutions ("iso" = same) - two or more solutions that have equal concentrations of solute. 2.) hypotonic solution ("hypo" = less) - one solution has less solute (more water) than the other; a cell that is in a hypotonic environment will lyse (burst); ex. placing a cell in distilled water would cause the cell to lyse - water would move into the cell to where the water concentration is lower. 3.) hypertonic solution ("hyper" = more) - one solution has more solute (less water) than the other; a cell that is in a hypertonic environment will crenate (shrink), because the water in the cell moves out of the cell to an area of lower water concentration; ex. placing a cell in water with a high salt or sugar concentration would cause the cell to crenate water would move out of the cell to where the water concentration is lower. Note: The above examples describe the environment that the cell is in (i. e., the solution is hypotonic or hypertonic to the cell). You can also talk about the cell in relation to its environment (i. e., the cell is hypertonic or hypotonic to its environment). You have to make this distinction!! The cells in our bodies try to maintain the isotonic condition so that they are not in danger of lysing or crenating. 3. Facilitated Diffusion - Again, only small, nonpolar molecules readily diffuse across the cell membrane. Polar & charged molecules get "stuck" in the fatty acid part of the lipid bilayer. Small, polar molecules, like water, and some ions can diffuse through channel proteins. Most biologically important molecules, however, are polar & are much larger an water (ex. glucose) and cannot fit through channel proteins. Special selective carrier proteins are located in the membrane to transport molecules like glucose. In facilitated diffusion, carrier proteins move molecules from a high concentration to a low concentration like in simple diffusion; it is believed that changes in the shape of the carrier protein allow it to envelop and then release the transported substance. B. ACTIVE TYPES OF TRANSPORT ACROSS THE CELL MEMBRANE These processes use energy (ATP)!!! 1. Active Transport - Carrier proteins move molecules move from low concentration to high concentration (against the concentration gradient). Examples: Sodium-Potassium Pump solute pump important in the propagation of nerve impulses; maintains a higher sodium concentration outside the nerve cell & a higher potassium concentration inside the nerve cell.

3 2. Vesicle Mediated Transport - vesicles from the cell membrane, the endoplasmic reticulum (smooth or rough), or the golgi complex form around large molecules; this type of transport can down the gradient or against the gradient. Two types: Exocytosis - substances are exported out of the cell in vesicles formed from the golgi complex or the e. r.; these vesicles move to the surface of the cell & fuse with the cell membrane, expelling their contents to the outside; ex. hormones made in the smooth e. r. are transported to the golgi complex for further processing - the golgi complex then transports the hormone to the surface of the cell in a vesicle & the hormone is released to the outside. Endocytosis - substances are imported into the cell; vesicles are formed from the cell membrane, sometimes in response to the triggering of a receptor membrane protein (called receptor-mediated endocytosis); the cell membrane envelopes the substance to be imported & pinches off to form a vesicle that moves into the cytoplasm; many endocytic vesicles fuse with enzyme-containing vesicles called lysosomes to digest their contents; Examples: 1.) Phagocytosis ("cell eating") - solids are imported into the cell; ex. a white blood cell engulfing a bacterium. 2.) Pinocytosis ("cell drinking") - liquids are imported into the cell; ex. absorption by columnar epithelial cells in the intestine. PARTS OF A GENERALIZED ANIMAL CELL: (what's inside the plasma membrane) (Note: no single cell will have this exact structure) A. NUCLEUS ("The Control Center of the Cell") Structure: nuclear envelope - double membrane with nuclear pores that surrounds the nucleus. nucleoplasm - like cytoplasm chromatin - genetic material composed of DNA & associated proteins; chromatin condenses & forms chromosomes during cell division. nucleolus (usually two or more per nucleus) - spherical bodies composed of proteins, DNA, & RNA; where RNA is constructed into ribosomes; not membrane-bound. Function: carrier of the hereditary information, which exerts a continuing influence over the ongoing activities of the cell through protein synthesis. The only thing your cell can make directly from DNA is protein! So how would the cell make a lipid if the only thing it can make from DNA is protein? B. CYTOPLASM (or cytosol) - Thick, semitransparent, elastic fluid inside the cell's cell membrane & external to the nucleus; it contains organelles. C. CYTOPLASMIC ORGANELLES (organelles little organs inside the cell that perform specific functions) 1. RIBOSOMES (may be free in the cytoplasm or attached to rough endoplasmic reticulum & the nucleus) structure - not membrane-bound; made up of RNA & protein. function - sites of protein synthesis (amino acids are assembled into polypeptides). 2. ENDOPLASMIC RETICULUM structure: interconnecting flattened sacs, tubes, & channels. types & functions: (both types support the cytoplasm & provide more surface area inside the cell for chemical reactions to take place): a.) Rough E. R. - (ribosomes are attached to it) - function: initial modification of proteins; process: polypeptide chains are formed at the ribosome & some of them are transported to the lumen of the e. r. for modification; if further modification is necessary, the polypeptides are then packaged in transport vesicles (a piece of the e. r. pinches off around the polypeptide); these vesicles transport the polypeptides to the golgi complex for further modification of the polypeptides into a proteins. b.) Smooth E. R. - (no ribosomes attached) - function: main site of lipid synthesis, including sex

4 hormone production and glyceride production (lipids are sent to the golgi body in transport vesicles for further modification & distribution); in liver cells it is involved in the detoxification of blood; in the muscle cells it stores & release calcium for muscle contraction; in muscle and liver cells it stores glycogen. 3. GOLGI COMPLEX ("the Wal-Mart Distribution Center") structure - 4 to 8 flattened, membrane-bound sacs loosely stacked on top of one another & surrounded by vesicles; looks like a stack of pancakes. function - final modification of proteins & lipids; process: transport vesicles from the E. R. fuse with the golgi complex; the contents of the vesicles are processed in the golgi complex; the finished product is pinched off in a piece of golgi membrane (another vesicle) & is transported to the part of the cell where it is needed; the golgi complex processes, packages, & distributes the material the cell manufactures. 4. VESICLES structure - membrane-bound sacs that could be pinched off pieces of golgi complex, E.R., or cell membrane function - transport material within the cell & into & out of the cell. some specialized vesicles: 1.) Lysosomes - large vesicles that pinch off from the golgi complex; contain enzymes for breaking down proteins, lipids, etc. (digestion within the cell); they fuse with other vesicles (such as phagocytic vesicles) to degrade or digest their contents. 2.) Peroxisomes - large vesicles that contain enzymes that break down toxic hydrogen peroxide into water & oxygen. 3.) Exocytic & Endocytic vesicles - already discussed 5. MITOCHONDRIA ("The Powerhouse of the Cell") structure - usually shown oval shaped; double membrane: smooth outer membrane & a folded inner membrane (folds provide more surface area for chemical reactions to take place). function - break down energy containing organic molecules (ex. carbohydrates) & repackage the energy into smaller units (ATP) that can be used by the cells; 6. CYTOSKELETON structure - network of filamentous protein structures called microtubules & microfilaments. functions - give the cell shape (support), anchor the organelles, transport substances through the cell, involved in cell division, involved in cell motility (flagella), involved in the contraction of muscle cells. 7. CENTRIOLES structure - paired cylindrical structures composed of protein filaments. function - during cell division, organize a microtubule network, called spindle fibers; spindle fibers are responsible for moving the chromosomes around in the cell (we ll talk more about this in mitosis section). 8. CILIA & FLAGELLA Cilia - short, hairlike, motile cellular extensions that occur on the surfaces of certain cells; ex. ciliated columnar epithelial cells line the respiratory tract propel mucus to trap foreign debris (dust, bacteria, etc.) upward from the lungs to the back of the throat where it can be coughed up and swallowed. Flagellum - in humans, the single, long, hairlike cellular extension that occurs in sperm cells; involved in sperm motility. MITOSIS A. GENERAL 1. Different Types of Cellular Division Briefly Defined: a. Mitosis & Meiosis (nuclear division) b. Cytokinesis (cytoplasmic division) c. Uses of Mitosis & Cytokinesis in humans: tissue growth & repair. d. Uses of Meiosis & Cytokinesis in humans: gamete (sperm & egg) formation in the testes and ovaries for sexual reproduction. B. A LITTLE ABOUT CHROMOSOMES

5 1. Chromosome Defined - In human cells, DNA (deoxyribonucleic acid) & special proteins form linear structures called chromosomes. Sections of the DNA (called genes) code for the production of specific proteins. 2. How many chromosomes? All individuals of the same species have the same number of chromosomes in their body cells or somatic cells. Human somatic cells or body cells each have 46 chromosomes (23 pair). Human gametes (sperm & egg) each have 23 chromosomes. 3. More on Mitosis & Meiosis: a. Mitosis is a type of nuclear division that maintains the parental number of chromosomes for daughter cells (after mitosis, the daughter cells have the same number of chromosomes as the original parent cell). Mitosis occurs in the somatic cells. Mitosis in a single cell results in two daughter cells that are identical to the parent cell. b. Meiosis is a type of nuclear division that reduces the parental chromosome number by half (after meiosis, the daughter cells have half the number of chromosomes as the original parent cell). Meiosis occurs in the reproductive organs to produce sperm & egg - the sperm & egg will each have only 23 chromosomes, so that when the sperm & egg nuclei fuse during fertilization, the resulting zygote will have 46 chromosomes. Meiosis in a single cell results in 4 cells that are different from each other & from the parent cell. C. THE CELL CYCLE: (Involves 3 major phases: interphase, mitosis, & cytokinesis) 1. INTERPHASE - growth & replication phase of the cell cycle. a. The cell increases in size. b. All organelles & molecules increase in number. Chromosomal (DNA) replication takes place. The genetic material (DNA) is in the threadlike form called chromatin; each strand of DNA replicates itself; the replicated strand & the original strand remain attached to one another at a central point called the centromere - the two strands are now called sister chromatids & are identical to one another. c. The chromatin begins to coil & condense into thicker, rodlike forms called chromosomes; this process is called chromosome condensation. Why do you think condensation occurs? 2. MITOSIS = division of the nucleus; 4 phases (PMAT): a. Prophase - the nucleoli disappear; the nuclear envelope begins to disappear; chromatin condensation is completed; the centriole pairs move to opposite poles of the cell (one pair at each pole); these centrioles organize protein filaments to form the spindle apparatus, which will help move the chromosomes around during division. b. Metaphase - the nuclear envelope has completely disappeared; spindle fibers from both poles attach to the centromere region of each chromosome; the spindle fibers arrange the chromosomes at the equator or midline of the cell. c. Anaphase - sister chromatids of each chromosome are separated from each other & are drawn to opposite poles by the spindle fibers when the fibers contract. d. Telophase - the spindle apparatus disperses; new nuclear envelopes reform around the two sets of chromosomes; nucleoli begin to reappear; the chromosomes decondense to form chromatin again. 3. CYTOKINESIS - "division of the cytoplasm" usually begins during late anaphase or telophase; the cell is divided into two equal parts; a furrow appears in the cell membrane & deepens into a groove. Lab Objectives: Id. the stages of mitosis on a slide (metaphase, anaphase, telophase). Make sketches of what you observe. Look in your lab manual and/or textbook for great photomicrographs to guide you. Also look at the models of mitosis. Identify the following: Cell Cycle: Interphase, Mitosis, Cytokinesis Mitotic Phases: Prophase, Metaphase, Anaphase, Telophase (don t worry about specifically identifying early, middle, late) Spindle Fiber Apparatus Centriole Pairs

6 Centromere Chromososmes Chromosome Condensation DNA Replication Sister Chromatids