II. CELLS • Quick write (10 points) – If you go from one cell (at conception) to 1014 cells (as an adult), does this violate the 2nd law of Thermodynamics? – Explain Chapter Goals (cells structure) After studying this chapter, students should be able to 1. describe the structure of the cell membrane and explain its functional significance. 2. state which cells in the human body transport themselves by amoeboid movement and explain how they perform this movement. 3. describe the structure of cilia and flagella, and state some of their functions. 4. explain the functions of the cytoskeleton, lysosomes, mitochondria, and the endoplasmic reticulum. 5. describe the structure of the cell nucleus and explain its significance. 6. describe the structure and function of the rough endoplasmic reticulum and Golgi complex and explain how they function in the secretion of proteins. 7. describe diffusion and explain its physical basis. 8. explain how non-polar molecules, inorganic ions, and water can diffuse through a cell membrane. 9. state the factors that influence the rate of diffusion through cell membranes. Chapter Goals (cells structure) After studying this chapter, students should be able to 10. define the term osmosis and describe the conditions required for osmosis to occur. 11. define the terms osmolality and osmotic pressure and explain how these factors relate to osmosis. 12. define the terms tonicity and distinguish between isotonic, hypertonic and hypotonic solutions. 13. describe the characteristics of carrier-mediated transport. 14. describe the facilitated diffusion of glucose through cell membranes, and give examples of where this occurs in the body. 15. explain the processes of phagocytosis, pinocytosis, and receptor-mediated endocytosis, and exocytosis. 16. explain what is meant by active transport and describe how the Na+/K+ pumps work. II. CELLS • A. Protoplasm • B. Membranes • C. Morphology • D. Transport A. Protoplasm 1. Water - 70-85% (0.3 nm) 2. Electrolytes (ions) - K+, Na+, Ca++, Mg++, SO4--, PO4-3, HCO3-, Cl- are most abundant 3. Proteins - 10-20% a. Structural b. Enzymes 4. Lipids - 2-3% (most in membranes) 5. Carbohydrates - 1% (glycogen; energy source) B. Membranes 1. Composition – Proteins – Phospholipids 2. Fluid- Mosaic Models of Structure 3.3 C. Morphology 2.1 Endoplasmic Reticulum 2.2 Golgi & ER 2.4 Golgi 2.5 Mitochondrion 2.10 Microtubule 2.18 Axonal Transport 2.19 Cilium 2.21 Microfilament 2.18 Amoeboid Movement 4th Ed 2.25a Sol-Gel Reversibility 2.25b Cytoskeleton 2.25 D. Transport • Diffusion • Osmosis • Facilitated Diffusion • Active Transport • Filtration • Bulk Transport Diffusion • Net random movement of substances toward a lower concentration. 3.11 Diffusion Rate • Fick’s Law • Q= DC.P .A/MW .DX – Q = Diffusion Rate – DC = Concentration gradient of substance – P = Permeability of membrane to substance – MW = Molecular weight of substance – DX = Distance (thickness) Diffusion Assignment •Which dye has larger molecules? •What does this tell you about diffusion? •Why do the liquids diffuse faster than the solids? Effect of Lipid Solubility • Lipid soluble - substances pass through membranes freely (e.g. O2, CO2). Likes dissolve likes. • Not lipid soluble - Substances excluded or must pass through channels (gates)(e.g. Na+). 3.12 6.13 Osmosis • Net random diffusion of water through a selectively permeable membrane. 3.14 3.15 3.16 3.17 3.14 Tonicity • ___tonic iso (equal) hyper (greater than) hypo (less than) Osmotic pressure • pressure required to stop osmosis 6.6 6.9 Transport Kinetics 6.16 Carrier-mediated Transport • Facilitated Diffusion -- carrier is typically proteinaceous) -- down concentration gradient • Active Transport -- against concentration gradient 3.19a 3.19b 3.19c 3.21 3.22 3.23 Bulk Transport • Endocytosis – Phagocytosis – Pinocytosis) • Exocytosis – Secretion – Excretion) 2.9a 2.9b 2.9c 2.6 Chapter Summary Cell Membrane and Associated Structures I. The structure of the cell (plasma) membrane is described by a fluid-mosaic model. A. The membrane is composed predominately of a double layer of phospholipids. B. The membrane also contains proteins most of which span its entire width. II. Some cells move by extending pseudopods; cilia and flagella protrude from the cell membrane of some specialized cells. III. In the process of exocytosis, invaginations of the cell membrane allow the cells to take up molecules from the external environment. A. In phagocytosis, the cell extends pseudopods, which eventually fuse together to create a food vacuole; pinocytosis involves the formation of a narrow furrow in the membrane which eventually fuses. B. Receptor-mediated endocytosis requires the interaction of a specific molecule in the extracellular environment with a specific receptor protein in the cell membrane. C. Exocytosis is the reverse of endocytosis and is a process that allows the cell to secrete its products. Chapter Summary Cytoplasm and Its Organelles I. Microfilaments and microtubules produce a cytoskeleton, which aids movements of organelles within a cell. II. Lysosomes contain digestive enzymes and are responsible for the elimination of structures and molecules within the cell and for digestion of the contents of the phagocytic food vacuoles. III. Mitochondria serve as the major sites for energy production within the cell. They have an outer membrane with a smooth contour and an inner membrane with infoldings called cristae. IV. The endoplasmic reticulum is a system of membranous tubules in the cell. A. The rough endoplasmic reticulum is covered with ribosomes and is involved in protein synthesis. B. The smooth endoplasmic reticulum provides a site for many enzymatic reactions and, in skeletal muscles, serves to store Ca2+. Chapter Summary Cell Nucleus I. The cell nucleus is surrounded by a double-layered nuclear membrane. At some points, the two layers are fused by nuclear pore complexes that allow for the passage of molecules II. Proteins destined for secretion are produced in ribosomes located on the rough endoplasmic reticulum and enter the cisternae of this organelle. III. Secretory proteins move from the rough endoplasmic reticulum to the Golgi complex, which consists of a stack of membranous sac. A. The Golgi complex modifies the proteins it contains, separates different proteins, and packages them in vesicles. B. Secretory vesicles from the Golgi apparatus fuse with the cell membrane and release their products by exocytosis. Chapter Summary Diffusion and Osmosis I. Diffusion is the net movement of molecules or ions from regions of higher to regions of lower concentration. A. This is a type of passive transport, energy is provided by the thermal energy of the molecules, not by cellular metabolism. B. Net diffusion stops when the concentration is equal on both sides of the membrane. II. The rate of diffusion is dependent on a variety of factors. A. The rate of diffusion depends on the concentration difference across the two sides of the membrane. B. The rate depends on the permeability of the cell membrane to the diffusing substance. C. The rate depends on the temperature of the solution. D. The rate of diffusion through a membrane is also directly proportional to the surface area of the membrane, which can be increased by such adaptations as microvilli. Chapter Summary Diffusion and Osmosis III. Simple diffusion is the type of passive transport in which small molecules and inorganic ions move through the cell membrane. A. Inorganic ions, such as Na+ and K+ pass through specific channels in the membrane. B. Steroid hormones and other lipids can pass by simple diffusion directly through the phospholipid layers of the membrane. Chapter Summary Diffusion and Osmosis IV. Osmosis is the simple diffusion of solvent (water) through a membrane that is more permeable to the solvent than it is to the solute. A. Water moves from the solution that is more dilute to the solution that has a higher solute concentration. B. Osmosis depends on a difference in total solute concentration, not on the chemical nature of the solute. 1. The concentration of total solute, in moles per kilogram (liter) of water, is measured in osmolality units. 2. The solution with the higher osmolality has the higher osmotic pressure. 3. Water moves by osmosis from the solution of lower osmolality and osmotic pressure to the solution of higher osmolality and osmotic pressure. Chapter Summary Diffusion and Osmosis C. Solutions that have the same osmotic pressure as plasma (such as 0.9% NaCl and 5% glucose) are said to be isotonic to plasma. 1. Solutions with a lower osmotic pressure are hypotonic; those with a higher osmotic pressure are hypertonic. 2. Cells in a hypotonic solution gain water and swell; those in a hypertonic solution lose water and shrink (crenate). D. The osmolality and osmotic pressure of the plasma is detected by osmoreceptors in the hypothalamus of the brain and maintained within a normal range by the action of antidiuretic hormone (ADH) released from the posterior pituitary. 1. Increased osmolality of the blood stimulates the osmoreceptors. 2. Stimulation of the osmoreceptors causes thirst and triggers the secretion of antidiuretic hormone (ADH) from the posterior pituitary. 3. ADH promotes water retention by the kidneys, which serves to maintain a normal blood volume and osmolality. Chapter Summary Carrier-Mediated Transport I. The passage of glucose, amino acids, and other polar molecules through the cell membrane is mediated by carrier proteins in the cell membrane. A. Carrier-mediated transport exhibits the properties of specificity, competition, and saturation. B. The transport rate of molecules such as glucose reaches a maximum when the carriers are saturated. This maximum rate is called the transport maximum, or T m. II. The transport of molecules such as glucose from the side of higher to the side of lower concentration by means of membrane carriers is called facilitated diffusion. A. Like simple diffusion, this is passive transport, cellular energy is not required. B. Unlike simple diffusion, facilitated diffusion displays the properties of specificity, competition, and saturation. Chapter Summary Carrier-Mediated Transport III. The active transport of molecules and ions across a membrane requires the expenditure of cellular energy (ATP). A. In active transport, carriers move molecules or ions from the side of lower to the side of higher concentration. B. One example of active transport is the action of the Na+/K+ pump. 1. Sodium is more concentrated on the outside of the cell, whereas potassium is more concentrated on the inside of the cell. 2. The Na+/K+ pump helps to maintain these concentration differences by transporting Na+ out of the cell and K+ into the cell.
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