Cell Physiology & Membrane Transport

Transcription

1 Muma Bio 6 Cell Physiology & Membrane Transport Study Objectives: Chapter 2: Cell Physiology 1. Explain the structure and functions of nucleus structures: nuclear envelope, nucleolus, and nuclear pores 2. Describe the structure and function of the following cell structures: cytoplasm, mitochondria, rough ER, smooth ER, golgi apparatus, lysosomes, peroxisomes, ribosomes, cytoskeleton, centrioles, cilia, flagella, microvilli. Chapter 3: Membrane Transport 1.Describe the general structure of the plasma membrane and its overall functions: phospholipid bilayer, proteins (peripheral, integral), cholesterol, and glycocalyx 2. Explain Fick s law and the factors that affect the rate of diffusion 3. Define these terms, be able to recognize examples of each, and apply them: passive transport vs. active transport, simple diffusion, facilitated diffusion, osmosis, hypertonic, hypotonic, isotonic, filtration, solute pumping (primary transport, secondary transport) exocytosis, and endocytosis (phagocytosis, pinocytosis, receptor mediated) 4. Explain the effects of hypertonic, hypotonic, and isotonic solutions would have on cells and the direction solutes and water would diffuse. 1

2 Cells & Membrane Transport Outline I. Cell Theory a. Cells are the smallest structural and functional units of life b. All living organisms are composed of one or more cells c. Cells arise from other cells II. Plasma Membrane - separates the living cell from its nonliving surroundings a. General Functions i. Barrier separates extracellular fluid from intracellular fluid ii. Selective permeability controls what enters and exits the cell iii. Cell markers and receptors cell recognition, binds hormones, cell communication iv. Adhesion between other cell membranes or extracellular materials b. Structure fluid mosaic model (see figure 3-3 in textbook) i. Phospholipid bilayer 1. Hydrophilic heads orientate themselves towards the extracellular and intracellular fluid 2. Hydrophobic tails orientate themselves inward, away from the fluid 3. Sketch the arrangement of the phospholipid bilayer: ii. Cholesterol stabilizes the membrane iii. Glycocalyx serve as biological markers iv. Proteins 1. Peripheral attach to inner or outer surface of the membrane 2. Integral embedded in or span the membrane 3. Functions of membrane proteins: a. Transport i. Channel proteins water filled pathways that allow select ions in/out of the cell ii. Carrier proteins- transport select substances across the membrane 2

3 b. Cell adhesion molecules play a role in anchoring cells to each other and the cytoskeleton, responsible for stickiness of cells c. Receptors cell recognition, cell signaling, binding of hormones d. Enzymes facilitate chemical reactions on inner and outer membrane surfaces III. Plasma Membrane Transport two types of transport passive vs. active a. Passive transport does not require energy to move solutes across a membrane i. Diffusion solutes move down their concentration gradient until evenly distributed throughout the solution 1. Simple diffusion solutes diffuse across the membrane unassisted a. Small non-polar and lipid-soluble solutes b. Examples given in lecture: oxygen or carbon dioxide 2. Facilitated diffusion proteins carry or assist solutes across the membrane a. Charged ions move through protein channels b. Large molecules such as glucose or amino acids are carried across by carrier proteins c. Carrier proteins (see figure 3-14 in textbook and watch the carrier-mediated animation posted on Canvas) i. Transports a specific substance (for example you have specific glucose transporters in the membrane of some cells) ii. Can reach saturation when all binding sites are occupied (Transport maximum) iii. Competitive inhibitor - other closely related compounds can compete for the same binding sight 3

4 3. Fick s law of diffusion factors that affect the rate of diffusion a. the magnitude of the concentration gradient i. if you increase the concentration gradient then would the rate of diffusion increase or decrease? b. the permeability of the plasma membrane to a substance. i. if you increase the permeability of the membrane to a substance then would the rate of diffusion increase or decrease? c. the surface area of the membrane across which diffusion takes place i. if you increase the surface area of the membrane to a substance then the rate of diffusion would increase or decrease? d. the molecular weight of a substance i. if you increase the molecular weight of a substance then would the rate of diffusion increase or decrease? e. the distance through which diffusion takes place i. if you increase the distance a substance must diffuse then would the rate of diffusion increase or decrease? f. Temperature i. if you increase the temperature then would the rate of diffusion increase or decrease? See Table 3-1 in your textbook for a summary of factors influencing rate of diffusion. ii. Osmosis diffusion of water across a membrane down its concentration gradient 1. Tonicity ability of a solution to change the shape of a cell by altering its internal water volume, depends on concentration of non-penetrating solutes 4

5 a. Isotonic solution contains equal concentration solutes as the cell i. What effect would this solution have on cell volume? b. Hypertonic solution contains more solutes than the cell i. What effect would this solution have on cell volume? c. Hypotonic solution contains less solutes than the cell i. What effect would this solution have on cell volume? *See figures 3-10, 3-11, 312, and 3-13 in your textbook to support these osmotic concepts. iii. Filtration water and solutes are pushed across a membrane from an area of higher pressure to an area of lower pressure 1. Non-selective process, only large molecules cannot pass iv. Summary: Types of passive transport 1. Diffusion: simple or facilitated 2. Osmosis 3. Filtration b. Distribution of Solutes In Fluid Compartments i. Osmotic equilibrium total amount of solutes per volume of fluid is equal ii. Chemical disequilibrium some solutes are more concentrated in one fluid compartment than another (requires input of energy) c. Active transport movement of solutes across the membrane requires energy (ATP). Occurs during movement of solutes against their concentration gradient or very, very large molecules i. Solute pumping proteins use ATP to transport solutes against concentration gradient 5

6 1. Cotransporters carrier proteins that transport two or more substrates across a membrane (See figure 3-17) a. Symport: moves two substrates in same direction b. Antiport: moves two substrates in opposite directions 2. Types of solute pumping: a. Primary active transport energy is provided directly by the hydrolysis of ATP i. Example: Sodium-Potassium pump maintains a higher concentration of potassium inside the cell and a higher concentration of sodium outside the cell. Pumps 3 Na+ out and 2 K+ in. (See figure 3-16 for illustration) b. Secondary active transport primary transport of one molecule creates an ion gradient used to drive another molecule against its concentration gradient (See figure 3-18 for illustration) ii. Exocytosis - moves material from cell interior to the extracellular space (Figure 2-5a) 1. Vesicles fuse with the plasma membrane expelling the contents out of the cell iii. Endocytosis- moves material from extracellular space into the interior of the cell (Figure 2-5b) 1. Phagocytosis cell eating 2. Pinocytosis cell drinking 3. Receptor mediated endocytosis receptors bind specific substances and initiates endocytosis (See figure 2-8b) iv. Summary of Types of Active Transport: 1. Solute Pumping: primary or secondary 2. Exocytosis 3. Endocytosis: phagocytosis, pinocytosis, or receptor mediated *There is a helpful summary of membrane transport methods in Table 3-2 of your textbook. 6

7 Post-lecture Practice 1. Circle all of the following factors that would increase a solute s diffusion rate: a. Increasing temperature b. Decreasing surface area for diffusion c. Increasing the distance d. Lower molecular weight 2. Look at the following illustrations of solutions whose solute is indicated by small circles. A B C D E a. Solution A is hypertonic to solution(s). b. Solution A is hypotonic to solution (s). c. Solution A is isotonic to solution(s). 3. A cell containing 4% NaCl is suspended in a solution that consists of 15% NaCl. Assume the sac is permeable to all substances: a. Which direction will water initially move? i. Into the cell ii. Out of the cell iii. It will not move b. Which direction will NaCl initially move? i. Into the cell ii. Out of the cell iii. It will not move Cell 4% NaCl Solution 15% NaCl 4. List four examples of active transport: 7