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Transcript
Chapter 3 Lecture Outline page 1 I. cell structure cells consist of cytoplasm surrounded by the cell membrane the cytoplasm consists of cytosol plus organelles each cell has a nucleus* that is located somewhere inside the cell *red blood cells eject their nuclei before entering the blood A. membrane structure 1. lipid bilayer a. phospholipids each molecule has a hydrophilic “head” and a hydrophobic “tail” they automatically arrange themselves in a double layer so the tails are always inside BIOL 2404 Strong/Fall 2006 Chapter 3 Lecture Outline page 2 b. cholesterol molecules among the tails keep the membrane flexible and stable 2. proteins sit between the phospholipid molecules a. receptors b. channels c. carriers d. enzymes e. anchors f. recognition 3. carbohydrates are attached to the outer surface of phospholipids and proteins a. adhesives b. recognition B. cytosol is the same as intracellular fluid (ICF) slightly viscous water, ions, proteins, carbohydrates, amino acids, lipids BIOL 2404 Strong/Fall 2006 Chapter 3 Lecture Outline page 3 C. organelles are intracellular structures that perform specific functions 1. cytoskeleton - protein fibers for shape, attachment, movement, intracellular transport 2. microvilli - short finger-like extensions of cell membrane supported by microtubules that increase the cell’s surface area 3. centrioles used in cell division 4. cilia - long hair-like extensions of the cell membrane supported by microtubules that move materials across the cell’s surface 5. flagellum - very long hair-like extension of the cell membrane supported by microtubules that moves the cell 6. ribosomes - small structures made of protein and RNA that are either in the cytosol or attached to the endoplasmic reticulum they read RNA molecules that are copies of parts of the DNA in the nucleus, and use the information to make proteins 7. endoplasmic reticulum (ER) - network of connected membrane tubes attached to the nuclear envelope a. smooth ER (SER) has no ribosomes makes lipids and carbohydrates for all membranes makes steroids makes and stores glycogen b. rough ER (RER) has ribosomes on its surface makes proteins both SER and RER deliver molecules to the Golgi apparatus BIOL 2404 Strong/Fall 2006 Chapter 3 Lecture Outline page 4 8. Golgi apparatus - stack of flattened membrane discs that a. make and package secretions b. make new membranes c. package enzymes for intracellular use 9. lysosomes - hydrolytic enzymes enclosed in a membrane break down and recycle old cell parts kill engulfed pathogens 10. peroxisomes - enzymes enclosed in a membrane break down some organic molecules produce hydrogen peroxide (a free radical) 11. mitochondria double membrane inner membrane has wrinkles called cristae fluid inside inner membrane is matrix enzymes in matrix and cristae break down fuel molecules to make ATP this process requires oxygen to get rid of the byproducts (aerobic) mitochondria contain DNA that is different from nuclear DNA mitochondria are inherited from the maternal parent they replicate themselves the number of mitochondria in a cell depends on the cell’s energy needs D. nucleus usually one per cell stores DNA (genetic information) surrounded by a double membrane with pores (nuclear envelope) human DNA occurs in long molecules called chromosomes all cells except eggs and sperm have 46 chromosomes (2 sets of 23 chromosomes each) BIOL 2404 Strong/Fall 2006 Chapter 3 Lecture Outline page 5 II. functions of the cell membrane separates ICF and extracellular fluid (ECF) controls movement into and out of the cell responds to signals from outside the cell attaches cells together in some tissues A. transport through the cell membrane 1. permeability determines which molecules can pass through a membrane cell membranes are selectively permeable, allowing some things to pass in or out but not others factors that affect the ability of a molecule to pass though a membrane are: size: lipid solubility: (molecules that are polar or have an electrical charge have low lipid solubility) 2. energy is required for all forms of transport a. kinetic energy (diffusion) b. ATP (active transport, vesicular transport) 3. diffusion a. physical basis molecules move and collide randomly the amount of movement depends on their level of kinetic energy the level of kinetic energy depends on the temperature eventually, molecules become evenly distributed BIOL 2404 Strong/Fall 2006 Chapter 3 Lecture Outline page 6 b. definition random motion makes it look like molecules are moving from where their concentration is higher to where their concentration is lower c. diffusion can occur inside the cell (in the ICF) outside the cell (in the ECF) across the cell membrane o through the lipid bilayer o through channels d. osmosis is the diffusion of water through a cell membrane it appears as if water moves towards the side of the membrane with the higher solute concentration assume the solutes have a force that attracts water this force is called osmotic pressure the higher the solute concentration of a solution, the higher its osmotic pressure BIOL 2404 Strong/Fall 2006 Chapter 3 Lecture Outline page 7 when a cell is in a solution with the same solute concentration (solute concentration of ICF = solute concentration of ECF): osmotic pressure is equal on both sides of the membrane no net movement of water through the membrane when a cell is in a solution with a lower solute concentration (solute concentration of ICF < solute concentration of ECF): osmotic pressure is higher in the ICF net movement of water into the cell when a cell is in a solution with a higher solute concentration (solute concentration of ICF > solute concentration of ECF): osmotic pressure is higher in the ECF net movement of water out of the cell BIOL 2404 Strong/Fall 2006 Chapter 3 Lecture Outline page 8 4. carrier mediated transport specific membrane proteins assist molecules through the membrane carriers are specific carriers may take more than one molecule or more than one type of molecule per trip carriers may move molecules in opposite directions a. facilitated diffusion is required when: molecule is going down its concentration gradient but is too large to fit through channels is not lipid soluble enough to go through the lipid bilayer b. active transport is required when molecules must be moved against their concentration gradient example: Na/K-ATPase (sodium-potassium pump) 5. vesicular transport involves small membrane sacs is required when large molecules or large volumes must be moved across the cell membrane a. endocytosis molecules to be moved into cell are surrounded by cell membrane to form vesicle inside cell vesicle separates from membrane BIOL 2404 Strong/Fall 2006 Chapter 3 Lecture Outline page 9 examples: phagocytosis – bacteria, dead cells pinocytosis – drops of ECF b. exocytosis molecules to be moved out of cell are packaged into a vesicle the vesicle joins the inside of the cell membrane and opens to the outside, releasing its contents also use to add more cell membrane B. membrane potentials a combination of channels and carriers in the cell membranes of resting cells maintains an unequal and opposite distribution of ions and electrical charges on the inside and outside surface of the cell membrane this is a form of potential energy BIOL 2404 Strong/Fall 2006