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Transcript
Components of a Cell Membrane (and all other membranes that surround the organelles) Each organelle in a eukaryotic cell, is surrounded by its own membrane (hence the term “membrane-bound” organelles) The individual membranes are not all identical but they have many of the same components. Cell Membrane • The entire cell is surrounded by a thin membrane. • Cell membrane is considered selectively permeable. • Q: What does this mean? • A: Some things can pass through with ease, others need some help, and some cannot pass through at all. • The cell membrane is not rigid; it is fluid (or flexible) in its movement. • The more unsaturated fatty acids chains more fluidity the membrane has. • The C.M. is also a mosaic. What does “mosaic” mean? • Its made up of many individual parts; many parts making a whole. The structure of the cell membrane is known as the: Components of a Cell Membrane 1. Lipid Bilayer 2. Proteins: Peripheral and Integral (A. channel, B. carrier, C. anchoring, D. marker proteins) 3. Structural Fibers 4. Exterior Proteins and Glycolipids Phospholipids • Cell membrane contains Phospholipids • Phospholipids contain a Polar Head and a Non polar tail • What does this mean? • The “head” of the phospholipid is hydrophilic and the “tails” are hydrophobic. These phospholipids are arranged in 2 layers making a lipid bilayer Components of a Cell Membrane 1. Lipid Bilayer: two layers of lipids Head-philic Tail- phobic -Long carbon chain -can be saturated or unsaturated Lipid Bilayer •Polar heads are on the outside and the inside of the cell. •Non-polar tails make up the inside of the cell membrane •This forms a lipid bilayer Components of a Cell Membrane • 2. Proteins –Peripheral and Integral: (channel, carrier, anchoring, marker proteins) proteins that float on or embedded into the lipid bilayer. Peripheral proteins – located both on the interior surface and the exterior surface of the membrane. (receptor proteins) Integral proteins- embedded in the lipid bilayer part of the protein that extends through the bilayer. These proteins allow certain organic compounds to cross the cell membrane through: channels, pores, hydrophobic interactions The Typical Cell Membrane • is actually made up of two very different types of membranes: • 1) The passive phospholipid part (75-95%) and • 2) the active protein part (5-25%). • Those cells that have to do more exchanging of materials, such as glandular cells, have more of the protein membrane. • Those cells that have minimal exchange of materials, such as fat cells, have less protein membrane. • The protein part of the cell membrane provides: communication, "I.D." tags, anchors to microtubules, gates of exchange for large molecules and pumps for maintaining ionic balance. Types of Proteins Found in Cell Membrane Integral proteins: A. Channel Proteins~ it is like a tunnel that allows molecules to freely cross the cell membrane. B. Carrier (Transport) Proteins •Carrier proteins are specific •Selectively interacts with a specific molecule or ion so that it can cross the membrane •After specific molecule/ion attaches protein goes through a conformational change. (changes shape) •Carrier proteins help move molecules that are NOT lipid soluble : Amino Acids, Glucose Carrier protein C. Anchoring Proteins 1. Microfilaments: extend through the cytoskeleton, anchoring peripheral proteins to the cell membrane 2. Microtubules: bundles of microfilaments making a strong structure. Ex. Red Blood cell- spectrin. Length of one cable: 7,650 feet Diameter of one cable: 36 3/6 inches Wires in each cable: 27,572 Total wire used: 80,000 miles Weight of cable (suspenders and accessories): 24,500 tons The main span is 4,200 feet D. Marker Proteins • a.k.a. Cell Recognition Proteins •Are shaped in such a way that a specific molecule can bind to it. •This evokes a response inside the cell -“many signals to listen to, but the cell knows which signal to respond to” (Like listening to one person when 3 are speaking) How Marker (receptor) Proteins Work: Each receptor protein has a 3-dimensonal shape that fits the shape of a specific molecule 1. Signal molecule of right shape approaches the receptor protein, the two bind together. 2. Changes shape of protein producing a response in the cell. 3. The cell responds to the signal molecules that fit the particular set of receptor proteins it possesses. It ignores other signals. Various Protein Types Marker protein Who’s Who in the Cell Membrane • Receptor Protein: Informers of the cell. They gather info. about the environment around the cell and sends messages to the nucleus. • Channel Protein: acts like an alleyway, transporting substances into and out of the cell. • Marker Protein: “Name Tag” of the cell; Identifies what kind of cell it is. “Hi, I’m a Liver Cell ” • Gated Channel Protein: acts like a gate, controlling which substances go into and out of the cell. • Carbohydrate group: a “surface marker” which IDs the cell as YOURS rather than an invaders. “I belong to Mrs. Pires” • Cytoskeleton: supports the cell membrane • Transport (Carrier) Proteins: Help molecules pass through the cell membrane. • Glycoproteins: have structural functions; can form connective tissues such as collagen, also forms mucus secretions. • Cholesterol: helps prevent extremes-- whether too fluid, or too firm-- in the consistency of the cell membrane. http://www.youtube.com/watch?v=Qqsf_UJcfBc 3. Structural Fibers • Cytoskeletal elements (matrix) that interact with the proteins in the cell and influence cell shape and motility. 4. Glycoconjugates (Glycoproteins and Glycolipids): -Act as receptors on cell surfaces that bring other cells and proteins (collagen) together giving strength and support to a matrix. -work with Immune cells to attract bacteria to these sites, bind them, and then destroy them.. - vary between species to species, individual to individual, even from cell to cell within an individual. of glycoconjugates -Each cell developsTypes its own type and pattern of chain + protein = glycoproteins and1.Sugar glycolipids. glycoprotein 2.Sugar chain + lipid = glycolipid 3.Extremely long sugar chains (glycosaminoglycan) + protein = proteoglycan -The carbohydrate chains extending from the glycolipids and glycoproteins serve as “fingerprints” of the cell -Many different variations of sugar chains -Branched -Immune system is able to recognize that the foreign tissue’s cells do not have the same glycolipids/proteins as the rest of the body. The immune system will attack the newly received transplant. This is called transplant rejection. To succeed, an individual has to take anti-rejection medication usually for the rest of their life. These medications suppress the Immune system, weakens it, but doesn’t destroy all of the T and B cells. The body can still can fight off most infections. Cons of medication: People who take immunosuppressive drugs are more likely to develop diabetes, kidney disease, infections and cancer. Pros of medication: They get to live! Successful Transplants Face Transplants The recipient of the world's first partial face transplant was a 38-yearold Frenchwoman named Isabelle Dinoire. In May 2005, Dinoire took sleeping pills and passed out on her couch. When she awoke and tried to light a cigarette, she was surprised to find that it would not stay between her lips. A glance in the mirror revealed a horrible sight -- Dinoire's black Labrador had chewed off the lower part of her face, including her chin, lips and much of her nose, leaving her teeth and gums completely exposed. The donor was a 46-year-old woman who had been left brain dead from a suicide attempt. Bear Attack: Do Now! 1. What does it mean to be selectively permeable? 2. Why is the cell membrane described as a fluid mosaic model? 3. What is the difference between peripheral and Integral proteins? 4. Draw a phospholipid and label the hydrophobic and hydrophillic parts. 5. Why would a transplanted organ be rejected? Cell Membrane and Its parts 7.3 Cell Transport (& Homeostasis) Two Main Types of Transport Passive Transport: Does not need energy Active Transport: Needs energy Like floating down a river, passive transport does NOT need energy to occur Passive Transport Diffusion – molecules move across a given space without the use of energy from high concentration to low concentration until equilibrium is reached. Osmosis - specifically water moving across a membrane without the use of energy from HC LC until equilibrium is reached. Facilitated Transport- No energy, “help” moving from HC LC (channel, carrier proteins) until equilibrium is reached. Solute concentration –particles inside and outside the cell, effecting whether water moves INTO the cell, or OUT of the cell. More solutes means less room for water (hypertonic solution) Less Solutes More room for water Osmosis : Three solutions Water will move from an area of high concentration to an area of low concentration 1. Hypotonic –water moves into the cell (cell can “pop”) Example: Distilled water Cytolysis – cell burst 2. Isotonic – no movement; equal concentration of water on each side of the membrane. Ex. Tap water, spring water, purified water 3. Hypertonic – water moves out of the cell (cell shrinks- called plasmolysis) Ex. Salt water, sugar water. http://www.youtube.com/watch?v=gWkcFU-hHUk Plant cell Watering a Plant (Think of blowing up a balloon) Turgor Pressure: The pressure that water molecules exert against the cell wall is Turgor Pressure. Plasmolysis- Cell shrinks away from the cell wall, turgor pressure is lost. Plant begins to Wilt http://www.youtube.com/watch?v=GOxouJUt EhE&feature=related Plant plasmolysis: Cell Collapse due to water loss • Elodea: • http://www.youtube.com/watch?v=JaCCKP yE6I4&feature=related • Onion • http://www.youtube.com/watch?v=gYbt7hh IxPo&feature=related Diffusion/Osmosis Lab • • • • Elodea in 3 different solutions. Red onion in 3 different solutions. Potato: Guess the solution Dialysis tubing (starch baggy in iodine) Important! Cytoplasmic streaming: http://www.youtube.com/ watch?v=8edk6nGMwMs Order of solutions: 1) isotonic 2) hypertonic 3) hypotonic Bio Rocks! (3 types) Like paddling upstream, active transport requires a lot of energy! I. ExocytosisDischarge of materials from vesicles at the cell surface. Animal cells- provide a mechanism for secreting many hormones, neurotransmitters, digestive enzymes and other substances. What is the difference between a secretion and an excretion? II. Endocytosisprocess the plasma membrane extends outward and envelops food particles. A. Pinocytosis:cell drinking B. Phagocytosis: cell eating http://www.youtube.com/watch?v=4 http://www.youtube.com/watch?v= gLtk8Yc1Zc&NR=1 UeuL3HPfeQw&feature=related • “melt” into your cells through the lipid bilayer even if your cell do not want the substance. Ex. Alcohol and Ether Particles can move independent of the concentration gradient by using “pumps” within the cell membrane. Cells that perform a lot of active transport, require a lot of mitochondria. Ex. Nerve and Muscle cells (both perform a lot of active transport) • Almost all of the active transport in animal cells is carried out by only two kinds of pumps: 1. The sodium-potassium pump and 2. The proton pumps. 1/3 of the body’s energy is used to work this pump! Background info to understand sodium potassium pump The cell’s energy is in the form of ATP When the cell needs energy, it breaks off a P and the high energy is released for active transport. Sodium (Na) can have a positive charge (Na+) and potassium K+ will be positive too Na+/K+ pump: Very Important ! 1. Carrier protein has a shape that allows 3 Na + to enter 2. ATP (energy) splits, phosphate attaches to carrier (split by enzyme in carrier) 3. Change in shape allows 3 Na +’s to be dumped outside cell 4. New Shape allows 2 K+’s to enter carrier protein 5. Phosphate group is released (conformational change) 6. Carrier protein changes back to original shape, releasing 2 K +’s inside the cell. http://www.you tube.com/watch ?v=9CBoBewd S3U Na+/K+ pump continued Pump results in concentration gradient and electrical gradient across the cell. 3 Na+’s outside cell, 2 K+ inside cell. Outside is more positive than the inside of the cell. Na+ via diffusion, 300 Na per sec per carrier Animation: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__ho w_the_sodium_potassium_pump_works.html How does so much Na+ get in the cell (and K+ out of the cell) in the first place?_ Cl- is electrically attracted to Na+ and follows it by flowing through CFTR Cl- channels allowing reabsorption of salt in excess of water. This results in the production of dilute sweat, so that we can be cooled by evaporation without losing an undue amount of salt. Cystic Fibrosis: •Inherited disorder, caused by a faulty Cl- ion channel. Too much salt (NaCl) builds up outside the cell membrane creating a hypertonic solution. This causes the cells to lose water creating a thick mucous which collects in airways and in pancreatic and liver ducts. Liver ducts-clogged, liver becomes cirrhotic. Lifespan: about 28-30 with meds, liver transplant may be necessary, gene therapy works in mice not humans (yet) http://www.pbs.org/wgbh/nova/genome/media/2809_q056_09.html 7.4 LEVELS OF ORGANIZATION The organization at each level determines both the structural characteristics and the functions of the higher levels. Something that affects a system will ultimately affect each of the system’s components. Ex. the heart cannot pump effectively after massive blood loss.