Chapter 5Membrane Structure and. Function

Transcription

1 Chapter 5Membrane Structure and Function

2 Cell (plasma) membrane Cells need an inside & an outside separate cell from its environment ability to discriminate chemical exchanges

3 Phospholipid Bilayer

4 A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer (fluid mosaic model) Cholesterol maintains membrane fluidity The carbohydrates are not inserted into the membrane too hydrophilic attached to embedded proteins -glycoproteins.

5 Membrane Carbohydrates Play a key role in cell-cell recognition ability of a cell to distinguish neighboring cells from another important in organ & tissue development basis for rejection of foreign cells by immune system

6 Cholesterol Provides stability in animal cells temperature buffer quality for membrane Replaced with sterols in plant cells

7 Selectively permeable membrane Nonpolar, hydrophobic molecules dissolve in the membrane and cross with ease Polar, hydrophilic molecules that are small enough to pass between lipids (H20, ethanol) move with ease Larger molecules (glucose) and ions (Na+) have difficulty passing hydrophobic layer transport proteins hydrophilic tunnel specific for the substance they move

8 Membrane Proteins Proteins determine most of membrane s specific functions cell membrane & organelle membranes each have unique collections of proteins Membrane proteins: peripheral proteins = loosely bound to surface of membrane integral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane proteins

9 Membrane Protein Types Channel proteins wide open passage Ion channels gated Aquaporins water only, kidney and plant root only Carrier proteins change shape Transport proteins require ATP Recognition proteins - glycoproteins Adhesion proteins anchors Receptor proteins - hormones

10 Bell Ringers Your table has a glucose-starch solution in front of you: what macromolecule is glucose? starch? which is larger? you also have a glucose testing strip in front of you. This is used to test the glucose concentration in urine. what color does the strip turn when dipped in the solution (may take a minute or two). What condition would result in excessive amounts of glucose in urine? Record the color of the water in the beaker on your lab handout. The Lugol s agent has been added

11 Getting through the cell membrane Passive transport no energy needed movement down concentration gradient Active transport movement against concentration gradient low to high requires ATP

12 Diffusion 2nd Law of Thermodynamics universe tends towards disorder energy disperses or spreads out Diffusion movement from high to low concentration result of intrinsic kinetic energy result from random molecular motion rate regulated by the permeability of the membrane

13 Diffusion of 2 solutes Each substance diffuses down its own concentration gradient, independent of concentration gradients of other substances not influenced by other substances

14 When is diffusion needed? Respiratory and Circulatory systems Oxygen and carbon dioxide transport into and out of bloodstream skin, gills, aveoli, capillaries Excretory systems Movement of waste into or out of blood skin, nephridia, nephrons, gills

15 Countercurrent exchange system Water carrying gas flows in one direction, blood flows in opposite direction

16 How does countercurrent exchange work? Blood and water flow in opposite directions maintains diffusion gradient over whole length of gill capillary maximing oxygen transfer from water to blood

17 Gas Exchange on Land Advantages higher concentration of O2 O2 and CO2 diffuse much faster through air respiratory surfaces exposed to air do not have to be ventilated as thoroughly as gills air is much lighter than water and therefore easier to pump less energy moving air in and out Disadvantages keeping larger respiratory surface moist causes high water loss

18 Facilitated diffusion Move from high to low concentration through an integral protein channel passive transport no energy needed facilitated =with help Share some properties with enzymes specific for the solute they transport help diffusion of ions that are impeded Two models conformational change when solute binds selective channels for specific solutes

19 Cells may need molecules to move against concentrations need to pump against concentration requires energy (ATP) oscillates between two conformations Plants have nitrate and phosphate pumps in their roots- why? why do they need N or P? Active Transport

20 What about large molecules? Moving large molecules into & out of cell requires ATP(energy)! through vesicles & vacuoles endocytosis phagocytosis = cellular eating pinocytosis = cellular drinking receptor-mediated endocytosis exocytosis export macromolecules

21 Osmosis is diffusion of water Diffusion of water from high concentration of water to low concentration of water across a semi-permeable membrane that may not allow for diffusion of molecules

22 Direction of osmosis is determined by comparing total solute concentrations Hypertonic - more solute, less water than compared to inside the cell Hypotonic - less solute, more water than compared to inside the cell Isotonic - equal solute, equal water

23 Water Potential Water moves from a place of greater water potential to a place of lesser water potential (net). which area has the greatest potential to move? As the concentration of a solute increases in a solution, the water potential will decrease accordingly. Which has the greater water potential: 0.2M or 0.8M? Which has the greater water potential: 20% or 80% water?

24 Water Potential Solute potential decreases with increasing solute concentration Results in decrease in overall water potential

25 Water Potential i= 2 i= 1

26 Animal systems evolved to support multicellular life Diffusion is too slow for clustered cells what reduces when cells are clumped together? Distance for diffusion is reduced because the circulatory system connects cells with organs specific for exchange Developed exchange systems for: distributing nutrients circulatory system removing waste excretory system

27 Intracellular Waste Animals poison themselves from the inside by digesting proteins What do we digest our food into? Carbohydrate= CHO -> CO2 +H20 Lipids= CHO -> CO2 + H20 Proteins= CHON -> CO2 + H20+ N Nucleic acids = CHONP -> CO2+H20+P+N Water Soluble

28 Nitrogen Waste Aquatic organisms can afford to lose water ammonia most toxic Terrestrial need to conserve water can t excrete ammonia fast enough urea less toxic (100,000x less) Terrestrial egg laying need to conserve water need to protect embryo in egg uric acid least toxic released with almost no water= paste-like

29 Land Animals Nitrogen waste disposal on land need to conserve water must process ammonia so less toxic Liver combines ammonia with CO2 urea= large molecule= less soluble= less toxic cost energy to synthesize with CO2 can be stored safely which reduces the water necessary for release urea= ammonia +CO2 Kidney filter solutes out of blood reabsorb H20 excrete waste urine= urea +salts+excess sugar + H20

30 Kidneys Kidneys generate urine by filtering waste from blood Nephrons- basic unit of kidney water will move towards urine as it becomes hypoteronic via aquaporins anti-diuretic hormone increase water movement back to blood Blood pressure highly regulated by kidney no pressure = no filtration = toxic blood

31 Osmotic Control in Nephron How is all this re-absorption achieved? tight osmotic control to reduce the energy cost of excretion use diffusion instead of active transport wherever possible countercurrent exchange

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33 Osmoregulation- battling osmosis Water balance vs habitat freshwater hypotonic to body fluids water flows into cells and salt loss saltwater hypertonic to body fluids water loss from cells terrestrial dry environment need to conserve water