How Is A Membrane’s Structure Adapted To Its Function?

The plasma membrane separates the living cell from its nonliving surroundings. This thin barrier, 8 nm thick, controls traffic into and out of the cell. Like other membranes, the plasma membrane is selectively permeable, allowing some substances to cross more easily than others. A. Introduction

The main macromolecules in membranes are lipids and proteins, but include some carbohydrates. The most abundant lipids are phospholipids. Phospholipids and most other membrane constituents are amphipathic molecules.  Amphipathic molecules have both hydrophobic regions and hydrophilic regions. Hydro- philic “head” Hydro- phobic “tails”

 A membrane is a fluid structure with proteins embedded or attached to a double layer of phospholipids.  This membrane structure is fluid and dynamic. B. Basic structure of a cell membrane

C. Membrane models have evolved to fit new data OBSERVATIONINFERENCE Substances that dissolve in lipids enter cells faster than those that are insoluble. (1895) Charles Overton hypothesized that membranes are made of lipids. Chemical analysis of red blood cell membranes shows that the membranes contain lipids and proteins. (1915) Membranes are composed of lipids and proteins.

C. Membrane models have evolved to fit new data OBSERVATIONINFERENCE Amphipathic phospholipids make up most membranes. (1925) E. Gorter & F. Grendel state that cell membranes must be a phospholipid bilayer, two molecules thick. Aqueous (water) solutions both fill and surround cells. http://everythingmaths.co.za/science/lifesciences/grade- 10/02-the-basic-units-of-life/02-the-basic-units-of-life- 03.cnxmlplus Use Macromole app to view phospholipids & bilayers.

Identify which of the following diagrams accurately represents a phospholipid bilayer in our cells. Explain. The molecules in the bilayer are arranged such that the hydrophobic fatty acid tails are sheltered from water while the hydrophilic phosphate groups interact with water. ABCD water

Phospholipid Song (to the tune of “Oh My Darling”) Oh, my lipid Phos-pho-lipid Oh, my lipid ‘Round the cell You are made of Fat-ty a-cids And a phos-phate head as well. Add the backbone Made of glyc’rol Add the backbone To join three All together = Phospholipids Make the cells of you and me Oh, my lipid Phos-pho-lipid Oh, my lipid ‘Round the cell Hy-dro-pho-bic Fat-ty a-cids Fear the water they re-pel Oh, my lipid Phos-pho-lipid Oh, my lipid ‘Round the cell Hy-dro-phil-ic Are the phos-phates Touching water, there they dwell

C. Membrane models have evolved to fit new data OBSERVATIONINFERENCE Actual membranes adhere more strongly to water than do artificial membranes composed only of phospholipids. Proteins on the surface of membranes increase adhesion.

Davson and Danielli Model of the Cell Membrane In 1935, H. Davson and J. Danielli proposed a sandwich model in which the phospholipid bilayer lies between two layers of globular proteins.

Two observations were inconsistent with the Davson-Danielli Model 1) Not all membranes were alike; they differed in thickness, appearance when stained, and percentage of proteins to lipids. 2) Membrane proteins are actually not very soluble in water. Membrane proteins are amphipathic, with hydrophobic and hydrophilic regions. If at the surface, the hydrophobic regions would be in contact with water and this doesn’t make sense.

In 1972, S.J. Singer and G. Nicolson proposed that the membrane proteins are dispersed and individually inserted into the phospholipid bilayer. https://www.brooklynmuseum.org/opencollection/ objects/17101/Mosaic_of_Personification_of_Ro ma_in_a_Medallion/right_tab/tags/ D. Fluid Mosaic Model of the Cell Membrane

In this fluid mosaic model, the hydrophilic regions of proteins and phospholipids are in maximum contact with water and the hydrophobic regions are in a nonaqueous environment.

Electron microscopy opened up new ways to study the cell membrane. The microscope forms an image by shooting electron beams (not light) through or at an object. Limits of Resolution  Light microscope = 200 nm  1930’s electron microscope = 10 nm  1944 electron microscope = 2 nm SOURCE: http://authors.library.caltech.edu/5456/1/hrst.mit.edu/hrs/materials/public/El ectronMicroscope/EM_HistOverview.htm https://en.wikipedia.org/wiki/E lectron_microscope

A specialized preparation technique, freeze-fracture, splits a membrane along the middle of the phospholipid bilayer prior to electron microscopy. This shows protein molecules interspersed with a smooth matrix, supporting the fluid mosaic model. How did scientists prove that proteins were embedded within the lipid bilayer?

Membrane molecules are held in place by relatively weak hydrophobic interactions. Most of the lipids and some proteins can drift laterally in the plane of the membrane, but rarely flip-flop from one layer to the other. E. Membranes are fluid Youtube video on fluidity of membrane

The lateral movements of phospholipids are rapid, about 2 microns per second. Many larger membrane proteins move more slowly but do drift.  Some proteins move in very directed manner, perhaps guided/driven by the motor proteins attached to the cytoskeleton.  Other proteins never move, anchored by the cytoskeleton.

How could scientists test the speed at which membrane proteins drift? FRYE & EDIDIN (1970) – mouse human supercell membrane proteins of human & mouse labeled with different colored fluorescent dyes cells fused to form hybrid cell with a continuous membrane hybrid cell membrane had initially distinct regions of each color dye in less than an hour, the two colors were intermixed

Membrane fluidity is influenced by temperature and by its constituents. As temperatures cool, membranes switch from a fluid state to a solid state as the phospholipids are more closely packed. Factors Affecting Membrane Fluidity

Membranes rich in unsaturated fatty acids are more fluid than those dominated by saturated fatty acids because the kinks in the unsaturated fatty acid tails prevent tight packing. Fluidity: Role of types of fatty acids

The steroid cholesterol is wedged between phospholipid molecules in the plasma membrane of animals cells. At warm temperatures, it restrains the movement of phospholipids and reduces fluidity. Fluidity: Role of cholesterol  At cool temperatures, it maintains fluidity by preventing tight packing.

List three factors that enhance membrane fluidity and three that decrease fluidity. ENHANCE unsaturated fatty acid tails b/c kinks at the C-C double bonds hinder close packing of phospholipids increased TEMPERATURE (in animals) increased cholesterol AT LOWER TEMPERATURES DECREASE More sat. fatty acids decreased TEMPERATURE (in animals) increased CHOLESTEROL at HIGHER TEMPERATURES (i.e., human body temperature 37°C) b/c cholesterol restrains phospholipid movement

TOK: The explanation of the structure of the plasma membrane has changed over the years as new evidence and ways of analysis have come to light. Under what circumstances is it important to learn about theories that were later discredited?

A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer. F. Membranes are mosaics of structure and function Voyage Inside the Cell: membrane video about membrane proteins

Proteins determine most of the membrane’s specific functions. The plasma membrane and the membranes of the various organelles each have unique collections of proteins. There are two populations of membrane proteins based on location.  Peripheral proteins & Integral proteins

 Peripheral proteins are not embedded in the lipid bilayer at all.  They are loosely bound to the surface of the membrane, often connected to the other membrane proteins. Peripheral membrane proteins

 Integral proteins penetrate the hydrophobic core of the lipid bilayer, often completely spanning the membrane (a transmembrane protein). Where they contact the core, they have hydrophobic regions with nonpolar amino acids, often coiled into alpha helices. Integral membrane proteins  Where they are in contact with the aqueous environment, they have hydrophilic regions with polar or charged amino acids.

One role of membrane proteins is to reinforce the shape of a cell and provide a strong framework.  On the exterior side, some membrane proteins attach to the fibers of the extracellular matrix.  On the cytoplasmic side, some membrane proteins connect to the cytoskeleton.

 The two layers may differ in lipid and protein composition.  Proteins in the membrane have a clear direction.  The outer surface also has carbohydrates. Membranes have distinctive inside and outside faces. Animation of membrane structure

The proteins in the plasma membrane may provide a variety of major cell functions.

The membrane plays the key role in cell-cell recognition.  Cell-cell recognition is the ability of a cell to distinguish one type of neighboring cell from another. Membrane carbohydrates are important for cell-cell recognition

Why might it be so important for a cell to be able to recognize its neighbors?  For cell sorting and organization as tissues and organs develop.  The basis for identification and rejection of foreign cells by the immune system. Importance of cell-cell recognition

Membrane carbohydrates are usually branched oligosaccharides with fewer than 15 sugar units. They may be covalently bonded either to lipids, forming glycolipids, or, more commonly, to proteins, forming glycoproteins, collectively called the glycocalyx. Cells recognize other cells by keying on surface molecules, often carbohydrates, on the plasma membrane.

The oligosaccharides on the external side of the plasma membrane vary from species to species, individual to individual, and even from cell type to cell type within the same individual. Ex: The four human blood groups (A, B, AB, and O) differ in the external carbohydrates on red blood cells. animation

Draw a 2D fluid mosaic model of the membrane. Be sure to include phospholipids, integral proteins, peripheral proteins, cholesterol, and glycoproteins.

A steady traffic of small molecules and ions moves across the plasma membrane in both directions.  For example, sugars, amino acids, and other nutrients enter a muscle cell and metabolic waste products leave.  The cell absorbs oxygen and expels carbon dioxide.  It also regulates concentrations of inorganic ions, like Na +, K +, Ca 2+,and Cl -, by shuttling them across the membrane. The structure of the membrane influences its function of transport. G. The structure of the membrane influences its function of transport.

Types of Membrane Transport Movement of substances can either require added energy (active transport) or not (passive transport)

4 ways that substances can cross into/out of a cell Simple diffusion Facilitated diffusion Active transport Bulk transport With/down or against/up concentration gradient With/down Against/upWith or against Need ATP? No Yes (to change shape of transport protein) Yes (to move & rearrange membrane) Need membrane proteins? NoYes Endocytosis or exocytosis

Fig. 8.16 Both diffusion and facilitated diffusion are forms of passive transport of molecules down their concentration gradient, while active transport requires an investment of energy to move molecules against their concentration gradient.

What factors determine what kind of transport occurs? Chemical nature of the substance crossing the membrane. The concentrations of the substance across the membrane. The amount of the substance crossing the membrane.

Membranes are selectively permeable. Permeability of a molecule through a membrane depends on the interaction of that molecule with the hydrophobic core of the membrane.

 Small hydrophobic (nonpolar) molecules, like CO 2, O 2, and some hydrocarbons, can dissolve in the lipid bilayer and cross easily.  Also, steroids like testosterone or estrogen can move easily through the lipid bilayer as well. Membranes are selectively permeable.

This includes small molecules, like water, and larger critical molecules, like glucose and other sugars. Ions, whether atoms or molecules, and their surrounding shell of water also have difficulty penetrating the hydrophobic core. Ions (charged particles) and polar molecules pass through with difficulty

Specific ions and polar molecules can cross the lipid bilayer by passing through transport proteins that span the membrane. http://2012books.lardbucket.org/books/an-introduction- to-nutrition/s10-04-protein-s-functions-in-the-bod.html How do ions and polar molecules pass through the membrane?

 Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane.  Others bind to these molecules and carry their passengers across the membrane physically http://2012books.lardbucket.org/books/an-introduction- to-nutrition/s10-04-protein-s-functions-in-the-bod.html How do transport proteins work?

Each transport protein is specific as to the substances that it will translocate (move). For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer.

Identify the molecules that can cross the phospholipid bilayer easily. O 2, CO 2, fatty acids, hydrocarbons, steroids (cholesterol, testosterone, estrogen) Identify several molecules that need a protein to help them cross the phospholipid bilayer. Ions (Ca 2+, Na +, Cl -, K + ) Polar molecules (water, glucose) COMMAND TERM: IDENTIFY: Provide an answer from a number of possibilities.

Diffusion is the tendency of molecules of any substance to spread out in the available space  Diffusion is driven by the intrinsic kinetic energy (thermal motion or heat) of molecules. Movements of individual molecules are random. H. Passive transport requires no additional energy input animation McGrawHillHow DiffusionWorks animation

For example, if we start with a permeable membrane separating a solution with dye molecules from pure water, dye molecules will cross the barrier randomly. The net movement of dye will be from higher to lower concentration until both solutions have equal concentrations of the dye. At this dynamic equilibrium, as many dye molecules pass one way as cross in the other direction.

1. Calculate the concentration of red dye in each solution: 2. Identify in which direction the red dye will tend to diffuse. Explain.

3. A student states that diffusion occurs when a substance moves from where there is more of the substance to where there is less. Explain the inaccuracy of this statement using the solutions given. B C

The membrane is permeable to water, but not salt. 4. Identify the direction of the net water movement. Explain. 5. Predict what will happen to the cell. 95% water 5 % salt 97% water 3 % salt A4: Out of the cell, because more water moves from higher concentration (in cell) to lower concentration (in beaker) A5: Cell will shrink from losing cytoplasm

The membrane is permeable to water, but not salt. 99% water 1 % salt 97% water 3 % salt A6: Into the cell, because more water moves from higher concentration (in beaker) to lower concentration (in cell). A7: Cell will swell and possibly burst. 6. Identify the direction of the net water movement. Explain. 7. Predict what will happen to the cell.

A substance will diffuse from where it is more concentrated to where it is less concentrated, down its concentration gradient. Each substance diffuses down its own concentration gradient, independent of the concentration gradients of other substances.

The diffusion of a substance across a biological membrane is passive transport because it requires no energy (no ATP) from the cell to make it happen. Diffusion of molecules with limited permeability through the lipid bilayer may be assisted by transport proteins. (facilitated diffusion)

Differences in the relative concentration of dissolved materials in water can lead to the movement of ions from one solution to the other. I. Osmosis is the passive transport of water across a selectively permeable membrane McGrawHillHowOsmo sisWorks animationanimation

Review of Diffusion and Osmosis Compare diffusion and osmosis. Contrast diffusion and osmosis. Both are examples of PASSIVE TRANSPORT and they do NOT require added energy Osmosis only involves WATER moving and it occurs across a semi-permeable membrane COMMAND TERM: Compare and Contrast: Give an account of similarities and differences between two (or more) items or situations, referring to both (all) of them throughout.

The solution with the higher concentration of solutes is hypertonic. The solution with the lower concentration of solutes is hypotonic. These are comparative terms. Solutions with equal solute concentrations are isotonic. Osmosis terminology Tap water is hypertonic compared to distilled water but hypotonic when compared to sea water.

Imagine that two sugar solutions differing in concentration are separated by a membrane that will allow water through, but not sugar. The hypertonic solution has a higher solute concentration (and lower water concentration) than the hypotonic solution.  More of the water molecules in the hypertonic solution are bound up in hydration shells around the sugar molecules, leaving fewer unbound water molecules. http://bioap.wikispaces.com/Ch +3+Collaboration

What do you predict will happen over time?

Review U-tube diagram: Initially, in what direction is the glucose diffusing? Sucrose? Water? If you examine side A after 3 days, what would happen to the concentration of Sucrose? Glucose? Water?

After the system reaches equilibrium, what will happen to the water level on sides A and B?

Unbound water molecules will move from the hypotonic solution where they are abundant to the hypertonic solution where they are rarer. Osmosis continues until the solutions are isotonic.

The direction of osmosis is determined only by a difference in total solute concentration.  The kinds of solutes in the solutions do not matter.  This makes sense because the total solute concentration is an indicator of the abundance of bound water molecules (and therefore of free water molecules). When two solutions are isotonic, water molecules move at equal rates from one to the other, with no net osmosis.

Osmotic Terminology There are many ways to describe the movement of water across a selectively permeable membrane:  Molecules move from their own high concentration to their low concentration...this includes water.  Water moves from a hypotonic (hypoosmotic) solution to a hypertonic (hyperosmotic) solution.

The movement of water can also be described by the following: Water goes to where “there is more stuff dissolved”...(more stuff, lower water concentration). Water goes to where there are more osmotically active particles (“stuff”). Water goes to where there is a higher osmotic pressure (a tendency of a solution to take up water by osmosis).

Water (osmotic) potential also describes the movement of water. Water potential is defined as the tendency of water to leave one place in favor of another. Water always moves from an area of higher water potential to an area of lower water potential. The addition of solute molecules lowers the water potential value. The numerical value of pure distilled water is zero. Any solution with dissolved solute has a water potential value with a negative number.

Changes in water potential can explain why water travels up a tree. The water potential in the roots is -24.7 bars. The water potential in the stems is The water potential in the leaves is The water potential in the atmosphere is Therefore, the movement of water is from a high to low water potential …from the roots, to the stems, to the leaves and then out to the atmosphere by transpiration. -57.6 bars -98.3 bars -203.1 bars

What is DIALYSIS? the diffusion of SOLUTES across a selectively permeable membrane. Usually used when different solutes are separated by the use of a selectively permeable membrane.

An animal cell immersed in an isotonic environment experiences no net movement of water across its plasma membrane.  Water flows across the membrane, but at the same rate in both directions.  The volume of the cell is stable. J. Cell survival depends on balancing water uptake and loss

The same cell in a hypertonic environment will lose water, shrivel or crenate and probably die. A cell in a hypotonic solution will gain water, swell, and burst.

For a cell living in an isotonic environment, osmosis is not a problem. Similarly, the cells of most land animals are bathed in an extracellular fluid that is isotonic to the cells. Organisms without rigid walls have osmotic problems in either a hypertonic or hypotonic environment and must have adaptations for osmoregulation to maintain their internal environment.

The cells of plants, prokaryotes, fungi, and some protists have walls that contribute to the cell’s water balance. A plant cell in a hypotonic solution will swell until the elastic wall opposes further uptake. At this point the cell is turgid, a healthy state for most plant cells. Turgid cells contribute to the mechanical support of the plant.

animation If a cell and its surroundings are isotonic, there is no net movement of water into the cell and the cell is flaccid and the plant may wilt.

animation In a hypertonic solution, a plant cell loses water, and its volume shrinks. Eventually, the plasma membrane pulls away from the wall. This plasmolysis is usually lethal.

K. Application Questions Use terms water potential, hypertonic, hypotonic in your answers. 1. What would happen to the cells of a person who had an IV fluid filled with distilled water? 2. What would happen to the cells of grass alongside a road heavily salted on a winter day? 3. What would happen to the cells of a marine organism like a shark if it was placed in a pond?

Many polar molecules and ions that are normally impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane. The passive movement of molecules down its concentration gradient via a transport protein is called facilitated diffusion. L. Specific proteins facilitate passive transport of water and selected solutes: a closer look Animation of facilitated diffusion

Transport proteins have much in common with enzymes.  They may have specific binding sites for the solute.  Transport proteins can become saturated when they are translocating passengers as fast as they can.

Many transport proteins simply provide corridors allowing a specific molecule or ion to cross the membrane.  These channel proteins allow fast transport.  For example, water channel proteins, aquaporins, facilitate massive amounts of diffusion.

Some channel proteins, gated channels, open or close depending on the presence or absence of a physical or chemical stimulus. The chemical stimulus is usually different from the transported molecule. For example, when the chemical stimulus neurotransmitters bind to specific gated channels on the receiving neuron, these channels open.  This allows sodium ions into a nerve cell.  When the neurotransmitters are not present, the channels are closed. Gated and nongated channel animation

Some transport proteins do not provide channels but appear to actually translocate the binding site and solute across the membrane as the protein changes shape. These shape changes could be triggered by the binding and release of the transported molecule.

Active transport involves moving solutes from where they are less concentrated to the side where they are more concentrated. This active transport requires the use of energy- ATP! Active transport is critical for a cell to maintain its internal concentrations of small molecules that would otherwise diffuse across the membrane. M. Active transport is the pumping of solutes against their gradients

Active transport is performed by specific proteins embedded in the membranes. ATP supplies the energy for most active transport.  Often, ATP powers active transport by shifting a phosphate group from ATP (forming ADP) to the transport protein.  This may cause a change in the transport protein that moves the solute across the membrane.

Who remembers? 1. Does active transport require energy? 2. Does active transport move substances from high to low concentration or low to high concentration? 3. What molecule is the “battery”that provides cells energy? YES! low to high concentration ATP

The sodium-potassium pump actively maintains the gradient of sodium (Na + ) and potassium ions (K + ) across the membrane.  Typically, an animal cell has higher concentrations of K + and lower concentrations of Na + inside the cell.  The sodium-potassium pump uses the energy of one ATP to pump three Na + ions out and two K + ions in. The sodium-potassium pump

Since three Na + ions are pumped out for every two K + ions in, cells are like “salty bananas” – high potassium inside and high sodium outside. The sodium-potassium pump K+K+ K+K+ K+K+ K+K+ K+K+ Na + http://www.clipartpanda.com/categories/banana -clipart-black-and-white

animation: animation

All cells maintain a voltage (charge difference) across their plasma membranes.  The cytoplasm of a cell is negative in charge compared to the extracellular fluid because of an unequal distribution of ions on opposite sides of the membrane.  Since 3 Na+ are pumped out of cell vs. 2K+ pumped in….this creates the voltage! N. Some ion pumps generate voltage across membranes

The membrane potential acts like a battery. The membrane potential favors the passive transport of cations (+ ions) into the cell and anions (- ions) out of the cell. Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane:  a chemical force based in an ion’s concentration gradient  an electrical force based on the effect of the membrane potential on the ion’s movement.

In plants, bacteria, and fungi, a proton pump is the major electrogenic pump, actively transporting H + out of the cell. animation Proton pumps create electrochemical gradients

Proton pumps in the cristae of mitochondria and the thylakoids of chloroplasts, concentrate H + behind membranes, thus storing energy that can be used for cellular work. Proton pumps also work in the human stomach to create its highly acidic environment. Applications of proton pumps

A single ATP-powered pump that transports one solute can indirectly drive the active transport of several other solutes through cotransport via a different protein. As the solute that has been actively transported diffuses back passively through a transport protein, its movement can be coupled with the active transport of another substance against its concentration gradient. O. In cotransport, a membrane protein couples the transport of two solutes

animation

1.Identify (A, B, or C) the examples of active transport. 2.Explain why these are active, not passive. 3.Identify the process (A, B, or C) that is passive. 4.What provides the energy to pump the protons? 5.What provides the energy to move the sucrose into the cell against its concentration gradient? 6.What causes H+ to move through the cotransporter molecule?

Plants commonly use the gradient of hydrogen ions that is generated by proton pumps to drive the active transport of amino acids, sugars, and other nutrients into the cell.  The high concentration of H + on one side of the membrane, created by the proton pump, leads to the facilitated diffusion of protons back, but only if another molecule, like sucrose, travels with the hydrogen ion/proton.  After the sodium-potassium pump occurs, Na+ ions diffuse back into the cell through facilitated diffusion. Glucose travels in with Na+ through cotransport.

Small and non polar molecules enter or leave the cell through the lipid bilayer or by transport proteins. Large molecules, such as polysaccharides and proteins, cross the membrane via vesicles. During exocytosis, a transport vesicle buds from the Golgi apparatus and is moved by the cytoskeleton to the plasma membrane. When the two membranes come in contact, the bilayers fuse and spill the contents to the outside. P. Exocytosis and endocytosis transport large molecules (bulk transport)

During endocytosis, a cell brings in large molecules by forming new vesicles from the plasma membrane. Endocytosis is a reversal of exocytosis.  A small area of the plasma membrane sinks inward to form a pocket  As the pocket into the plasma membrane pinches in, it forms a vesicle containing the material that had been outside the cell. Click for youtube animation

One type of endocytosis is phagocytosis, “cellular eating”. In phagocytosis, the cell engulfs a particle by extending pseudopodia around it and packaging it in a large vacuole. The contents of the vacuole are digested when the vacuole fuses with a lysosome. Click pic. for movie Youtube video Mcgraw hill animation

In pinocytosis, “cellular drinking”, a cell creates a vesicle around a droplet of extracellular fluid.  This is a non-specific process. Phschool animation

Receptor-mediated endocytosis is very specific in what substances are being transported. This process is triggered when extracellular substances bind to special receptors, ligands, on the membrane surface, especially near coated pits. This triggers the formation of a vesicle animation

Receptor-mediated endocytosis example: Human cells use this process to absorb cholesterol.  Cholesterol travels in the blood in low-density lipoproteins (LDL), complexes of protein and lipid.  These lipoproteins bind to LDL receptors and enter the cell by endocytosis.  In hypercholesterolemia, an inherited disease, the LDL receptors are defective, leading to an accumulation of LDL and cholesterol in the blood.  This contributes to early atherosclerosis. animation

What is the main difference between passive and active transport? Passive transport does not need added energy because random motion of molecules themselves causes diffusion to occur. Active transport requires the use of ATP as energy to move substances from low to high concentration.

Q. Review: 4 ways that substances can cross into/out of a cell Simple diffusion Facilitated diffusion Active transport Bulk transport With/down or against/up concentration gradient With/down Against/upWith or against Need ATP? No Yes (to change shape of transport protein) Yes (to move & rearrange membrane) Need membrane proteins? NoYes Endocytosis or exocytosis

R.Review Questions for the Test 1.What are the major components of a phospholipid which occurs in cellular membranes? 2.Animal cell membranes contain cholesterol to maintain proper membrane fluidity. Since plant cell membranes do not contain cholesterol, how do they maintain membrane fluidity? 3.Differentiate between a peripheral and an integral protein when examining a cell membrane. 4.Which end of the phospholipid is hydrophobic?_______________Which is hydrophilic?___________ 5.What general type of membrane proteins would make up channel proteins? 6.Name 6 general functions of cell membrane proteins. 7.Explain what membrane glycoproteins are.

8.Compare and contrast passive and active transport. 9.State two examples of passive transport. 10. How does facilitated diffusion compare to simple diffusion? 11.Since protein pumps use ATP to transport materials across the cell membrane, what type of transport is said to occur? 12.What structures carry materials from the rER to the Golgi apparatus and then to the plasma membrane? 13.What is the value of the fluidity of the membrane in the process of endocytosis and exocytosis? 14.What happens in endocytosis? Give an example. 15.What happens in exocytosis? Give an example. 16.What substance moves in osmosis?

17. Describe the major characteristic of a membrane in osmosis. 18.Compare a hypertonic solution to a hypotonic solution. 19.When looking at a hypertonic solution on one side of a membrane and a hypotonic solution on the other side, which way will water passively flow? 20. Complete the following statements: a)Small and non-polar molecules cross membranes______________. b)Large and polar molecules cross membranes with______________. 21. What two major factors affect whether a substance can move across a membrane? 22.What is cotransport? 23. Give an example of cotransport.

24.Out of the following, which would most easily pass through a membrane? ___Chloride ions ___Glucose ___Oxygen molecules ___Sucrose ___Carbon dioxide ___Water ___Sodium ions 25.What type of transport is the sodium-potassium pump an example of? 26.In the Na-K pump, do sodium ions move in or out of the cell? 27.In the Na-K pump, do potassium ions move in or out of the cell? 28.How is the Na-K pump involved with the human nervous system? 29.When the cells of the pancreas produce insulin and secrete it into the bloodstream, what type of transport is occurring? 30.Contrast endocytosis and exocytosis. 31. What are three examples of endocytosis.

S. How do organisms use all these different kinds of transport to maintain homeostasis? Neurons and the action potential Osmoregulation and kidney function

T. The Na+/K+ pump and voltage gated ion channels are essential to the functioning of your neurons (nerve cells). In the axon of the neurons, the Na+/K+ pump is used to restore the resting membrane potential after a nerve impulse has occurred. The opening and closing of ion channels create the nerve impulse.

Click picture for movie

Click here for animation on action potential McGraw Hill animation with questions Get Body Smart Interactive Animation of Na+/K+ pump

Draw a picture of a neuron and label all of the key parts without using your notes!!! Include the following:  Dendrites  Axon  Terminal Branches  Cell body (cyton)  Myelin Sheath  Nodes of Ranvier  Indicate the pathway of an action potential  Indicate the area where the Na+/K+ pump is found.

Did you get this??

Click here for animation on action potential

Label the neuron Dendrite Cell Body nucleus Myelin sheath/ Schwann cell axon Terminal branches/ axon tips

Label the diagram a) Resting state; Na+-K+ pump working (Active transport)

Label the diagram b) Depolarization- sodium channels open so Na+ rushes into cell (facilitated diffusion)

Label the diagram c) Repolarization- sodium channels close; Potassium channels open so K+ diffuses out of cell (facilitated diffusion)

Label the diagram d) Na-K pump re-establishes resting potential (Active transport)

1. WHAT IS CAUSING THE CHANGE IN THE MEMBRANE POTENTIAL SEEN AROUND THE LETTER A, B, C, AND D IN THE GRAPH? 2. THE PERIOD OF TIME WHERE THE SODIUM-POTASSIUM PUMP IS WORKING TO RESTORE THE MEMBRANE'S RESTING POTENTIAL (SEEN IN THE PART OF THE GRAPH LABELED D BELOW) IS CALLED THE _______ PERIOD AND DURING THIS TIME, THE NEURON CAN'T ______, Using the next slide, answer the following:

In “A” of the graph, a signal is causing some of the sodium channels to open making the axon more positive. In “ B” of the graph, the opening of sodium channels (caused by crossing the threshold potential) and the rushing in of positively charged sodium ions into the axon of the neuron. (What kind of transport is this?) In “C” of the graph, the opening of potassium channels (caused by the depolarization of the membrane) which is allowing positively charged potassium ions to flow out of the cell.,

Around “D” of the graph, The end of the action potential occurs. Some of the K+ gates close, causing a slow down in the leakage of K+ out of the neuron. The drop in membrane potential below the resting potential at the end of the action potential is called the "overshoot" and is caused by more K+ channels being opened than there are normally during the resting potential. As these gates close, more K+ stays inside and moves the inside of the neuron to the more positive average of -70mV compared to the -80mV during the overshoot- Hyperpolarization The Na+/K+ pump resets the resting potential to -70mV

The period of time where the sodium- potassium pump is working to restore the membrane's resting potential (is called the refractory period and during this time, the neuron can't respond

http://hyperphysics.phy-astr.gsu.edu/hbase/biology/actpot.html 5  6 Na+-K+ Pump resets the resting potential

If an axon is ______, the action potential (impulse) moves down the axon even faster because it leaps from node to node in a jumping fashion The body distinguishes between a strong outside stimulus and a weak one by the _________of the action potentials. myelinated frequency

What happens when an action potential reaches the end of the neuron?,

The entrance of _____ through gated channels in the presynaptic membrane stimulates vesicles to fuse with the presynaptic membrane, releasing calcium

The small space between the terminal axon branch of one neuron and the dendrite of the post-synaptic cell is called a(n) _____. Synapse The cytoplasm at the end of an axon contains many small vesicles. What's in those vesicles? Neurotransmitters The entrance of _____ through gated channels in the presynaptic membrane stimulates vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the synapse. Calcium ions (Ca +2)

What opens the calcium channels in the presynaptic membrane of the axon terminus? Once in the synapse, neurotransmitters bond with ______ embedded in the postsynaptic membrane. Neurotransmitters in the synapse are either destroyed by _____ or taken back into the presynaptic neuron (reuptake) _____. Depolarization of the membrane caused by an arriving action potential (the calcium channels are voltage-gated channels) Receptors Enzymes Active transport

U. Osmoregulation Management of the body’s water content and solute composition, osmoregulation, is largely based on controlling movements of solutes between internal fluids and the external environment.  This also regulates water movement, which follows solutes by osmosis.  Animals must also practice excretion, removal of metabolic waste products before they accumulate to harmful levels.

Types of metabolic wastes WASTEProcess that produces it Carbon dioxideAerobic respiration WaterAerobic respiration & dehydration synthesis Nitrogenous wastes (ammonia, urea, uric acid) Amino acid breakdown (deamination) and nucleic acid breakdown Mineral saltsAll metabolic processes

Types of Nitrogenous Wastes Nitrogenous Waste OrganismsToxicitySolubility in water Ammonia Aquatic (protists, hydra, fish) High Urea Terrestrial (humans) Medium Uric acid Flying (insects, birds) or dry land (desert lizards) LowLow – solid (Solid white part of bird excrement)

In general, the kinds of nitrogenous wastes excreted depend on an animal’s evolutionary history and habitat - especially water availability.

Review of Metabolic Wastes Match the waste with the description DescriptionCell Type 1. Nitrogenous waste produced by birds and insects ____ 2. Nitrogenous waste produced by most fish and aquatic organisms.____ 3. Produced as a result of aerobic respiration. ____ and ____ 4. Produced from amino acid and nucleic acid breakdown. ___ ____ ____ 5. Most toxic nitrogenous waste____ 6. Least toxic nitrogenous waste____ a. Ammonia b. Urea c. Uric acid d. Carbon dioxide e. Water f. Mineral salts C A D AB A E C C

For example, Paramecium, a protist, is hypertonic when compared to the pond water in which it lives.  In spite of a cell membrane that is less permeable to water than other cells, water still continually enters the Paramecium cell.  To solve this problem, Paramecium have a specialized organelle, the contractile vacuole, that functions as a bilge pump to force water out of the cell. (exocytosis) animation

Try the practice question on contractile vacuoles…smartboard

Insects and other terrestrial arthropods have organs called Malpighian tubules that remove nitrogenous wastes and also function in osmoregulation.

Review of adaptations for excretion – try to complete the chart CO 2 Uric acid, salts, little water Uric acid Lungs Kidneys Liver Bird Salts, uric acid, little water CO 2, little water Malpighian tubules & intestine Tracheal tubes Grasshopper Water, salts, ammonia, urea Water, CO 2 Nephridia Skin Earthworm Water, CO 2, salts, ammonia Plasma membraneHydra/jellyfish Water, CO 2, salts, ammonia Water Plasma membrane Contractile vacuole Paramecium Metabolic WastesAdaptations for excretion Organism

Human adaptations for excretion Excretory OrganWaste excreted KidneysUrea, uric acid, water, salts LungsCO 2 and water LiverMake urea, uric acid SkinWater, salts, urea

Osmoregulation in Plants Plants share with animals the problems of obtaining water and in disposing of the surplus. Certain plants develop methods of water conservation. Xerophytes are plants in dry habitats such as deserts which are able to withstand prolonged periods of water shortage. Succulent plants such as the cactus have water stored in large parenchyma tissues. Other plants have leaf modifications to reduce water loss, such as needle-shaped leaves, sunken stomata and thick, waxy cuticles as in the pine.

The sodium potassium pump helps to regulate the functioning of the kidneys! Take a closer look at the functional unit of the kidneys- THE NEPHRONS and how urine is produced….

The nephron is where the action occurs to filter wastes from the blood to produce urine. animation Animation 2

Filtrate from Bowman’s capsule flows through the nephron and collecting ducts as it becomes urine. Fig. 44.22

1.Briefly summarize what happens in the proximal tubule. 2.What happens to the filtrate concentration in the descending limb of the Loop of Henle? 3.What events occur in the ascending limb of the Loop of Henle? 4.What occurs in the distal tubule to the filtrate? 5.Discuss what happens in the collecting duct? 6.What substances make up the final contents of urine?

The Na/K pump helps make it possible for water to be reabsorbed back into the blood http://interactivehuman.blogspot.com/2008/06/animation-kidney-parts- of-nephron.html

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 44.24a ADH is the hormone that regulates Water reabsorption In the kidneys. How does This hormone Illustrate The concept Of feedback? http://www.youtube.com/watch?v=glu0dzK4dbU

How Is A Membrane’s Structure Adapted To Its Function?

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How Is A Membrane’s Structure Adapted To Its Function?

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