Today is Friday (!), October 11th, 2013

Today is Friday (!), October 11th, 2013
In This Lesson: Cell Membranes and Cell Transport (Lesson 3 of 5) Today is Friday (!), October 11th, 2013 Pre-Class: Today is our first look at the cell. First, choose one of the following to answer in your notes: What do the terms diffusion, osmosis, or passive/active transport mean to you? Have you ever had Aquafina or Dasani water? Why is it different from Poland Spring, for example? Do you know the name of the process? Also, take a worksheet from the turn-in box and get a paper towel for your pair. This will be on the test on Friday.

Today’s Cell membrane [Part 1] Brief aside on blood type
Form Brief aside on blood type Cell transport [Part 2] Function Doodling on whiteboards Yes, you will be making pictures. Where is this in my book? Academic: P Honors: P. 79 and following… Today’s “Objectives” - get it? I’ve included the book pages so that you will have some reference when you’re studying. There may be some new material in my notes, but the vast majority of what I’m about to tell you was taken from the book.

But First, a Word About Size…
Ye Olde BioScale What It Looks Like Scale of the Universe Many people on their exams seemed to be confusing different-sized objects. Here is a good list to orient you as to what we’re talking about. Also, this link provides a good illustration of how small we’re actually getting. It’s always best to remember “where we are” in space.

Osmosis and Diffusion Pre-Class
What did you come up with? We will talk about the details of these processes today and later in the week. One other thing… When you hear me mention an organic molecule today, raise your hand. Keep your ears open! So did anyone think of what contains the cell? Does anyone know? So what exactly does a cell need to do to carry on life, in the most basic terms. How does it get those things? Basically, I’m just trying to get you to think of the function of a cell, so that you’ll know why the structure is the way it is.

The Cell Membrane Like the “shell” of the cell.
Also called the plasma membrane. Double layer of phospholipids called a bilayer. Separates the cell’s cytoplasm from the extra-cellular matrix. ECM Which one is outside, which is inside? Remember phospholipids? This is what goes into the cell membrane, for the most part. Now, the cell membrane is the divider between the outside of the cell, called the “Extra-Cellular Matrix” or ECM, and the inside, called the cytoplasm. It’s easy to remember the difference here. ET, from the movie, was an Extra-Terrestrial, meaning he came from someplace outside earth. “Extra” generally means just that - not common, or not normally from a certain place.

Permeability Some things are “impermeable:”
Raincoats, balloons, brick walls. Some things are “permeable:” Air, water. Some things are “semi-permeable:” Nets, gates, cell membranes. Semi-permeability is sometimes called selective permeability. Can you guys think of more examples for these?

The Phospholipid Bilayer
Most plant and animal cells have a double-layered cell membrane called a phospholipid bilayer. The phospholipid bilayer acts as its own gate. Because the cell is in and made of water, a polar substance, the non-polar tails stay on the inside of the layer. This polar/non-polar deal makes the phospholipid amphipathic. Polar > Non-Polar Back to that bilayer. Now that we know what it does in terms of being semi-permeable, we can now study how it does that. Polar molecules (remember those?) like water surround the cell and are in the cell. This means that the non-polar part of the phospholipid - the tails, stay on the inside, sheltered from the outside. This also means that mostly only non-polar molecules can cross the membrane on their own. What if a cell needed something polar (besides water)? How could it get that? We’ll learn in just a minute…

Phospholipids? P Fun fact: A phospholipid is actually just like a triglyceride molecule… …but it’s usually unsaturated… …missing a fatty acid chain (diglyceride)… …and with a phosphate group. Glycerol Molecule Fatty Acid Chains

What It Looks Like This is a college-level diagram of what a cell looks like. Remember that for animal cells, they’re generally shaped like a sphere, so this is just a segment of the outer layer, or shell. This would completely surround the cell in a ball shape.

Modeling the Cell Membrane
Time for a class bonding experience. The Classroom Cell! So to summarize, you are a phospholipid. You have a polar [hydrophilic] “head” (your upper body) and a non-polar [hydrophobic] “tail” (your legs). The desks are like the imaginary dividing line between polar and non-polar. Polar Non-Polar Okay, so everyone sitting here in the center part of the room can be considered the lipid bilayer. Your heads are like the phospholipid heads, and your legs can be like the phosopholipid tails. Your desktops are like the imaginary dividing line between the hydrophilic and hydrophobic sections of the phospholipid. Also, don’t forget that there’s another layer below you, and upside down, like this… Polar Non-Polar

Now for the Proteins Membrane proteins are embedded in some places in the cell membrane. They might have one of many jobs: Marker Proteins Receptor Proteins Enzymes Transport Proteins Phospholipids are not the only things that make up the cell membrane. The next thing in the membrane we’ll learn are the embedded proteins. Check page 61 for a good diagram of these proteins. This illustration is different, but still pretty good.

And we return to the model…
More “Classroom Cell!” Embedded Protein! This time with added proteins! [I pick several students spread out in the room to stand up. These people represent the embedded proteins. I will also explain about transmembrane proteins and others, and that they’re not always necessarily “taller”]

There’s more… Attached to some proteins are carbohydrates (remember them?) that help in cell-cell recognition. It’s hard to see on this illustration (page 61 in your book has it, too), but there are carbohydrates attached to some cells. These help other cells and substances to recognize the cell with the carbohydrates, which can be very, very important, particularly in your body. Each of your cells must be recognized as one of your own, and not something else, or there could be trouble. Remember these carbohydrates - not only will they be on the exam in some form, but they also might be the exit ticket for today.

And we return to the model one last time…
More “Classroom Cell!” This time with added carbohydrates! [Of the “embedded protein students,” I pick one or two to lift their arms at funny angles to represent carbohydrate receptors]

Okay, one last thing… Cell membranes are fluid.
What does this mean? The cell’s phospholipids and embedded proteins flow around the membrane and are in motion. Called the Fluid Mosaic Model. A certain lipid (actually, a steroid) can slow down or stop this fluidity. Do you know what it is? Phospholipids in our cell membranes are in motion. Proteins too may be moving around the surface of the cell. This would be like if all of you moved one seat over every day. There’s something, though, that can prevent it, and it’s something that only comes from animal sources.

Fluid Mosaic Model Remember, it moves!

Challenge Question We know that carbohydrates are attached to proteins in the cell membrane so that other cells can identify them. What do you think might happen if a cell lost its carbohydrate receptors in your body?

Blood Type For a look at how important these small signal molecules are, we’ll look at blood type. Anyone know their blood type in here? We’re going to keep blood type simple for today, so let’s assume there are only four total blood types: A, B, O, and AB.

Blood Type Each red blood cell (except O) has a specific kind of receptor on it (in this case called an antigen).

White Blood Cells You also have white blood cells (leukocytes) – they’re like angry policemen in your blood vessels. Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor  Receptor 

Blood Type The wrong type of blood cell receptors causes agglutination (clumping) . Example: My dad has Type A blood. If you give him Type B blood, the white blood cells will treat it as an invader. Type O blood has no antigens so anyone can receive it. More on blood when we get to the Genetics unit.

Micro Assignment Tear a small piece of paper out of your notebook, write your name on it, and answer this question: Which organic molecules play a role in the cell membrane? What roles do they play?

Molecular Transport [Part 2]
Question: You have a sealed container holding one liter of pure oxygen (O2). You set the container on a table and leave it alone. After one week, are the oxygen molecules moving? Why or why not? Remember that molecules are constantly in motion. In most cases, though, their movements are balanced. As many oxygen molecules are coming toward our faces right now as are those moving away.

Molecular Movement Molecules are always in motion.
Gas, liquid, and solid. Molecules only stop moving at absolute zero. So, even after a week (or two or three), the oxygen molecules would still be bouncing around.

Predictive Doodling Today we’re going to do something I’m calling “Predictive Doodling.” It’s like the Challenge Questions we do on the whiteboards, only you’ll be drawing instead of writing. I’ll give you the “before,” you give me the “after.”

Before Your whiteboard is a square container of water.
The dots are dissolved solutes. What happens next? Talk to your partner – then draw it.

Diffusion Analogy Imagine for a second that at the beginning of class I jammed all of you into the corner of the room. Then, I just said, “Okay, relax,” and let you do what you wanted. Would all of you stay put or would you spread out?

Note Organizer Use this Cell Transport worksheet in place of your notebook for now…

Now let’s take a look at what the science says…
Diffusion is the passive “spreading out” of particles of a substance until the particles are spread out equally. “Passive” meaning “no energy required.” Diffusion is a form of passive transport. Heat generally makes diffusion go faster. Let’s try a little demo or two…

Diffusion Demos Diffusion in Water Diffusion in Air

Diffusion Imagine a crowded room, filled with claustrophobic people. There is a door leading to another room of the same size, except that room is empty. If we open the door and wait a few minutes, what happens? Will everyone move? Not everyone will move, because then we’ll have the same crowd in the other room. Insead people might slowly move from one room to the other until they’re about even. This is, essentially, diffusion, but there’s a catch. First, a visualization [slide diagram]. The analogy works pretty well, but we need to think of these claustrophobic people as hyperactive claustrophobic people. They never stop moving around randomly. In fact, when the two rooms “even out,” there are still people moving from one to the other, but the rate it which people move from Room 1 to Room 2 is balanced by the rate at which people move from Room 2 to Room 1.

Concentration Gradient
Concentration refers to the amount of a substance in a certain area. Particles diffuse down their concentration gradient. What does that mean? In passive transport, particles always go from an area of high concentration to an area of low concentration.

Warning: Steep Grade High Low

High Concentration In Passive Transport, particles move from areas of high concentration to areas of low concentration. Substance Concentration Gradient Low Concentration

Predictive Doodling Again
The line in the middle is permeable to water, but not to solute. What happens next?

Osmosis Osmosis is basically the same thing as diffusion, only with water molecules and some form of a barrier. Osmosis is another form of passive transport. Just like in diffusion, in osmosis, water moves from areas of high water concentration to low water concentration. Or, water moves from areas of low solute concentration to areas of high solute concentration.

Osmosis Which drink has more liquid in it? Drink A Drink B ICE ICE ICE

Which side has more water on it?
Osmosis in a U-Tube Side A Side B Here’s a way to look at it all put together. Notice how the water level will even change - that’s how strong this force is. Which side has more water on it?

Osmosis in Carrots Remember when I put the carrots in these beakers?
They were roughly equal carrots at the time. For the carrot in the salt water, there is more solute outside the carrot than inside the carrot. Which way does the water go? What kind of change can we expect to find in the carrots?

Tonicity Hypertonic solution Hypotonic solution Isotonic solution
Relatively more solute than surroundings. Water flows TOWARD a hypertonic solution. Hypotonic solution Relatively less solute than surroundings. Water flows AWAY FROM a hypotonic solution. Isotonic solution The same amount of solute as the surroundings. No net water change. A hypertonic solution is one that has relatively more solute. Think of hyper = “more!” Water will flow TOWARD a hypertonic solution. A hypotonic solution is the opposite. An isotonic solution -guesses? It’s one with no relative difference in solution levels. It is already at equilibrium.

Substance Isotonic Solutions
Water does not experience a net movement in isotonic solutions. There is no concentration gradient. Substance No concentration gradient No net movement of water

And now, I present to you…
…the key to EVERYTHING!!!!!!* *osmosis-related. Draw this in your notebook. Make it BIG. Hypotonic Hypertonic H2O Flow

What’s the connection? Blood hypertonic, surroundings hypotonic
Imagine an animal cell. More “stuff” is dissolved in the animal’s cytoplasm than is dissolved outside in the ECM. What happens to the cell? What happens If it has a LOT more dissolved in it than the outside? What if the outside has more? [slide picture] What might be a solution to having a cell burst from being hypotonic? Which kinds of organisms have solved this? [Fungi/Plant Cells with Cell Walls] So how do animal cells without cell walls deal? That’s for Thursday. For now, here’s a little bit of a preview as we learn about the next kind of passive transport. Blood hypertonic, surroundings hypotonic Blood hypotonic, surroundings hypertonic Isotonic solutions

Osmosis Videos Egg Osmosis Onion Osmosis Gummi Bear Osmosis

Osmosis in Plant Cells

Osmosis in Plant Cells As we will soon learn, plant cells are good at holding water. If they’re placed in a hypertonic solution, however, they lose water and wilt. Their cells undergo plasmolysis. Place them in a hypotonic solution and they will swell slightly, like a garden hose with water. Their cells become turgid. In animal cells, without a cell wall, the cell may burst in a process called cytolysis.

Osmosis in Kidneys

Osmosis in Kidneys The proximal Loop of Henle is the part of the nephron (kidney component) responsible for re-absorbing water from urine. With this in mind, would you guess that desert animals have larger or smaller Loops of Henle than other animals?

Osmosis in Kidneys

Osmosis in Merriam’s Kangaroo Rats

One last note… If you buy a car for $1000 and sell it for $3000, how much profit did you make? $2000 If you take two steps forward and three steps back, how many steps have you moved forward? -1 These are examples of net gains and losses. How many steps did you take (total)? 5 (but this is not your net steps)

One last note… Remember that question we did about oxygen gas molecules? Molecules, especially of liquids and gases, constantly move or vibrate. They do this without adding any energy. Even after diffusion or osmosis has stopped, the molecules are still moving.

Equilibrium For things like diffusion and osmosis, eventually the solutes reach a point where there is no net change in molecule movement. This is equilibrium. We call it “dynamic equilibrium” because the molecules are still moving, but there is no net change in concentration or movement.

Equilibrium When dynamic equilibrium is reached, diffusion and osmosis stop. Molecular motion continues, though. 1.0% Sugar Before Net Water Flow Inward 0.75% Sugar After No Net Water Flow WATER WATER 0.50% Sugar WATER WATER

Osmosis Practice Problems
First, let’s do these as a class. Then, log-in to Quia. Take the quiz labeled Osmosis Practice Problems. These aren’t easy. That’s why this isn’t graded and we’ll be taking it a few times. I encourage you to work together.

By the way… Dasani and Aquafina use a process called reverse osmosis.
They make water go from high solute concentration to low solute concentration – the opposite direction! This is part of their purification process. Why do they do this? Because their water is actually just purified tap water!

Closure [Part 1] Find a blank sheet in your notebook for a nice little concept map of what we’re doing!

Closure [Part 2] Diffusion What’s wrong with this picture?
This very image is how I first heard of osmosis, but I now realize it’s wrong. Why?

Diffusion and Membranes
Diffusion occurs across the cell membrane without much trouble for small molecules. For some things, water included due to the non-polar inner section of the membrane, diffusion can’t really happen well. Some molecules are too large or charged or polar/non-polar to just fit right through. They need help.

Facilitated Diffusion
When a molecule needs help to diffuse, (but does NOT need energy), the process is called facilitated diffusion. Basically it just means that a special channel protein had to let the molecule in because it couldn’t fit elsewhere.

Facilitated Diffusion
Lastly, one other kind of diffusion: facilitated diffusion. Like our original idea, let’s imagine we have two areas with claustrophobic people, except separating them is not a door but a large river. They need to take a ferry to get across. The ferry is like the transport protein - a membrane-linked protein that assists molecules across the membrane WITH their concentration gradient. And, just like the ferry, the protein can be used repeatedly.

Channel Protein Remember when we modeled the cell membrane as a class? We had certain proteins standing up. [Re-model if necessary/time] [slide picture] If one of these were an ion channel, it would be like a tunnel through the cell membrane. Remember that the cell membrane has a non-polar region in the middle, like our legs in the model we did. Most polar molecules cannot pass through on their own, so they need to take the tunnel into the cell. Sometimes, these tunnels are always open. Sometimes they’re closed until there’s enough of a charge waiting to come in or go out. Interestingly, while there’s a concentration gradient based on the concentration of each chemical, there is also a gradient because of the charge of the ions themselves. This is called the electrochemical gradient. Nerve cells require this kind of electrochemical gradient in order to survive.

Facilitated Diffusion Example
Nerve cells:

Facilitated Diffusion Example

Practice Problems Visit Quia for the following activity and quiz in this order: Diffusion/Osmosis Battleship Play till you win Osmosis Virtual Lab More information next slide… Osmosis Practice Problems

Osmosis Virtual Lab Visit this website:
Found in Biology Links or can be run from Supporting Documents (Osmosis Virtual Lab). Use the simulation to run through the various osmotic scenarios shown on your worksheet. Note: If you run this from my website and not from the Glencoe site, you won’t get the “directions” on the left side of the screen, but you won’t need ‘em, really.

Osmosis Gizmo You’re looking for the Osmosis gizmo
[Log-in Instructions] You’re looking for the Osmosis gizmo Also open Quia for the Osmosis Gizmo in a new tab. When finished with the lab, open the Quia activity called Osmosis Gizmo Lab Cloze.

Quia Things to Try Osmosis Practice Problems
On your own. Diffusion and Osmosis Battleship On your own – did you win or lose?

Active Transport In short, active transport is the movement of a substance up or against its concentration gradient. Substance moves from a low concentration area to a high concentration area. This requires energy!

Passive Transport High Concentration Substance Concentration Gradient Low Concentration

High Concentration Active Transport Substance Concentration Gradient ENERGY NEEDED! Low Concentration

Active Transport Basically, they’re all ways for the cell to move things against their concentration gradient.

Paths for Active Transport
Three processes using the membrane: Molecular Transport: Pumping stuff in/out using membrane proteins. Endocytosis: Bringing stuff into the cell in cell membrane packages. Phagocytosis: “Cell eating” – bringing in solids (big stuff) Pinocytosis: “Cell drinking” – bringing in liquids (small dissolved stuff) Exocytosis: Dumping stuff out of the cell in cell membrane packages. Fun fact: Endo-/exocytosis are sometimes called vesicular transport. Another way a cell might actively transport something relates to cell organelles. You guys all did very well on the organelle test, so you should know the answer to this: Which organelle is responsible for packing and shipping materials? What does it use?

One Way: Using a Pump A pump uses a channel protein in the membrane.
Called “Molecular Transport” by your book. One thing it could do is to use a pump – a carrier protein (remember facilitated diffusion?) in the membrane that moves ions into the cell, and usually moves others out. In the body, your nerve cells, or neurons, need to do this A LOT. They pump sodium in and potassium out, even though there’s already more sodium in the cell and potassium outside. Sounds pretty good, right? If something would just diffuse in, the cell can more or less let it happen. If it needs more of something already plentiful in the cell, it just pumps more in. What’s the cost? As always, energy. Biology is a big story of costs and benefits. Here, the benefit is the cell can, in a sense, override physics and bring more inside, but the cost is energy, and that’s nothing to sneeze at. Energy is precious. And what form is this energy? ATP, as always.

Endocytosis/Exocytosis

Active Transport These two main processes of active transport (pumps or endo/exocytosis) are important! Used in signaling: Exocytosis/Endocytosis: Chemical Signaling Hormones Molecular Transport: Electrical Signaling Nervous System

For Example: Protein Receptors
Keep in mind, here, that a hormone is not the only form of chemical cell signal, but it’s a good example. Let’s say a hormone (what we would call a signal molecule) is floating along in the bloodstream and finally reaches a cell. It attaches to a receptor protein on the outside of the cell [DIAGRAM], which causes that protein to activate another protein inside the cell. That protein then activates an enzyme, which makes a new signal molecule, a new messenger. So here’s our first messenger, here’s our other. What do we call the next one? The second messenger, of course. Note that this is just one way this all could occur. Another might be if the receptor protein just makes the new molecule itself. But, when we’re talking about membrane receptor proteins, at the very least a signal molecule activates a protein which causes a change inside the cell. Sometimes it may lead to a second messenger or more complicated actions.

How this is used… Heroin addict Came up when I Googled “Beta Blockers”
Some connections: this is how many drugs work, legal or not. Heroin can act as a signal molecule. Beta blockers, a drug used to treat high heart rate, act as signal molecules themselves and block natural signal molecules from attaching to the heart and increasing its rate. Heroin addict

Video! CrashCourse – Membranes and Transport

A “Big-Picture” Example: Neurons
Whenever a nerve cell transmits an impulse (called an action potential), cell transport occurs. You won’t need to know this for this class, but here’s a look at how it works. Just in case you were thinking cell transport isn’t that important.

Neurons exist in a “resting state” making them negative. To keep this negative charge, the neuron actively pumps out Na+ ions. It pumps in some K+ ions. The neuron’s Na channels open, allowing Na+ ions to diffuse into the cell, making the cell more positive. Eventually, changes in voltage potentials cause K channels to open, allowing K+ to diffuse out of the cell, making the cell more negative and eventually returning the cell to normal. The neuron’s action potential travels down the axon to the axon terminal. There, the neuron allows Ca2+ ions to diffuse into the cell, which releases neurotransmitters by exocytosis into the synaptic cleft. The process continues in the next neuron (or until a muscle is reached). The first neuron returns to resting state and the process repeats.

Closure Part 1: Let’s finish the cell transport concept map!
Part 2: TED: Ethan Perlstein - Insights into Cell Membranes Via Dish Detergent Part 3: WhipAround

Today is Friday (!), October 11th, 2013

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