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Cell Membrane What is the main job of the cell membrane?
1. Controls what materials move into and out of the cell
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Lipids of cell membrane
Membrane is made of special kind of lipid phospholipids “split personality” Hydrophobic: Water-fearing Hydrophilic: Water-loving Membrane is a double layer phospholipid bilayer Hydrophilic: “attracted to water” phosphate inside cell outside cell Phospholipid bilayer HYDROPHOBIC Hydrophobic: “repelled by water”
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Semi-permeable membrane
Selective permeability is the special term used to describe how a cell membrane controls what gets in or out Need to allow some materials — but not all — to pass through the membrane semi-permeable only some material can get in or out sugar lipids aa O2 H2O salt waste
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Crossing the cell membrane
What molecules can go STRAIGHT through the cell membrane (phospholipid bilayer) directly? fats and oils can pass directly through lipid inside cell outside cell salt waste but… what about other stuff? sugar aa
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Cell membrane channels: add to your phospholipid bilayer
Need to make “doors” through membrane protein channels allow substances in & out specific channels allow specific material in & out salt channel, sugar channel, etc. inside cell aa sugar salt outside cell waste
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Protein channels Proteins act as doors in the membrane allowing specific molecules to pass through cell membrane HIGH Donuts! 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. Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane. These channel proteins allow fast transport. For example, water channel proteins, aquaprorins, facilitate massive amounts of diffusion. LOW
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Why does the cell need to move material?
Maintain homeostasis…What does that mean? The stable internal condition of a living thing This can only happen by moving material in and out of the cell How does a cell maintain this equilibrium (balance)? Through Passive and Active Transport
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Facilitated Diffusion
No Energy Required Passive Transport Diffusion Osmosis Facilitated Diffusion
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Diffusion Diffusion Molecules move from an area of HIGH concentration to LOW concentration until they reach equilibrium Molecules are CO2, O2, fats (non-polar) Movement from high concentration of that substance to low concentration of that substance.
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CARROT APPLICATION What did you fill in?
The carrot submerged in the salt solution was _________________ (bendable or not bendable) compared to my carrot submerged in distilled water What do you think happened based on your knowledge of diffusion? Think about the cells of the carrot compared to the salt solution it was submerged in
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Diffusion Let’s try it out!
Molecules move from HIGH to LOW concentration passive transport no energy needed Let’s try it out!
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Simple Diffusion: In a cell
Move from HIGH to LOW fat fat fat Which way will fat move? inside cell fat fat fat LOW HIGH fat outside cell fat fat fat fat fat fat fat
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Inside & Outside of the Cell
Now what happens in a cell? Molecules Diffuse Into the Cell Higher Concentration Outside the Cell Equal Concentration Inside & Outside of the Cell
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Did you get it?? You and your friends decide to go see the movie IT. During the movie, because you were so scared you ate an entire container of salty, salty popcorn. You came out of the movie theater, scared and SUPER thirsty… what happened to your cells? HINT: What happened to our carrot? Partner A: Explain what you think and why. Partner B no talking… only listening!!!! Partner B in ONE MINUTE: Paraphrases (NOT repeats) Partner A’s answer Tells what they agree with Tells what they disagree with Tells their idea.
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More on Diffusion Concentration Gradient: The relative density of one chemical substance versus/compared to another Factors that affect diffusion: Steepness of concentration gradient Temperature Charge of molecule Diameter of diffusing molecule
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Facilitated Diffusion
Molecules moving from HIGH concentration to LOW concentration through a channel protein NO ENERGY sugar sugar sugar inside cell sugar LOW Which way will sugar move? HIGH outside cell sugar sugar sugar sugar sugar sugar sugar sugar sugar
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FACILITATED DIFFUSION
Helps move molecules like sucrose, glucose, and starch across lipid bilayer, without using energy using carrier proteins High to Low concentration The protein changes shape to allow the molecule to move through the lipid bilayer Back to animation- facilitated diffusion
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Simple vs. facilitated diffusion NO ENERGY REQUIRED!
simple diffusion (#1) facilitated diffusion (#4) lipid inside cell outside cell inside cell outside cell sugar protein channel sugar
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Osmosis Osmosis is the movement of water across a membrane from an area of high concentration to an area of low concentration until is reaches equilibrium This is specific to WATER molecules!! Back to animation- Osmosis
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Solute, Solvent, & Solution
What is a… Solute: Substance dissolved in the solution Solvent: substance in which the solute is dissolved Solution: Mixture in which one or two substances/solutes are uniformly distributed in another substance EXAMPLES: Salt Water: Salt = solute and Water = solvent Sugar Water: Sugar = solute and Water = solvent When we deal with OSMOSIS we are dealing with WATER and how it moves!!!
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Sally Seashell with a science twist
Sally Science sat stirring her solute salt into the solvent and saw a solution
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Osmosis In real cells (Animal & Plants)
Hypertonic: high conc. of solute molecules with a low conc. of water Hypotonic: low conc. of solute molecules with a high conc. of water Isotonic: equal conc. of water and solutes Shrink Swell
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Applying “solute” to Osmosis
I’m shrinking, I’m shrinking! Why? KABOOM! Low Water Concentration High Water Concentration Which cell is in a hypertonic solution (a or b)? Cell a is in a Hypertonic Solution, therefore it is Hypotonic High Water Concentration Low Water Concentration REMEMBER Water moves from an area of HIGH concentration to LOW concentrations
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Equilibrium A state during which there are equal concentrations of molecules on either side of a membrane or throughout a space.
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Did you get it?? You don’t drink ANY water while running during your cross-country practice and at the end of your work out collapse with dehydration. You are taken to the hospital and when you get there they accidently give you an IV of pure distilled water. Predict what you think will happen to your cells when they give you this IV. Hyper tonic or hypotonic? HINT: What happened to our carrot? Partner B: Explain what you think and why. Partner B no talking… only listening!!!! Partner A in ONE MINUTE: Paraphrases (NOT repeats) Partner B’s answer Tells what they agree with Tells what they disagree with Tells their idea.
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In which direction will the water diffuse?
60 % Sugar, 40% Water 40 % Sugar, 60% Water Remember…Water moves from a hypotonic to hypertonic solution Semi permeable membrane
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Time to apply this knowledge!!
PASSIVE TRANSPORT White board practice Paper simulation
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Active Transport ENERGY required!
Endocytosis Cotransport Ion Pumps (energy) = ATP
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Active transport Cells may need molecules to move against their concentration “hill” need to pump “uphill” from LOW to HIGH using energy protein pump requires energy ATP Which organelle makes ATP? Mitochondria Plants have nitrate & phosphate pumps in their roots. Why? Nitrate for amino acids Phosphate for DNA & membranes Not coincidentally these are the main constituents of fertilizer. ATP
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ENDOCYTOSIS Vesicle forms 2 types Pinocytosis: liquid
Ingestion of BIG molecules Vesicle forms 2 types Pinocytosis: liquid Phagocytosis: food
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EXOCYTOSIS Release of contents from inside the cell to the outside
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Review ACTIVE TRANSPORT
Requires energy to move molecules Moving molecules from an area of lower concentration to a higher concentration (EXACT opposite of diffusion/osmosis) Molecules move AGAINST their concentration gradient Help from the Carrier Proteins Carrier proteins assist BOTH in Active and Passive transport In active transport the carrier proteins are called “pumps”
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Compare & Contrast Passive Vs. Active Transport
Both use Carrier Proteins Passive: HigherLower Active: Lower Higher (with ATP)
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AMOEBA SISTERS Let’s watch and learn!!!
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