Lesson 2 - The Great Divide - BIOL 1441 PDF

Lesson 2: The Great Divide (and How to Cross It) BIOL 1441 Cell & Molecular Biology  Learning Objectives (a.k.a. Study Guide) By the end of this lesson, students will be to determine whether or not it cou...

Lesson 2: The Great Divide (and How to Cross It) BIOL 1441 Cell & Molecular Biology  Learning Objectives (a.k.a. Study Guide) By the end of this lesson, students will be to determine whether or not it could diffuse across able to: the membrane. 1. Explain the fundamentals of atomic structures and 7. Explain what a concentration gradient is. define a bond. 8. Use the direction of a concentration gradient to 2. Explain the main function of a cell’s plasma determine which way a molecule would move (into membrane. or out of a cell). 3. Describe the functions of phospholipids & 9. Explain how passive transport is different from transport proteins in the plasma membrane. active transport. 4. Identify the hydrophobic & hydrophilic regions of 10.Explain why active transport is important to a cell. the phospholipid bilayer. 11.Identify similarities & differences between these 5. List the kinds of molecules that can & cannot transport processes: diffusion, facilitated diffusion, diffuse across the membrane. osmosis, primary active transport, secondary active 6. Use the chemical properties of a molecule transport. (hydrophobic, hydrophilic, polar, nonpolar, charged)  How do your cells get the The glucose in glucose in the donut enters your your food? bloodstream. You eat a donut. The plasma Your cells use a transport membrane won’t let protein (i.e. the car), powered glucose diffuse into by the concentration gradient the cell. (It’s polar, of Na+ (i.e. the car's gas) to large, & there’s move glucose (i.e. the piggy already A LOT inside!) bank) into your cells.  First- a brief review of atoms and chemical bonds An atom is a particle of matter that consists of a nucleus that is surrounded by one or more negatively charged electrons. A chemical bond is a lasting attraction between atoms or ions that enables the formation of molecules. There are different types of bonds (some are stronger than others). When the bonds break, energy is released. When new bonds are formed, energy is absorbed and stored in the bond.  Stop & Think It Through! We will be talking quite a bit about ATP in this course. Which of the following molecules would have more energy (left or right)? Which molecule (left or right) has more chemical bonds? What would be required for the reverse reaction to occur? Side note- one line is a chemical bond, two is a double-bond! Side note- each “point” or “corner” is a carbon atom!  Cells & the Plasma Membrane The human body is made of 30 trillion cells Every cell has a plasma membrane Function: dividing the inside of a cell from its environment Cytosol (a.k.a. intracellular fluid) is found inside the cell Extracellular fluid is found in the environment The plasma membrane is selectively permeable Definition: only certain molecules can pass straight through it The membrane’s selective permeability is based on its structure  The Phospholipid Bilayer Head Fatty acid The plasma membrane (a.k.a. the phospholipid bilayer) is tails made of two rows of phospholipids Each phospholipid has a head group & two fatty acid tails The head group is hydrophilic → “water loving” The fatty acid tails are hydrophobic → “water fearing” By grouping the fatty acid tails together in the middle of the membrane, a hydrophobic barrier is created between the inside & outside of the cell This barrier means water & water-loving molecules CANNOT easily move back & forth through the membrane  Polarity electron chemical bond Water is made of 2 hydrogens (H) & 1 oxygen (O) electron To build water, the H's and O's share electrons with each other Electrons are small particles with a negative charge electron When electrons are shared, a chemical bond is formed In water's chemical bonds, electrons are NOT shared equally Oxygen "gets" them more often, so it is slightly negative The hydrogens "get" them less often, so they are slightly positive *Electrons spend more time here* Because it has areas of partial positive & partial O negative charge, water is considered a polar molecule H Anything else with these partial charges (glucose, H insulin, and ATP) is also considered polar  Let's Draw It! On the image, label these regions of the plasma membrane: ❑The hydrophilic regions ❑The hydrophobic regions Then, label the locations where water would be found. Based on your picture, which parts of phospholipids are touching water? The hydrophilic parts The hydrophobic parts  Selective Permeability Only molecules that “match” the chemical properties of the fatty acid tails can diffuse across the membrane Things that do “match” Hydrophobic molecules, like steroid hormones Gases, which are nonpolar Steroid Nonpolar molecules share their electrons equally hormones Nonpolar molecules have NO positive or negative regions Polar molecules don’t match, but some can diffuse through the membrane Polar molecules have partial positive & partial negative regions Small polar molecules can squeeze between the fatty acid tails, but NOT large ones  Transport Proteins For most things that don't "match" the fatty acid tails, a transport protein is required to move in or out Examples of things that require transport proteins: Glucose, a cell’s “favorite food” Glucose is polar and too large to sneak between the fatty acid tails Amino acids, the monomers of proteins Amino acids are too large to squeeze between fatty acid tails Ions, which are fully positive or fully negative Having an extra electron makes one ion negative Having one less electron makes the other ion positive  Summary of Membrane Permeability Blue arrows show molecules Black arrows can diffuse show that a straight across transport protein the plasma is required to membrane. move the molecule across the plasma membrane.  Stop & Think It Through! Which of these molecules could diffuse straight through the plasma membrane of your cells? *More than one may be correct!* A. Aspartic acid, a negatively-charged amino acid B. Carbon dioxide, a hydrophobic gas C. Chloride, a negatively-charged ion D. Propofol, a nonpolar anesthesia medication E. Sucrose, a hydrophilic molecule F. Tetracycline, a large polar antibiotic  Types of Passive Transport Diffusion (a.k.a. simple diffusion): Passive transport is any kind of molecules travel straight through the movement across the plasma membrane plasma membrane that does Hydrophobic & nonpolar molecules cross the membrane via diffusion NOT require energy. Facilitated diffusion: molecules use transport proteins to travel through Passive transport includes: the plasma membrane (Simple) diffusion Hydrophilic, polar, & large molecules cross the membrane via facilitated diffusion Facilitated diffusion Osmosis Osmosis: water travels through the plasma membrane  Types of Passive Transport Channel proteins are open on both sides Carrier proteins change their shape to of the membrane at the same time. move things across the membrane. Channel Carrier protein protein (Simple) Diffusion Facilitated Diffusion Osmosis In osmosis, water uses In (simple) diffusion, molecules In facilitated diffusion, molecules use a transport protein to move straight across the a transport protein to move across move across the plasma membrane. the plasma membrane. plasma membrane.  Stop & Think It Through! Which specific transport process would each of these molecules use to move across the plasma membrane? (Simple) diffusion Facilitated diffusion Osmosis A. Aspartic acid, a negatively-charged amino acid B. Carbon dioxide, a hydrophobic gas C. Chloride, a negatively-charged ion D. Propofol, a nonpolar anesthesia medication E. Water, a hydrophilic molecule F. Tetracycline, a large polar antibiotic  Concentrations The fluids of the body are solutions Higher Lower Definition: liquids with dissolved things in them concentration concentration The liquid part of a solution is called the solvent In the body, the solvent is water The dissolved things in a solution are called the solutes The concentration of a solution represents the number of solutes dissolved in it Solutions with a high concentration have A LOT of solutes (dissolved things) Many solutes Fewer solutes (dissolved things) (dissolved things) Solutions with a low concentration have A FEW solutes (dissolved things)  Concentration Gradients & Movement When two solutions have different concentrations, there is a concentration gradient (difference) between them Molecules naturally move DOWN (a.k.a. with) their concentration gradient Meaning: they move out of a solution with a high concentration and into a solution with a low concentration Moving DOWN a concentration gradient Semipermeable membrane (from high to low) does NOT require energy Movement of solutes When solutes (dissolved things) move DOWN their concentration gradient, this is known as (simple) diffusion or facilitated diffusion High solute Low solute Equal solute co These are passive transport processes concentration concentration ncentrations  Concentration Gradients & Movement Water can also move down its concentration gradient Meaning: water moves from where High Water Low Water there is A LOT of water to where there is Concentration Concentration a little water This movement is called osmosis High Low water co Equal water co water concen ncentration ncentrations tration To determine the concentration Semipermeable membrane Movement of water gradient of water, consider this: A solution with A LOT of water has a little solute (a low solute concentration) A solution with a little water has A LOT of solute (a high solute concentration) Low solute High solute Hint: remember “water follows solute” concentration concentration Equal solute c oncentrations  Osmosis & The Human Body The level of water in your body is constantly changing Things like eating & drinking increase water levels in the body Things like sweating, defecating, & urinating decrease water levels in the body With changing water levels, the concentrations of your body fluids also change Low water levels leads to increased fluid concentrations High water levels leads to decreased fluid concentrations Water constantly moves into & out of your cells based on the concentration gradient between your cytosol & other body fluids  Osmosis on a Cellular Level #2 #1 LOTS of salt With increased water inside the cell When you drink outside a cell, the salt water, the salt concentration of the concentration of the fluids outside your cytosol appears cells decreases. higher... Low salt Higher Less salt concentration means salt concentration outside the cell higher water means lower water concentration. concentration. #3 When water enters the cell, it is moving from a region of HIGH water concentration to a region of low water concentration.  -tonic Words Hypertonic solution Cytosol When comparing the concentration of a fluid to the concentration of cytosol, -tonic words can be used A hypertonic solution has a HIGHER concentration of solutes than cytosol Isotonic This means it has a LOWER concentration of water solution Cytosol An isotonic solution has THE SAME concentration of solutes as cytosol This means it has the same concentration as water Hypotonic solution A hypotonic solution has a LOWER concentration of Cytosol solutes than cytosol This means it has a HIGHER concentration of water  Osmosis in Action In "normal" conditions, the fluid When you are dehydrated, When you drink a lot of outside your cells is isotonic to the fluid outside your cells water, the fluid outside your cytosol can become hypertonic to cells can become cytosol. hypotonic to cytosol. This means there is the same amount of water inside & outside your cells, This means there is more water This means there is more so water enters & leaves your cells at INSIDE your cells than outside your water OUTSIDE your the same rate in isotonic solutions cells than inside our cells, cells, so water leaves your cells. so water enters your cells.  Passive Transport: A Review Passive transport does NOT require energy It moves molecules (solutes or solvents) from areas of HIGH concentration to areas of low concentration Types of passive transport Diffusion: molecules move directly across the plasma membrane Facilitated diffusion: molecules use a transport protein to move across the plasma membrane Osmosis: water moves across the membrane High Water Low Water Concentration Concentration Remember: passive transport can only move molecules DOWN (a.k.a. with) their concentration gradient!  Active Transport Sometimes a cell needs to move a Two kinds of energy can be used in molecule UP (a.k.a. against) its active transport : concentration gradient #1: ATP Example: concentrating a molecule inside the cell ATP stores energy in its chemical bonds When a cell does this, it's moving that molecule from where there is a little to Break ATP's bonds & energy is where there is already A LOT released This movement requires energy #2: A concentration gradient As one molecule moves down its concentration gradient, that movement pushes a different molecule up its own gradient  Primary Active Transport In primary active transport, ATP is the energy source for the movement UP (a.k.a. against) a concentration gradient Example: the sodium-potassium pump Sodium (Na+) is pumped out of the cell, where there is already A LOT Potassium (K+) is pumped into the cell, where there is already A LOT Why use ATP to do this? The sodium-potassium pump polarizes the cell membrane This means the charges inside & outside are different A polarized membrane allows cells to perform complex tasks (like neuron signaling & muscle contraction)  Secondary Active Transport In secondary active transport, movement down LOTS of Na+ outside one concentration gradient is used to power Little glucose outside movement up a different concentration gradient Outside the cell Example: the sodium-glucose cotransporter ◦ Sodium (Na+) rushes into the cell, where there is a little ◦ This means Na+ is moving DOWN its concentration gradient ◦ As Na+ enters the cell, glucose “sneaks” into the cell with it, where there is already A LOT ◦ This means glucose is moving UP its concentration gradient Why use energy to do this? ◦ The sodium-glucose cotransporter helps a cell get glucose, its favorite food ◦ While cells already have a lot of glucose inside, they Inside the cell continue to "hoard" as much as they can from Little Na+ inside their environment LOTS of glucose inside  Tying the Processes Together... First: Then: Cells use ATP to Cells use sodium’s pump sodium (Na+) concentration (Na+) out of the gradient to “sneak” cell. glucose into the cell. This creates a strong concentration Glucose is already concentrated inside gradient that favors the cell, so it is Na+ movement back moving UP its into the cell. concentration gradient. Result: the cell builds a stockpile of its "favorite food"  So… how do your The glucose in cells get the the donut enters your glucose in bloodstream. your food? You eat a donut. The plasma So… your cells use a transport membrane won’t let protein (i.e. the car), powered glucose diffuse into by the concentration gradient the cell. (It’s polar, of Na+ (i.e. the car's gas) to large, & there’s move glucose (i.e. the piggy already A LOT inside!) bank) into your cells.  To Prepare for Next Class… ❑ Review your class notes Use the eTextbook & Other Helpful Resources to supplement your lecture notes ❑ Complete the homework assignment and use it to direct your studying ❑ Print the slides for Lesson #3 – Teamwork Makes the Dream Work