REVISED Cell membrane powerpoint diffusion and osmosis revisedPresentation Transcript
Cell Boundaries Chapter 6
What are boundaries? We have borders surrounding countries We have boundaries on a playing field Why are borders important?
What are the borders of a cell? Cell membrane Thin, flexible barrier Cell wall Plant, algae, fungi, prokaryotes Strong supporting layer
Cell Membrane What does it do for cell? Controls what goes in and out Regulates molecules moving from one liquid side of the cell to the other liquid side of the cell Protects Supports
Cell Membrane Lipid bilayer What are lipids? What does bi- mean? What’s a layer? A cell membrane is made of two layers of lipid molecules
Cell membrane Phospholipids bilayer Made of a negatively charged phosphate “head” PO43- Attracts water because the phosphate is charged (-) Water is a polar , slightly positive ends and slightly negative ends Attached to the phosphate group are 2 fatty acid chains Hydrophobic= don’t like water So the inside of the cell membrane doesn’t let water in but the outside allows cells to be dissolved in aqueous environments
Other things in the membrane… Proteins embedded in lipid bilayer Carbohydrates attached to proteins So many different molecules in membrane, we call it a “mosaic” of different molecules
Proteins Proteins help things get across membrane Kinda like a pump
Carbohydrates… Chemical identification cards “ID” card of cell Helps individual cells id each other
Cell Walls Outside cell membrane (does NOT replace membrane!!!) Plants, algae, fungi, prokaryotes Have pores to allow things in Function: SUPPORT and PROTECT
Cell walls made of… Protein and carbs Plant cell walls made up of CELLULOSE This is a tough carbohydrate Wood and paper
A biological membrane Cells exist in liquid environments Things need to get in and out of cell Different ways to do this…. The Cell Membrane
Concentration (conc.) Solution Mix of 2 or more substances Solutes Substance dissolved in solution Concentration Molarity (M) is # of Moles of a substance per liter of solution 6.02 x 1023 “small things” (molecules, atoms, ions, electrons, ions, etc) Moles is a unit for measuring EXTREMELY small things is mass of SOLUTE in a given volume of solution (g/L) What is the concentration of 12 grams of salt dissolved in 3 liters of water? 12g/3L= 4g/L
Diffusion Particles constantly move Collide randomly Spread out randomly Diffusion is moving from area of HIGH conc. to area of LOW conc. This is what we call the CONCENTRATION GRADIENT
Equilibrium When the conc. Of a system is the same throughout (same conc. on both sides)
What happens when we reach equilibrium? Particles continue moving across membrane but in both directions!***No more changes in concentration
If things can cross a membrane we call the membrane PERMEABLE If things canNOT cross a membrane we call the membrane IMPERMEABLE
What’s this have to do with cells? Cell have liquid inside and are found in liquid environment We have substances (solutes) inside and outside cell Unequal concentrations means we get DIFFUSION!!! B/c diffusion depends on random particle movements, substances diffuse across membranes without requiring the cell to use energy
What diffuses across the membrane??? Small, uncharged (non-polar) molecules Examples: Carbon dioxide Oxygen
Cells are always trying to Maintain Equilibrium by… PASSIVE Transport Requires NO energy Goes with Conc. Gradient 3 types: SIMPLE DIFFUSION- No protein required Small, uncharged particles FACILITATED DIFFUSION- CHANNEL or CARRIER proteins Trans-membrane protein channel Protein with a specific shape; open-close mechanism Ex. Osmosis and ligand-gated channels ACTIVE Transport REQUIRES Energy Goes Against Conc. Gradient ACTIVE TRANSPORT Involves “transporter” membrane protein and ENERGY (ATP)
Osmosis Water (H2O) can pass easily through most biological membranes Def: Diffusion of Water through a semi-permeable membrane Small molecules of water can sometimes diffuse across easily (no protein needed) AQUAPORIN: What does “aqua” mean??? Protein in cell membrane that allows water through (speeds up diffusion of water across the membrane) Type of Facilitated diffusion (more on this later)
How Osmosis works… We have water molecules and some other molecules, let’s say sugar If we have more water on one side of the membrane (HIGH conc. of H2O), then the water will diffuse across… Membrane will let water thru but not sugar Water can move back and forth (not sugar)
Water moves from areas of HIGH conc. To areas of LOW conc. Water moves across till equilibrium is reached Isotonic: when conc. Of both solutions is equal Hypertonic: “above strength” When we begin with more sugar in water More concentrated sugar solution on side A Hypotonic: “below strength” When we end with less sugar Dilute sugar solution on side A
Osmotic Pressure Central vacuole fills with water and exerts and out ward pressure on cell membrane and cell wall Cell wall does NOT allow cell to expand past a certain size Osmoregulation
means by which cells keep the concentration of cell cytoplasm or blood at a suitable concentration.
Problems in Plant Cell
Osmotic Pressure Pressure exerted by osmosis on the HYPERTONIC side of a semi-permeable membrane Think about blowing up a balloon… Can cause serious problems for cell Cell is full of sugar, salts, proteins, molecules Inside of cell is Hypertonic Osmotic pressure should make fresh water go…? In or Out? In Cell will become inflated/swollen Too much cell will burst like a balloon
Why don’t all our cells burst? What are our cells (animal) contained in? Fresh water? No…..blood or other fluids, which are ISOTONIC The conc. Of sugars, salts, proteins and molecules in these fluids is the same as the conc. in the cell Bacteria and plant cells They DO come in contact with fresh water…what do they have PROTECTING them? CELL WALL Prevent cells from expanding even when there’s a lot of osmotic pressure But, cell walls are prone to injuries when there is too much osmotic pressure
Which is a RBC in isotonic solution? RBC in hypertonic solution? RBC in hypotonic solution?
How do big molecules diffuse across a membrane so quickly if the membrane is selectively permeable?
Problems for diffusion… Things too large (like Glucose!) Charged molecules and Polar molecules Positive/negative Opposites attract but likes do not… These all present serious problems for things getting across membranes…
Facilitated Diffusion What does facilitate mean? Proteins are the extra help “escorts” across the membrane We call these protein channels… Allow specific things thru
takes place through proteins, or assemblies of proteins, embedded in the plasma membrane
Facilitated Diffusion (continued) FAST SPECIFIC Still diffusion so we only see it from high concentration to low Does NOT require energy
What about when we want to go against the concentration? (From low concentration to high?)
What do we need??? ENERGY!!!!
ACTIVE transport Process that moves molecules against the concentration gradient Requires ENERGY A protein pumps small molecules and ions across a cell membrane against the conc. Gradient Direct and Indirect Active transport (see animation) Direct: every 3 Na+ ions pumped across for every 2 K+ ions Indirect: Build up of ions on one side opens up another channel to shuttle in other molecules Electrochemical gradient membrane potential (cell membrane is negative) To pump large molecules and clumps… 2 other processes: Exocytosis Endocytosis The can change shape of membrane
Types of Active transport Molecular Transport (Direct and Indirect) When small ions and molecules are carried across membrane Endocytosis Endo- means…. -Cyto- means… -sis mean…. Exocytosis Exo- means…. -Cyto- means… -sis mean….
Molecular Transport Proteins are used to pump small molecules and ions across membrane even against the conc. Gradient The cell devotes a lot of ENERGY to pumping things across membrane Potassium, calcium, and sodium are some things that need to pumped across
Build up of Na+ ions on one side of membrane from Na+/K+ pump Now Na+ will flow thru another channel that allows one glucose in too! Pretty convenient!
Endocytosis When cells need to take in large material Process of taking material into the cell by process of infolding, or pockets, of the cell membrane Pocket breaks loose from cell membrane and forms a vacuole or vesicle inside the cell Two Types… Phagocytosis Pinocytosis
Two types of endocytosis: 1. Phagocytosis “cell eating” Extensions of cytoplasm surround the particle and package it within a food vacuole Cell then engulfs the package Amoebas 2. Pinocytosis “cell drinking” When cell needs to take up liquid Tiny pockets in cell membrane form Fill with liquid Then pinch off to form vacuoles inside of cell
Exocytosis Exo- means… Cyto means… Sis means… When cell releases large amounts of material Excretes stuff Membrane of vacuole surrounding particle inside cell fuses with the cell membrane The contents in vacuole are then forced out of the cell We see this in removal of water by contractile vacuoles