Cell Membrane Structure and Function Lecture #16 Ms. Day Honors Biology

What is the Cell Membrane? separates living cell from its environment Controls what substances can cross into cell Controls what substances can cross into cell Also called the phospholipid bilayer or plasma membrane

The plasma membrane exhibits selective permeability The plasma membrane exhibits selective permeability. It is semi-permeable. which means it lets only certain things into the cell which means it lets only certain things into the cell Wow… it’s so detailed!

Cellular membranes are made of 2 MAIN components (pieces) Phospholipids (LIPID) Phospholipids (LIPID)  most abundant lipid in membrane  They are amphipathic  have both hydrophobic and hydrophilic regions

Phospholipid Bilayer Phosphate Groups in “head” (- charge) 2 Fatty Acids in “tail” (hydrocarbon) Figure 7.2 Hydrophilichead Hydrophobictail WATER NO WATER

Proteins Membrane movement animation Polar heads love water & dissolve. Non-polar tails “hide” from water. Carbohydrate cell markers Fluid Mosaic Model of the cell membrane

The Fluidity of Membranes Phospholipids in the plasma membrane  Can move within the bilayer Proteins are larger & drift (move) less Figure 7.5 A Lateral movement (~10 7 times per second) Flip-flop (~ once per month) (a) Movement of phospholipids

Another view…

lower temps  lowers lipid movement  lowers fluidity What 2 things help the cell membrane from freezing solid? 1.) some phospholipids need unsaturated fatty acid tails Figure 7.5 B FluidViscous Unsaturated hydrocarbon tails with kinks Saturated hydro- Carbon tails (b) Membrane fluidity Fluidity is enhanced

“cholesterol” - cholesterol in membrane  hinders (stops) solidification 2.) the steroid “cholesterol” stops fatty acid tails from packing together (only in animal cells) - cholesterol in membrane  hinders (stops) solidification **acts as a temp “buffer” (c) Cholesterol within the animal cell membrane Cholesterol

Glycoprotein Carbohydrate Microfilaments of cytoskeleton Cholesterol Peripheral protein Integral protein CYTOPLASMIC SIDE OF MEMBRANE EXTRACELLULAR SIDE OF MEMBRANE Glycolipid Membrane Proteins and Their Functions A membrane A membrane  Includes different proteins in bilayer Fibers of extracellular matrix (ECM ) 2 major types of membrane proteins

1. Integral (transmembrane) proteins  Go through the hydrophobic core of the lipid bilayer  completely span the membrane  Amphipatic EXTRACELLULAR SIDE Figure 7.8 CYTOPLASMIC SIDE Span of 1+ stretches of Nonpolar amino acids Wait…what’s that word for a polar & nonpolar molecule?

2. Peripheral proteins surface Are loosely bound to the surface of the membrane

Why have Carbohydrates on Cell Membrane proteins? Cell-cell recognition  Helps distinguishes one type of cell from another  It’s their “ID” tag

Example:

Chapter 7 Cell Transport Ms. Gaynor AP Biology

Remember…Cell Membranes are FLUID MOSAIC MODELS LET’S REVIEW THE CELL MEMBRANE  Click on “Membranes and Transport” Listen to animation #1 and #2 (8 minutes long)…get ready!!!

Membrane structure LEADS TO selective permeability A cell must exchange materials with its surroundings selectively permeable  a process controlled by the selectively permeable plasma membrane

Cell Transport Means moving things INTO and OUT of the cell Cells need to take in  Food, gases, water  Get rid of waste products ( excretion )  Give out such useful substances as hormones and enzymes ( secretion ).

Permeability and Cell Transport Hydrophobic (non polar) molecules  Are lipid soluble (can dissolve)  can pass through membrane easily Ex: Hydrocarbons, CO 2, O 2 Hydrophilic (Polar) molecules  Are NOT lipid soluble (can’t dissolve) Lipid INsoluble  Do not cross membrane easily Ex: Na +, Cl -, Glucose/ other sugars NOTE: CHARGED molecules need “help” to cross membraneNOTE: CHARGED molecules need “help” to cross membrane

Types of Cellular Transport Passive Transport cell do NOT use energy 1.Diffusion 2.Facilitated Diffusion 3.Osmosis Active Transport cell DOESuse energy 1.Protein Pumps 2.Endocytosis 3.Exocytosis high low This is going to be hard! high low Weee!

Types of Passive Transport Diffusion population ANY Diffusion = tendency for a population of molecules (of ANY substance) to spread out evenly into available space  A “net” movement Ex: Perfume, a fart, tea, food coloring in water

DIFFUSION In absence of other forces…  Molecules move (diffuse) from area of HIGH [ ] to an area of lower [ ] OWN  A.k.a.  Molecules move DOWN its OWN concentration gradient the difference in [ ] of a substance from one area to another No chemical work (ATP energy) is used  diffusion is spontaneous!

Substances diffuse down their OWN concentration gradient Figure 7.11 B (b) Net diffusion Equilibrium

Factors Affecting Diffusion 1. Temperature Higher temperature  more kinetic energy  molecules move faster (Example: Tea) 2. Pressure Higher pressure  molecules move faster

Effects of Osmosis on Water Balance Osmosis water (water diffusion) semipermeable membrane The movement of water (water diffusion) across a semipermeable membrane  Involves the movement of FREE water molecules down a water [ ] gradient High solute  low “free” water [ ] or…. High solute  low “free” water [ ] or…. Low solute  high free water [ ] Low solute  high free water [ ]

Osmosis is affected by the concentration gradient of dissolved substances ( solutes ) OsmosisOsmosis animation

3 Different Types of Solutions Recall: SOLUTION = a uniform mixture of 2 or more substances ** compare solutions OUTSIDE cell to inside cell 1. If a solution is isotonic  [solutes] is the same outside as inside the cell “ iso -” means “same” NO  There will be NO net movement of water

ISOTONIC SOLUTION Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)

hypertonic 2. If a solution is hypertonic  [solutes] is greater outside than inside the cell The cell will lose water and shrivel or wilt  “hyper” means more  (high [solute]) Ex: when salinity increases in lake, fish can die!

HYPERTONIC SOLUTION Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)!

3.hypotonic 3. If a solution is hypotonic  [solutes] is less outside than it is inside the cell The cell will gain water and swell (and maybe lyse or burst)  “ hypo ” means “less” (low [solute])  Think: Hypo- sounds like hippo… hippos are big & round; cells in hypotonic solutions get big & round  Also, think “hypo” is “low” meaning “low” solutes SURROUNDING cell “Hypo” is LOW!!!

HYP0TONIC SOLUTION Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)!

Osmosis Animations for isotonic, hypertonic, and hypotonic solutionsOsmosis

Water Balance of Cells with Walls Cell walls Cell walls  Help maintain water balance Cell walls are in:  Plants  Prokaryotes  Fungi  Some protists

If a plant cell is turgid  It is in a hypotonic environment  It is very firm  A healthy state in most plants If a plant cell is flaccid  It is in an isotonic or hypertonic environment  Cells are limp Plasmolysis = when plasma membrane pulls away from cell wall in hypertonic solutions ; causes cell with walls to wilt & can be lethal.

Water balance in cells with walls Plant cell. Plant cells are turgid (firm) and generally healthiest in a hypotonic environ- ment, where the uptake of water is eventually balanced by the elastic wall pushing back on the cell. (b) H2OH2OH2OH2O H2OH2O H2OH2O Turgid (normal)Flaccid Plasmolyzed Figure 7.13

How Organisms Deal with Osmotic Pressure Bacteria and plants have cell walls that prevent them from over-expanding. In plants the pressure exerted on the cell wall is called tugor pressure. A protist like paramecium has contractile vacuoles that collect water flowing in and pump it out to prevent them from bursting. Salt water fish pump salt out of their specialized gills so they do not dehydrate. Animal cells are bathed in blood. Kidneys keep the blood isotonic by remove excess salt and water.

Types of Passive Transport #1 #1 Passive Transport  DOES NOT require chemical energy (ATP)  Moves DOWN (WITH) [ ] gradient  Kinetic energy drives movement #2 #2 Active Transport  DOES require chemical energy ( A TP)  Moves A GAINST its [ ] gradient 

2 Types of PASSIVE TRANSPORT 1. SIMPLE DIFFUSION **INCLUDES DIFFUSION  Uses NO membrane proteins  GOES DOWN CONCENTRATION GRADIENT (no ATP needed) Molecules move HIGH [ ]  low [ ]  Uncharged & lipid-soluble molecules also pass freely through bilayer. solutes move down a concentration gradient Examples: CO2, O 2… H 2 O WAIT!!! Isn’t water polar?

Aquaporins water is polar but very small  It can pass easily through membrane  uses aquaporins Oh…now I get it! EXTRACELLULAR FLUID AQUAPORIN Channel protein Water CYTOPLASM

2 Types of PASSIVE TRANSPORT. FACILITATED DIFFUSION 2. FACILITATED DIFFUSION needs a little “help” needs a little “help” Uses help of channel or carrier proteins Uses help of channel or carrier proteins  GOES DOWN CONCENTRATION GRADIENT (no ATP needed)  Moves POLAR molecules  can NOT easily pass through HYDROPHOBIC region of membrane. Example: ions, smaller polar molecules (ex: sugar) Example: ions, smaller polar molecules (ex: sugar) Channel/carrier proteins  specific receptor site for substances they “help.” Channel/carrier proteins  specific receptor site for substances they “help.”

Cha nnel proteins -Provide “tu nnel s” Figure 7.15 EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM A channel protein (purple) has a channel through which water molecules or a specific solute can pass. (a) Channel Proteins animationsChannel Proteins

Carrier proteins -Undergo a subtle change in shape “carry” solute across the membrane Carrier protein Solute

2 Types of Passive Transport

Active transport energy Uses energy to move solutes against their [ ] gradients across the cell membrane  EnergyATP  Energy required  usually ATP Carrier proteins Carrier proteins are used… NEVER channel proteins  Ex: sodium-potassium pump

Passive vs. Active Transport Figure 7.17

1. PROTEIN PUMPS Protein Pumps - transport proteins that require energy to do work Examples: Na + /K + Pumps are important in nerve responses Antiports and Symports (Cotransport) H + (proton) pump Sodium Potassium Pumps Sodium Potassium Pumps (Active Transport using proteins) Protein changes conformational shape to move molecules: this requires energy!

Cotransport, Proton Pumps and Sodium/Potassium Pumps… ANIMATIONS hill.com/sites/ /student_view0/ chapter6/animations.html# hill.com/sites/ /student_view0/ chapter6/animations.html# online.com/objects/ViewObject.aspx?ID=a p11203http:// online.com/objects/ViewObject.aspx?ID=a p11203 REVIEW OF ACTIVE TRANSPORT… ANIMATIONS

2. Bulk transport across the plasma membrane exocytosis endocytosis Occurs by exocytosis and endocytosis BOTH MOVE “BIG” AMOUNTS OF STUFF in OR out OF THE CELL BOTH MOVE “BIG” AMOUNTS OF STUFF in OR out OF THE CELL

Exocytosis exocytosis In exocytosis  Transport vesicles move to the plasma membrane, fuse with it, and release their contents  “exo-” means “exit”  Ex: hormone excretion; nerve cells and transmitters; removal of wastes

ER ROUGH ER Glycolipid Vesicle Membrane glycolipid Secreted protein GOLGI APPARATUS

Endocytosis endocytosis In endocytosis  Cell takes in macromolecules by forming new vesicles from the plasma membrane  “endo-” means “enter”

2 types of Endocytosis 1. Phagocytosis “cell eating” Cell engulfs SOLIDS into vesicle & “digests” it 2. Pinocytosis (think “pineapple juice) “cell drinking” Cell engulfs LIQUIDS into vesicle & “digests” it

hill.com/sites/ /student_view0/chapter2/ animation__phagocytosis.html

Endocytosis and Exocytosis Animations hill.com/sites/ /student_view0/ chapter6/animations.html# hill.com/sites/ /student_view0/ chapter6/animations.html#

REVIEW ANIMATIONS  Click on “Membranes and Transport” Listen to animation #3 (7 minutes long) ogy1111/animations/passive3.swf ogy1111/animations/passive3.swf  Excellent Review all Passive (simple/facilitated diffusion) and Active Transport No verbal explanation…you have to read the tutorial!