Regents Biology Cell Membranes & Movement Across Them

Regents Biology Cell (plasma) membrane  Cells need an inside & an outside…  separate cell from its environment  cell membrane is the boundary IN food - sugars - proteins - fats salts O2O2 H2OH2O OUT waste - ammonia - salts - CO 2 - H 2 O products (secretions) - proteins cell needs materials in & products or waste out

Regents Biology Building a membrane  How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? What substance do you know that doesn’t mix with water?  FATS   LIPIDS  Remember: oil & water don’t mix!!

Regents Biology Lipids of cell membrane  Membrane is made of special kind of lipid  phospholipids  “split personality”  Membrane is a double layer  phospholipid bilayer inside cell (cytoplasm – mostly water) outside cell (watery environment-humans have blood) lipid “repelled by water” “attracted to water” phosphate

Regents Biology Semi-permeable membrane  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 aa H2OH2O sugar lipidssalt waste So what needs to get across the membrane? O2O2 substances that are small

Regents Biology Crossing the cell membrane  What molecules can get through the cell membrane directly?  fats and oils can pass directly through inside cell outside cell lipid salt aa H2OH2O sugar waste but… what about other stuff?

Regents Biology Cell membrane channels  Need to make “doors” through membrane  protein channels allow substances in & out  specific (based on shape) channels allow specific material in & out  H 2 O channel, salt channel, sugar channel, etc. inside cell outside cell sugaraa H2OH2O salt waste

Regents Biology How do you build a semi-permeable cell membrane?  Channels are made of proteins  proteins both “like” water & “like” lipids bi-lipid membrane protein channels in bi-lipid membrane

Regents Biology Passive Transport – NO ENERGY required  Diffusion  move from HIGH to LOW concentration Dynamic – molecules still moving

Regents Biology Simple Diffusion  Move from HIGH to LOW concentration  passive transport  no energy needed diffusionosmosis diffusion of water Cell cannot control “FREE”

Regents Biology Facilitated Diffusion  Move from HIGH to LOW through a channel inside cell outside cell sugar Which way will sugar move? sugar LOW HIGH

Regents Biology Passive Transport  Move from HIGH to LOW concentration 1. directly through membrane  simple diffusion  no energy needed 2. help through a protein channel  facilitated diffusion (with help)  no energy needed HIGH LOW Like going downhill 3.Osmosis – water  no energy needed

Regents Biology Active transport  Cells may need molecules to move against concentration “hill”  need to pump “uphill”  from LOW to HIGH using energy  protein pump  requires energy  ATP ATP NO equilibrium at the end

Regents Biology Active Transport – moving large particles in and out of the cell  Endocytosis – moving into the cell – example - (white blood cells engulfing bacteria in a vesicle)  m/watch?v=1w10R9lv7 eQ&feature=related m/watch?v=1w10R9lv7 eQ&feature=related  Exocytosis – moving out of the cell – example (secretions – remember pathway of proteins???)

Regents Biology Transport summary simple diffusion facilitated diffusion active transport ATP osmosis 1.Large particles 2.Endocytosis 3.Exocytosis 4.Protein pumps

Regents Biology Osmosis  Water is very important, so we talk about water separately  Osmosis  diffusion of water from HIGH concentration of water to LOW concentration of water  across a semi-permeable membrane Dots = solute (salt or glucose)

Regents Biology Maintaining water balance - homeostasis  Cell survival depends on balancing water uptake & water loss freshwater balancedsaltwater hypotonic isotonic hypertonic Cell swells Animal cells can burst – NO cell wall Water in = water out Water in > water out Water in < water out Cell wilts Cell membrane pulls away from cell wall

Regents Biology Keeping right amount of water in cell  Freshwater  a cell in fresh water  high concentration of water around cell  cell gains water  example: Paramecium  problem: cells gain water, swell & can burst  water continually enters Paramecium cell  solution: contractile vacuole  pumps water out of cell freshwater No problem, here KABOOM! * Need ATP *

Regents Biology Controlling water  Contractile vacuole in Paramecium FULL EMPTY Acts as a “pump”

Regents Biology Keeping right amount of water in cell  Saltwater  a cell in salt water  low concentration of water around cell  cell loses water  example: shellfish  problem: cell loses water  in plants: plasmolysis  in animals: shrinking cell  solution: take up water saltwater I will survive! I’m shrinking, I’m shrinking! wilting

Regents Biology Red Blood Cells  5E7BijQ&feature=related

Regents Biology Keeping right amount of water in cell  Balanced conditions  no difference in concentration of water between cell & environment  cell in equilibrium  example: blood  problem: none  water flows across membrane equally, in both directions  volume of cell doesn’t change balanced I could be better… That’s better! Water in = Water out

Regents Biology Cellular Communication  Cells communicate by sending chemical signals  Usually proteins – h_________, e________, n_______________, or ions

Regents Biology Target Cell  The cell or tissue meant to get the signal

Regents Biology Cells communicate by:  1. Direct contact  2. Chemical signals

Regents Biology There are also signals from the environment  Come from outside the organism –  Ex: t_______, length of _______, and l________

Regents Biology Too much information???  Receptor proteins with specific shaped binding sites make sure cell get the right information

Regents Biology Remember…  Proteins are made of ______________  The order of the amino acids give the protein a __________________  The shape of the protein determines the _____________  Shape and function are _____________