Anderson Spring 2017 College of the Redwoods Cell Membranes Anderson Spring 2017 College of the Redwoods

What did we learn last week? Eukaryotic cells have endomembrane systems (organelles surrounded by membrane) Prokaryotic cells have no organelles or nucleus Membranes are made up of a phospholipid bilayer, with integrated proteins Organelles have specific structure and function Let’s review the organelles!

How to Cells Communicate? Extracellular matrix Space outside of cell that holds cells together to form tissue and allows for communication Intercellular Junctions Direct contact of neighboring cells that exist within tissue

Intercellular Junctions Plants - plasmodesmata Animals Adhesion – “welds” that allow for stretching Tight – watertight seal Gap – channels between cells for transportation

Able to flow and change position but still keep basic integrity Cell Membrane Phospholipid bilayer – hydrophobic and hydrophilic Proteins – many roles Cholesterol – regulates fluidity Carbohydrates – self recognition Able to flow and change position but still keep basic integrity

Membrane Proteins Integral proteins – embedded in membrane Peripheral proteins – on exterior or interior surface

Cholesterol’s Role Cholesterol reduces fluidity at moderate temperatures Keeps membrane from solidifying in low temperatures

Glycoproteins (example) The CD4 receptor (glycoprotein) on white blood cell interacts with HIV – injects genetic material into host cell HIV has binding sites on outer coat, which mimics those found on human cells – fools human cell

Membrane Permeability Selective permeability – membrane allows some substances to enter and leave, but not others ✔ Hydrophobic substances can pass through membrane easily ✔ Small non-polar molecules can pass through (O2, CO2) Polar molecules can’t get through hydrophobic region (except H2O) Large molecules are too big to pass through

Passive Transport Movement of molecules that does NOT require energy Substances move from HIGH to LOW concentration, across a concentration gradient Diffusion - Movement of molecules based on concentration

Rate of Diffusion Concentration gradient Mass of molecule Temperature Larger difference in concentration, the faster the diffusion Slower diffusion when close to equilibrium Mass of molecule Larger molecules move slower – harder to move between molecules their diffusing through Temperature Higher temperatures increase energy and molecule movement, which increases rate of diffusion Solvent density Higher density of solvent, lower diffusion rate

Facilitated Transport Passive transport across concentration gradient Moves substances that wouldn’t diffuse easily or quickly Polar molecules Use integral proteins Channels Carriers

Membrane limits the diffusion of solutes in the water Osmosis Diffusion of WATER (only) across a semipermeable membrane (like a cell membrane) WATER moves from HIGH to LOW concentration Membrane limits the diffusion of solutes in the water

Relation of osmolarity of extracellular vs intercellular fluid Tonicity/Osmolarity Tonicity – amount of solute in solution Osmolarity – measure of solutes in solution (measure of tonicity) Relation of osmolarity of extracellular vs intercellular fluid Hypotonic – extracellular lower solutes vs inside cell – extracellular higher water concentration Hypertonic – extracellular higher solutes vs inside cell – extracellular lower water concentration Isotonic – equal solutes extracellular and inside cell

Tonicity/Osmolarity Plant cells slightly hypertonic to outside so water is always going in

1. 2. Water: 60% Solute: 40% Water: 30% Solute: 70% Water: 20% Hypotonic Hypertonic Hypertonic Hypotonic 3. 4. Water: 90% Solute: 10% Water: 90% Solute: 10% Water: 55% Solute: 45% Water: 60% Solute: 40% WATER WATER Isotonic Hypertonic Isotonic Hypotonic

Active Transport Movement of molecules that requires energy Substances move from LOW to HIGH concentration, against the concentration gradient Movement of large molecules Primary Active Transport – uses ATP Secondary Active Transport – coupled transport

Adenosine Triphosphate

Electrochemical Gradient Most proteins are negatively charged, thus making the inside of a cell electrically negative, extracellular fluid is positive More sodium ions (Na+) outside than inside More potassium ions (K+) inside than outside Na+ will move with concentration and electrical gradient K+ will move with concentration gradient but against electrical gradient

Sodium-Potassium Pump It’s necessary for Na+ concentrations to stay higher outside and K+ higher inside Ions have to be actively transported against gradient, which uses energy Primary active transport – ATP used to move Na+ out and K+ in

Glucose Sodium Transporter Na+ will enter cell with electrochemical gradient Glucose can be transported into cell with Na+, against concentration gradient Secondary active transport – no ATP used, uses energy from electrochemical gradient from primary transport

Endocytosis Active transport that moves large particles into cell though vacuole formation (membrane invagination) Phagocytosis – membrane surrounds particle and pinches off Pinocytosis – membrane surrounds fluid (solutes) and pinches off Receptor-mediated – substance binds to receptor on outside

Exocytosis Process of expelling material from cell Vacuole fuses with cell membrane to expel contents

Have you been paying attention?! Socrative Time Have you been paying attention?!