What’s wrong with this picture? Cell Membranes What’s wrong with this picture? http://www.studyblue.com/notes/note/n/osmolality-and-osmo-gap/deck/1598495

The Plasma Membrane Lay the phospholipid bilayer with the cytoskeleton facing toward you. We will call this the inside of the cell.

Membranes Cells separate “inside and outside” with lipid barriers called membranes. Organelle membranes separate too. Limits passage of polar substances. Protein channels allow specific passage. BILL: What is the difference between polar and charged? In journal: What is the difference between polar and charged?

What passes freely? Small, uncharged polar molecules Small nonpolar molecules like N2 Model simple diffusion http://www.studyblue.com/notes/note/n/biology-172-lecture-7-flashcards/deck/124266

Cell Walls Are outside the membrane Structural Plant cell walls are made of cellulose Prokaryotes and fungi also have cell walls. Discuss plasmodesmata. Relate to the onion osmosis. http://www.phschool.com/science/biology_place/biocoach/plants/walls.html

Phospholipid Bilayer This represents a phospholipid- The tails are fatty acid, the head, phosphorylated alcohol These form a sheet two molecules thick. Polar head-Hydrophilic-label Nonpolar tail-Hydrophobic-label At your table, combine your macromolecule pieces to model the membrane. Review. http://en.wikipedia.org/wiki/Phospholipid

Why the embedded cholesterol? What might a membrane in an arctic dweller look like? Interaction with the relatively rigid cholesterol decreases the mobility of hydrocarbon tails of phospholipids. But the presence of cholesterol in a phospholipid membrane interferes with close packing of fatty acid tails in the crystal state, and thus inhibits transition to the crystalline state. Phospholipid membranes with a high concentration of cholesterol have a fluidity intermediate between the liquid crystal and crystal states. Increase or decrease fluidity depending on temperature.(Decreases fluidity when warm, increases fluidity when cold…keeps membranes fluid at very cold temperatures) *

Membrane Proteins Function in Transport- Enzyme Surface receptors ID Markers Cell-cell connection Attachment http://www.pc.maricopa.edu/Biology/pfinkenstadt/BIO201/201LessonBuilder/UnitOne/Membrane/index.html

Embedded Proteins Can be hydrophilic with charges and polar side groups or… Hydrophobic, with nonpolar Place your proteins in the membrane. Place your proteins in the membrane. http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect08.htm

Anchoring in the membrane A hydrophobic core What could keep proteins in the membrane? *

Transmembrane Proteins Carriers- change shape Active and passive transport Sodium potassium pump Channels- are tunnels through the hydrophobic core Receptors Transmit information from the outside of the cell Hormone receptors, neurotransmitters.

What needs a channel? Hydrophilic substance like large polar molecules and ions Label the membrane hydrophobic and hydrophilic. Make a hydrophilic. /hydrophobic protein. Discuss evolution and conserved elements. http://www.cipsm.de/en/publications/researchAreaF/2007/index.html

Have you seen shape changes before? Carrier proteins Have you seen shape changes before? Holds ion or molecule Changes shape To move something across the membrane Green ball is one K+ in a potassium pump Campbelll p 125 8th edition.

What might the positively charged region do? Aquaporins Channel Protein Each aquaporin allows 3 billion water molecules per second to pass into the cell single file. Fig 3. Passage of water molecules through the aquaporin AQP1. Because of the positive charge at the center of the channel, positively charged ions such as H3O+, are deflected. This prevents proton leakage through the channel. What might the positively charged region do? http://www.bio.miami.edu/~cmallery/150/memb/water.channels.htm *

Receptor Proteins Example: G protein linked receptor neurotransmitter

Cell Surface Markers Glycoproteins- a carbohydrate combined with a protein. Add a carbohydrate chain to a protein embedded in the membrane. Add and label Important in the self recognition. Recognized by the immune system. Glycolipid- a carbohydrate combined with a lipid . Add a carbohydrate to a lipid. Add and label. Important in tissue recognition. Example is blood group marker.

Cell surface markers Glycocalyx- “Sugar coating” You Me Glycoproteins- “self” recognition The protein/carbohydrate chain shape is different person to person. For example, the major histocompatibility complex proteins are recognized by the immune system. Glycolipids-tissue recognition The lipid/carbohydrate chain shape is specific for a certain tissue. For example blood group markers.

Transport Modes Through the cell membrane Passive - Down the concentration gradient-primary role in importing resources and exporting waste Diffusion Facilitated Diffusion- membrane proteins help charged and polar molecules pass. Osmosis Active- Against the concentration gradient. Energy requiring. Requires membrane proteins. Endocytosis/Exocytosis Na+/K+ Pump Proton Pump

Diffusion Often by Ion Channels Direction of movement determined by Relative concentration Voltage Each channel is specific for one or a few ions Nervous system

Facilitated Diffusion Carrier Proteins Specific also Bind/release Moves things down the concentration gradient Passive transport Can become saturated

Active Transport Uses Energy Moves things against the gradient Na/K Pump Coupled Transport Gradients created by one process can power another

Sodium Potassium Pump Cytoplasmic Na+ binds (high affinity in this shape). Na+ binding stimulates phosphorylation by ATP Phosphorylation causes shape change, lower Na+ affinity, now high K+ affinity. The K+ binding causes phosphate to be released Phosphate release causes shape to return. Now low K+ affinity, Work the pump with model pieces.

Endocytosis and Exocytosis Exocytosis-internal vesicles fuse with the plasma membrane to release large macromolecules out of the cell. Endocytosis-cell takes in macromolecules and particulate matter by forming new vesicles from the plasma membrane. Endocytosis Activity

Bulk Transport Endocytosis Phagocytosis-particulate Pinocytosis-liquid Receptor-Mediated endocytosis Clathrin coated pits bind to specific molecules.

Bulk Transport Exocytosis Neurotransmitter discharge Hormone secretion Digestion enzymes Explain the diagram. http://www.kscience.co.uk/as/module1/pictures/endoexo.jpg

Eukaryotic cells are compartmentalized By Membranes These special areas let things happen by… Minimizing competing interactions Increasing surface area where reactions can occur Compartmentalizing metabolic processes and enzymatic reactions. Examples: Endoplasmic Reticulum, mitochondria, chloroplast, Golgi, nuclear envelope Archaea and Bacteria generally lack internal membranes and organelles.

Protein Pieces