Presentation on theme: "I. MEMBRANE STRUCTURE AND FUNCTION"— Presentation transcript:
1 I. MEMBRANE STRUCTURE AND FUNCTION Chapter 7I. MEMBRANE STRUCTURE AND FUNCTIONA. Membranes organize the chemical activities of cells by allowing things in and out1. The plasma membrane exhibits selective permeability--screenB. Phospholipids1. Form a bilayer in water.a. Why they are selectively permeable.b. Nonpolar moleculesc. Polar molecules2. Amphipathic moleculea. the head (glycerol and phosphate) is polaror hydrophilic.b. the tail (the fatty acids) are nonpolaror hydrophobicC. Read about how Fluid mosaic model was developed (pg. 126)
2 C. The fluid mosaic model. 1. Mosaic… 2. Fluid… a. Refers to the way the lipids and proteins behave in a membrane.b. Molecules are not bonded together, so are free to shift.c. Must remain "fluid" for membranes to function.3. Some proteins are attached to the cytoskeleton and fibers in the extracellular matrix.4. Most of the phospholipids have kinked tails…5. Also contains cholesterol…a. keeps the membrane from solidifyingb. keeps the membrane from being total liquid6. Glycoproteins…protein with attached sugar on outside ofmembrane.Glycolipid…lipid with attached sugar on outside of membrane.FibronectinCollagenIntegrin
3 Ways to keep membrane fluid Hibernation animals increase cholesterol production
4 D. Proteins give the membrane function 1. Made in the rough ER2. Functions of proteins in the membranesa. Transportb. Enzymatic activityc. Signal Transduction (Receptor sites for signals)d. Intercellular Joininge. Cell-cell recognitionf. Attachment to cytoskeleton and extracellular matrix3. Types of membrane proteinsa. Integral - inserted into the lipid bilayer.b. Peripheral - not embedded in the lipid bilayer, but are attached to the membrane surface.How do the integral proteins stick to the membrane?
5 D. Proteins give the membrane function 1. Made in the rough ER2. Functions of proteins in the membranesa. Transportb. Enzymatic activityc. Signal Transduction (Receptor sites for signals)d. Intercellular Joininge. Cell-cell recognitionf. Attachment to cytoskeleton and extracellular matrix3. Types of membrane proteinsa. Integral - inserted into the lipid bilayer.b. Peripheral - not embedded in the lipid bilayer, but are attached to the membrane surface.How do the integral proteins stick to the membrane?By the solubility of their amino acids.
7 1. The lipid composition of the two layers is different. E. Membranes are Bifacial (meaning, there is an inside and outside face)1. The lipid composition of the two layers is different.2. The proteins have specific orientations3. Carbohydrates are found only on the outer surfacea. Branched oligosaccharides form glycolipids and glycoproteins on external surface.b. Function - recognition of "self" vs "other”.Question: On which side of a vesicle membrane are the carbohydrates?
8 Question: How do materials get across a membrane Answer:First, there are two problems.1. The lipid bilayer is hydrophobic. Hydrophilic materials don’t cross easily.2. Large molecules don’t cross easily. Too big to get through membrane.So…. There are two mechanisms1. Passive transport (diffusion, osmosis, facilitated diffusion)2. Active transport (carrier mediated, endocytosis, exocytosis)
9 F. Transport proteins1. Hydrophilic substances can avoid contact with the lipid bilayer by passing through these proteins.2. “Channel Proteins”a. Aquaporins3. “Carrier Proteins”4. These proteins are specific in what they transport.a. glucose carrier protein is so specific that fructose can’t even flow through.5. What determines the direction substances flow?
10 G. Diffusion: passive transport across a membrane 1. Definitiona. lungsb. water2. Passive transport3. Concentration gradient…a. 2 or more substances move independently of each other.b. Solute/Solventc. Concentration4. Equilibrium
12 5. Factors that Effect Diffusion a. Concentrationb. Temperaturec. Particle sized. Mixing
13 H. Osmosis: passive transport of water 1. Definition2. Tonicity: the ability of a solution to cause a cell to gain or lose watera. Hypertonicb. Hypotonicc. Isotonic
14 GFP labeled Aquaporins a. newly found channels for osmosisGFP labeled Aquaporins
15 I. Osmoregulation1. Definition2. Animal cell versus Plant cell (why different?)a. Flaccidb. Turgidc. shriveled and death
16 J. Facilitated Diffusion (carrier proteins and channel proteins) 1. Two types of channel proteinsa. open hydrophilic channelsb. gated channels (ion channels)2. If protein not present…3. Passive transport4. Rate of diffusion
18 2. Against the concentration gradient. K. Active Transport1. Definition2. Against the concentration gradient.3. Steps: (see picture)4. Examples:a. Na+- K+ pumpb. Electrogenic or H pumps (CR & Ps)c. Cotransport Movement of H+ that allows other materials to be transported into the cell as the H+ diffuses back across the cell membrane.Example - Sucrose transport
21 CotransportA “pump” that is powered by ATP builds up a concentration gradient that is then used by another carrier protein to transport something else. The energy for the second transport is from the flow of the first substance down its concentration gradient.
22 L. Exocytosis and Endocytosis 1. Exo means outside2. Kytos means cell3. Exocytosis4. Endo means inside5. EndocytosisThree types:a. Phagocytosisb. Pinocytosisc. Receptor-mediated endocytosis
24 M. Bad membranes can cause more cholesterol to be in blood. 1. Our liver removes excess cholesterol from our blood.a. receptor-mediated endocytosis2. People with high cholesterol either do not have receptors or have low amounts of protein receptors on the membrane of liver cells.