Bio 117 Ch 5 Membranes 2024 PDF

Bio 117 Ch 5 The reputation of a thousand years may be determined by the conduct of one hour. -- Japanese proverb Membranes Chapter 5  The Big Picture 1. The building blocks of membranes. A. The phospholid bilayer B. “Things” (proteins, etc) stuck thr...

Bio 117 Ch 5 The reputation of a thousand years may be determined by the conduct of one hour. -- Japanese proverb Membranes Chapter 5  The Big Picture 1. The building blocks of membranes. A. The phospholid bilayer B. “Things” (proteins, etc) stuck through and on the phospholipid bilayer! 2. Why the membrane structure is the way it is aka the chemistry makes it so…  Membrane Structure Phospholipids arranged in a bilayer Globular proteins inserted in the lipid bilayer Fluid mosiac model – mosaic of proteins floats in or on the fluid lipid bilayer like boats on a pond Cellular membranes have 4 components 1. Phospholipid bilayer Flexible matrix, barrier to permeability 2. Transmembrane proteins Integral membrane proteins 3. Interior protein network Peripheral membrane proteins 4. Cell surface markers Glycoproteins and glycolipids  1. Phospholipids Structure consists of – Glycerol – a 3-carbon polyalcohol – 2 fatty acids attached to the glycerol Nonpolar and hydrophobic (“water-fearing”) – Phosphate group attached to the glycerol Polar and hydrophilic (“water-loving”) Spontaneously forms a bilayer – Fatty acids are on the inside – Phosphate groups are on both surfaces The social defensive behavior of the muskox (Ovibos moschatus) should remind you of the phospholipid bilayer of cell membranes -- heads out, tails in. Two questions to consider… 1. Phosphate portion is hydrophilic. Why? 2. Lipid portion is hydrophobic. Why?  Hydrophilic Heads What causes the head to be hydrophilic? It is polar. i.e. + ion the N and - ion the O on the right side of the P molecule  Hydrophobic tails What causes the tail to be hydrophobic? – It is non-polar.  Bilayers are fluid Hydrogen bonding of water holds the 2 layers together Individual phospholipids and unanchored proteins can move through the membrane  Environmental Influences Why do saturated fatty acids make the membrane less fluid than unsaturated fatty acids? KINKS! Others?.... Cellular membranes have 4 components 1. Phospholipid bilayer Flexible matrix, barrier to permeability 2. Transmembrane proteins Integral membrane proteins 3. Interior protein network Peripheral membrane proteins 4. Cell surface markers Glycoproteins and glycolipids  Membrane Proteins (some of the “things”) Various functions: 1. Transporters 2. Enzymes 3. Cell-surface receptors 4. Cell-surface identity markers 5. Cell-to-cell adhesion proteins 6. Attachments to the cytoskeleton  Structure relates to function Diverse functions arise from the diverse structures of membrane proteins Have common structural features related to their role as membrane proteins Peripheral proteins – Anchoring molecules attach membrane protein to surface Anchoring molecules are modified lipids with 1. Nonpolar regions that insert into the internal portion of the lipid bilayer 2. Chemical bonding domains that link directly to proteins Membrane Proteins- Example Pores – Extensive nonpolar regions within a transmembrane protein can create a pore through the membrane – Cylinder of  sheets in the protein secondary structure called a -barrel Interior is polar and allows water and small polar molecules to pass through the membrane Why do membranes not break apart easily every time an animal moves?  Question 1 How are transmembrane proteins held in the correct position in the membrane? a. Covalent bonding to the phosphate group b. Hydrophobic domain is held in place by hydrophobic exclusion c. Cytoskeleton filaments keep them in place d. Glycoproteins prevent the free movement of transmembrane proteins e. The cell wall keeps the proteins in place  Question 2 Some of the glycoproteins on a cell’s surface are identity markers. What would happen if the cell did not possess these particular molecules? a. Lipid bilayer would split apart b. The plasma membrane would be anchored to the cytoskeleton c. Transmembrane proteins would not be in the correct position d. The immune system would attack the cell e. Material would not be able to diffuse across the membrane  Question 3 Which part of the phospholipid is responsible for H bonding with water? a. Fatty acid chains b. Phosphate head c. Glycerol molecule d. Non polar tails e. Nitrogenous bases  Stand and Jump! We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths. --Walt Disney Membranes: MOVING DAY! Getting from here to there… Summary: cheap to pricey  Free!!! Passive Transport Passive transport is movement of molecules through the membrane in which – No energy is required – Molecules move in response to a concentration gradient 1. Diffusion 2. Facilitated Diffusion 3. Osmosis Free!!! 1. Diffusion Movement of molecules from high concentration to low concentration Will continue until the concentration is the same in all regions  Free!!! 2. Facilitated diffusion – Molecules that cannot cross membrane easily may move through proteins – Move from higher to lower concentration – Channel proteins Hydrophilic channel when open – Carrier proteins Bind specifically to molecules they assist Extracellular fluid Extracellular fluid Extracellular fluid Cytoplasm Cytoplasm Cytoplasm  Channel proteins Free!!! Extracellular fluid Extracellular fluid Cytoplasm Cytoplasm Ion channels – Allow the passage of ions – Gated channels – open or close in response to stimulus (chemical or electrical) – 3 conditions determine direction Relative concentration on either side of membrane Voltage differences across membrane Gated channels – channel open or closed  Carrier proteins Free!!! Extracellular fluid Cytoplasm Can help transport both ions and other solutes, such as some sugars and amino acids Requires a concentration difference across the membrane Must bind to the molecule they transport – Saturation – rate of transport limited by number of transporters  Carrier protein transports specific molecule down the concentration gradient Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Definition Alert: Solute, Solvent, Solution Free!!! 3. Osmosis Cytoplasm of the cell is an aqueous solution – Water is solvent – Dissolved substances are solutes Osmosis – net diffusion of water across a membrane toward a higher solute concentration  Osmosis – diffusion of water Water accumulates on side with most solute $$$ Active Transport Requires energy – ATP is used directly or indirectly to fuel active transport Moves substances from low to high concentration Requires the use of highly selective carrier proteins $$$ Ex. Sodium–potassium (Na+–K+) pump Direct use of ATP for active transport Uses a protein to move 3 Na+ out of the cell and 2 K+ into the cell – Against their concentration gradient ATP energy is used to change the conformation of the carrier protein Affinity of the carrier protein for either Na+ or K+ changes so the ions can be carried across the membrane $$$ Ex. Coupled transport Uses ATP indirectly Uses the energy released when a molecule moves by diffusion to supply energy to active transport of a different molecule Glucose–Na+ protein captures the energy from Na+ diffusion to move glucose against a concentration gradient $$$ Bulk Transport 1. Endocytosis – Movement of substances into the cell – Phagosytosis – cell takes in particulate matter – Pinocytosis – cell takes in only fluid – Receptor-mediated endocytosis – specific molecules are taken in after they bind to a receptor 2. Exocytosis – Movement of substances out of cell  In the human genetic disease familial hypercholesterolemia, the LDL receptors lack tails, so they are never fastened in the clathrin-coated pits and as a result, do not trigger vesicle formation. The cholesterol stays in the bloodstream of affected individuals, accumulating as plaques inside arteries and leading to heart attacks.  Exocytosis – Movement of materials out of the cell – Used in plants to export cell wall material – Used in animals to secrete hormones, neurotransmitters, digestive enzymes Test Prep