Cell Membranes and Organization Lecture Notes PDF

Cell membranes and cell organization Spring 2025 Dr. Maximilian Lyon MWF, 12:00-12:50 pm ISE 211 Housekeeping Office hour and SI schedule: Wednesday: Gauri 4-5 pm in Ritter 106; Katie 5-6 pm in Ritter 323 Thursday: Betsy 11-12 pm in Ritter 314 Friday: Lyon 10...

Cell membranes and cell organization Spring 2025 Dr. Maximilian Lyon MWF, 12:00-12:50 pm ISE 211 Housekeeping Office hour and SI schedule: Wednesday: Gauri 4-5 pm in Ritter 106; Katie 5-6 pm in Ritter 323 Thursday: Betsy 11-12 pm in Ritter 314 Friday: Lyon 10-11 am in Macelwane 100 Attendance/participation will start tracking this week Questions can be posted to discussion page or after class iClicker poll AKA the most electronegative Which element is MOST LIKELY to form polar bonds? A. Carbon B. Hydrogen C. Nitrogen D. Oxygen E. They are all equally likely What makes something hydrophobic What kind of substance would be least likely to dissolve in water? A. One with only polar covalent bonds B. One with only non-polar covalent bonds C. One with only ionic bonds D. All would dissolve easily E. None would dissolve easily Learning Objectives 1. Explain how the structure and properties of phospholipids determine their tendency to form bilayers in water. 2. Describe the structure and properties of biological membranes (phospholipid bilayers), and the structure of prokaryotic and eukaryotic cells 3. Describe the basic function of cell walls in prokaryotes, plants and fungi 4. Predict how the structure and properties of amino acid side chains will affect their localization within transmembrane proteins. Life is carbon-based Organic molecules – contain at least one carbon, usually have many C-C and C-H bonds Most biomolecules have O (oxygen) and N (nitrogen) Nucleic acids (DNA and RNA) also contain P (phosphorus) 5’-phosphate group Proteins can also contain S (sulfur) Methionine and cystine side-chains Most* biomolecules are soluble Lipids are mostly nonpolar and grouped due to hydrophobicity Primarily contain large number of C and H atoms Only major biomolecule category not made of polymers Phospholipids Three major categories: Fats (fatty acid shown) Steroids Fat saturation Type of C-C bonds in hydrocarbon chain influences form and function High melting temp = solid at room temp. Double bonds cause a rigid bend Unsaturated fats can be mono- or poly-unsaturated Low melting temp = liquid at room temp. Predicting water interactions Based on the atoms that are present, what part of this molecule would have the most interactions with water? Our focus - phospholipids Polar group Phosphate group (polar) Glycerol Fatty acid tail Going both ways Amphipathic – has hydrophilic and hydrophobic regionsS Polar “head” Hydrophilic Fatty acid tails Hydrophobic The shape of water Orient and arrange so that hydrophilic end faces water Hydrophobic end secluded from water, drives structure formation Liposomes Micelles and liposomes – fatty pockets Detergents form micelles around hydrophobic particles Liposomes have many uses in biomedical research Phospholipid bilayers Bilayers (“two layers”) are fluid – phospholipids can move laterally (sideways) but not flip between layers Selective permeability – cellular checkpoint Saturation and permeability The boundaries of life All cells are separated from their environment by plasma membranes Biological membranes are made of phospholipids with embedded proteins Plasma membrane Internal membranes (organelles) Prokaryotic cell Eukaryotic cell The Fluid Mosaic Model Plasma membranes contain both lipids and proteins Keep unwanted materials out Allow specific materials in Facilitate chemical reactions Proteins in the membrane have a large range of functions Amino Acids Amino acids are ionized in water At pH 7 both the amino and carboxyl groups ionize Charged ends help solubilize molecule Foundation for polymerization Side chains There are 20 common side chains that can be grouped by properties DO NOT MEMORIZE THEM ALL Primary organization Chain has directionality, N-terminus and C-terminus Side chains extend from backbone, interact with water and each other Intracellular machines Protein function is often determined by its shape Most work done in the cell is done by proteins Four levels of organization Different parts of the same protein may be at different levels Organization Proteins can be huge Whole protein may be at a single level or have regions at different levels Quaternary mostly means that there are multiple polypeptides (subunits) Like dissolves like If you find a protein embedded in a plasma membrane, which amino acid side chain would most likely be facing the fatty acid tails? In the membrane Polar and charged R groups are hydrophilic, face water in the cell fluid (cytosol) or outside Nonpolar R groups can’t H-bond with water, hydrophobic, packed inside or in membranes From form, function You can use amino acid hydrophobicity to predict which parts of a protein are in the membrane Hydrophobic parts are in the tails Hydrophilic parts stick out of the membrane Brenker, C., Zhou, Y., Müller, A., Echeverry, F. A., Trötschel, C., Poetsch, A.,... & Strünker, T. (2014). The Ca2+-activated K+ current of human sperm is mediated by Slo3. Elife, 3, e01438. Schreiber, M., Wei, A., Yuan, A., Gaut, J., Saito, M., & Salkoff, L. (1998). Slo3, a novel pH-sensitive K+ channel from mammalian spermatocytes. Journal of Biological Chemistry, 273(6), 3509-3516. Lead balloons Plants and algae (protists) Plasma membranes are fluid, relatively delicate Cell walls are found in all prokaryotes, fungi, plants, and some protists, no animals Located outside of plasma membrane and provides structural support Different composition in each group Prokaryotes – simple cells Archaea and Bacteria No membrane-bound organelles Unicellular or colonial 5-100x smaller than Eukaryotic cells Cell wall and plasma membrane No nucleus, single circular chromosome Have some specialized protein- based structures Eukaryotes – not simple Eukarya Many membrane-bound organelles with specific specialized functions Unicellular, colonial, or multicellular Some have cell walls Multiple linear chromosomes stored in a nucleus Multicellular organisms can have many specialized cell types Why walls, why? Some cells have cell walls in addition to plasma membranes in order to: A. Keep unwanted materials out B. Allow specific materials in C. Provide more rigid structure D. Facilitate chemical reactions For next class: Complete the reading quiz – due Friday at 12:00 pm Read Chapters 4.2 and 4.4 (intro only) Follow my highlights: https://macmillan.vitalsource.com/home/subscribe/maximilian.lyon%40slu.edu