Chapter 5: Cell Membranes and Signaling
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Bacterial Cell Membrane
BACTERIAL CELL MEMBRANE Dr. Rakesh Sharda Department of Veterinary Microbiology NDVSU College of Veterinary Sc. & A.H., MHOW CYTOPLASMIC MEMBRANE ➢The cytoplasmic membrane, also called a cell membrane or plasma membrane, is about 7 nanometers (nm; 1/1,000,000,000 m) thick. ➢It lies internal to the cell wall and encloses the cytoplasm of the bacterium. ➢It is the most dynamic structure of a prokaryotic cell. Structure of cell membrane ➢The structure of bacterial plasma membrane is that of unit membrane, i.e., a fluid phospholipid bilayer, composed of phospholipids (40%) and peripheral and integral proteins (60%) molecules. ➢The phospholipids of bacterial cell membranes do not contain sterols as in eukaryotes, but instead consist of saturated or monounsaturated fatty acids (rarely, polyunsaturated fatty acids). ➢Many bacteria contain sterol-like molecules called hopanoids. ➢The hopanoids most likely stabilize the bacterial cytoplasmic membrane. ➢The phospholipids are amphoteric molecules with a polar hydrophilic glycerol "head" attached via an ester bond to two non-polar hydrophobic fatty acid tails. ➢The phospholipid bilayer is arranged such that the polar ends of the molecules form the outermost and innermost surface of the membrane while the non-polar ends form the center of the membrane Fluid mosaic model ➢The plasma membrane contains proteins, sugars, and other lipids in addition to the phospholipids. ➢The model that describes the arrangement of these substances in lipid bilayer is called the fluid mosaic model ➢Dispersed within the bilayer are various structural and enzymatic proteins, which carry out most membrane functions. ➢Some membrane proteins are located and function on one side or another of the membrane (peripheral proteins). -
Size Changes in Eukaryotic Ribosomes
Proc. Nat. Acad. Sci. USA Vol. 68, No. 12, pp. 3021-3025, December 1971 Size Changes in Eukaryotic Ribosomes (diffusion constant/sedimentation constant/ribosomal dissociation/chick embryo) JOHN VOURNAKIS AND ALEXANDER RICH Department of Biology, Massachusetts Institute of Technology, Cambridge, Mass. 02139 Contributed by Alexander Rich, September 20, 1971 ABSTRACT Evidence is presented that ribosomes two particles are similar. However, these changes suggest active in protein synthesis and attached to messenger that when the ribosome is attached to messenger RNA it has a RNA on polysomes have a smaller diameter than free cytoplasmic single ribosomes. Measurements have been smaller diameter than is found for the free cytoplastic ribo- made on these two types of ribosomes of differences in some. This more compact form of the ribosome is maintained sedimentation velocity and diffusion constant. Differences even when the nascent polypeptide chain is relased by puro- in these quantities suggest about a 20-A decrease in the mycin. We thus infer that there are substantial differences diameter of the ribosomes from chick embryo muscles in the interactions between the ribosomal subunits when when they are attached to messenger RNA. Similar dif- they ferences are also observed in rabbit reticulocytes and are attached to messenger RNA as compared to the free cyto- mouse ascites tumor cells. These two ribosomal states plasmic single ribosome, which is inactive in protein synthesis. have different sensitivity to Pronase digestion and dis- sociate into ribosomal subunits at different KCI concen- METHODS AND MATERIALS trations. This size difference is not associated with a sig- nificant difference in overall ribosomal mass and appears Preparation of Ribosomes. -
The Endomembrane System and Proteins
Chapter 4 | Cell Structure 121 Endosymbiosis We have mentioned that both mitochondria and chloroplasts contain DNA and ribosomes. Have you wondered why? Strong evidence points to endosymbiosis as the explanation. Symbiosis is a relationship in which organisms from two separate species depend on each other for their survival. Endosymbiosis (endo- = “within”) is a mutually beneficial relationship in which one organism lives inside the other. Endosymbiotic relationships abound in nature. We have already mentioned that microbes that produce vitamin K live inside the human gut. This relationship is beneficial for us because we are unable to synthesize vitamin K. It is also beneficial for the microbes because they are protected from other organisms and from drying out, and they receive abundant food from the environment of the large intestine. Scientists have long noticed that bacteria, mitochondria, and chloroplasts are similar in size. We also know that bacteria have DNA and ribosomes, just like mitochondria and chloroplasts. Scientists believe that host cells and bacteria formed an endosymbiotic relationship when the host cells ingested both aerobic and autotrophic bacteria (cyanobacteria) but did not destroy them. Through many millions of years of evolution, these ingested bacteria became more specialized in their functions, with the aerobic bacteria becoming mitochondria and the autotrophic bacteria becoming chloroplasts. The Central Vacuole Previously, we mentioned vacuoles as essential components of plant cells. If you look at Figure 4.8b, you will see that plant cells each have a large central vacuole that occupies most of the cell's area. The central vacuole plays a key role in regulating the cell’s concentration of water in changing environmental conditions. -
Cell Membrane
John Lenyo Corrina Perez Hazel Owens Cell Membrane http://micro.magnet.fsu.edu/cells/plasmamembrane/plasmamembrane.html • Cell membranes are composed of proteins and lipids. • Since they are made up of mostly lipids, only certain substances can move through. spmbiology403.blogspot.com •Phospholipids are the most abundant type of lipid found in the membrane. Phospholipids are made up of two layers, the outer and inner layers. The inside layer is made of hydrophobic fatty acid tails, while the outer layer is made up of hydrophilic polar heads that are pointed toward the water. academic.brooklyn.cuny.edu •Membrane structure relies on the tendency of fatty acid molecules to spread on the surface of water. • Membrane proteins (which take up half of the membrane) determine what gets into and leaves the cell. •Glycolipids are found on the outer part of the cell membrane. Single Chain vs. Phospholipid • Single chain lipids were assumed to be the first of those to form cell membranes with the more complex phospholipids evolving later • Phospholipids can be synthesized in an abiotic environment without enzymes now • Phosphoplipid bilayers now make up the plasma cell membranes that regulate movement into and out of prokaryotic and eukaryotic cells. Single chain lipid http://web.nestucca.k12.or.us/nvhs/staff/whitehead/homewor http://clincancerres.aacrjournals.org/content/11/5/2018/F1. k.htm expansion Types of Lipids • Today Plasma Membranes are made primarily of phospholipids • It is thought that early membranes may have been made of simpler fatty acids. http://exploringorigins.org/fattyacids.html Properties of Fatty Acids • They are Ampipathic, meaning that they have a hydrophobic (“water hating”) end and a hydrophilic (water loving”) end. -
Endoplasmic Reticulum-Plasma Membrane Contact Sites Integrate Sterol and Phospholipid Regulation
RESEARCH ARTICLE Endoplasmic reticulum-plasma membrane contact sites integrate sterol and phospholipid regulation Evan Quon1☯, Yves Y. Sere2☯, Neha Chauhan2, Jesper Johansen1, David P. Sullivan2, Jeremy S. Dittman2, William J. Rice3, Robin B. Chan4, Gilbert Di Paolo4,5, Christopher T. Beh1,6*, Anant K. Menon2* 1 Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada, 2 Department of Biochemistry, Weill Cornell Medical College, New York, New York, United States of a1111111111 America, 3 Simons Electron Microscopy Center at the New York Structural Biology Center, New York, New a1111111111 York, United States of America, 4 Department of Pathology and Cell Biology, Columbia University College of a1111111111 Physicians and Surgeons, New York, New York, United States of America, 5 Denali Therapeutics, South San a1111111111 Francisco, California, United States of America, 6 Centre for Cell Biology, Development, and Disease, Simon a1111111111 Fraser University, Burnaby, British Columbia, Canada ☯ These authors contributed equally to this work. * [email protected] (AKM); [email protected] (CTB) OPEN ACCESS Abstract Citation: Quon E, Sere YY, Chauhan N, Johansen J, Sullivan DP, Dittman JS, et al. (2018) Endoplasmic Tether proteins attach the endoplasmic reticulum (ER) to other cellular membranes, thereby reticulum-plasma membrane contact sites integrate sterol and phospholipid regulation. PLoS creating contact sites that are proposed to form platforms for regulating lipid homeostasis Biol 16(5): e2003864. https://doi.org/10.1371/ and facilitating non-vesicular lipid exchange. Sterols are synthesized in the ER and trans- journal.pbio.2003864 ported by non-vesicular mechanisms to the plasma membrane (PM), where they represent Academic Editor: Sandra Schmid, UT almost half of all PM lipids and contribute critically to the barrier function of the PM. -
IB DIPLOMA PROGRAMME Debora M
OXFORD IB PREPARED BIOLOGY IB DIPLOMA PROGRAMME Debora M. Primrose Contents Introduction iv 9 Plant biology (AHL) 1 Cell biology 9.1 Transport in the xylem of plants 103 9.2 Transport in the phloem of plants 107 1.1 Introduction to cells 2 9.3 Growth in plants 110 1.2 Ultrastructure of cells 4 9.4 Reproduction in plants 113 1.3 Membrane structure 6 1.4 Membrane transport 7 10 Genetics and evolution (AHL) 1.5 The origin of cells 9 10.1 Meiosis 117 1.6 Cell division 11 10.2 Inheritance 121 2 Molecular biology 10.3 Gene pools and speciation 125 2.1 Molecules to metabolism 14 11 Animal physiology (AHL) 2.2 Water 15 11.1 Antibody production and vaccination 128 2.3 Carbohydrates and lipids 16 11.2 Movement 133 2.4 Proteins 20 11.3 The kidney and osmoregulation 137 2.5 Enzymes 21 11.4 Sexual reproduction 141 2.6 Structure of DNA and RNA 23 2.7 DNA replication, transcription and translation 24 12 Data-based and practical questions 147 2.8 Cell respiration 26 2.9 Photosynthesis 28 A Neurobiology and behaviour 3 Genetics A.1 Neural development 157 A.2 The human brain 159 3.1 Genes 30 A.3 Perception of stimuli 161 3.2 Chromosomes 32 A.4 Innate and learned behaviour (AHL) 165 3.3 Meiosis 33 A.5 Neuropharmacology (AHL) 167 3.4 Inheritance 35 A.6 Ethology (AHL) 169 3.5 Genetic modification and biotechnology 37 B Biotechnology and bioinformatics 4 Ecology B.1 Microbiology: organisms in industry 172 4.1 Species, communities and ecosystems 40 B.2 Biotechnology in agriculture 174 4.2 Energy flow 43 B.3 Environmental protection 178 4.3 Carbon cycling 45 -
Predicting Protein-Membrane Interfaces of Peripheral Membrane
bioRxiv preprint doi: https://doi.org/10.1101/2021.06.28.450157; this version posted June 29, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Predicting protein-membrane interfaces of pe- ripheral membrane proteins using ensemble machine learning Alexios Chatzigoulas1,2,* and Zoe Cournia1,* 1Biomedical Research Foundation, Academy of Athens, 4 Soranou Ephessiou, 11527 Athens, Greece, 2Depart- ment of Informatics and Telecommunications, National and Kapodistrian University of Athens, 15784 Athens, Greece *To whom correspondence should be addressed. Abstract Motivation: Abnormal protein-membrane attachment is involved in deregulated cellular pathways and in disease. Therefore, the possibility to modulate protein-membrane interactions represents a new promising therapeutic strategy for peripheral membrane proteins that have been considered so far undruggable. A major obstacle in this drug design strategy is that the membrane binding domains of peripheral membrane proteins are usually not known. The development of fast and efficient algorithms predicting the protein-membrane interface would shed light into the accessibility of membrane-protein interfaces by drug-like molecules. Results: Herein, we describe an ensemble machine learning methodology and algorithm for predicting membrane-penetrating residues. We utilize available experimental data in the literature for training 21 machine learning classifiers and a voting classifier. Evaluation of the ensemble classifier accuracy pro- duced a macro-averaged F1 score = 0.92 and an MCC = 0.84 for predicting correctly membrane-pen- etrating residues on unknown proteins of an independent test set. -
An Overview of Lipid Membrane Models for Biophysical Studies
biomimetics Review Mimicking the Mammalian Plasma Membrane: An Overview of Lipid Membrane Models for Biophysical Studies Alessandra Luchini 1 and Giuseppe Vitiello 2,3,* 1 Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark; [email protected] 2 Department of Chemical, Materials and Production Engineering, University of Naples Federico II, Piazzale Tecchio 80, 80125 Naples, Italy 3 CSGI-Center for Colloid and Surface Science, via della Lastruccia 3, 50019 Sesto Fiorentino (Florence), Italy * Correspondence: [email protected] Abstract: Cell membranes are very complex biological systems including a large variety of lipids and proteins. Therefore, they are difficult to extract and directly investigate with biophysical methods. For many decades, the characterization of simpler biomimetic lipid membranes, which contain only a few lipid species, provided important physico-chemical information on the most abundant lipid species in cell membranes. These studies described physical and chemical properties that are most likely similar to those of real cell membranes. Indeed, biomimetic lipid membranes can be easily prepared in the lab and are compatible with multiple biophysical techniques. Lipid phase transitions, the bilayer structure, the impact of cholesterol on the structure and dynamics of lipid bilayers, and the selective recognition of target lipids by proteins, peptides, and drugs are all examples of the detailed information about cell membranes obtained by the investigation of biomimetic lipid membranes. This review focuses specifically on the advances that were achieved during the last decade in the field of biomimetic lipid membranes mimicking the mammalian plasma membrane. In particular, we provide a description of the most common types of lipid membrane models used for biophysical characterization, i.e., lipid membranes in solution and on surfaces, as well as recent examples of their Citation: Luchini, A.; Vitiello, G. -
Membrane Proteins Are Associated with the Membrane of a Cell Or Particular Organelle and Are Generally More Problematic to Purify Than Water-Soluble Proteins
Strategies for the Purification of Membrane Proteins Sinéad Marian Smith Department of Clinical Medicine, School of Medicine, Trinity College Dublin, Ireland. Email: [email protected] Abstract Although membrane proteins account for approximately 30 % of the coding regions of all sequenced genomes and play crucial roles in many fundamental cell processes, there are relatively few membranes with known 3D structure. This is likely due to technical challenges associated with membrane protein extraction, solubilization and purification. Membrane proteins are classified based on the level of interaction with membrane lipid bilayers, with peripheral membrane proteins associating non- covalently with the membrane, and integral membrane proteins associating more strongly by means of hydrophobic interactions. Generally speaking, peripheral membrane proteins can be purified by milder techniques than integral membrane proteins, whose extraction require phospholipid bilayer disruption by detergents. Here, important criteria for strategies of membrane protein purification are addressed, with a focus on the initial stages of membrane protein solublilization, where problems are most frequently are encountered. Protocols are outlined for the successful extraction of peripheral membrane proteins, solubilization of integral membrane proteins, and detergent removal which is important not only for retaining native protein stability and biological functions, but also for the efficiency of downstream purification techniques. Key Words: peripheral membrane protein, integral membrane protein, detergent, protein purification, protein solubilization. 1. Introduction Membrane proteins are associated with the membrane of a cell or particular organelle and are generally more problematic to purify than water-soluble proteins. Membrane proteins represent approximately 30 % of the open-reading frames of an organism’s genome (1-4), and play crucial roles in basic cell functions including signal transduction, energy production, nutrient uptake and cell-cell communication. -
The Structure of Biological Membranes
The Structure of Biological Membranes Func7ons of Cellular Membranes 1. Plasma membrane acts as a selecvely permeable barrier to the environment • Uptake of nutrients • Waste disposal • Maintains intracellular ionic milieau 2. Plasma membrane facilitates communicaon • With the environment • With other cells • Protein secreon 3. Intracellular membranes allow compartmentalizaon and separaon of different chemical reac7on pathways • Increased efficiency through proximity • Prevent fu8le cycling through separaon Composi7on of Animal Cell Membranes • Hydrated, proteinaceous lipid bilayers • By weight: 20% water, 80% solids • Solids: Lipid Protein ~90% Carbohydrate (~10%) • Phospholipids responsible for basic membrane bilayer structure and physical proper8es • Membranes are 2-dimensional fluids into which proteins are dissolved or embedded The Most Common Class of PhospholipiD is FormeD from a Gycerol-3-P Backbone SaturateD FaJy AciD •Palmitate and stearate most common •14-26 carbons •Even # of carbons UnsaturateD FaJy AciD Structure of PhosphoglyceriDes All Membrane LipiDs are Amphipathic Figure 10-2 Molecular Biology of the Cell (© Garland Science 2008) PhosphoglyceriDes are Classified by their Head Groups Phosphadylethanolamine Phosphadylcholine Phosphadylserine Phosphadylinositol Ether Bond at C1 PS and PI bear a net negave charge at neutral pH Sphingolipids are the SeconD Major Class of PhospholipiD in Animal Cells Sphingosine Ceramides contain sugar moies in ether linkage to sphingosine GlycolipiDs are AbunDant in Brain Cells Figure 10-18 Molecular -
Cell Wall Ribosomes Nucleus Chloroplast Cytoplasm
Cell Wall Ribosomes Nucleus Nickname: Protector Nickname: Protein Maker Nickname: Brain The cell wall is the outer covering of a Plant cell. It is Ribosomes read the recipe from the The nucleus is the largest organelle in a cell. The a strong and stiff and made of DNA and use this recipe to make nucleus directs all activity in the cell. It also controls cellulose. It supports and protects the plant cell by proteins. The nucleus tells the the growth and reproduction of the cell. holding it upright. It ribosomes which proteins to make. In humans, the nucleus contains 46 chromosomes allows water, oxygen and carbon dioxide to pass in out They are found in both plant and which are the instructions for all the activities in your of plant cell. animal cells. In a cell they can be found cell and body. floating around in the cytoplasm or attached to the endoplasmic reticulum. Chloroplast Cytoplasm Endoplasmic Reticulum Nickname: Oven Nickname: Gel Nickname: Highway Chloroplasts are oval structures that that contain a green Cytoplasm is the gel like fluid inside a The endoplasmic reticulum (ER) is the transportation pigment called chlorophyll. This allows plants to make cell. The organelles are floating around in center for the cell. The ER is like the conveyor belt, you their own food through the process of photosynthesis. this fluid. would see at a supermarket, except instead of moving your groceries it moves proteins from one part of the cell Chloroplasts are necessary for photosynthesis, the food to another. The Endoplasmic Reticulum looks like a making process, to occur. -
The Still Valid Fluid Mosaic Model for Molecular Organization of Biomembranes: Accumulating Data Confirm It
DISCOVERIES 2013, Oct-Dec; 1(1): e7 DOI: 10.15190/d.2013.7 The still actual fluid mosaic model for membrane organization Focused REVIEW The still valid fluid mosaic model for molecular organization of biomembranes: accumulating data confirm it Mircea Leabu1,* 1University of Medicine and Pharmacy “Carol Davila”, Department of Cellular and Molecular Medicine; “Victor Babes” National Institute of Pathology; University of Bucharest, Research Center for Applied Ethics *Correspondence to: Mircea Leabu, PhD, “Victor Babes” National Institute of Pathology, 99101, Splaiul Independentei, 050096, Bucharest, Romania; E-mail: [email protected] Citation: Leabu M. The still valid fluid mosaic model for molecular organization of biomembranes: accumulating data confirm it. Discoveries 2013, Oct-Dec; 1(1): e7. DOI: 10.15190/d.2013.7 ABSTRACT Keywords: membrane organization, membrane fluidity, membrane microdomains, Singer-Nicolson More than forty years passed since Singer and model, science history Nicolson launched the fluid mosaic model related to molecular organization and dynamics of cell Introduction membranes, applicable to endomembranes as well. For 20 years I and perhaps many other professors During this period of time, that will reach half a have been teaching students in medicine about the century soon, accumulating data all confirm, but not molecular organization of the cell membrane, infirm the brilliant idea of such a model. presenting with a high enthusiasm the fluid mosaic Sometimes, the results developed the model in a model launched by Seymour Jonathan Singer and very impacting manner, as was the case with the Garth L. Nicolson in 19721, and considering it as an introduction of the membrane microdomain concept inspired, still actual scientific and even pedagogic (mainly lipid rafts organization).