Components and Architecture of Cell Membrane
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
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. -
Biological Membranes and Transport Membranes Define the External
Biological Membranes and Transport Membranes define the external boundaries of cells and regulate the molecular traffic across that boundary; in eukaryotic cells, they divide the internal space into discrete compartments to segregate processes and components. Membranes are flexible, self-sealing, and selectively permeable to polar solutes. Their flexibility permits the shape changes that accompany cell growth and movement (such as amoeboid movement). With their ability to break and reseal, two membranes can fuse, as in exocytosis, or a single membrane-enclosed compartment can undergo fission to yield two sealed compartments, as in endocytosis or cell division, without creating gross leaks through cellular surfaces. Because membranes are selectively permeable, they retain certain compounds and ions within cells and within specific cellular compartments, while excluding others. Membranes are not merely passive barriers. Membranes consist of just two layers of molecules and are therefore very thin; they are essentially two-dimensional. Because intermolecular collisions are far more probable in this two-dimensional space than in three-dimensional space, the efficiency of enzyme-catalyzed processes organized within membranes is vastly increased. The Molecular Constituents of Membranes Molecular components of membranes include proteins and polar lipids, which account for almost all the mass of biological membranes, and carbohydrate present as part of glycoproteins and glycolipids. Each type of membrane has characteristic lipids and proteins. The relative proportions of protein and lipid vary with the type of membrane, reflecting the diversity of biological roles (as shown in table 12-1, see below). For example, plasma membranes of bacteria and the membranes of mitochondria and chloroplasts, in which many enzyme-catalyzed processes take place, contain more protein than lipid. -
Membrane Transport, Absorption and Distribution of Drugs
Chapter 2 1 Pharmacokinetics: Membrane Transport, Absorption and Distribution of Drugs Pharmacokinetics is the quantitative study of drug movement in, through and out of the body. The overall scheme of pharmacokinetic processes is depicted in Fig. 2.1. The intensity of response is related to concentration of the drug at the site of action, which in turn is dependent on its pharmacokinetic properties. Pharmacokinetic considerations, therefore, determine the route(s) of administration, dose, and latency of onset, time of peak action, duration of action and frequency of administration of a drug. Fig. 2.1: Schematic depiction of pharmacokinetic processes All pharmacokinetic processes involve transport of the drug across biological membranes. Biological membrane This is a bilayer (about 100 Å thick) of phospholipid and cholesterol molecules, the polar groups (glyceryl phosphate attached to ethanolamine/choline or hydroxyl group of cholesterol) of these are oriented at the two surfaces and the nonpolar hydrocarbon chains are embedded in the matrix to form a continuous sheet. This imparts high electrical resistance and relative impermeability to the membrane. Extrinsic and intrinsic protein molecules are adsorbed on the lipid bilayer (Fig. 2.2). Glyco- proteins or glycolipids are formed on the surface by attachment to polymeric sugars, 2 aminosugars or sialic acids. The specific lipid and protein composition of different membranes differs according to the cell or the organelle type. The proteins are able to freely float through the membrane: associate and organize or vice versa. Some of the intrinsic ones, which extend through the full thickness of the membrane, surround fine aqueous pores. CHAPTER2 Fig. -
Construction and Loss of Bacterial Flagellar Filaments
biomolecules Review Construction and Loss of Bacterial Flagellar Filaments Xiang-Yu Zhuang and Chien-Jung Lo * Department of Physics and Graduate Institute of Biophysics, National Central University, Taoyuan City 32001, Taiwan; [email protected] * Correspondence: [email protected] Received: 31 July 2020; Accepted: 4 November 2020; Published: 9 November 2020 Abstract: The bacterial flagellar filament is an extracellular tubular protein structure that acts as a propeller for bacterial swimming motility. It is connected to the membrane-anchored rotary bacterial flagellar motor through a short hook. The bacterial flagellar filament consists of approximately 20,000 flagellins and can be several micrometers long. In this article, we reviewed the experimental works and models of flagellar filament construction and the recent findings of flagellar filament ejection during the cell cycle. The length-dependent decay of flagellar filament growth data supports the injection-diffusion model. The decay of flagellar growth rate is due to reduced transportation of long-distance diffusion and jamming. However, the filament is not a permeant structure. Several bacterial species actively abandon their flagella under starvation. Flagellum is disassembled when the rod is broken, resulting in an ejection of the filament with a partial rod and hook. The inner membrane component is then diffused on the membrane before further breakdown. These new findings open a new field of bacterial macro-molecule assembly, disassembly, and signal transduction. Keywords: self-assembly; injection-diffusion model; flagellar ejection 1. Introduction Since Antonie van Leeuwenhoek observed animalcules by using his single-lens microscope in the 18th century, we have entered a new era of microbiology. -
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. -
Chapter 2 Cell Membranes
Chapter 2 Cell Membranes © 2020 Elsevier Inc. All rights reserved. Figure 2–1 The hydrophobic effect drives rearrangement of lipids, including the formation of bilayers. The driving force of the hydrophobic effect is the tendency of water molecules to maximize their hydrogen bonding between the oxygen and hydrogen atoms. Phospholipids placed in water would potentially disrupt the hydrogen bonding of water clusters. This causes the phospholipids to bury their nonpolar tails by forming micelles, bilayers, or monolayers. Which of the lipid structures is preferred depends on the lipids and the environment. The shape of the molecules (size of the head group and characteristics of the side chains) can determine lipid structure. (A) Molecules that have an overall inverted conical shape, such as detergent molecules, form structures with a positive curvature, such as micelles. (B) Cylindrical-shaped lipid molecules such as some phospholipids preferentially form bilayer structures. (C) Biological membranes combine a large variety of lipid molecular species. The combination of these structures determines the overall shape of the bilayer, and a change in composition or distribution will lead to a change in shape of the bilayer. Similarly a change in shape needs to be accommodated by a change in composition and organization of the lipid core. © 2020 Elsevier Inc. All rights reserved. 2 Figure 2–2 The principle of the fluid mosaic model of biological membranes as proposed by Singer and Nicolson. In this model, globular integral membrane proteins are freely mobile within a sea of phospholipids and cholesterol. © 2020 Elsevier Inc. All rights reserved. 3 Figure 2–3 Structure of phospholipids. -
Cell Wall Constrains Lateral Diffusion of Plant Plasma-Membrane Proteins
Cell wall constrains lateral diffusion of plant SEE COMMENTARY plasma-membrane proteins Alexandre Martinièrea, Irene Lavagia, Gayathri Nageswarana, Daniel J. Rolfeb, Lilly Maneta-Peyretc, Doan-Trung Luud, Stanley W. Botchwayb, Stephen E. D. Webbb, Sebastien Mongrandc, Christophe Maureld, Marisa L. Martin-Fernandezb, Jürgen Kleine-Vehne, Jirí Frimlf, Patrick Moreauc, and John Runionsa,1 aDepartment of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom; bCentral Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Oxfordshire OX11 0QX, United Kingdom; cLaboratoire de Biogenèse Membranaire, Unité Mixte de Recherche 5200 Centre National de la Recherche Scientifique, Université Bordeaux Segalen, 33076 Bordeaux, France; dLaboratoire de Biochimie et Physiologie Moléculaire des Plantes, Institut de Biologie Intégrative des Plantes, Unité Mixte de Recherche 5004, Centre National de la Recherche Scientifique/Unité Mixte de Recherche 0386 Institut National de la Recherche Agronomique, 34060 Montpellier, France; eDepartment of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, 1190 Vienna, Austria; and fDepartment of Plant Biotechnology and Genetics, Ghent University, 9052 Ghent, Belgium Edited by Daniel J. Cosgrove, Pennsylvania State University, University Park, PA, and approved May 16, 2012 (received for review February 3, 2012) A cell membrane can be considered a liquid-phase plane in which yeast lines lacking -
Biological Membranes Transport
9/15/2014 Advanced Cell Biology Biological Membranes Transport 1 1 9/15/2014 3 4 2 9/15/2014 Transport through cell membranes • The phospholipid bilayer is a good barrier around cells, especially to water soluble molecules. However, for the cell to survive some materials need to be able to enter and leave the cell. • There are 4 basic mechanisms: 1. DIFFUSION and FACILITATED DIFFUSION 2. OSMOSIS 3. ACTIVE TRANSPORT 4. BULK TRANSPORT AS Biology, Cell membranes and 5 Transport 11.3 Solute Transport across Membranes 6 3 9/15/2014 Passive Transport Is Facilitated by Membrane Proteins Energy changes accompanying passage of a hydrophilic solute through the lipid bilayer of a biological membrane 7 Figure 11.2 Overview of membrane transport proteins. 4 9/15/2014 Figure 11.3 Multiple membrane transport proteins function together in the plasma membrane of metazoan cells. 5 9/15/2014 • Facilitated transport – Passive transport – Glucose – GLUT Cellular uptake of glucose mediated by GLUT proteins exhibits simple enzyme kinetics 11 12 6 9/15/2014 Regulation by insulin of glucose transport by GLUT4 into a myocyte 13 Effects of Osmosis on Water Balance • Osmosis is the diffusion of water across a selectively permeable membrane • The direction of osmosis is determined only by a difference in total solute concentration • Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration 7 9/15/2014 Water Balance of Cells Without Walls • Tonicity is the ability of a solution to cause a cell to gain -
Questions in Cell Biology
Name: Questions in Cell Biology Directions: The following questions are taken from previous IB Final Papers on the subject of cell biology. Answer all questions. This will serve as a study guide for the next quiz on Monday 11/21. 1. Outline the process of endocytosis. (Total 5 marks) 2. Draw a labelled diagram of the fluid mosaic model of the plasma membrane. (Total 5 marks) 3. The drawing below shows the structure of a virus. II I 10 nm (a) Identify structures labelled I and II. I: ...................................................................................................................................... II: ...................................................................................................................................... (2) (b) Use the scale bar to calculate the maximum diameter of the virus. Show your working. Answer: ..................................................... (2) (c) Explain briefly why antibiotics are effective against bacteria but not viruses. ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... .............................................................................................................................................. -
Is Lipid Translocation Involved During Endo- and Exocytosis?
Biochimie 82 (2000) 497−509 © 2000 Société française de biochimie et biologie moléculaire / Éditions scientifiques et médicales Elsevier SAS. All rights reserved. S0300908400002091/FLA Is lipid translocation involved during endo- and exocytosis? Philippe F. Devaux* Institut de Biologie Physico-Chimique, UPR-CNRS 9052, 13, rue Pierre-et-Marie-Curie, 75005 Paris, France (Received 28 January 2000; accepted 17 March 2000) Abstract — Stimulation of the aminophospholipid translocase, responsible for the transport of phosphatidylserine and phosphati- dylethanolamine from the outer to the inner leaflet of the plasma membrane, provokes endocytic-like vesicles in erythrocytes and stimulates endocytosis in K562 cells. In this article arguments are given which support the idea that the active transport of lipids could be the driving force involved in membrane folding during the early step of endocytosis. The model is sustained by experiments on shape changes of pure lipid vesicles triggered by a change in the proportion of inner and outer lipids. It is shown that the formation of microvesicles with a diameter of 100–200 nm caused by the translocation of plasma membrane lipids implies a surface tension in the whole membrane. It is likely that cytoskeleton proteins and inner organelles prevent a real cell from undergoing overall shape changes of the type seen with giant unilamellar vesicles. Another hypothesis put forward in this article is the possible implication of the phospholipid ‘scramblase’ during exocytosis which could favor the unfolding of microvesicles. © 2000 Société française de biochimie et biologie moléculaire / Éditions scientifiques et médicales Elsevier SAS aminophospholipid translocase / membrane budding / spontaneous curvature / liposomes / K562 cells 1. Introduction yet whether clathrin polymerizes and then pinches off the membrane to form the buds or if polymerization takes During the last 10–15 years, a large number of proteins place around a pre-formed bud.