DOCSLIB.ORG

Phospholipids and Membrane Structure © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT for SALE OR DISTRIBUTION NOT for SALE OR DISTRIBUTION

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Phospholipids and Membrane Structure © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT for SALE OR DISTRIBUTION NOT for SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett4 Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Phospholipids and Membrane Structure © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 4.1 The Big Picture 4.2 Phospholipids Are the Basic Building Blocks of Cellular Membranes © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE4.3 TheOR Fluid–MosaicDISTRIBUTION Model Explains How PhospholipidsNOT FOR SALE OR DISTRIBUTION and Proteins Interact within a Cellular Membrane 4.4 The Smooth Endoplasmic Reticulum and Golgi Apparatus Build Most Eukaryotic Cellular Membrane Components© Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC 4.5 Chapter SummaryNOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 117 3RD PAGES © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. © Jones & Bartlett Learning, LLC4.1 The Big Picture© Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONThe purpose of this chapterNOT is to FOR introduce SALE the OR general DISTRIBUTION structure and assembly of mem- branes. The presence of at least one membrane is required for any organism to be consid- ered alive, but this does not mean that all membranes are alike. Recall from Chapter 1 that, despite its relatively simple structure, the carbon atom is capable of forming a multitude © Jonesof different & Bartlett molecules; Learning, this is LLCespecially evident when one© considers Jones the& Bartlettmolecules Learning,that LLC NOT FORcompose SALE a membrane. OR DISTRIBUTION Unlike nucleic acids and proteins, NOTwhich FORare built SALE from ORsimple DISTRIBUTION nucleotide and amino acid subunits, membranes are much larger structures composed of a tremendous variety of molecules. Phospholipids are some of most abundant mol- ecules in membranes, so in this chapter we will focus on them; our goal is to discuss © Jones & Bartlett theLearning, common featuresLLC shared by all membranes,© Jones and &thus Bartlett complete Learning, our survey LLC of the NOT FOR SALE ORbuilding DISTRIBUTION blocks of cells. We will reserve theNOT details FOR concerning SALE membrane OR DISTRIBUTION specialization for later chapters. This chapter contains three major sections: Unlike nucleic acids and proteins, phospholipids are not composed of linear © Jones & Bartlett Learning, LLC polymers of a small© Jonesgroup of &subunits; Bartlett instead, Learning, they are branchedLLC molecules, and NOT FOR SALE OR DISTRIBUTION each branch is oftenNOT unique, FOR making SALE it OR nearly DISTRIBUTION impossible to memorize them all. Because of this, our strategy for learning phospholipid structure will rely heavily on generalizations, such that we can more easily understand the structural details of specific phospholipids in later chapters. © Jones & BartlettThe fluid–mosaic Learning, modelLLC explains how phospholipids© Jones and other& Bartlett molecules Learning, are LLC arranged to yield a biologically functional membrane. Our focus will be on the NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION general concepts that apply to all membranes. Understanding the implications of these concepts will be crucial when we begin discussing specific membranes in later chapters, so this idea will likely require more attention than the first. Phospholipid synthesis and membrane formation occur in an assembly-line-like © Jones & Bartlett Learning,fashion. LLC This concerns the molecular© Jones mechanisms & Bartlett cells useLearning, to build phospho- LLC NOT FOR SALE OR DISTRIBUTIONlipids and organize them into functionalNOT FOR membranes. SALE NoticeOR DISTRIBUTION that the first two ideas are focused on what these structures are, while this idea addresses how they are made. It is important to understand the sequence of events, and the reasons why each step is necessary. Fully understanding this information will require © Jones & Bartlett Learning, LLC solid comprehension© Jones of the basic& Bartlett chemistry Learning, we discussed LLC in Chapter 1, because NOT FOR SALE OR DISTRIBUTION we will be discussingNOT enzymatic FOR SALE reactions OR that DISTRIBUTION give rise to the structurally complex molecules, including phospholipids, that compose membranes. © Jones4.2 & Bartlett Phospholipids Learning, LLC Are the Basic© Jones Building & Bartlett Learning, LLC NOT FOR SALEBlocks OR DISTRIBUTION of Cellular MembranesNOT FOR SALE OR DISTRIBUTION Key ConCeptS © Jones & Bartlett Learning, of the four majorLLC classes of molecules that serve© Jones as the building & Bartlett blocks for Learning, cells (sugars, LLCnucleic acids, proteins, phospholipids), phospholipids are the most structurally complex. NOT FOR SALE OR DISTRIBUTION phosphoglycerides are the most common phospholipids;NOT FOR they SALE are composed OR DISTRIBUTION of two fatty acyl groups and a polar head group attached to a glycerol backbone. the length and degree of saturation of the fatty acyl tails can vary between different phospholipids. the primary function of phospholipids is to form the lipid bilayer that is characteristic of all © Jones & Bartlett Learning, LLC cellular membranes. © Jones & Bartlett Learning, LLC phospholipid bilayers are selectively permeable to solutes. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 118 Chapter 4 phospholipids and Membrane Structure 3RD PAGES 3RD PAGES © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION. © Jones Phospholipids& Bartlett Learning, are structurally LLC and functionally different© from Jones the &other Bartlett cellular Learning,building LLC blocks we have discussed in Chapters 1, 2, and 3. Before we begin our detailed examina- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION tion of phospholipids, let’s compare their structural properties to these other basic building blocks. In Chapter 2, we learned that nucleic acids are, structurally, some of the simplest biomolecules in cells; they are composed of only four different nucleotide subunits, joined into linear polymers by one type of chemical bond (the phosphoester bond), and stabi- lized as linear pairs by© hydrogen Jones bonds.& Bartlett The complexityLearning, of LLCnucleic acids arises not from© Jones & Bartlett Learning, LLC their basic structure, butNOT from FOR their SALE tremendous OR sizeDISTRIBUTION—the average lengths of prokaryotic NOT FOR SALE OR DISTRIBUTION and eukaryotic genes are approximately 900 and 1,300 base pairs, respectively. Structures of this size can adopt a wide variety of shapes, giving rise to the different folded forms of nucleoid and chromatin (see Chapter 2, DNA Packaging Is Hierarchical). The© Jones same pattern & Bartlett is evident Learning, in proteins. LLC Polypeptides are composed© ofJones 20 different & Bartlett Learning, LLC aminoNOT acids, FOR joined SALE into linear OR polymers DISTRIBUTION by one type of chemical bond (theNOT peptide FOR bond), SALE OR DISTRIBUTION and stabilized by five different types of chemical bonds (see Chapter 3, Five Classes of Chemical Bonds Stabilize Protein Structure). The average length of a protein ranges from ~250 to ~300 to ~470 amino acids in archaea, prokaryotes, and eukaryotes, respectively. © Jones &Notice Bartlett that over Learning, the course LLCof evolution from archaea to ©eukaryotes, Jones &the Bartlett length of Learning,an aver- LLC NOT FORage SALE protein OR nearly DISTRIBUTION doubled. NOT FOR SALE OR DISTRIBUTION The pattern continues for sugars. Oligosaccharides and polysaccharides are some of the most diverse types of biomolecules, yet most of them are composed of fewer than 20 monosaccharide subunits joined by a small number of bonds (principally the glycosidic bond, a form of ether bond). But size alone does not account for the tremendous diversity © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC of oligosaccharides and polysaccharides. Cells employ two additional strategies for increas- NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ing variation in these structures: branching and chemical modification. In branching, sugar subunits in these polymers form polygonal, ring-like structures, and the carbon atoms that form most of the vertices in these polygons contain functional groups capable of forming covalent bonds with similar groups on other sugars. This means that a single sugar sub- unit (a© monosaccharide)Jones & Bartlett can form Learning, bonds with LLC two or more neighboring sugars,© Jones forming & Bartlett a Learning, LLC branchedNOT network FOR SALE(see Figure OR 1-14). DISTRIBUTION This way, the same number of monosaccharidesNOT FOR SALEcan OR DISTRIBUTION be combined into multiple combinations, increasing
Load more

Recommended publications
  • Common Features of All Cells Bacterial
    www.denniskunkel.com Tour of the Cell part 1 Today’s Topics • Finish Nucleic Acids Cells • Properties of all cells – Prokaryotes and Eukaryotes • Functions of Major Cellular Organelles – Information – Synthesis&Transport – Energy Conversion – Recycling – Structure and Movement Bacterial cell Animal Cell 9/12/12 (Prokaryote) (Eukaryote) 2 www.denniskunkel.com Common features of all cells • Plasma Membrane – defines inside from outside • Cytosol – Semifluid “inside” of the cell • DNA “chromosomes” - Genetic material – hereditary instructions • Ribosomes – “factories” to synthesize proteins 4 Plasma membrane Bacterial (Prokaryotic) Cell Ribosomes! Plasma membrane! Bacterial Cell wall! chromosome ! Phospholipid bilayer Proteins 0.5 !m! Flagella! No internal membranes 5 6 1 Figure 6.2b 1 cm Eukaryotic Cell Frog egg 1 mm Human egg 100 µm Most plant and animal cells 10 m µ Nucleus Most bacteria Light microscopy Mitochondrion 1 µm Super- 100 nm Smallest bacteria Viruses resolution microscopy Ribosomes 10 nm Electron microscopy Proteins Lipids 1 nm Small molecules Contains internal organelles 7 0.1 nm Atoms endoplasmicENDOPLASMIC RETICULUM reticulum (ER) ENDOPLASMIC RETICULUM (ER) NUCLEUS NUCLEUS Rough ER Smooth ER nucleus Rough ER Smooth ER Nucleus Plasma membrane Plasma membrane Centrosome Centrosome cytoskeletonCYTOSKELETON CYTOSKELETON Microfilaments You should Microfilaments Intermediate filaments know everything Intermediate filaments Microtubules in Fig 6.9 ribosomesRibosomes Microtubules Ribosomes cytosol GolgiGolgi apparatus apparatus Golgi apparatus Peroxisome Peroxisome In animal cells but not plant cells: In animal cells but not plant cells: Lysosome Lysosomes Lysosome Lysosomes Figure 6.9 Centrioles Figure 6.9 Centrioles Mitochondrion lysosome Flagella (in some plant 9sperm) Mitochondrion Flagella (in some plant10 sperm) mitochondrion Nuclear envelope Nucleus Nucleus 1 !m Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Pores Pore complex Rough ER Surface of nuclear envelope.
    [Show full text]
  • 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).
    [Show full text]
  • Membrane Structure Overview Pathology > Cellular Biology & Genetics > Cellular Biology & Genetics
    Membrane Structure Overview Pathology > Cellular Biology & Genetics > Cellular Biology & Genetics PLASMA MEMBRANE • Phospholipid bilayer: bilayer that comprises mostly phospholipids • Fluid mosaic: mosaic of proteins embedded within a fluid phospholipid bilayer • Selectively permeable: some substances move through passively, others use proteins for transport MEMBRANE COMPONENTS • Phospholipids • Proteins • Cholesterol • Carbohydrates PHOSPHOLIPIDS • Amphipathic: hydrophilic head and hydrophobic fatty acid tails • Form liposomes in aqueous environment • Weak hydrophobic interactions = membrane fluidity • Saturated phospholipids: maximize hydrogens in fatty acid tails, no kinks • Unsaturated phospholipids: double bond produces kink, increases fluidity CHOLESTEROL • Temperature buffer • Moderate temperature: decreases fluidity, lessens lateral movement • Low temperature: increases fluidity, prevents solidification PROTEINS • Includes transmembrane proteins that span the bilayer (other types exist) • Proteins provide about half the mass of the membrane CARBOHYDRATES • Glycoproteins: branched carbohydrates covalently bound to proteins • Glycolipids: carbohydrates covalently bound to lipids (extracellular only) 1 / 5 CLINICAL CORRELATION: Blood types • Carbohydrates on surface of red blood cells must be compatible between donor & recipient in blood transfusion FUNCTIONS OF THE CELL MEMBRANE • Cell communication • Import and export of molecules • Cell growth • Cell motility Eukaryotes have internal membranes within the cell, prokaryotes do not.
    [Show full text]
  • 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.
    [Show full text]
  • Phosphatases and Differentiation of the Golgi Apparatus
    J. Cell Sci. 4, 455-497 (1969) 455 Printed in Great Britain PHOSPHATASES AND DIFFERENTIATION OF THE GOLGI APPARATUS MARIANNE DAUWALDER, W. G. WHALEY AND JOYCE E. KEPHART The Cell Research Institute, Tlie University of Texas at Austin, Texas, U.S.A. SUMMARY Cytochemical techniques for the electron microscopic localization of inosine diphosphatase, thiamine pyrophosphatase, and acid phosphatase have been applied to the developing root tip of Zea mays. Following formaldehyde fixation the Golgi apparatus of most of the cells showed reaction specificity for IDPase and TPPase. Following glutaraldehyde fixation marked localiza- tion of IDPase reactivity in the Golgi apparatus was limited to the root cap, the epidermis, and the phloem. A parallelism was apparent between the sequential morphological development of the apparatus for the secretion of a polysaccharide product, the fairly direct incorporation of tritiated glucose into the apparatus to become a component of this product and the develop- ment of the enzyme reactivity. Acid phosphatase, generally accepted as a lysosomal marker, was found in association with the Golgi apparatus in only a few cell types near the apex of the root. The localization was usually in a single cisterna at the face of the apparatus toward which the production of secretory vesicles builds up and associated regions of what may be smooth endoplasmic reticulum. Since the cell types involved were limited regions of the cap and epidermis and some initial cells, no functional correlates of the reactivity were apparent. Despite the presence of this lysosomal marker, no structures clearly identifiable as ' lysosomes' were found and the lack of reaction specificity in the vacuoles did not allow them to be so defined.
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • Living Cell Cytosol Stability to Segregation and Freezing-Out: Thermodynamic Aspect
    1 Living Cell Cytosol Stability to Segregation and Freezing-Out: Thermodynamic aspect Viktor I. Laptev Russian New University, Moscow, Russian Federation The cytosol state in living cell is treated as homogeneous phase equilibrium with a special feature: the pressure of one phase is positive and the pressure of the other is negative. From this point of view the cytosol is neither solution nor gel (or sol as a whole) regardless its components (water and dissolved substances). This is its unique capability for selecting, sorting and transporting reagents to the proper place of the living cell without a so-called “pipeline”. To base this statement the theoretical investigation of the conditions of equilibrium and stability of the medium with alternative-sign pressure is carried out under using the thermodynamic laws and the Gibbs” equilibrium criterium. Keywords: living cellular processes; cytosol; intracellular fluid; cytoplasmic matrix; hyaloplasm matrix; segregation; freezing-out; zero isobare; negative pressure; homogeneous phase equilibrium. I. INTRODUCTION A. Inertial Motion in U,S,V-Space A full description of the thermodynamic state of a medium Cytosol in a living cell (intracellular fluid or cytoplasmic without chemical interactions is given by a relationship matrix, hyaloplasm matrix, aqueous cytoplasm) is a between the internal energy U, entropy S and volume V [5]. combination of the water dissolved substances. It places in the The mathematical procedure for a negative pressure supposes cell between the plasma membrane, the nucleus and a vacuole; using absolute values of the internal energy U and entropy S. it is a medium keeping granular-like and whisker-like The surface φ(U,S,V) = 0 corresponds to the all structures.
    [Show full text]
  • Introduction to the Cell Cell History Cell Structures and Functions
    Introduction to the cell cell history cell structures and functions CK-12 Foundation December 16, 2009 CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the “FlexBook,” CK-12 intends to pioneer the generation and distribution of high quality educational content that will serve both as core text as well as provide an adaptive environment for learning. Copyright ©2009 CK-12 Foundation This work is licensed under the Creative Commons Attribution-Share Alike 3.0 United States License. To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/3.0/us/ or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA. Contents 1 Cell structure and function dec 16 5 1.1 Lesson 3.1: Introduction to Cells .................................. 5 3 www.ck12.org www.ck12.org 4 Chapter 1 Cell structure and function dec 16 1.1 Lesson 3.1: Introduction to Cells Lesson Objectives • Identify the scientists that first observed cells. • Outline the importance of microscopes in the discovery of cells. • Summarize what the cell theory proposes. • Identify the limitations on cell size. • Identify the four parts common to all cells. • Compare prokaryotic and eukaryotic cells. Introduction Knowing the make up of cells and how cells work is necessary to all of the biological sciences. Learning about the similarities and differences between cell types is particularly important to the fields of cell biology and molecular biology.
    [Show full text]
  • 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.
    [Show full text]
  • PEX5 Regulates Autophagy Via the Mtorc1-TFEB Axis During Starvation
    Eun et al. Experimental & Molecular Medicine (2018) 50:4 DOI 10.1038/s12276-017-0007-8 Experimental & Molecular Medicine ARTICLE Open Access PEX5 regulates autophagy via the mTORC1-TFEB axis during starvation So Young Eun1,JoonNoLee2,In-KooNam2, Zhi-qiang Liu1,Hong-SeobSo 1, Seong-Kyu Choe1 and RaeKil Park2 Abstract Defects in the PEX5 gene impair the import of peroxisomal matrix proteins, leading to nonfunctional peroxisomes and other associated pathological defects such as Zellweger syndrome. Although PEX5 regulates autophagy process in a stress condition, the mechanisms controlling autophagy by PEX5 under nutrient deprivation are largely unknown. Herein, we show a novel function of PEX5 in the regulation of autophagy via Transcription Factor EB (TFEB). Under serum-starved conditions, when PEX5 is depleted, the mammalian target of rapamycin (mTORC1) inhibitor TSC2 is downregulated, which results in increased phosphorylation of the mTORC1 substrates, including 70S6K, S6K, and 4E- BP-1. mTORC1 activation further suppresses the nuclear localization of TFEB, as indicated by decreased mRNA levels of TFEB, LIPA, and LAMP1. Interestingly, peroxisomal mRNA and protein levels are also reduced by TFEB inactivation, indicating that TFEB might control peroxisome biogenesis at a transcriptional level. Conversely, pharmacological inhibition of mTOR resulting from PEX5 depletion during nutrient starvation activates TFEB by promoting nuclear localization of the protein. In addition, mTORC1 inhibition recovers the damaged-peroxisome biogenesis. These data suggest that PEX5 may be a critical regulator of lysosomal gene expression and autophagy through the mTOR-TFEB- autophagy axis under nutrient deprivation. 1234567890():,; 1234567890():,; Introduction Mitochondrial antiviral-signaling protein (MAVS) func- Peroxisome is an essential cellular organelle for per- tions as an antiviral signaling platform to induce the forming various metabolic activities, including oxidation interferon-independent signaling pathways4.
    [Show full text]
  • Membrane Fluidity and the Perception of Environmental Signals In
    Progress in Lipid Research 42 (2003) 527–543 www.elsevier.com/locate/plipres Review Membrane fluidity and the perception of environmental signals in cyanobacteria and plants Koji Mikami, Norio Murata* Department of Regulation Biology, National Institute for Basic Biology, Okazaki 444-8585, Japan Accepted 22 April 2003 Abstract Photosynthetic organisms, namely, plants and cyanobacteria, are directly exposed to changes in their environment and their survival depends on their ability to acclimate to such changes. Several lines of evi- dence suggest that temperature stress, such as unusually low or high temperatures, and osmotic stress might be perceived by plants and cyanobacteria via changes in the fluidity of their cell membranes. The availability of techniques for gene-targeted mutagenesis and gene transfer, as well as for the analysis of genomes and transcripts, has allowed us to examine and evaluate this hypothesis and its implications. In this review, we summarize recent studies of the regulation of gene expression by changes in the extent of unsaturation of fatty acids and membrane fluidity, and we present a discussion of the induction of gene expression by environmental stress and of sensors of environmental conditions and relationships between their activity and the fluidity of membranes in cyanobacteria and plants. # 2003 Elsevier Ltd. All rights reserved. Contents 1. Introduction ..........................................................................................................................................................
    [Show full text]