Cell Biology Chapter 7 Flashcards
What are the membrane functions?
Define boundaries of a cell and organelles and act as permeability barriers; Serves as sites for biological functions, such as electron transport; possess transport proteins that regulate the movement of substances into and out of cells and organelles, contain protein molecules that act as receptors to detect external signals, provide mechanisms for cell to cell contact, adhesion, and communication; Membranes define boundaries of the cell and its components: they are effective permeability barriers because their interior is hydrophobic, the plasma membrane surrounds the whole cell, whereas intracellular membranes compartmentalize functions within the cell; the plasma membrane separates a cell rom its surroundings, enabling the molecular composition of a cell to differ from that of its environment: in some bacteria the plasma membrane is the only membrane, eukaryotic cells also have internal membranes that enclose individual organelles, all cell membranes prevent molecules on one side from freely mixing with those on the other
What is the membrane and transport?
Membranes are associated with specific functions, the molecules responsible for the functions are embedded in or localized on membranes, membrane proteins carry out and regulate the transport of substances across the membrane, cells and organelles take up nutrients, ions, gases, water, and other substances, and they expel products and wastes, some substances diffuse directly across membrane whereas others must be moved by specific transporters
What is the membrane and its signals?
a cell receives information at their surface from its environment: electrical signals and chemical signals, signal transduction- mechanisms by which signals are transmitted from the outer surface to the interior of a cell, chemical signal molecules usually bind to membrane proteins called receptors, these receptors are located on the outer surface of the plasma membrane, in nearly all types of cells membrane receptors allow cells to: recognize and transmit, respond to a variety of specific signals; binding of signal molecules to their receptors, triggers chemical events on the inner membrane surface, ultimately lead to changes in cell function. Types of junctions between cells in animal tissues: Tight junctions form seals that block the passage of fluids between cells, Adhesive junctions hold cells together, Gap junctions allow for communication between adjacent animal cells,In plants, plasmodesmata perform a similar function,
What is the membrane and cell to cell communication?
Adheren junctions are a type of adhesive junction where membrane proteins and actin hold membranes together, Adherens junctions are built from: Cadherins-Transmembrane proteins whose extracellular segments bind to each other and whose intracellular segments bind to catenins, Catenins - are connected to actin filaments and Cadherins
What is the membrane model and organization? Know how to label its components
The fluid mosaic bilayer model has two key features: 2 fluid layers of lipids - fluid lipid bilayer, A mosaic of proteins attached to or embedded in the bilayer; Most integral membrane proteins have one or more hydrophobic segments that span the lipid bilayer, These transmembrane segments anchor the protein to the membrane; Membranes are: Not homogenous, freely mixing structures, Ordered through dynamic micro domains called lipid rafts (discussed below), Most cellular processes that involve membranes depend on structural complexes of specific lipids and proteins
What are the Membrane Lipids general role and main classes?
Membrane lipids are important components of the “fluid” part of the fluid mosaic model, The main classes of membrane lipids are: Phospholipids, Glycolipids, Sterols; Phospholipids are the most abundant lipids in membranes Phospholipids are made of: the glycerol-based phosphoglycerides, the sphingosine-based sphingolipids, The kinds and relative proportions of phospholipids vary greatly among types of membranes; Glycolipids are formed by the addition of carbohydrates to lipids, Some are glycerol based (the glycoglycerolipids), and some are sphingosine based (the glycosphingolipids); The membranes of most eukaryotes contain significant amounts of sterols, The main sterol in animal cell membranes is cholesterol, Cholesterol is needed to stabilize and maintain membranes; Fatty acids are components of all membrane lipids except the sterols, Their long hydrocarbon tails provide a barrier to diffusion of polar solutes, Fatty acids vary considerably in the presence and number of double bonds, Saturated fatty acids – NO double bonds between carbons Unsaturated fatty acids Double bonds between carbons
What are the Membrane Lipids membrane asymmetry and maintenance
Membrane asymmetry - is the difference between the monolayers, Depends on the kind of lipids present and the degree of saturation of fatty acids in the phospholipids, Most of the glycolipids in the plasma membrane of animal cells are in the outer layer, Membrane asymmetry is established during the synthesis of the membrane; Enzymes in the ER make the new phospholipids, These phospholipids are deposited in the cytosolic part of the lipid bilayer, Membranes grow evenly, Therefore, lipids must move between layers to maintain balanced composition; Once established, membrane asymmetry does not change much, The movement of lipids from one monolayer to another requires their hydrophilic heads to move all the way through the hydrophobic interior of the bilayer, This transverse diffusion (or “flip-flop”) is relatively rare compare to the fluidity within the monolayer, Phospholipid flip-flop does occur in natural membranes
Some membranes, have proteins that catalyze the flip-flop of membrane lipids, These proteins are called phospholipid translocators
What are the Membrane Lipids membrane fluidity and mobility of lipids
Scramblase – flips lipids back and forth the monolayers for equilibrium; Flippase – flips from outer to cytosolic; Floppase – flips from cytosolic to outer; Lipids are mobile within their monolayer, Rotation of phospholipids about their axes can occur, Phospholipids can also move within the monolayer, via lateral diffusion, Both types of movement are rapid and random; Fluidity of a membrane depends mainly on the fatty acids that it contains, The length of fatty acid chains and the degree of saturation both affect the fluidity of the membrane; Saturated fatty acids pack together well in the membrane, Fatty acids with one or more double bonds have bends in the chains that prevent them from packing together neatly, Thus, unsaturated fatty acids are more fluid than saturated fatty acids, Most plasma membrane fatty acids vary in chain length and degree of saturation, This helps to ensure that membranes are fluid at physiological temperatures; Membrane fluidity is influenced by sterols, The intercalation of rigid cholesterol molecules into a membrane decreases its fluidity, Cholesterol prevents hydrocarbon chains of phospholipids from packing together tightly
What are the Membrane Lipids lipid rafts?
Localized regions of membrane lipids in association with specific proteins are called lipid microdomains, or lipid rafts, These are dynamic structures, changing composition as lipids and proteins move into and out of them, Lipid rafts in the outer monolayer of animal cells have elevated levels of cholesterol and glycosphingolipids and are less fluid than the rest of the membrane; Lipid rafts contain actin-binding proteins, suggesting that the cytoskeleton may play a role in their formation and organization; Depleting cholesterol from a membrane or disrupting the actin cytoskeleton can both interfere with the targeting of proteins to rafts; Lipid rafts are thought to have roles in detecting and responding to extracellular signals; When a receptor molecule on the outer surface of the plasma binds its ligand, it can move into lipid rafts also located in the outer monolayer, Lipid rafts containing receptors are coupled to lipid rafts on the inner monolayer, Some lipid rafts contain kinases, enzymes that generate second messengers in a cell via phosporylation of target molecules
What are membrane proteins general roles and different types and their structure Integral membrane proteins?
The mosaic part of the fluid mosaic model includes lipid rafts and other lipid domains, Membrane proteins are the main components of the mosaic part of the membrane; Membrane proteins have different hydrophobicites and so occupy different positions in or on membranes; Membrane proteins fall into three categories: Integral, Peripheral, Lipid anchored; Integral membrane proteins - are embedded in the lipid bilayer because of their hydrophobic regions, Integral membrane proteins possess one or more hydrophobic regions with an affinity for the interior of the lipid bilayer, Integral monotropic proteins are embedded in just one side of the bilayer, Transmembrane proteins span the membrane and protrude on both sides, Transmembrane proteins cross either once (singlepass proteins) or several times (multipass proteins), Most transmembrane proteins are anchored to the lipid bilayer by one or more hydrophobic transmembrane segments
Singlepass Membrane Proteins, Singlepass membrane proteins have the C-terminus extending from one surface of the membrane and the N-terminus from the other
Multipass Membrane Proteins, Multipass membrane proteins have 2–20 (or more) transmembrane segments, passing though the membrane one or more times. The Structures of Two Integral Membrane Proteins. (a) Glycophorin is a singlepass integral membrane protein (b) Bacteriorhodopsin is a multipass integral membrane protein in the plasma membrane of Halobacterium.
What are membrane proteins general roles and different types and their structure Peripheral membrane proteins?
Peripheral proteins - are hydrophilic and located on the surface of the bilayer; Peripheral membrane proteins lack discrete hydrophobic regions and do not penetrate the lipid bilayer, Some hydrophobic residues play a role in anchoring them to the membrane surface
What are membrane proteins general roles and different types and their structure Lipid-anchored membrane proteins?
The polypeptide chains of lipid-anchored membrane proteins are located on the surfaces of membranes, They are covalently bound to lipid molecules embedded in the bilayer; Proteins can be isolated form the membranes and studied through X-ray crystallography. Membrane proteins are hard to isolate and crystallize; Hydropathy Analysis can be used to also predict membrane proteins by predicted residues that would be likely located in the membrane
What are membrane proteins function and how do they travel from ER to plasma membrane?
The study of membrane proteins has been revolutionized by DNA sequencing and recombinant DNA technology, Amino acid sequence can be deduced from DNA sequence, Site-specific mutagenesis allows determination of how certain amino acids affect protein function; Enzymes - accounts for the localization of particular functions to specific membranes, Electron transport proteins are closely related to enzymes in function keeping gradients of electrons on each side of the membrane, Transport proteins - facilitate the movement of nutrients across membranes, Channel proteins - provide hydrophilic passageways through hydrophobic membranes, Transport ATPases - use the energy of ATP to transport ions across membranes, Receptors - recognize and mediate the effects of specific chemical signals on the surface of the cell; Membrane proteins involved with intercellular communication include:
Proteins that form connexons at gap junctions in animal cells, Proteins that make up plasmodesmata in plant cells; Membrane proteins play roles in uptake and secretion of substances by endocytosis and exocytosis, They take part in targeting, sorting, and modifying proteins in the endoplasmic reticulum and Golgi complex, They participate in autophagy, the digestion of a cell’s own organelles or structures; Membrane-associated proteins play structural roles in stabilizing and shaping the cell membrane, In animal cells, a cytoskeletal meshwork of peripheral membrane proteins underlies the plasma membrane of many kinds of cells
What are membrane proteins modifications?
Membrane proteins exhibit asymmetric orientation with respect to the lipid bilayer, Once in place, in or on one of the monolayers, proteins cannot move across the membrane from one surface to the other; Glycoproteins are membrane proteins with carbohydrate chains covalently linked to amino acid side chains, The addition of a carbohydrate side chain to a protein is called glycosylation, Glycoproteins are most prominent in plasma membranes, where they play a role in cell-cell recognition, The carbohydrate groups protrude on the outer surface of the cell membrane; Glycocalyx – surface coat in animal cells formed from carbohydrate groups of plasma membrane,The glycocalyx is a type of identifier that the body uses to distinguish between its own healthy cells and transplanted tissues, diseased cells, or invading organisms, The glycocalyx are also cell-adhesion molecules that enable cells to adhere to each other
What are membrane proteins mobility?
Membrane proteins are more variable than lipids in their ability to move freely within the membrane, Some proteins can move freely, whereas others are constrained because they are anchored to protein complexes; Diffusion of many membrane proteins is restricted to a limited area of the membrane; Some membranes consist of separate membrane domains that differ in protein composition and therefore in function, Membrane proteins aggregate within the membrane, forming large, slow-moving complexes, Membrane proteins also form structures that become barriers to diffusion, creating membrane domains; The most common restraint on mobility of membrane proteins is anchoring of such proteins to structures to one side of the membrane or the other, Many proteins of the plasma membrane are anchored either to cytoskeleton or to extracellular structures; One of the main peripheral proteins of the red blood cells plasma membrane is spectrin, Spectrin and its associated proteins provide mechanical support to the plasma membrane
