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MEMBRANE STRUCTURE AND FUNCTIONS - Coggle Diagram
MEMBRANE STRUCTURE AND FUNCTIONS
passive transport
movement of small molecules across membrane without energy input
may require transport proteins
examples are
diffusion
movement of particles of any substance so that they spread out evenly into available space
substances diffuse down their concentration gradient
facilitated diffusion
transport proteins speed the passive movement of molecules across the plasma membrane
transport proteins include channel and carrier proteins
aquaporins facilitate the diffusion of water
ion channels facilitate the transport of ions
gated channels open or close in response to electrical stimulus
example in nerve cells
carrier proteins move substances down their concentration gradient
no energy input is required
osmosis
diffusion of water molecules not clustered around another substance across a selectively permeable membrane
active transport
movement of small molecules with energy
transport protein required
examples are
endocytosis
cells take in large molecules byy forming vesicles
three types
phagocytosis
cellular eating
pinocytosis
cellular drinking
receptor-mediated endocytosis
triggered by solute binding to receptor
human cells use to take in cholesterol carried in particles called low -density lipoproteins
exocytosis
cells release large molecules or waste using vesicles
example cells in pancreas secrete insulin by exocytosis
cotransport
occurs when active transport of solute indirectly drives tranport of other substances
fluid mosaic model
lipids and proteins are the main components of membrane
carbohydrates are also inclusive and mainly composed of phospholipids
phospholipids are amphipathic
containing hydrophobic and hydrophilic regions
depicts membrane as a mosaic of protein molecules bobbing in fluid bilayer of phospholipids
membranes are mainly held together by weak hydrophobic interactions
must be fluid to work properly
too fluid cannot support protein function
membranes rich in unsaturated fatty acids are more fluid
distribution of proteins, lipids, and carbohydrates are asymmetrical across the membrane
a membrane is a collage fof different proteins, often clustered in groups
phospholipid form the main fabric of membrane but proteins determine most of the membrane functions
two major types of protein membrane
peripheral proteins
bound to the surface of the membrane
integral proteins
penetrate the hydrophobic core
transmembrane proteins
are integral proteins that span the membrane
hydrophobic regions consist of no polar amino acids often coiled into an alpha helices
proteins called integrins attach to fibers of the extracellular matrix
cell surface membrane proteins can carry out several functions like
transport
enzymatic activity
signal transduction
cell-cell recognition
intercellular joining
role of carbohydrates in cell-cell recognition
glycolipids
carbohydrate bonded to lipids
glycoproteins
carbohydrates bonded to proteins
permeability of lipid bilayer
nonpolar molecules dissolve in the lipid and pass through the membrane rapidly
examples are hydrocarbons, carbon dioxide and oxygen
transport proteins
hydrophilic substances cross membranes more quickly through transport proteins
channel proteins
certain molecules can use as a tunnel
also called aquaporins
carrier proteins
bind molecules and change shape to shuttle them across the membrane
move only specific substances
water balance of cell without cell wal
tonicity
ability of a surrounding solution to cause a cell to gain or lose water
isotonic
if its solute concentratio is the same
plant cells become flaccid and the plant wilt
hypertonic
if the solute concentration is greater than inside the cell
plasmolysis
cell shrivels and the membrane pulls away from the cell wall in multiple locations
plant may wilt and die
hypotonic
if the solute concentration is less than that inside the cell
turgid
a plant cell takes up water and swells until the inelastic wall exerts back a pressure on the cell
membrane potential
is the voltage across a membrane
electrochemical gradient
drive the diffusion of ions across a membrane
chemical force
the ion's concentration gradient
an electrial foce
the effect of the membrane potential on the ion's movement
electrogenic pump
generates voltage across a membrane storing energy that can be used for cellular work
in animals its the sodium potassium pump
in plants, fungi and bacteria its the proton pump