membrane functions- i

8/7/2019 Membrane Functions- I

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MembraneMembrane

FunctionsFunctions-- IIosmosis, active transport, ionchannels and ion pumps

Presented by:-Apurva Patel

Sem- VIM.Sc.BiotechnologyV.N.S.G.University.


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contentscontentsIntroduction

Functions

Permeability of membrane

Transport across membrane Passive transport

Osmosis

Ion channelsCarrier protiens

Active transport

Summary


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All cells have a plasma or cell membrane, which contains the

cell. Scanning electron micrograph (SEM) of adipocytes (Ad)

Introduction


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Intro uctionIntro uction

Prokaryotic cell- bacteria


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Membrane functionsMembrane functions


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Per eability of e branePer eability of e brane


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Transport across e braneTransport across e brane1. Passive transport

1. Diffusion of water (Osmosis)

2. Diffusion of ions (Ion channels)

3. Faciliated diffusion (Carrier proteins)

2. Active transport1. Primary active transport

1. ATP Driven

1. P type

2. V type3. ABC Transporter

2. Light Driven

1. bacteriorhodopsin

2. Secondary active transport

1. Ion Gradient


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Passive Transport (Diffusion)Passive Transport (Diffusion) Transport of solutes from a region of higher

concentration to the region of lower concentration tillboth the concentration becomes the same

Depends on random thermal motion of solutes

An exergonic process driven by an increase in entropy.G= RTLn [Ci]/[Co]

Where,

G= free energy change

T= temperature

R= gas constant

[Ci]/[Co]= concentration of solute inside/concentration ofsolutes outside


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Diffusion of water=Diffusion of water= Os osisOs osisOsmosis is the passive transport of water

Water moves readily through a semi permeablemembrane from a region of lower soluteconcentration to a region of higher soluteconcentration. This process is called as osmosis.


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Osmotic ShockOsmotic Shock


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Osmosis in Pocket Switch NetworksOsmosis in Pocket Switch Networks

(PSNs)(PSNs) Osmosis for file sharing!!! This scheme forwards lookups in an epidemic

fashion & then take advantage of the traces

left behind to route reply messages. By analogy to the natural phenomenon of

osmosis in biology, those traces representthe solute & define the potential of nodesover the network.

The reply messages then flow towards highpotential areas, closer & closer to theoriginal lookup sender.


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In 1995, Alan Hodgkin & RichardKeynes first proposed that cellmembrane contain ion channels.

Ion channels are transmembraneprotien that function as selective poresthrough which molecules or ions candiffuse across the membrane.

About 1 billion ions/sec are

transported through each channel. Have Gates that open & close.

Diffusion of ions =Diffusion of ions = Ion ChannelsIon Channels


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Classification of ion channelsClassification of ion channels Ligand gated channels

Nicotinic Acetylcholine receptor

Voltage gated channels

K+ ion channelKcsA

Kv

Second messenger gated channels

G-protiens Mechanosensitive channels

Movements of streocilia on hair cells 0f innerear

Gap junctions, porins not gated


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Nicotine Acetylcholine receptorNicotine Acetylcholine receptor


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Potassium ion channelsPotassium ion channels


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The Transient ReceptorThe Transient Receptor

Potential (T

RP) Ion channelsPotential (T

RP) Ion channels TRP shows diverse biophysical properties &

gating mechanism.

Were found to play an important role in

sensory physiology, being involved in almostevery sensory signal initiation from painsensation to the 5 senses.

Plays a major role in the transepithelial Ca+2 &Mg+2 transport.

Eg. TRPC1 & TRPA1--- MechanosensitiveTRPV4 --- thermo sensitive


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Diseases causes due to defectsDiseases causes due to defects

in ion channelin ion channelCystic fibrosis (CFTR)

Liddles syndrome ( ENac)

Long-Qt syndrome

(KVLQTI)


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Faciliated diffusion =Faciliated diffusion = carrier moleculescarrier molecules Carrier proteins dont have pores!!!

The substance being transported is initially bound to aspecific site on carrier protein.

This causes conformational changes in protein whichexpose the substance to the solution on other side ofmembrane & finally it dissociates from protein.

This passive carrier mediated transport is called asfaciliated diffusion.

Eg. Glucose transporter.


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Glucose transporterGlucose transporter

Humans have atleast 5 isoforms of glucose

transporter.These isoforms termed as GLUT1 to GLUT5are distinguished by the tissues in which theyare located.


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Difference between passive & activeDifference between passive & active

transporttransport


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Active TransportActive Transport Protein mediated transport of molecules across the cell

membrane against a concentration medium

Of 2 types Primary

secondary


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Pri ary active transportPri ary active transport Coupled directly to source of energy

like

Protein that carry out primary activetransport are called pumps!!!

2 types

ATP Driven

P type

V type

ABC transporter

Light driven

bacteriorhodopsin


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P class ion pumpsP class ion pumps Use ATP hydrolysis to create ion gradients

required for function of ion channels and cation

coupled carriers

ATP hydrolysis provides the energy that drivesthe pump

Use high energy ATP intermediate


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V Class ion pumpsV Class ion pumps Use ATP energy to move protons from cytosol

into organelles (lysosomes)

Generally function to maintain the low pH ofacidic vesicles

Protons flow against the gradient !!!


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ABCTransporterABCTransporter Largest transport ATPase family

(> 50 members)

Containsfour domains: twohydrophobic domainseach with

six transmembrane span(function to translocate)and twoATP-bindingcassettes (ABC)

Inprocaryotes, the transporterlocates in the inner membrane

tocarrynutrients into thecell Thecounterpartof the

eucaryotic:multidrugresistance(MDR)protein, which produceresistance to drug.


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Ion pumps as targets forIon pumps as targets for

therapeutic interventiontherapeutic interventionSodium-potassium pump ofcadiac cells

Diseases------ congestive

heart failureCause--------- high force

of concentration due toincrease systolic calcium

indirectly related tosodium pump inhibition.

Treatment---- blocking ofsodium pump by digoxin.


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Secondary Active transportSecondary Active transport Co-transport- a membrane protein couples the transport

of 2 solutes.

A substance that has been pumped across a membrane cando work as it leaks back by diffusion.

Plant cell can uses hydrogen gradeint generated by protonpumps to drive active transport of amino acids, sugars &other nutrients.


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ReferencesReferences Lehninger_biochemistry

Cell and molecular biology-gerald karp

Plant physiology- Taiz & Zeiger

Cell membrane tranport- Arnost & Karel

Cell biology LABFAX- Dealtry & Rickwood

Cell biology for biotchnologist- A.Stanley

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David S. Perlin;EJB Electronic Journal of Biotechnology ISSN: 0717-3458Vol.1No.2, Issue of August 15, 1998.1998 by Universidad Catlica de Valparaso -Chile

The Transient Receptor Potential (TRP) Ion Channels A Remarkable MultifunctionalSuperfamily Ofra Gohar, Ph.D.

Mechanisms of Disease FRANKLIN H.EPSTEIN, M.D.,Editor Ion channelsbasicscience andclinical disease.. Michael J.Ackerman, M,D,Ph,D.. AndDavidE, clapman,M.D., Ph.D.

Osmosis in Pocket SwitchedNetworks Pan Huiy, Jeremie Leguayzx, JonCrowcroft, James Scotty, Timur Friedmanz, Vania Conanx; University ofCambridge; Intel Research Cambridge; Universit e Pierre et Marie Curie,Laboratoire LIP6CNRS Thales Communications


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membrane functions- i

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