Lecture 3- cell membranes

Endoandexcocytosisallowtheimportandexportof

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Unformatted text preview: o*energy*required !the*diffusion*of*molecules*across*a*membrane*through* the*aid*of*a*transporter !transport*depends*upon*a*concentration*gradient* across*the*membrane!*when*the*gradient*falls*to*0,* diffusion*stops 31 !Transport*proteins*display*a*high*degree*of*substrate* • Transport proteins have much in common with enzymes. – specific binding sites for the solute. – can become saturated when they are translocating passengers as fast as they can. – can be inhibited by molecules that resemble the normal “substrate.” speci+icity;*similar*to*enzymes !This*speci+icity*allows*various*cells*and*cellular* compartments*to*tightly*control*whatt*gets*in*and*out • When these bind to the transport proteins, they outcompete the normal substrate for transport. 10:25 Gardiner 2013 32 • Many transport proteins simply provide corridors allowing a specific molecule or ion to cross the membrane. – These channel proteins allow fast transport. – For example, water channel proteins, aquaprorins, facilitate massive amounts of diffusion. 10:25 !Channel*proteins*form*hydrophilic*pathways*in*the* membrane*through*which*molecules*can*pass !Channels*are*sculpted*to*ONLY*+it*speci+ic*molecules !Ex.*aquaprorins*facilitate*the*diffusion*of*water 33 11 Active*Transport:* !need*energy*(usually*in*the*form*of*ATP) !travel*AGAINST*gradient:*movement*from*low* concentration*to*high*concentration !takes*ions*from*the*low*concentration*side*and*transfers* it*to*the*high*concentration*side Transport Proteins !ex.*sodium*potassium*pump – Most molecules are accumulated in the cell against a concentration gradient – Energy is required – Some molecules are allowed to freely pass – glucose transporter in red blood cells 10:25 Gardiner 2013 1202B • Passive Transport BIOLOGY • Active Transport Passive*Transport: !movement*of*a*substance*across*a*membrane*without* energy !Diffusion*drives*passive*transport:*diffusion*is*the*net* movement*of*a*substance*from*a*region*of*higher* concentration*to*a*region*of*lower*concentration !The*larger*the*gradient,*the*faster*the*rate*of*diffusion !Diffusion*is*an*entropy!driven*process*and*when* maximum*disorder*is*reached,*the*molecules*release*free* 34 energy*which*can*accomplish*work *See*+igure*5.1*on*page*105*of*tex...
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This note was uploaded on 02/11/2014 for the course BIO 1202B taught by Professor Almanke during the Winter '12 term at UWO.

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