LECT21 memb2.PPT

8/9/2019 LECT21 memb2.PPT

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Membrane TransportA Thermodynamic Perspective


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4 ways to penetrate the Cell

Membrane

Simple Diffusion

Passive transport (facilitateddiffusion)

Active transport (enery!dependent)

"eceptor!mediated endocytosis


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Simple Diffusion

#nitial

$ih

%ow

&inal


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'A the chemical potential of A

(also called the partial molar free enery)

'Ao chemical potential of standard state

'A 'A(in) ! 'A(out) (final ! initial)

Thus*

e+eronic#f ,A-out is . ,A- in/ 'A is neative

#f ,A-out ,A-in/ 'A is 0ero

#f ,A-out is 1 ,A- in/ 'A is positive enderonic

'A2 'Ao "Tln,A- (free enery varies with conc3 A)

'A 'A(in) ! 'A(out) RTln,A-in

,A-out


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7alanced

Rule:

Rule: Free energy change is zero when the

concentration of A on both sidesis the same

'A(in) 'A(out)

(out)(in)

&inal state 2 #nitial state

' 8


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'A(in) . 'A(out)

Rule: When chemical potential of A(in) is greater than

A(out) energy must be provided to drive A across

the membrane i!e! ma"e free energy change negative

Rule: When chemical potential of A(in) is greater than

A(out) energy must be provided to drive A across

the membrane i!e! ma"e free energy change negative

(out)

nery ATP or a proton radient

&inal state 2 #nitial state ' positive

(in)


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Rule:Rule:

The movement of ions presents a separate challengebecause not only must the mass difference

(chemical potential) be ta"en into account but also the

charge differential (electrochemical potential)

electrochemical potentialrefers to the state of

(#) ($) charges on both sides of the membrane

The electrochemical potential is referred to as the

membrane potentialwhen dealing with cells


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and

'A 'A(in) ! 'A(out) 9A&

lectrochemical potentiallectrochemical potential

Total neryTotal nery

'A 'A(in) ! 'A(out) RTln,A-in

,A-out

'A RTln,A-in

,A-out: 9A&

Membrane potential

Chemical potentialChemical potential

Te+tp;


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'5a: RTln

,A-in

,A-out: 9A&

=3;>4 + (;>8 ?) + ln ,838>8-,83>@8-

: (>) B3= Emole

5a: 5a

:

5a : 5a

:

5a :

5a:

5a:

5a:

5a:

5a :

5a:

5a:5a

:

5a:

>@8 mM >8 mM

>@*>

(! 8 mF)

G

GG

:

::


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5a: 5a

:

5a : 5a

:

5a :

5a:

5a:

5a:

5a:5a

:

5a:

>@8 mM >8 mM(: 8 mF)

G

G

G

:

::

#nHut

5a:

5a :

5a:

5a :

'5a: RTln

,A-out

,A-in: 9A&

=3;>4 + (;>8 ?) + ln ,83>@8-,838>8-

: (>) B3= Emole


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Cl2

>@8 mM >8 mM(: 8 mF)

G

GG

:

::

#nHut

'Cl! RTln

,A-in

,A-out: 9A&

=3;>4 + (;>8 ?) + ln ,838>8-,83>@8-

: (>) 38 Emol


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Cl2

>@8 mM >8 mM(2 8 mF)

G

G

G

::

:

#nHut

'Cl! RTln

,A-out

,A-in: 9A&

=3;>4 + (;>8 ?) + ln,83>@8-

,838>8-: (>) 3>< Emol


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&acilitated Diffusion (Mediated Transport)


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Modes of Transport


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ATP!Driven (Active) Transport ,CaB:!ATPase-


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Vesicle Trafficking

The secretory pathway

The trans-Golgi network

The signal hypothesis

Protein targeting


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"ule* Proteins destined for secretion from a cell or forrelocation to a membrane or a specific oranelle are

synthesi0ed on the rouh endoplasmic reticulum ("")

Definition* The "" consists of ribosomes bound to

membranes enclosin an internal hollow space or cisternae

Action* Proteins pass into the space and transit to the 'oliwhile entrapped in vesicles

Selection* Proteins possess a signal se%uencethat isreconi0ed by a receptor on the membrane


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'oli

Secretory

ranule

""

Cis 'oli

Trans

Protein inserted

in plasma membrane

Pre!lysosome


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Sinal $ypothesis

Proteins destined for secretion or transit to membranes and

oranelles/ have a sinal peptide that allows them to enter the

"" cisternae

The sinal peptide is reconi0ed by a receptor called the

Jsinal reconition particleK (S"P) on the "" membrane

Sinal seLuences on the 5!terminal represent a strin of

leucine!rich hydrophobic amino acids that allow the

peptide to doc with the receptor

The sinal peptide is removed after the peptide has

penetrated the membrane


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'TP

S"P

Docin

:5$;

'TP

:5$;

Carbohydrate

'DP

"ouh ndoplasmic "eticulum

%umen of cisternae

Sinal $ypothesis

S"P receptor

Sinal Peptide

cleaved

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