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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