Cell membrane, transport...Blood,Vol 89, No 10 (May 15), 1997: pp 3745-3754 Daunorubicin, an amine...
Transcript of Cell membrane, transport...Blood,Vol 89, No 10 (May 15), 1997: pp 3745-3754 Daunorubicin, an amine...
This lecture:
• Essential Cell Biology: chapters 11-12
All the pages are required, but:
• ion channels, the pumps and mechanisms relevant to
Ca, osmo- and pH regulation, also included in this
chapter of the book, will be discussed in other lectures
• - lecture slides marked by: contain basic
information absolutely required for tests and exams!
!
Lipid
bilayer
5 nm
Functions of the
plasmamembrane:
barrier
transport
signal transduction
Composition:
40-60 % lipid
30-50 % protein
10 % carbohydrate
RevisionMembrane structure and function
Revision
the carbohydrate components of the membrane (from the glycocalyx)
functions:
- surface protection
- cell communication,
recognition
- cell adhesion, extracellular
matrix
Membrane structure: carbohydrates
glycolipids (rare) and glycoproteins (common)
Membrane proteins – function and structure Revision
Inositol
GPI-linked protein
GPI = glycosil-
phosphatydilinositol
Membrane proteins interact with the Cell Cortex(actin meshwork in the cytosol ”below” the membrane)
Red blood cell membrane and its
connections with the cell cortex
Important proteins: actin, ankyrin
(anchor to transmembrane proteins)
spectrin (dimer, forms a mesh)
Intracellular side!!!
!
Molecular complexity of membrane – cell cortex connection
Red blood cell:
Over 50 transmembrane proteinsOutlook
Figure 4. Red cell morphology. Hereditary
spherocytosis (HS; top panel); nonhemolytic
hereditary elliptocytosis (HE; middle panel);
elliptocytes, poikilocytes, and fragmented red cells in
hemolytic HE (bottom panel). BLOOD, 2008, 112(10)
Cell shape is determined by
cell cortex cytoplasmic content
E
S
Hb-S Hb-A
Defects in the vertical spectrin interactions:
spherocytosis (S)
Defects in horizontal interactions:
elliptocytosis (E).
A Info
!
Lipid synthesis and steady-state composition of various membrane
structures
Mitochondria
have bacterial
lipids.
Low cholesterol
in Mitoch., ER,
nuclear envelope
Major
differences
between
organelles
site of synthesis: mostly SER (also Golgi, plasma membrane inner surface)
mammals
yeastsInfo
!
!
!
!
!
1. lipid incorporation into cytoplasmic leaflet
2. flippases/floppases scramblases
3. selective retention
The lipid composition of the cytoplasma
membrane is asymmetric
PS exposure on
the surface of
dying cells: ”eat-
me” signal for the
phagocytes
!
Asymmetric
composition curvature
Lipid shape determines membrane curvature
©2011 by Cold Spring Harbor Laboratory Press
curvature
Info
cylinders (e.g.: PC)
cones (e.g.: PE)
inverted cones
(e.g.: lysoPC)
PC: phosphatidyl choline; PE : phosphatidyl ethanolamine
PS PS
repel
…unless shielded by cholesterol,
so in equilibrium
CHOL/PS/CHOL/PS/CHOL can be flat, but
after extracting cholesterol, PS/PS/PS/PS is curved
Lipid charge also matters…
Mobility may be restricted by…
(E)(D)
!
Lateral mobility
… clustering / molecular interactions
… and molecular fences
Frye-Edidin expt.
Focal adhesion
Immune synapse
signalosome
hypotonic isotonic
ghostvvt
- Allows diffusion of hydrophobic substances
- Renders membranes deformable
- Explains their regenerative capacity
Deformability – important e.g. in
capillaries
Expreimnt
demonstrating
regenerative
capacity
Right side out
Inside out
Membrane fluidity
3. Energetics– Passive
• Simple diffusion
• Facilitated transport
– Active
• Primary
• secondary
4. Solubility of transported
substance– hydrophylic
– hydrophobic
1. Membrane structure– lipid bilayer
– complete biological membrane
– one or two bilayers
2. Number of different transported
substances and direction of transport– uniport
– Cotransport
– Symport
– Antiport
m
aq
C
CR
Classification of membrane transport from various aspects !
RevisionReal (biological) membranes: passive and active
transport
Passive transport
Along electrochemical
gradient
Active transport
Against electrochemical
gradient
Simple
diffusion
Channel transporter/
carrier
Electrochemical
gradient *
* For charged particle, make sure to use ”Electrochemical
gradient”, concentration gradient is wrong!
mechanism
resembles that of
valinomycin, an
ionophore antibiotic
K+
!Facilitated diffusion = Carrier-mediated (passive) transport
E.g. Glucose uniport(see examples in the Biophysics lecture!)
symport antiport
P V F ABCNa/K* Pgp,etc
Vacuolar
Mitochondrial
Secondary active
transporters, carriers
!Main categories of active transport
* The Na/K-ATPase is also
antiport by directionality, but it is
not a coupled/secondary active
transporter; it is a P-type pump.
See next lecture
!ATP- driven pumps. 1. P-type ATPases
P-type ATPases get transiently phosphorylated during their duty cycle
Typical examples are the Na/K-ATPase (see Biophysics lecture also! and the calcium
ATPases (see calcium homeostasis lecture).
!ATP- driven pumps: 2. V and F type ATPases
- V-type ATPases DO NOT get
transiently phosphorylated
- ‚V’ for Vacuole or Vesicle
- Responsible for acidification of
lysosomes
- Against H+ gradient
Pro
ton
gra
dien
tP
roto
n g
rad
ien
t
lysosome Mitoch.
matrix
- F0F1 ATPases DO NOT get
transiently phosphorylated
- Structurally related to V-type
- Generates ATP in mitochondira
- Uses H+ gradient
- Works in reverse as compared to
V-type under physiological
conditions (but can be reversed)
What do you expect to
occur when inhibiting
the Na/K-pump? (with
digitalis or ouabain)
!Intestinal glucose transport
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/sympo.htm
~ 30% of total energy consumption in the cell!
!
Most coupled (secondary active) transport processes depend on the
Na+ gradient, which is built up by the Na/K ATPase
What makes intestinal glucose transport unidirectional (rectified)?
Segregation of specific transport proteins
(„Gram-negative”) bacteria have two cell membranes
outer membrane: porins render it permeable
inner membrane: transporters
Lodish, Fig.
15-15
Alberts, Fig.
11-17
info
Transport of hydrophobic molecules
• Passive transport depends on:
– R (lipid / water partition coeff.)
– i.c. partition - Henderson-Hasselbalch eq.
• Active transport:
– ABC (ATP binding casette) transporters – next lecture
– Other transporters
pH = pK + log(M/M+)
1C
Caq
m
R
Hydrophobic
!
lipid-water partition coeff.
effe
ctiv
eco
nce
ntr
atio
nLipid-water partition coefficient (R) !
For non-charged molecules, lipid-water partition coefficient alone
determines accumulation in the membrane and in the cell. The higher
the R, the more the concentration in the membrane and also in the
cytosol.
General anaesthetics are usually
lipid soluble. Their efficacy is
proportional to their R value, so
the higher their R, the smaller
concentration is sufficient for
reaching an anaesthetic effect.
General anaesthetics can change the conformation of ion channels
through embedding into the membrane and as a result increasing
lateral pressure within the membrane.
hydrostatic
pressure
ether
Ether added to the fishtank
partitions into the cell membrane
(also) of the fish’s neurons, and
inhibits Na+ channels. Incerasing
hydrostatic pressure (e.g. filling
up the tank with a high level of
water) exprimes the ether
molecules from the membrane
and the fish wakes up.
R-NH2
lysosome
pH ≈ 5cytoplasm
pH ≈ 7
R-NH2
R-NH3+
R-NH3+
pH-dependent partitioning !
”Lysosomotropic amines” can accumulate in lysosomes. At physiological pH, these
compounds are mostly unionized and passively diffuse across the lipid bilayers of
organelles. Upon entering the acidic environment of the lysosome they become
predominantly ionized and therefore less able to diffuse out, resulting in their
accumulation. The high cc. (1) is harmful for the lysosomes and (2) sequesters much of
the drug, decreasing its effect on other targets. Local anaesthetics (e.g. lidocaine) and
some cytostatic drugs (e.g. daunorubicine) are examples.
pH = pK + log(M/M+)pK: the pH where the concentration of
neutral and charged forms is equalHenderson-Hasselbalch: determines intracellular
distribution of amphiphilic materials
Daunorubicin accumulation in lysosomes
Blood,Vol 89, No 10 (May 15), 1997: pp 3745-3754
Daunorubicin, an amine that can be protonated, is a DNA-intercalating drug used in
cancer treatment . It exerts its effect partly in the nucleus. Tumor cells with high
lysosomal activity may defer some of its nuclear effect by sequestering it in acidic
lysosomes.
Keywords
• amphiphilic (amphipathic)
compounds
• lipid bilayer
• electrochemical gradient
• lipid-water partitioning
coefficient
• Henderson-Hasselbach equation
and its meaning
• facilitated diffusion
• carrier mediated passive
transport
• passive and active transport
• coupled transport (secondary
active) transport, examples of
(Na/glucose and Na/Ca)
• Na/K pump,
• glucose uniport
• P-type, V-type transporters
!