Biomembrane Structure and
Function
Dr Sherline Brown
Learning Objectives

Describe the structural relationships of the
components of the membrane and general functional
roles served by each of them

Describe the processes by which small solutes, ions
and macromolecules cross biomembranes

Describe various membrane transport pumps
including their energy source, and functional
significance
Biomembrane structure


Cell (plasma membrane):
defines cell boundaries
Internal membranes define a
variety of cell organelles
-Nucleus
-Mitchondria
-Endoplasmic reticulum
-Golgi apparatus
-Lysosomes
-Peroxisomes
-Chloroplasts
Biomembranes




Surrounds cell
Separates cell from environment
– Allows cellular specialization
Separate some of the cellular organelles
– Allows specialization within the cell
Continuity of membranes between adjoining cells
(tight junctions) can separate two extracellular
compartments
– Important in organ function
Features of a biomembrane

Sheet like structures

Consists mainly of lipids and proteins

Lipids have hydrophilic and hydrophobic moieties

Specific proteins mediate specific functions of the
membrane (pumps, channels, receptors etc)
Features of a biomembrane

Membranes are non-covalent entities

Membranes are asymmetric

Membranes are fluid structures

Electrically polarized (plays a role in transport)
Composition of a biomembrane

Phospholipid bilayer (basic structure)

Various membrane protein (depending on
membrane function)

Glycolipids and glycoproteins (proteins and lipids
attached to carbohydrate)

Cholesterol (in animal cells)
Membrane lipids
There are 5 general types of membrane lipids

Glycerophospholipids :hydrophobic region consists of
fatty acids joined to glycerol

Glycolipids & sulfolipids :fatty acids esterified to
glycerol, lack phosphate
Membrane lipids
Tetraether lipids : (archae) 2 long alkyl chains linked to
gylcerol at both ends

Sphingolipids: single fatty acid joined to fatty amine

Sterols /cholesterol: 4 fused hydrocarbon rings
Membrane Lipids

Phospholipids
-Major lipid component of
most biomembranes
-Amphipathic (hydrophobic
and hydrophilic)
-Examples
phosphatidyl-choline
P-serine
P-ethanolamine
P-inositol
Phospholipid bilayer
Membrane lipids
Galactolipids and Sulfolipids
Galactolipids
Two galactose residues are joined to diacylglycerol

Predominate in plant cells

Located in thylokoid membranes of chloroplast

Make up 70-80% of the total lipids of vascular plants

They are the most abundant membrane lipids in the
biosphere
Membrane lipids
Galactolipids and Sulfolipids
Sulfolipids

Found in plant membranes

Sulfonated glucose residue is joined to
diacylglycerol
Membrane lipids
Sphingolipids

They are derivatives of
the lipid sphingosine

Sphingosine has a
long hydrocarbon tail,
and a polar domain that
includes an amino
group

.
Membrane lipids
Sphingolipids

They differ from
phospholipids and
galactolipids in that
they contain no
glycerol.
Membrane lipids
Sphingolipids

Sphingosine may be reversibly
phosphorylated to produce the
signal molecule sphingosine-1phosphate.

Other derivatives of sphingosine
are commonly found as
constituents of biological
membranes
Membrane lipids
Sphingolipids


The amino group of
sphingosine can form an
amide bond with a fatty
acid carboxyl, to yield a
ceramide.
Membrane lipids
Sphingolipids

There are three main types of sphingolipids
1.
Sphingomyelin has a phosphocholine or
phosphoethanolamine head group.
2. Sphingomyelins are common constituents of plasma
membranes of animal cells
Membrane lipids
Sphingolipids
Membrane lipids
Sphingolipids
2.
Glycosphingolipids (outer face of plasma
membrane)
Two types:
Cerebrosides (single sugar linked to ceramide)
Globosides (2 or more sugars linked to ceramide)
They are nuetral glycolipids
Membrane lipids
Sphingolipids
Glycosphingolipids
Membrane lipids
Sphingolipids
3.
Gangliosides is a ceramide with a polar head
group that is a complex oligosaccharide, including
the acidic sugar derivative sialic acid
Ganglosides are negatively charged
Functions of Sphingolipids

Protection of the cell surfaces against environmental
factors

Cell Signaling

Cell recognition

Determination of human blood groups
(glycosphingolipids)
Membrane lipid
Cholesterol
-Steriod; lipid soluble
-Found in both leaflets of
bilayer
-Amphipathic
-Found in animal cells
-Membrane fluidity buffer
-Synthesized in
membranes of ER
Membrane proteins

Two types of membrane protein
A.
Integral protein (interacts extensively with
hydrocarbon chains of membrane lipids)
B.
Peripheral membrane proteins
(bound to membranes primarily by
electrostatic and hydrogen bond interactions)
Membrane proteins
Integral Proteins


Penetrate bilayer or
span membrane
Can only be removed
by disrupting bilayer
Membrane proteins
Integral Proteins
Types
 Transmembrane
proteins
– Single-pass or
Multiple-pass
 Covalently
tethered integral
proteins
Membrane proteins
Integral Proteins

Many are glycoproteins
 Covalently-linked
via asparagine, serine, or
threonine to sugars
–
Synthesized in rough ER
–
Function: enzymatic, receptors, transport,
communication, adhesion
Membrane proteins
Integral Proteins
Membrane proteins

Types I and II (1
transmembrane helix)

Type III (multiple
transmembrane helices in a
single polypeptide)

Type IV (transmembrane
helices in many polypeptides
forms channels
Membrane proteins

Type V (held by covalent bonds
to the lipids)

Type VI (transmembrane
helices and lipid anchors)
Membrane proteins
Peripheral (extrinsic) proteins
– Do not penetrate bilayer
– Not covalently linked to other membrane components
Form ionic links to membrane structures
• Can be dissociated from membranes
• Dissociation does not disrupt membrane integrity
– Located both extracellular and intracellular sides of membrane
Synthesis
• Cytoplasmic (inner) side – cytoplasm
• Extracellular (outer) side – made in ER and
exocytosed
Membrane proteins
Lateral mobility


Biomembranes are a two-dimensional “mosaic” of
lipids and proteins
Most membrane lipids and protein can move through
the membrane plane within limits
Fluid Mosaic Model

Membranes are two-dimensional solutions of
oriented lipids and globular proteins

The lipid bi-layer acts as solvent for integral
membrane proteins and a permeability barrier

Membrane lipids: supporting structure
– Phospholipids
– Glycolipids
– Cholesterol
Fluid mosaic model

Membrane proteins:
–
Integral (intrinsic) proteins
–
Peripheral (extrinsic) proteins
Membrane fluidity

Many membrane processes depend on membrane
fluidity
-transport
-signal transduction

Membrane fluidity is dependent on the properties of the
fatty acid chain

Transition temperature is dependent on the length of the
fatty acid chains and on their degree of unsaturation
Membrane fluidity


Movement of hydrophobic tails
Depends on temperature and lipid composition
How does lipid composition affect fluidity?
Lipids and membrane fluidity

Interactions between hydrophobic tails decrease
fluidity (movement):
–
Shorter tails have fewer interactions
–
Unsaturated fatty acids are kinked and decrease
interactions
Lipids and membrane fluidity

Cholesterol “buffers”
fluidity:
Prevents interactions
Restricts tail movement
Microbial growth at Cold temperatures
Molecular Adaptation to Psychrophily

The cytoplasmic membranes of psychrophiles have
a higher content of unsaturated fatty acids.

This helps to maintain a semifluid state of the
membrane at low temperatures
Microbial growth at Cold temperatures
Molecular Adaptation to Psychrophily

Lipids of some psychrophiles contain
polyunsaturated fatty acids or other long chained
hydrocarbons with multiple bonds

These fatty acids remain more flexible at lower
temperatures than saturated or monounsaturated
fatty acids
Microbial Growth at High Temperature

Molecular Adaptations to Thermophily
–
Modifications in cytoplasmic membranes to ensure
heat stability
 Bacteria
have lipids rich in saturated fatty acids
 Archaea
have lipid monolayer rather than bilayer
Microbial Growth at High Temperature

Archaea have lipid
monolayer rather than
bilayer

Lipid monolayers are
quite resistant to
peeling apart

When the lipid layers
peel apart they cause
cell lysis
Membrane asymmetry

The inner and outer leaflets of the membrane have
different compositions of lipids and proteins
Membrane asymmetry


Sphingomyelin and phophatidyl choline are
located on the outer leaflet
Phosphatdidylserine is located in the inner leaflet
Biomembrane
Cell to cell interactions and adhesions
• Integrins are
transmembrane
proteins of the
plasma membrane
• They act to attach
cells to each other
• They carry message
between the
extracellular matrix
and the cytoplasm
(extracellular matrix
Biomembrane
Cell to cell interactions and adhesions
• Integrins regulate many
processes
- platelet aggregation at
the site of a wound
- tissue repair
-activity of immune cells
-invasion of tissue by a
tumor
Mutation can result in
leukocyte adhesion
Biomembrane
Cell to cell interactions and adhesions
• Other plasma membrane
proteins involved in
surface adhesions:
• Cadherins
• Immunoglobin-like
proteins
• Selectins: essential part
of the blood clotting
process
Biomembrane
Membrane fusion and biological processes

Integral proteins (fusion
proteins) facilitate this
event

Membrane continuity is
maintained

Entry into host cell by
viruses
Fusion of sperm and egg
Release of neurotoxins by
exocitosis


Membrane carbohydrates

Membranes play key role in cell-cell recognition

Carbohydrates are usually branched
oligosaccharides with fewer than 15 sugar units
Membrane carbohydrates

Oligosaccharides on external of membranes are
different among species, or individuals, or cells
Membrane functions

Cell communication and signalling

Cell-cell adhesion and cellular attachment

Cell identity and antigenicity

Conductivity
Transport of Ions and Small
Molecules Across Cell Membrane
Membrane transport


All cells require the molecules and ions they
need from ECF (extracellular fluid).
There are two problems to be considered
Relative concentrations
-diffusion
-active transport
2. Lipid bilayers are impermeable to most
essential molecules and ions
1.
Membrane transport
Solving the Problem
Mechanisms by which cells solve this problem
include:
1.
Active transport
2. Facilitated diffusion
Active Transport
Active transport is the pumping of molecules or
ions through a membrane against their
concentration gradient. It requires

a transmembrane protein (a complex of
them) called a transporter

Energy. ATP (source)
Active Transport

Active transport
enzymes couple net
solute movement
across a membrane
to ATP hydrolysis.
Active Transport
The energy of ATP may be used directly or
indirectly
There are two types of active transport
 Direct / Primary

Indirect/Secondary
Active Transport

Primary /Direct
– The transport system is an ATPase.
– The energy for transport comes directly
from ATP.
– Some cation transport systems fall into
this category. The NaK-pump is the prime
example.
Active Transport

Secondary/Indirect
–
–
The transport system utilizes the Na+
electrochemical gradient as an energy source to
move a solute against its electrochemical
gradient.
Na+ is transported down its electrochemical
gradient in the process. This is also referred to as
a Na-coupled or gradient-coupled transport.
Active Transport
Indirect Active Transport.
Transporters use energy already stored in the
gradient of a directly pumped ion.

Membrane Transport
Transporters are of two general classes:
carriers and channels.
These are exemplified by two ionophores (ion
carriers produced by microorganisms):
valinomycin (a carrier)
gramicidin (a channel).
Energetics of active transport

Active transport
– Metabolic energy expenditure is required.
– Solute moves against a gradient of
electrochemical potential.
– Assymetrical Km for carrier loading. Km
is generally higher on that side of the
membrane toward which active transport
occurs.
Carrier mediated membrane transport

Carriers exhibit saturation kinetics with
respect to solute concentration.

Carriers exhibit stereospecificity.
–
Glucose carrier transports D-glucose but not Lglucose.
Carrier mediated membrane transport

Carriers are susceptible to inhibition.

Carrier rates are susceptible to hormonal
control (although channels may be as well).
Influence of insulin on the glucose transporter
Influence of aldosterone on the Na-K transporter
(NaK-pump).
–
Kinetics of transport carriers
Carriers exhibit Michaelis-Menten kinetics.
The transport rate mediated by carriers is
faster than in the absence of a catalyst, but
slower than with channels.
A carrier transports only one or few solute
molecules per conformational cycle.
Energetics of carrier-mediated
transport
Diffusion
 Passive transport (facilitated diffusion)
–
–
–
–
No metabolic energy required.
Solute moves down a gradient of
electrochemical potential in combination with a
carrier.
Km is the same on the two sides of membrane.
Example - glucose transport in most cells.
Carrier proteins

Proteins that act as carriers are too large to move
across the membrane.

They are transmembrane proteins, with fixed
topology.

Example: GLUT1 glucose carrier, found in plasma
membranes of various cells, including erythrocytes.

GLUT1 is a large integral protein, predicted via
hydropathy plots to have 12 transmembrane ahelices.
Carrier proteins
conformation
change
conformation
change
Carrier-mediated solute transport

Carrier proteins cycle between
conformations in which a solute binding site
is accessible on one side of the membrane
or the other.
Carrier proteins
conformation
change
conformation
change
Carrier-mediated solute transport

There may be an intermediate conformation
in which a bound substrate is inaccessible to
either aqueous phase.

With carrier proteins, there is never an open
channel all the way through the membrane
Classes of carrier proteins
Uniport
A
Symport
A
B
Antiport
A
B
Classes of carrier proteins
Uniport
Uniport (facilitated
diffusion) carriers
mediate transport of
a single solute.
Uniport
A
Symport
A
B
Antiport
A
Examples include
GLUT1
B
Classes of carrier proteins
Uniport


These carriers can
undergo the
conformational change
associated with solute
transfer either empty or
with bound substrate.
Thus they can mediate
net solute transport.
Uniport
A
Symport
A
B
Antiport
A
B
Classes of carrier proteins
Symport
Symport (cotransport)
carriers bind 2
dissimilar solutes
(substrates) & transport
them together across a
membrane.
Transport of the 2 solutes
is obligatorily
coupled.
Uniport
A
Symport
A
B
Antiport
A
B
Classes of carrier proteins
Symport
An example is the plasma
membrane glucoseNa+ symport.
A gradient of one
substrate, usually an
ion, may drive uphill
(against the gradient)
transport of a cosubstrate.
Uniport
A
Symport
A
B
Antiport
A
B
Classes of carrier proteins
Symport
Trans-epithelial
transport:
In the example shown, 3
carrier proteins
accomplish absorption
of glucose & Na+ in the
small intestine.
glucose Na+
glucose-Na+ symport
apical end
Na+
glucose
ATP
ADP + Pi
basal end
Na+ pump
GLUT2
K+
intestinal epithelial cell
Classes of carrier proteins
Symport
.
The Na+ pump, at the
basal end of the cell, keeps
[Na+] lower in the cell than
in fluid bathing the apical
surface.
Na+
glucose-Na+ symport
glucose
apical end
Na+
glucose
ATP
ADP + Pi
basal end
Na+ pump
GLUT2
K+
intestinal epithelial cell
Classes of carrier proteins
Symport
.
•The Na+ gradient drives
uphill transport of glucose
into the cell at the apical
end, via glucose-Na+
symport. [Glucose] within
the cell is thus higher than
outside.
Na+
glucose-Na+ symport
glucose
apical end
Na+
glucose
ATP
ADP + Pi
basal end
Na+ pump
GLUT2
K+
intestinal epithelial cell
Classes of carrier proteins
Symport
.
•Glucose flows passively
out of the cell at the basal
end, down its gradient, via
GLUT2 (uniport related to
GLUT1).
Na+
glucose-Na+ symport
glucose
apical end
Na+
glucose
ATP
ADP + Pi
basal end
Na+ pump
GLUT2
K+
intestinal epithelial cell
Classes of carrier proteins
Antiport
Antiport (exchange
diffusion) carriers
exchange one
solute for another
across a
membrane.
Uniport
A
Symport
A
B
Antiport
A
B
Classes of carrier proteins
Antiport
Example: ADP/ATP
exchanger
(adenine nucleotide
translocase) which
catalyzes 1:1
exchange of ADP
for ATP across the
inner mitochondrial
membrane.
Uniport
A
Symport
A
B
Antiport
A
B
Classes of carrier proteins
Antiport


Usually antiporters
exhibit "ping pong"
kinetics.
One substrate is
transported across
a membrane and
then another is
carried back.
Uniport
A
Symport
A
B
Antiport
A
B
Active Transport





ATP dependent ion pumps are grouped into
classes, based on transport mechanisms as
well as genetic and structural homology.
Examples include
P-class pumps
F-class pumps
V-class pumps
Active Transport
There are four types of Direct Active transport
1.
2.
3.
4.
The Na+/K+ ATPase
The H+/K+ ATPase
The Ca 2+ ATPases
The ABC transporters
P-Type transporters
1.Na+/K+ ATPase
 H+/K+ ATPase
 Ca 2+ ATPase
They use the same basic mechanism:


Conformational change in proteins as they are
reversably phosphorylated by ATP

All three pumps can be made to run backwards

If the pumped ions are allowed to diffuse back through the membrane complex,
ATP can be synthesized from ADP and inorganic phosphate
P-Type transporters
The reaction mechanism
for a P-class ion pump
involves transient covalent
modification of the
enzyme.
O
Enzyme-C
OH
ATP
Pi
ADP
H2O
O
Enzyme- C
O
O
P
O-
P-Class Pumps
O-
Direct Active Transport
The Na+/K+ ATPase




K+ is 20 X higher in cytosol than
extracellular fluid
Na+ in extracellular fliud is 10X greater than
in cytosol
Concentration gradient is maintained by
active transport of both ions
The Na+/K+ ATPase transporter does both
jobs
Direct Active Transport
The Na+/K+ ATPase
The Na+/K+ ATPase transporter uses energy
from the hydrolysis of ATP to

Actively transport 3 Na+ ions out of the cell

For each 2 K+ ions pumped into the cell
The Na+/K+ ATPase transporter
–
Na+/K+-ATPase,
in plasma
membranes of
most animal cells,
is an antiport
pump.
Inward
3 Na+
Sodium
Flux
Extracellular
Cytosol
Mg++
ATP
2 K+
ADP + Pi
Outward
Potassium
Flux
The Na+/K+ ATPase transporter

Gradients for the Na+
and K+ is needed for
action potentials and
synaptic potentials
Inward
3 Na+
Sodium
Flux
Extracellular
Cytosol
Mg++
ATP
2 K+
ADP + Pi
Outward
Potassium
Flux
Direct Active Transport
The Na+/K+ ATPase Transporter
What does this accomplish
 It helps to establish a net charge across the
plasma membrane
 The accumulation of sodium ions outside of
the cell draws water out of the cell and
enables it to maintain osmotic balance.
Why is this important?
Direct Active Transport
The Na+/K+ ATPase Transporter
What does this accomplish
 The gradient of sodium ions is harnessed to
provide the energy to run several types of
indirect pumps
Mechanism Na+/K+ pump
• The mechanism is similar to that of the muscle
calcium pump
• In the E1 conformation the Na+/K+ ATPase has
three high affinity Na+ binding site and two low
affinity K+ sites accessible on the cytosolic side
Mechanism Na+/K+ ATPase pump
• In the E1 conformation the enzyme can bind ATP
and the Na+ ions occupy its binding site on the
enzyme
• The phosphoryl group is the transferred to
aspartate
Mechanism Na+/K+ ATPase pump
• The three bound Na+ ions become accessible to
the exoplasmic face and simultaneously the
affinity for the 3 Na+-binding sites become
reduced
• The Na+ ions then dissociate one at a time to the
Mechanism Na+/K+ ATPase pump
• The transition to the E2 conformation generates
two high-affinity K+ sites accessible to the
exoplasmic face, binding the K+ ions
• Upon dephosphorylation the enzyme undergoes
another conformational change and releases the
The Na+/K+ ATPase transporter
Inhibited by :
– Cardiac
glycosides
– Metabolic
inhibitors
– Heavy Metals
Inward
3 Na+
Sodium
Flux
Extracellular
Cytosol
Mg++
ATP
2 K+
ADP + Pi
Outward
Potassium
Flux
Digitalis inhibits the Na+/K+ Pump

Digitalis is a mixture of cardiotonic steroids

Digitoxigen and ouabain inhibitors

cardiotonic steriods – strong effect on heart

Increases the force of contraction of the heart
Digitalis inhibits the Na+/K+ Pump

Inhibit dephosphorylation of the
phosphorylated form of ATPase on the
extracellular face of the membrane

Leads to higher Na+ in the cytosol

Diminished Na+ gradient leads to slower
exclusion of Ca 2+ by Na-Ca exchanger
(antiporter)

Increase in intracellular levels of Ca 2+ enhances the ability of the
cardiac muscle to contract
Digitalis inhibits the Na+/K+ Pump
Inhibititors of the Na+/K+ Pump

Oubain (Samali for arrow poison steriod
derivative of ouabain)

Binds to the form of the Na+K+ ATPase that
is open to the extracellular side

Locks in Na+ and prevents the change in
conformation necessary for transport of ions
Inhibitors of the Na+/K+ Pump





Palytoxin (produced by coral found in Hawaii)
Binds to Na+K+ ATPase and locks it in
position so that the ion binding sites are
permanently accessible from both ends
Open channel
Exit of K+ from cells
Toxic
The H+/K+ ATPase Transporter
 (H+,
K+)-ATPase,
involved in acid
secretion in the
stomach, is an
antiport pump.
The H+/K+ ATPase Transporter
 It
catalyzes transport
of H+ out of the
gastric parietal cell
(toward the stomach
lumen) in exchange
for K+ entering the
cell.
Direct Active Transport
The Ca 2+ ATPase Transporter

The Ca 2+ ATPase is located in the plasma
membrane of all eukaryotic cells

1 ATP is used to pump 1 Ca 2+ out of the cell

20,000 fold conc gradient between Ca 2+ in
the cytosol and that in the extracellular fluid
(ECF)
The Ca 2+ ATPase Transporter

Ca 2+ -ATPase pump, in endoplasmic reticulum (ER)
& plasma membranes catalyze transport of Ca 2+
away from the cytosol, either into the ER lumen or
out of the cell.
There is some evidence that H+ may be transported in
the opposite direction.
– Ca 2+ -ATPase pumps keep cytosolic Ca 2+ low
(10-7M vs. 10-3 M in plasma), allowing Ca 2+ to
serve as a signal.
Direct Active Transport
The Ca 2+ ATPase Transporter

Resting skeletal muscle there is a higher
conc of Ca 2+ ions in the endoplasmic
reticulum than the cytosol

Activation of muscle fibre allows Ca 2+ to
pass into the cytosol, triggering contraction
Direct Active Transport
The Ca 2+ ATPase Transporter

After contraction the Ca 2+ is pumped back
into the sarcoplasmic reticulum
This is done by another Ca 2+ ATPase pump
Uses energy from each molecule of ATP to
pump 2 Ca 2+ ions
 The Ca 2+ pump is called SERCA

The Ca 2+ ATPase Transporter
• The catalytic cycle begins with the enzyme in
its unphosphorylated state with 2 calcium
ions bound
• In the E1 conformation the enzyme can bind
ATP. Conformational change occurs and the
The Ca 2+ ATPase Transporter
• The phosphoryl group is then transferred
from ATP to aspartate
• Upon ADP release the enzyme changes its
overall conformation (E2-P). This process is
called eversion
The Ca 2+ ATPase Transporter
• In the E2-P conformation the calcium binding
sites become disrupted and the calcium ions
are released to the side of the membrane
opposite to which they entered
• E2-P is then hydrolysed releasing the
inorganic phosphate
The Ca 2+ ATPase Transporter
• With the release of the phosphate the
stabilization of the E2 form is lost and the
enzyme everts back to the E1 conformation
• The binding of two calcium ions from the
cytosolic side completes the cycle
SERCA:Sarco Endo(plasmic)
Reticulum Ca 2+ ATPase
SERCA:Sarco Endo(plasmic)
Reticulum Ca 2+ ATPase
Direct Active Transport
ABC Transporters
ABC (ATP-Binding-Cassette) transporters are
transmembrane protein that
 Expose a ligand-binding domain at one
surface and a
 ATP-binding domain at the other surface
 The ligand binding domain is restricted to a
single type of molecule
Direct Active Transport
ABC Transporters

The ATP bound to its domain provides the
energy to pump the ligand across the
membrane
ABC Transporters
Mechanism

The catalytic cycle begins with the transporter being
free of both ATP and substrate

The transporter can interconvert between closed
and open forms

Substrate enters the central cavity of the open form
of the transporter from inside the cell
ABC Transporters
Mechanism

Substrate binding results in a conformational change
in the ATP binding cassette that increases their
affinity for ATP

ATP binds to the ATP-binding cassettes, changing
their conformations so that the two domains interact
strongly with each other
ABC Transporters
Mechanism

The strong interaction between the ATP-binding
cassettes induces a change in the relation between
the two domains releasing the substrate to the
outside of the cell

The hydrolysis of ATP and the release of ADP and
inorganic phosphate resets the transporter for
another cycle
ABC Transporters (Mechanism)
Direct Active Transport
ABC Transporters
The human genome contains 48 genes for
ABC transporters.
 CFTR- the cystic fibrosis transmembrane
conductance regulator
 TAP-the transporter associated with antigen
processing
 ABC transporters that pump
chemotherapeutic drugs out of cancer cells
Physiological effects of defects in
ABC Transporters
Genetic diseases such as:
 Cystic fibrosis
 Tangier disease
 Retinal degeneration
 Anemia
 Liver failure
Effects of ABC Transporters
ABC transporters can confer antibiotic
resistance in pathogenic microbes such as:
 Pseudomonas aeruginosa
 Staphylococcus aureus
 Candida albicans
 Neisseria gonorrhoeae