8/22/2019 Smas - Plasma Membrane
1/60
Membrane Structure and Composition
Plasma Membrane 1
Dr. Cynthia [email protected]
Dept. of Biochemistry & Cancer BiologyOffice:Rm 401D BHS; Lab: Rm 466 BHS
383-4527, 383-4131
Your questions are welcome at any time!
Wednesday 8/22/201210-12 p.m.
8/22/2019 Smas - Plasma Membrane
2/60
References and Readings:
Biochemistry (Stryer 7th ed.) Chapter 12 (relevant portions)
Harpers Illustrated Biochemistry, 29th ed. Chapter 40.
Optional: Molecular & Cellular Biology (Lodish 4th ed, 2000.) Chapter 5
Available free on-line through NCBI/PubMed.
http://www.ncbi.nlm.nih.gov/books/NBK21475/
(searchable only, cannot browse it)
Plasma Membrane 1
Also note the 5th edition of Stryer is also free through
NCBI/Books but is only searchable, not browsable
http://www.ncbi.nlm.nih.gov/books/NBK21154/
http://www.ncbi.nlm.nih.gov/books/NBK21475/http://www.ncbi.nlm.nih.gov/books/NBK21154/http://www.ncbi.nlm.nih.gov/books/NBK21475/8/22/2019 Smas - Plasma Membrane
3/60
Plasma Membrane 1Learning Objectives
1. Describe 3 common types of membrane lipids and discussamphipathic nature of each. Indicate how membrane lipid
structure facilitates self-assembly of the lipid bilayer.
2. Explain what types of molecules can pass directly throughthe lipid core of the membrane and which cannot and why.
3. Discuss the distinguishing features of integral and peripheralmembrane proteins, using glycophorin as an example.
4. Explain how lipids can serve to anchor some proteins in theplasma membrane.
8/22/2019 Smas - Plasma Membrane
4/60
5. Explain the impact of fatty acid length and saturation, andthe effects of cholesterol on membrane fluidity as reflectedby the melting temperature (Tm).
6. Discuss one example of asymmetry of membrane lipids andof membrane proteins. For example, the impact ofexoplasmic phosphatidylserine on cell destruction orthe asymmetric nature of glycosylation of membrane proteins.
7. Discuss the types of interactions among the key proteincomponents of the RBC membrane. Describe theircontribution to its strength and flexibility in health & disease, for example in
heriditary spherocytosis.
Plasma Membrane 1Learning Objectives (cont.)
8/22/2019 Smas - Plasma Membrane
5/60
The Cell & Intracellular Organellesare Surrounded by a Membrane Bilayer
Plants
(A composite eukaryotic cell)
Source: Molecular Cell Biology, Lodish et. a. 4th ed, W.H. Freeman, 2000
8/22/2019 Smas - Plasma Membrane
6/60
Regulate nutrient & ion transport into the cell
Regulate transport ofwaste out of the cell
Maintain correct chemical conditions in the cell
Provide a site for lipid-based chemical reactions
Interact with other cells or the ECM
Detect & transduce signals from environment to cell
Functions of the Plasma Membrane
Signal Transduction
8/22/2019 Smas - Plasma Membrane
7/60
Lipids & Many Membrane Proteins areLaterally Mobile in the Plane of the Membrane
The Fluid Mosaic Model
Source: Addison Wesley Longman, Inc.
Plasma Membrane/Cell Membrane/ Cell Surface
8/22/2019 Smas - Plasma Membrane
8/60
A.The Basic Architecture of theMembrane
1. Types of membrane lipids
2. Membrane proteins
B. Membrane FluidityC. Membrane Asymmetry
The Plasma Membrane - TopicsFluid Mosaic
Source: Addison Wesley Longman, Inc.
8/22/2019 Smas - Plasma Membrane
9/60
Biological Membranes Have 2 MainComponents- Lipids & Proteins
Lipids: Form a permeability barrier Define the basic architecture
Proteins:
Define the unique functions of membranes Determine selective permeability Transporters, channels, junctions Energy uptake, signal transduction
Protein to lipid ratio can vary with the cell type.This can be related to the function of that cell type.
8/22/2019 Smas - Plasma Membrane
10/60
Water-insoluble biomolecules
Highly soluble in organic solvents
Great variety of structures
Fuel and energy storage
Signaling
Membrane components
Lipids
8/22/2019 Smas - Plasma Membrane
11/60
1. Phospholipids
2. Glycolipids
3. Cholesterol
3 Common Types of Membrane Lipids
Membrane lipids have an amphipathicnature.
2-loves the hydrophilic aqueous environment andthe hydrophobic non-aqueous environment
Hydrophilic (polar) head groupHydrophobic (non-polar) acyl side chains (tails)
8/22/2019 Smas - Plasma Membrane
12/60
Phospholipids
Basic Structure & Examples
You do not need to know details of structure
Why is it amphipathic?
8/22/2019 Smas - Plasma Membrane
13/60
A Phospholipid is Composedof 4 Groups
16-18 C
1C
2C
3C
Hydrophobic Hydrophilic
Phospholipids are the Major Typeof Membrane Lipid
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
8/22/2019 Smas - Plasma Membrane
14/60
Phosphatidate (Diacylglycerol 3-phosphate)Example of a Simple Phosphoglyceride
GlycerolBackbone
Phosphatehead group
at C3 of
glycerol
C1 & C2
Amphipathic: Hydrophobic HydrophilicSource: Biochemistry, Stryer 5th ed. W.H. Freeman
Side chains
8/22/2019 Smas - Plasma Membrane
15/60
Commonly Occurring Membrane Phospholipids(Phosphoglycerides)
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
8/22/2019 Smas - Plasma Membrane
16/60
Glycolipids are sugar-containing lipids
A sugartakes the place of the phosphate group
Sphingosine
Membrane Lipids Can AlsoInclude Carbohydrate Moieties
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
Very enriched - where?
8/22/2019 Smas - Plasma Membrane
17/60
Cholesterol is Commonin the Plasma Membranes of Animals
4 LinkedHydrocarbon
Rings
Hydrophilic Hydrophobic
A lipid based on a steroid typestructure
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
8/22/2019 Smas - Plasma Membrane
18/60
In Aqueous Media Phospholipids and GlycolipidsReadily Form a Bilayer Sheet
Two faces of the plasma membrane (leaflets):
Exoplasmic- toward the extracellular environmentCytoplasmic- toward the intracellular environment
Source: Molecular Cell Biology, Lodish et. a. 4th ed, W.H. Freeman, 2000
Cross Section
Polar Head Groups Hydrophobic Interior Polar Head
Groups
8/22/2019 Smas - Plasma Membrane
19/60
Micelles Solubilization and purification ofmembrane proteins, LDL and bileparticles are mixed micelles
Liposomes * Used in functional study
of membrane proteins
* Important for drug deliveryand therapeutics.
Two Additional Structures Satisfythe 2-loves of Amphipathic Lipids
= drug
NOTE: Cut-away views half of a micelle and half of a liposome is shown
= membraneprotein
+ =
Or
TM
8/22/2019 Smas - Plasma Membrane
20/60
Hydrophobic interactions by exclusion of water drivesformation of energetically stable structures.
Van der Waals attractive forces between hydrocarbon tailsfavor close packing.
Electrostatic and H-bond attractions between the polarhead groups and water molecules also involved.
Membrane formation is due to the amphipathic nature ofmembrane lipids.
Why is this Bilayer SheetEnergetically Favored and Stable?
8/22/2019 Smas - Plasma Membrane
21/60
The lipid bilayer membrane is a cooperative
structure that is formed & maintained by multiple
noncovalent interactions.
The role of lipids in the plasma membrane are to definethe basic bilayer architecture which acts to form a
permeability barrier for the cell.
In summary:
8/22/2019 Smas - Plasma Membrane
22/60
A.The Basic Architecture of theMembrane
1. Types of membrane lipids
2. Membrane proteins
B. Membrane Fluidity
C. Membrane Asymmetry
The Plasma MembraneFluid Mosaic
Source: Addison Wesley Longman, Inc.
8/22/2019 Smas - Plasma Membrane
23/60
The Concept ofSelective
Permeability
Some molecules can passdirectly through lipid core.
If they cannot, membraneproteins must serve as
structures for passage. Channels, transporters,
junctions, pumps.
Lipid Bilayers Selectively Maintain DifferencesIn ECF and ICF Concentration
Source:Molecular Cell Biology, Lodish et. a. 4th ed, W.H. Freeman, 2000
Simple
diffusio
n
Category Examples
Membrane
*
*Depends on cellular/organ setting
8/22/2019 Smas - Plasma Membrane
24/60
Define the unique functions of membranes
Determine selective permeability
Examples - transporters, channels, junctions
Function in energy uptake, signal transduction
Today, I will present basic concepts regarding membrane proteins.Next time, several specific membrane proteins will be discussed in detail.
The PROTEINSof the membrane determine itsfunctional complexity for each specific cell type.
Proteins Carry Out Most Membrane Processes
8/22/2019 Smas - Plasma Membrane
25/60
eripheral- More loosely associated with the membranemoved with mild conditions (salt/pH)
Do not enter or span the hydrophobic core
Integral- More tightly associated with the membrane Removed only with harsh conditions (detergents).
Enters or spans the hydrophobic core (Single-pass or multiple-pass)
Membrane Proteins are TypicallyClassified as Either Peripheral or Integral
EXOPLASMIC
CYTOPLASMIC
OUTER
(LEAFLETS)
INNER
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
Yellow = IntegralBlue = Peripheral
8/22/2019 Smas - Plasma Membrane
26/60
-Helix -Barrel
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
Specific Secondary Structures EnablePolar Proteins to Happily Exist in the
Hydrophobic Lipid Core
(A single -helix is circled in blue)
Most commonly used in higher organisms Often utilized by bacteria
8/22/2019 Smas - Plasma Membrane
27/60
Why is the hydrophobic -helixperfectly suited to span the lipid core?
The peptide bond is polar Proteins contain charged AA
But the membrane core is hydrophobic! An -helix can function to span the core
A sequence of 20-25 AA, rich inhydrophobic/nonpolar AA with an
-helical structure often servesas a transmembrane segment.
The membrane spanning -helix
Membrane Proteins Often Have an -HelicalStructure to Span the Lipid Bilayer
8/22/2019 Smas - Plasma Membrane
28/60
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
Example - Glycophorin Uses This Type of-Helix to Span the Membrane
Hydrophobic AA arenot restricted tomembrane regionsbut a 20-25 AA stretch
suggests a possibletransmembranedomain.
Hydrophobicor Neutral
(+)
(-) Charged
The erythrocyte integral membrane glycoprotein glycophorin
is the basis for the MN blood group
Charged
Sugar
(glycoprotein)
8/22/2019 Smas - Plasma Membrane
29/60
Transmembrane -Helices Can BePredicted from Hydropathy Plots
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
Hydrophob
icityIndex
Alanine
Valine
Isoleucine Leucine
Methionine
Phenylalanine
Tyrosine
Tryptophan
Transmembrane - helicesmay likely include:
Multiple -helices predicted:
Which AA areunlikely in a
membrane-spanning region?
+4+3+2+10-1-2
-3 50 100 150 200
1 2 3 4
Inde
x
+4+3+2+10-1-2
-3 50 100 150 200
1 2 3 4
Amino Acid
8/22/2019 Smas - Plasma Membrane
30/60
Schematic Representations - Membrane Proteins
Source: Biochemistry, Stryer 5th ed. W.H. Freeman; Source: Addison Wesley Longman, Inc.
8/22/2019 Smas - Plasma Membrane
31/60
Prostaglandin H Synthase:An Example of an Integral* Membrane ProteinThat Enters but Does Not Span the Membrane
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
*The hydrophobic side chains of this -helicalstructure allow the protein to be tightly
associated (integral) with plasma membrane
*
8/22/2019 Smas - Plasma Membrane
32/60
Farnesylation
Palmitoylation
Myristoylation
GPI Anchor (Glycosylphosphatidylinositol)
Certain Proteins Rely on Specific Lipid Structuresfor Association with the Plasma Membrane
Source: Molecular Biolo o the CellAlberts, et.al. 3rd ed.
Lipid Anchorsare covalently
attached to specific proteins.
Lipid anchors are hydrophobic and canembed in the hydrophobic core of the
plasma membrane, to anchor (localize)
the protein at the membrane.
Types of lipid anchors(structures)
BOAT
ANCHOR
DOCK
ANCHORS
Protein
Thy-1,Ras, Src,or others
Lipid Core
of the
Plasma
Membrane
8/22/2019 Smas - Plasma Membrane
33/60
Alterations and Defects in Membrane ProteinsUnderlie Many Human Diseases
Cancer: Alterations of membrane protein and/or lipid arekey to metastasis and invasion of tumor cells asthey spread throughout the body.
Diabetes: Defective insulin signaling, defective functionof glucose transporters (More in next lecture)
Heart Disease: Defective cell-cell communication (example connexins in arrhythmias,
will be discussed by other instructors)
8/22/2019 Smas - Plasma Membrane
34/60
Reconstitution isOften Used to Study
Function ofMembrane Proteins
Why?Membrane proteins need to be present in
a membrane bilayer, and withcorrect topology to function properly
(even for lab studies)
They will denature otherwise
Source: Molecular Cell Biology, Lodish et. a. 4th ed, W.H. Freeman, 2000
8/22/2019 Smas - Plasma Membrane
35/60
Manipulation of Membrane Protein Functionin Disease Treatment
PRILOSEC GASTRIC H+/K+ ATPasePROZAC Na+-coupled serotonin transporterVast numbers of other membrane proteins . . .
Membrane proteins are highly useful drug targets:
The more details we know about membrane protein structureand function the better we can:
Make designer drugs targeting protein active sites
Predict how mutations in a gene for a membraneprotein may impact protein function
In general, the more we know about a protein, thebetter we can treat disease
8/22/2019 Smas - Plasma Membrane
36/60
A.The Basic Architecture of theMembrane
1. Types of membrane lipids
2. Membrane proteins
B. Membrane Fluidity
C. Membrane Asymmetry
The Plasma MembraneFluid Mosaic
Source: Addison Wesley Longman, Inc.
8/22/2019 Smas - Plasma Membrane
37/60
Membrane FluidityWhy Is It Important?
Influences arrangement of proteins and lipids
Foster assembly/disassembly of protein subunits andsignaling complexes in the membrane
Changes membrane permeability
Excessive fluidity leads to membrane destruction
Altering fluidity can alter membrane and/or cell function
Many Studies of Membrane Fluidity areConducted in Experimental Settings
Keep in Mind - Biological Membranes are Much More Complex !
M b Fl idit
8/22/2019 Smas - Plasma Membrane
38/60
Membrane FluidityEffects of Fatty Acid Composition
Desaturated:
Saturated:
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
Kink disrupts tight packingof hydrophobic side chains
Allows tight packingof hydrophobic side chains
8/22/2019 Smas - Plasma Membrane
39/60
Tm: Phase Transition Temperature(a.k.a. Melting Temperature)
Source: Addison Wesley Longman, Inc.
A Distinct Melting Temperature (Tm) is Noted forSimple (Non-Biological) Membranes
Shorter Acyl Chain Desaturated
Longer Acyl Chain Saturated
M
embraneFluidit
y
Need less heat energy todisrupt the membrane
Need more heat energy todisrupt the membrane
Tm higher
Tm lower
Curve will shift left if: Curve will shift right if:
Phasetransition
Lessfluid
Morefluid
8/22/2019 Smas - Plasma Membrane
40/60
Fatty Acyl Chain Length Effect on MembraneTransition Temperature (Melting Temperature)
Regulation of membrane fluidity by alteration of fatty acyl chainlength and saturation is employed by bacteria.
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
*
*
8/22/2019 Smas - Plasma Membrane
41/60
Cholesterol is the Key Determinant ofMembrane Fluidity in Animals
Disrupts regular interactionsof fatty acyl side chains
Makes membranes less likely toundergo phase transition
Source: Molecular Biology of the Cell. Alberts, et.al. 3rd ed.1944 Garland
Cholesterol acts as a buffer against changes to membrane fluidity
Cell membranes need to have a correct degree of fluidity for function.
This requires the right amount of cholesterol in the cell membrane.
The Effects of Cholesterol on Membrane Fluidity
8/22/2019 Smas - Plasma Membrane
42/60
Above Tm: Decreases fluidity
The Effects of Cholesterol on Membrane FluidityOutcome: Maintains Proper Tm
Below Tm: Increases fluidity* Below the melting temperature, the membrane
is gel-like or more solid
* The lipid side chains are tightly packed and orderly
* Introducing a kinked structure disrupts this, increases fluidity
* Above the melting temperature, the membrane is more fluid-like
* The lipid side chains are disorganized and moving
* Cholesterol acts to limit/restrict the overall free movement of the lipid sidechains due to its planar shape (steroid nucleus), thus making it less fluid
Source: Molecular Biology of the Cell. Alberts, et.al. 3rd ed.1944 Garland
M b Li id Hi hl M bil
8/22/2019 Smas - Plasma Membrane
43/60
Why is lipid flip-flop so very rare?
1 sec
LATER
AL
very rare
rapid
rapidrapid
rapid
Membrane Lipids are Highly Mobilein the Plane of the Membrane
8/22/2019 Smas - Plasma Membrane
44/60
The size of the molecule
Interactions with other molecules
Temperature
Lipid composition of the membrane
The composition of the protein
Membrane Proteins Also Have Lateral Mobility
This depends on:
How Do We Know Fluidity of Membrane Proteins?
8/22/2019 Smas - Plasma Membrane
45/60
How Do We Know Fluidity of Membrane Proteins?
FRAPMethod:
F luorescence
R ecoveryA fterP hotobleaching
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
Done on live cells -in real time.
Uses an antibody specific for the membrane protein you want to study.(Can also use other types of tools such eGFP fusion proteins . . .)
The antibody also has a fluorescent label linked to it (to allow us to see if).
Location of the protein under study shown by fluorescence (green) signal(fluorescence microscopy used).
Signal in any area of membrane can be obliterated (bleached by a laser).
The recovery of signal in bleached area (green) for your protein is observed.
This measurement shows rate of movement of this protein in the membrane.
Note: Only 1 molecule of a membrane proteinis shown, it is really in many on surface.Picture not drawn to scale.
FRAP Experimental Set up:
8/22/2019 Smas - Plasma Membrane
46/60
Visualization
Quantification
Time
Recovered
Recovered
FRAP Experimental Set up:
Cells (membrane protein) + Labeled Antibody ( ) =
Then -
8/22/2019 Smas - Plasma Membrane
47/60
A.The Basic Architecture of theMembrane
1. Types of membrane lipids
2. Membrane proteins
B. Membrane Fluidity
C. Membrane Asymmetry
The Plasma MembraneFluid Mosaic
Source: Addison Wesley Longman, Inc.
8/22/2019 Smas - Plasma Membrane
48/60
Asymmetry is Key to Function of MembranesAll Biological Membranes Are Asymmetric
The exoplasmic and cytoplasmic surfaces have different
proteins and different enzymatic and other activities.
An asymmetric distribution occurs for both membranelipids & proteins.
This asymmetry is key to proper function.
What are some examples of this asymmetry for membranelipids & proteins?
8/22/2019 Smas - Plasma Membrane
49/60
Membrane Asymmetry - Each Leaflet of theMembrane Has A Distinct Lipid Composition
The choline -containing phospholipids are mostly exoplasmic. The amino-phospholipids are mostly cytoplasmic. Flippases, floppases & scramblases can impact lipid
asymmetry.
Amino-containing
Fatty acyl side chains alsoshow leaflet enrichment.
RBC: Cytoplasmic leafletenriched in unsaturatedfatty acyl chains.
Choline-containing
8/22/2019 Smas - Plasma Membrane
50/60
Altered Distribution of Membrane LipidsCan Target Cells for Destruction
Platelet activation and aggregation:
Cascade of thrombin activation and protein C pathways Activation of alternative complement pathways
Recognition and removal of cells:
RBCs: Exposed phosphatidyl serine causes macrophagerecognition and destruction of these RBCs in the spleen.
Apoptosis (programmed cell death): Cells undergoing apoptosis expose phosphatidyl serine on
their exoplasmic leaflet. This triggers macrophage recognitionand destruction of apoptotic cells.
Exposure of phosphatidyl serine on the exoplasmic leafletoccurs in physiological and pathologic states.
8/22/2019 Smas - Plasma Membrane
51/60
Every Membrane Protein Has a Specific &Consistent Topology
Determined at time of their synthesis in the ER.
Maintained during their journey to the (plasma) membrane.
A protein requires proper topology for function.
They dont flip flop
Cytosolic
Exoplasmic
Source: Molecular Biology of the Cell. Alberts, et.al. 3rd ed.1944 Garland
Glycosylation Sites are One Example
8/22/2019 Smas - Plasma Membrane
52/60
Glycosylation Sites are One Example
of Asymmetry for Some Membrane Proteins
Source:
Molecular Biology of the Cell. Alberts. 3rd ed.1944 Garland
Some membrane proteins are glycosylated, occurs at sites in theirexoplasmic portion.
Complex sugar groups added in ER& Golgi by successive reactions.
(many types, much variety )
Can be N-linked (asparagine) orO- linked (serine, threonine).
Occurs only in the lumen of ER &Golgi.
Can confer specificity & function.
Example: Blood Group Antigens
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
Remember Glycophorin ?
= glycosylation sites
C f
8/22/2019 Smas - Plasma Membrane
53/60
Each Cell Type Has a Unique Repertoire of(Asymmetrically distributed)
Plasma Membrane Proteins
A. Erythrocytes
B. Retinal rod cells
C. Muscle (SR)
SDS-PAGE ANALYSIS(Protein Gel Electrophoresis)
Separates proteins by size
SIZ
EMW
Source: Biochemistry, Stryer 5th ed. W.H. Freeman
What is your interpretationof this
SDS-PAGE?
Higher MW
Lower MW
8/22/2019 Smas - Plasma Membrane
54/60
A Variety of Membrane Protein InteractionsGives Strength & Flexibility
to the Fluid Mosaic
Source: Molecular Cell Biology, Lodish et. a. 4th ed, W.H. Freeman, 2000
8/22/2019 Smas - Plasma Membrane
55/60
The RBC is a Key Example of the RelationshipBetween Membrane Proteins and Disease
Biconcave shape facilitates gas exchange.
Flexible shape for travel through tight spots (capillaries).
The functionality of the RBC is closely tied to plasmamembrane integrity. Defects in RBC membrane proteins are
often indicated by clearly visible alterations in RBC morphology.
Th R d Bl d C ll Pl M b i
8/22/2019 Smas - Plasma Membrane
56/60
The Red Blood Cell Plasma Membrane isOne of the Most Thoroughly Studied
SDS-PAGE analysis
of RBC membrane proteins
Creation of RBC ghosts to
study membrane function
Source: Molecular Cell Biology, Lodish et. a. 4th ed, W.H. Freeman, 2000
*Why?*
Major Proteins of
8/22/2019 Smas - Plasma Membrane
57/60
Major Proteins ofthe RBC
Plasma Membrane
Integral:Glycophorins (A,B,C)
single-pass, glycoproteinbasis of MN blood group
Anion exchange protein
multi-passexchange ofchoride for bicarbonate
Also called band 3
Inward tension is created via cytoskeleton/membrane protein interaction,this determines cell shape and flexibility.
Peripheral:
Spectrin (, form dimer)
Ankyrin
Band 4.1
Actin
G-3-P dehydrogenase
Tropomyosin
Proper Protein Interactions at the Membrane
8/22/2019 Smas - Plasma Membrane
58/60
Clinical Example - Hereditary Spherocytosis
* Mutations in genes for spectrin,ankyrin (or other genes) leads to ...
* Weakened interaction of peripheral
and integral membrane proteins
* Cytoskeletal architecture altered
* Detected by osmotic fragility test
* Autosomal dominant (1/5000).
* Spherocytic cells subject todestruction in the spleen - anemia.
pAre Key to Biconcave Shape/Function.
Due to defects in some RBC membrane proteins,
H. S. RBCs lack flexibility and clog upsplenic sinusoids, & are destroyed.
Which blood smear is normal RBC morphology&
which is abnormal (H.S.), why?
K C t
8/22/2019 Smas - Plasma Membrane
59/60
The plasma membrane is a selective permeability barrierthat is essential for proper cell function.
Proteins and amphipathic lipids are the two maincomponents of the bilayer membrane.
Membranes form spontaneously and are stable.
The lipids of the membrane define the basic architecture.
The proteins impart specific functions.
The lipids and proteins of the plasma membrane areanddynamic (fluid) and the asymmetrically distributed.
Plasma membrane proteins can interact with extracellularsignals (hormones, other cells, the extracellular matrix, other)
and the cytoskeleton.
Key Concepts
8/22/2019 Smas - Plasma Membrane
60/60
In my next lecture:
How does the plasma membrane function in
communication between cell and environment?
Top Related