Detailed aspects of cell membranes .

1. CELL MEMBRANE :CELL MEMBRANE :
CHEMICAL COMPOSITION ,CHEMICAL COMPOSITION ,
STRUCTURE AND MEMBRANESTRUCTURE AND MEMBRANE
DYNAMICSDYNAMICS
Presenter: Dr. Dnyanesh Amle
Moderator: Dr. Smita Kaushik

2. • Boundaries of all the cells are defined byBoundaries of all the cells are defined by
biological membranebiological membrane
• Barrier with selective permeabilityBarrier with selective permeability

4. COMMON PROPERTIES:COMMON PROPERTIES:
• Sheet like structures
• Contains mainly lipids and proteins
• Membrane lipids are small amphipathic
molecules
• Specific proteins mediate distinctive function

5. COMMON PROPERTIES:COMMON PROPERTIES:
• Non covalent assemblies
• Asymmetric
• Fluid structures
• Electrically polarized

6. • FUNCTIONS:FUNCTIONS:
– Maintenance of cell shape
– Cellular movements
– Controls movement of molecules between inside
and outside of the cell
– Cell-cell recognition and communication

7. • MAINLY COMPOSED OF :MAINLY COMPOSED OF :
– Lipids
– Proteins
– Carbohydrates

8. • LIPIDSLIPIDS :
– Phospholipids
– Glycolipids
– Cholesterol

9. 1) PHOSPHOLIPIDS1) PHOSPHOLIPIDS
• Based on the platform:
– Glycerophospholipids( Phosphoglycerides)
– Sphingolipids

10. PHOSPHOGLYCERIDESPHOSPHOGLYCERIDES
FATTY
ACID
FATTY
ACID
ALCOHOLPHOSPHATE
HYDROPHOBIC
PART
HYDROPHILIIC
PART

11. PHOSPHOGLYCERIDESPHOSPHOGLYCERIDES
• phosphatidate (diacylglycerol 3-phosphate),
the simplest phosphoglyceride
• Major phosphoglycerides are derivatives of
phosphatidate

12. • Phosphtidylinositol:
– Golgi body
– Endosomes
– Plasma membrane
• Cardiolipin:Cardiolipin:
– Inner mitochondrial membrane
• Phosphtidylcholine >
Phosphtidylethanolamine
• Plasmalogens:Plasmalogens:
– Nervous tissue
– Heart

13. SPHINGOLIPIDSSPHINGOLIPIDS
• Derived from sphingosine
• Ceramide
SS
P
H
I
N
G
O
S
I
N
E
FATTY ACID
ALCOHOLPHOSPHATE
S
P
H
I
N
G
O
S
I
N
E

14. 2)GLYCOLIPIDS:2)GLYCOLIPIDS:
• In animal cells: derived from sphingosine
• Sugar unit is attached to primary -OH group
• Simple glycolipid : cerebroside
– PhrenosinePhrenosine
• Complex glycolipid: Ganglioside

15. • Galactocerebroside:
– Brain and nervous tissue
• Glucocerebroside:
– Non neural tissue
• Ganglioside:
– 5-8% lipid in brain

16. 3)CHOLESTEROL:3)CHOLESTEROL:
• Third major membrane lipid

17. OH

18. • MEMBRANE LIPIDS : AMPHIPATHIC MOLECULESMEMBRANE LIPIDS : AMPHIPATHIC MOLECULES
Sphingo
lipids
glycero
Phospho
lipids
Cholesterol SHORTHAND
DEPICTION

19. AMPHIPATHIC NATURE:AMPHIPATHIC NATURE:
• Micelles
• Bilayer:
leaflets

20. PROPERTIES OF LIPID BILAYER:PROPERTIES OF LIPID BILAYER:
• Formation in aqueous environment is rapid and
spontaneous
• Hydrophobic interactions: major driving force
• Other forces:
– Van der waal’s attractive forces
– Electrostatic
– Hydrogen bonds
• Co-operative structures

21. HYDROPHOBIC INTERACTIONS:HYDROPHOBIC INTERACTIONS:
• Inherent tendency to be extensive
• Tend to close on themselves: forms
compartments
• Self sealing: As hole in lipid bilayer is
energetically unfavorable

22. • Type of structures formed depends on:
– Fatty acyl chains
– Degree of saturation
– Temperature

23. • LIPOSOMES:LIPOSOMES:
sonicating
Gel filtration

24. Uses
– To study the effect of different fatty acids on
membranes
– Drug delivery
– Concentrate in regions of increased blood flow :
Cell gatingCell gating
– Selective fusion

25. MEMBRANE PROTEINS:MEMBRANE PROTEINS:
• Integral
• Peripheral
• Amphitropic

26. Inside Outside
INTEGRAL MEMBRANE PROTEINS :INTEGRAL MEMBRANE PROTEINS :

27. +++++++_ _ _ _ _Phosphtidyl-
inositol
Membrane
Anchored protein
Cytoplasmic side
PERIFERAL MEMBRANE PROTEINS :PERIFERAL MEMBRANE PROTEINS :

28. • Membrane proteins structure
– Electron microscopy and X-ray crystallography
• Membrane spanning α helix
BACTERIORHODOPSIN

29. GLYCOPHORIN:GLYCOPHORIN:
• A protein containing single trans-membrane α
helical strand
• Present in plasma membrane of human
erythrocytes
• Amino terminus exterior to cell contains
various oligosaccharide unit including ABO
and MN blood group determinants

30. GLYCOPHORINE
74
95

31. • A channel can be formed from β strands
PORINE

33. Prostaglandin H2 synthase
PROSTAGLANDIN HPROSTAGLANDIN H22 SYNTHASE:SYNTHASE:

34. CARBOHYDRATES:CARBOHYDRATES:
• Rarely exists as free component
• Present as glycoprotein and glycolipid
• Always present on the outer side

35. BIOLOGICAL MEMBRANES DIFFER INBIOLOGICAL MEMBRANES DIFFER IN
COMPOSITION:COMPOSITION:
• Myelin: 18% protein , ↑ glycosphingolipids
• Plasma membrane : 50% protein
• Inner mitochondrial membrane : 75% protein,
↑ cardiolipins

36. FLUID MOSAIC MODEL:FLUID MOSAIC MODEL: 1972
• S Jonathan Singer & Girth Nicolson
• Membranes are two dimensional solution of
lipids and globular proteins
CARBOHYDRATES
LIPIDS
PERIFERAL
PROTEINS
INTEGRAL
PROTEINS

37. MEMBRANE DYNAMICSMEMBRANE DYNAMICS
• ↓ physiological temp. : gel phase
• ↑ physiological temp. : liquid-disordered
state
• Intermediate temp. : liquid-ordered state
• Unsaturated fatty acids
• Cholesterol

38. LATERAL DIFFUSION:LATERAL DIFFUSION:
• Biological membranes are not rigid structures
• Lipids > proteins are constantly in a lateral
motion
• Can be detected by FRAP
• S = (4Dt)1/2
• For lipid : D= 1µm2
/s
• S= 2 µm/S

39. • Proteins differ extremely in mobility
– Rhodopsin : D=0.4 µm/s
– Fibronectin : D = 10-2
µm/s
• fluidity increases with increase in
– No of short chain fatty acids
– Unsaturated fatty acids
– Temperature
• Cholesterol decreases fluidity at high temp
• Increases fluidity at low temp

40. • Flip flop occurs once in
several hours
• Flip flop of proteins have
not been observed
• Thus proteins play
important role in preserving
the asymmetry of the
membrane
• But sometimes Flip-Flop is
needed
TRANSVERSE DIFFUSION:TRANSVERSE DIFFUSION:

41. Cytosolic leaflet

42. MEMBRANE FLUIDITY : CLINICAL CORRELATIONMEMBRANE FLUIDITY : CLINICAL CORRELATION
• ↑cholesterol : alteration in membrane fluidity
• Spur cell anemia
• Alcohol intoxication
• Abetalipoproteinemia: ↑ sphingomyeline
↓phosphatidylcholine
• Lecithin cholesterol acyltransferase deficiency
• Hypertension
• Alzheimer’s

43. MEMBRANES : ASYMMETRIC STRUCTUREMEMBRANES : ASYMMETRIC STRUCTURE
• Inside-outside asymmetry:
– Phospholipids
– Proteins
– Carbohydrates
• Regional asymmetry
• Mechanism

44. MICRO DOMAINS OF LIPID PROTEIN COMPLEXMICRO DOMAINS OF LIPID PROTEIN COMPLEX
• Micro domain called lipid raft contains
distinctly organized bilayer structures
• Enriched in sphingolipids and cholesterols
•Biological
membranes are
actually mosaic of
Different micro-
domains

45. • Outer leaflet : ceramid and glycosphogilipids
with long chain fatty acids → thicker
• Inner leaflet ↑ saturated fatty acids → closed
packing

46. • Function : to segregate and concentrate
specific protein and to facilitate their activity
• Proteins are activated when
– several rafts fuse together
– Ligands binding which favors fusion of rafts

47. CAVEOLAE:CAVEOLAE:
• Caveoline cholesterol binding integral
membrane protein
• Forces bilayer to curve inwards forming
caveolae
• Functions : membrane trafficking, signal
transduction
Caveoline dimer
with six fatty
acid moeitis

48. MEMBRANE CURAVATURE :MEMBRANE CURAVATURE :
• Central to ability of membrane to undergo
fusion with other membrane
• Mechanisms
– Intrinsically curved protein binding
– Many subunits of scaffold protein into proteins
assembled into curved supra-molecular
complexes
– May insert one or more hydrophobic helices into
one face of bilayer

49. FUSION OF SYNAPTIC VESICLE:FUSION OF SYNAPTIC VESICLE:
• v-SNARESv-SNARES
• t-SNARESt-SNARES
• SNAP-25SNAP-25
• NSFNSF V-SNARE
t-SNARESNAP-25

50. Transferrin receptor cycle
TRANSFERRIN RECEPTOR CYCLE:TRANSFERRIN RECEPTOR CYCLE:

51. IN A NUTSHELLIN A NUTSHELL
• Biological membranes define cellular
boundaries, divide cells into discrete
compartments, organize complex reaction
sequences, and act in signal reception and
energy transformations.
• The lipid bilayer is the basic structural unit
explained by Fluid-mosaic model.
• Membranes are structarally and functionally
asymmetrical.

53. • Lipid > proteins are continuously in a state of
motion in the plane of cell membrane called
lateral diffusion
• But transverse diffusion or Flip-flop of lipids is very
slow except when specifically catalyzed by
flippases,floppases and scramblases.
• lipid rafts are rich in sphingolipids and cholesterol
consist of membrane proteins that are GPI-linked
• Specific proteins mediate the fusion of two
membranes, which accompanies processes such
as viral invasion and endocytosis and exocytosis

54. THANK YOU

55. HYDROPATHY PLOTHYDROPATHY PLOT
GLYCOPHORINE

56. STEPS IN FUSION:STEPS IN FUSION:
• Recognition
• Close opposing
• Local disruption
• Fusion
• Fusion proteins

57. TIGHT JUNCTION:TIGHT JUNCTION:
• Present between two cells that lies in close a
approximation
• Forms narrow hydrophilic channels
• Prevents the diffusion of macromolecules
• Only three layers of plasma membrane are
present
DESMOSOMES:DESMOSOMES: provide attachment of cells to
the basal tissue
• Mostly seen in epithelial cells