cellular organelles

4. Semi
permeable
Elastic
Thin
Proteins
are in and
out points

5. The Plasma Membrane, the flexible
boundary between the cell and its
environment, allows a steady supply of
nutrients to come into a cell no matter
what the external conditions are. Too
much of any of these nutrients or
substances can be harmful to the cell. If
levels become too high, excess is
removed through plasma membrane

6. Cell Membrane
• A semipermeable membrane that
surround cytoplasm of cell
• Encloses the entire cell
• Composed of a phospholipid
bilayer with embeded proteins
Plasma Membrane
• A semipermeable barrier that
surrounds cells or cellular
compartments
• Encloses cells or organelles
• Composition may change based
on requirements of cellular
compartments

8. Models of Plasma Membrane

9. Gorter and Grendel Model-
1925:
• Evert Gorter and
François Grendel (Dutch
physiologists)
• Phospholipid Bilayer
• Hydrophobic tails and
hydrophillic heads

10. Davson–Danielli model-1935:
• By Hugh Davson and James
Daniell.
• A phospholipid bilayer that
lies between two layers of
globular proteins which is
trilaminar and lipoprotinious.
• Also called Bimolecular
Leaflet Model.

11. Robertson Model- Unit
Membrane Model -1959:
• J. David Robertson.
• Suggested that all cellular
membranes share a similar
underlying structure, the
unit membrane.
• Three layers- Outer Protein
layer, Middle Lipid layer
and Inner Molecule layer.
• Glycoproteins are also
present.

12. Fluid Mosaic Model- 1972:
• By Singer and Nicholson.
• Disproved Robertson, Davson and
Danielli Models.
• Lipid bilayer kept
• Protein coat lost
• Two components of this model are:
• Fluid- all components are free to
diffuse in the plane of membrane
• Mosaic- Heterogeneity membrane
(proteins and lipids interspersed and
because of fluidity of plasm
membrane they are randomly
distributed)

18. Composition:
• Membrane Lipids- 90-99%
• Primary lipids- phospholipids
• Secondary lipids- Cholesterol/Sphingolipids( Fluidity- less cholesterol more fluidity-depends on type
of cell- like RBCs require more flexibility so have less cholesterol )
• Glycolipids- 5% Of Lipids (on extracellular side- Glycocalyx{Cell to Cell adhesion})
• Membrane Proteins- About 2% (essential for two membrane functions-Sensitivity,
Selective Permeability)
• Two types- Transmembrane proteins(Cross totally) & Peripheral proteins (towards or outwards to
cell side/ Partially cross membrane)
• A little percentage of Carbohydrates.
(Fluidity is due to main membrane components held by non-covalent
interactions)

23. Eukaryotes resemble prokaryotes in membrane structure and
functions except for sterols.

24. Peripheral proteins
• Loosely associated with
proteins/lipids
• Functions- Anchorage,
Intracellular signalling
molecules
Integral proteins
• Partially attached
• Glycoproteins with sugar
• Extend to outside
• Function- Glycocalyx
Formation

26. A transmembrane protein (TP) is a type of integral membrane protein that spans
the entirety of the cell membrane to which it is permanently attached.
There are five types of trans membrane proteins:
1. Receptor proteins
2. Channel proteins (always open)
3. Gate Channel proteins (closed-checkers-have gate but open)
4. Transport proteins- Carrier proteins (in pairs)
5. Glycocalyx attached proteins – Cam (Cell adhesion molecules (CAMs)-cell
adhesion proteins located on the cell surface)
Trans-Membrane Proteins:

27. Types of transmembrane proteins on basis of function:

31. Glycocalyx:
• The fuzzy coat external to
plasma membrane on all
animal cells, including
humans
• Acts as on “identification”
tag that enables the body to
distinguish its own healthy
cells from transplanted
tissue, invading organism,
diseased cells.

32. Functions:
•Transport
• Non facilitated Transport & Facilitated Transport(Facilitated
Active transport, Facilitated passive transport {Diffusion,
Osmosis})
•Mechanical Support
•Homeostasis

33. • Integrity of the cell- size and shape
• Controls transport- Since it is Selectively permeable
• Excludes unwanted materials from entering the cell
• Forms a physical barrier with the external environment
• Allows the cell to create different environments outside and inside
• Maintains the ionic concentration of cell and Osmotic pressure of the cytosol
• Allows for the creation of gradients- electrical and chemical
• Forms contacts with neighboring cells i.e. help in forming tissues
• Sensitivity- First part of cell that is affected by changes in the extracellular
environment

39. Properties of Plasma Membrane
Allows small
molecules either
polar (CO2 AND
H2O) or non polar(
oxygen and
ethanol)to pass
through freely
Don’t allow
macromolecules(
Glucose) and ions
(K+ and Na+) to
pass through freely
Have specific trans
membrane proteins
to regulate ion (ion
channel) and
molecules
(Transporter
proteins)
movements
The property of
Plasma
membrane to
selectively allow
some molecules
to pass through is
termed as
semipermeable

42. Passive mediated transport, or Facilitated diffusion- A specific molecule
flows from high to low concentration
Active transport- Transport from low to high concentration i.e. against
concentration gradient.

44. Na- K pump
(Active Transport)

54. As a part of ENDOMEMBRANE SYSTEM:
• Vesicle formation
• Transport Information- Proteins out or into cell
• Uses Energy- ATP
• Exocytosis,Endocytosis
• Golgi body produces vesicles, fuses with membrane materials
(hormones etc.), released out of cell

57. Intracellular Membranes:
• Nuclear Membrane
• Mitochondrial Membranes
• Chloroplast Membranes
• E.R as a part of endomembrane system
• Golgi as part of endomembrane system

58. • Campbell Biology by Urry, Cain, Wasserman Minorsky, Reese.
• M. Lodish (2003), Molecular cell biology, Chapter 3 Bio-membranes and
cell architecture, 5th edition
• Alberts B et al. (2002) in “The Molecular biology of the cell”, 4th edition.
Garland Science, New York.
• file:///E:/BOOKS/Cell%20Biology.pdf
• file:///E:/BOOKS/cellular_organization.pdf
• file:///E:/BOOKS/cholesterol.pdf
• https://bioproxnoob.files.wordpress.com/2011/03/propeertiesofplasm
amembrane.jpg

59. THANK YOU MY PUPILS