The plasma membrane surrounds plant and animal cells and is composed mainly of lipids and proteins. It is structured as a lipid bilayer that is 7.5 nm thick with phospholipid molecules forming inner and outer layers. Embedded within this bilayer are integral proteins that span the membrane as well as peripheral proteins that are attached to either surface. The fluid mosaic model describes the plasma membrane as a fluid structure with proteins and lipids able to move freely within it. The membrane acts as a selectively permeable barrier and uses different mechanisms like passive transport, facilitated transport, and active transport to regulate the movement of substances into and out of cells.

1. Plasma Membrane
P. HARITHA AND SHARATH DEEPIKA
Degree Lecturers in Botany
Telangana tribal welfare residential degree
colleges of Sangareddy and Medak,
Telangana

2. Introduction
O Do you what is the difference between
Protoplasm and Cytoplasm?
O Then what are biological membranes?
O The cytoplasm of the plant and animal cells are
surrounded by the Plasma membrane

3. Chemical Composition
OThese membranes are mainly composed
of lipoproteins.
OMeasuring 75 A in thickness, with three
concentric layers
OOuter and inner layer 20 A and middle
layer 35 A
1. Lipids
2. Proteins
3. Other constituents

4. Lipids
OMost common fats are glycolipids and
phospholipids
OAmphipathic – both hydrophobic and
hydrophilc parts
OLecithin, Choline, Cephalin are
important phospholipids
OGlucose and galactose in association
with lipids are important glycolipids

5. Proteins
OThese are the main components
O Three types depending on function
1. Structural proteins
2. Functional proteins
3. Carrier proteins
O Two types depending on their nature
1. Peripheral proteins
2. Integral proteins

6. 1. Structural Proteins: Backbone and strongly
lipophilic
2. Functional proteins: Responsible for several
reactions
3. Carrier proteins: transport of material
across the membrane
4. Proteins can be further differentiated into:
i. Peripheral protein: hydorphilic interaction
twith lipid bilayer
ii. Intergral proteins: Hydrophobic interaction
protruding inside

7. Other constituents
OSmall amounts of polysaccharides,
sialic acid, DNA, RNA coenzymes,
metal ions are distributed.
O An Extracellular membrane- Glycocalyx
membrane is seen outside the
membranes with a combination of
carbohydrates and collagen proteins and
glucosamine glycans

9. Models to explain-Structure of
the plasma membrane
O Several biologist have given several structural
explanations
O Five types
1. Lipid bilayer model
2. Danielli Davson model
3. Unit membrane model
4. Fluid mosaic model
5. The Micellar model

10. 1. Lipid Bilayer model
O Gorter and Grendal – 1925
O Lipid bilayer – first time
O Extracted cells from human erythrocytes – measured
the surface by placing it on water.
O Concluded that it is simple lipid bilayer – polar
groups to the periphery
O Later found that water soluble molecules move
through the membrane and concluded – non lipid
molecules
O Charged particles moved slowly and molecules like
glucose moved fast
O Concluded it could be proteins – holding charged
particles and freeing uncharged particles

11. Lipid bi layer model

12. 2. Danielli Davson Model
OJames Danielli and Hugh Davson – 1935
OStarfish egg membrane
OTwo layer of lipids with hydrophobic in
centre and hydrophilic to periphery
OPolar ends of lipid face outward and
associated with monolayer of polar globular
proteins
OIt appears as double layer of lipids
sandwiched in between two layer of globular
proteins
OLipid layer – 4.5nm and proteins 2.5nm

14. 3. Unit membrane
ORobertson – 1957
OFirst observed in Golgi complex, ER,
Nuclear envelope.
OLipid layer 35 A in the centre and protein
layer 20 A on either side
OLipids are Phospholipids
OOuter surface proteins are mucoproteins
OInner surface proteins are non mucoid
proteins

16. 4. Fluid Mosaic Model
O Singer and Nicholson – 1972
O Lipid bilayer model like a fluid and proteins present
in mosaic of discontinuous patterns
O These proteins resemble the iceberg in the sea of
lipids
O Hence plasma membrane is double layer of
phospholipids with polar ends facing opposite
sides
O And globular proteins ad sterols floating.
O Integrated proteins penetrate lipid bilayer and
project form extra cellular and cytoplasmic
sides
O And globular proteins attached loosely to
membrane lipids

18. 5. Micellar model
OHiller and Hoffman 1953
ORepeating globular units called micelles
OEach micelle is 40 – 70 A in diameter with
centre lipid core surrounded by hydrophilic
shell of proteins
OMicelles posses water filled pores 4 A
OGreen suggested membranes can be
monopartite – membrane without projections
(mitochondria outer wall) and multipartite –
membrane with projecting units
(mitochondira inner membrane)

20. Functions of the biological
membranes
o Compartmentalization: living boundaries
o Selectively permeable membrane: appropriate
substances to pass
o Transporting materials for metabolic essentials:
specialised transport pattern simple diffusion,
facilitated diffusion, pinocytosis etc.
o Responding to stimuli: some proteins act as
receptors
o Site for biochemical activities: Mitochondrial
membrane – respiration

21. Movement of substances
across the cell membranes
O In order to survive cell has to interact
O Essential molecules – oxygen, salts in to the cells
and waste like carbon dioxide out of the cell
O Two functions –retain the materials it require from
leakage and allow necessary exchange into and
out of the cell
O Four methods of transport – Passive Transport,
Facilitated transport, Active transport and Bulk
transport

22. 1. Passive transport
OSpontaneous movement of molecules from
region of higher concentration to the region of
lower concentration
OWater, oxygen and carbondioxide move by
this method
OMovement of water depends on solute
concentration – lower solute concentration to
higher solute concentration through a semi
permeable membrane
OIn to the cell endosmosis and out of the cell
exosmosis

23. 2. Facilitated transport
OEssential complex molecules move
through a specialized membrane
associated molecules/ carriers
OEg: Movement of glucose in to the
blood as it is primary source of
energy, amino acids etc.

24. 3. Active Transport
OSimilar to facilitated diffusion, through
carrier proteins but needs the
expenditure of energy in the form of
ATP
OFrom region of lower to higher
concentration
ONa K pump, H+, P Pumps, Ca2+.

25. 4. Bulk transport
O Bulk molecules are entering in to the cell by
membrane bound vesicles, forming endosome
and digested by hydrolytic enzymes
O Formation of endosome in Endocytosis (cell
eating) and Exocytosis (cell vomitting).
O If larger molecules greater than 0.2 micrometer
– phagocytosis (cell eating), similarly uptake of
smaller molecules – pinocytosis (cell drinking).
O Conversely, cell vomiting – intracellular vesicle
releases the components out of the cell –
neurotransmitter example

26. ACKNOWLEDGEMENTS:
• We would like to acknowledge
all the authors and owners for
the pictures used in our
presentation
• We would like to emphasize
that all pictures were taken
from the open source internet
medium