Transport membrane

physiology

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MEMBRANE
TRANSPORT

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Contents
Plasma Membrane: .............................................................................................................................4
Synonyms: .....................................................................................................................................4
Structure: .......................................................................................................................................4
Components: ..................................................................................................................................4
Functions: ......................................................................................................................................5
Fluid mosaic model:........................................................................................................................6
Structure: .......................................................................................................................................7
Lipid components: ..........................................................................................................................8
Properties: ......................................................................................................................................9
1) Amphiphatic in nature: .........................................................................................................9
2) Selective permeable: ............................................................................................................9
3) Transportation: ....................................................................................................................9
4) Conduction of nerve impulse: ............................................................................................. 10
5) Homeostasis: ..................................................................................................................... 10
Factors affecting the fluidity of membrane:..................................................................................... 10
Membrane Transport:............................................................................................................. 11
Passive Process:............................................................................................................................ 11
Simple Diffusion........................................................................................................................... 11
Types of Facilitated Diffusion .................................................................................................... 13
Channel Mediated ..................................................................................................................... 13
Carrier Mediated ....................................................................................................................... 13
Osmosis ....................................................................................................................................... 14
Exosmosis: ............................................................................................................................... 14
Endosmosis:.............................................................................................................................. 14
Solution Tonicity .......................................................................................................................... 15
Isotonic:.................................................................................................................................... 16
Hypotonic: ................................................................................................................................ 16
Hypertonic: ............................................................................................................................... 16
Active Process.................................................................................................................................. 18
Primary Active Process ................................................................................................................. 18
Secondary Active Process.............................................................................................................. 19
Bulk Movement/ Cytosis: .............................................................................................................. 22

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Types of Cytosis: ...................................................................................................................... 22
Exocytosis: ............................................................................................................................... 22
Endocytosis: ............................................................................................................................. 22
Types of endocytosis ................................................................................................................. 22
Receptor-Mediated Endocytosis: ................................................................................................ 23
References: ...................................................................................................................................... 26


Figure 1: Plasma Membrane ................................................................................................. 5
Figure 2: Unit Membrane Model .......................................................................................... 6
Figure 3: Fluid Mosaic Model ............................................................................................... 7
Figure 4: Membrane Protein Function .............................................................................. 8
Figure 5: Components of Plasma Membrane .................................................................. 9
Figure 6: Transport Membrane .......................................................................................... 11
Figure 7: Factors Affecting Diffusion Rate ................................................................... 12
Figure 8: Carrier Mediated Transport ............................................................................. 14
Figure 9: Endosmosis & Exosmosis ................................................................................. 15
Figure 10: Osmosis (left) Diffusion (right) ..................................................................... 15
Figure 11: Tonicity effect in animal and plant cell .................................................... 16
Figure 12: Transport Membrane Overview .................................................................... 17
Figure 13: Transport Membrane Flowchart .................................................................. 18
Figure 14: Primary Active Transport ............................................................................... 19
Figure 15: Secondary Active Transport – Sodium Cotransport ............................. 20
Figure 16: Primary & Secondary Active Process ........................................................ 20
Figure 17: Difference Between Primary & Secondary Active Process ............... 21
Figure 18: Secondary Active Process ............................................................................. 22
Figure 19: Endocytosis* ....................................................................................................... 23
Figure 20: Receptor Mediated Endocytosis .................................................................. 24
Figure 21: Difference Between Active & Passive Transport .................................. 24
Figure 22: Active Transport – Review ............................................................................. 25
Figure 23: Passive Transport – Review .......................................................................... 25

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What Is Plasma Membrane?
Plasma Membrane:
Biological membrane that forms the outer boundary of a cell.
 Present in both eukaryotic and prokaryotic cell.
 Outermost boundary of animal cell but covered by a cell wall in
plant cell.
 Covered by cell wall in case of plant, fungal and bacterial cells.
Synonyms: 1) Plasma membrane. 2) Semi-permeable membrane.
Structure:
 Delicate in nature.
 7-10 nm thick.
 Hydrophobic interior.
 Polar heads arranged towards extracellular/cytoplasmic side.
 Having repairing property by itself.
 Under electron microscope, it is lipid bilayered structure.
Components:
 Lipid (Phospholipid and cholesterol).
 Protein (Integral protein and peripheral protein).
 Carbohydrates.

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Functions:
 Hold the cell together.
 Protect the cell.
 Act as a barrier and separate cell from environment.
 Transport substances in and out of the cell.
 Receive and respond to stimuli.

Figure 1: Plasma Membran e

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Unit Membrane Model:
The Unit Membrane Model was given by J. David Robertson in
1959 after the Biomembrane model was proposed by Danielli
and Davson in 1935. This Biomembrane model proposed by
Robertson stated that;
‘‘Biomembranes are made up of three layers.’’
According to this model, cell membrane is composed of lipid bilayer,
sandwiched between inner and outer layers of protein.

Figure 2: Unit Membrane Model

Fluid Mosaic Model:
The fluid mosaic model was first proposed by S.J.
Singer and Garth L. Nicolson based on thermodynamic
principals of organization of membrane lipids and proteins in 1972.
According to this model, protein molecules are embedded in lipid
bilayer in a mosaic manner.

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Composition:
It is the phospholipids bilayer: phosphate polar head, fatty acid non-
polar tails and the proteins embedded in membrane.


Figure 3: Fluid Mosaic Model
Structure:
 Lipids (47%).
 Proteins (50%).
 Carbohydrates (3%).

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Lipid components:
 Phospholipid (75%).
 Cholesterol (20%).
 Glycolipids (5%).


Figure 4: Membrane Protein Function

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Figure 5: Components of Plasma M embrane
Properties:
1) Amphiphatic in nature:
 It consists of hydrophilic heads (phosphate polar head and
water loving) and hydrophobic tails (fatty acid non-polar tails
and water fearing).
2) Selective permeable:
 Smaller molecules can cross it easily while larger molecules are
unable to pass through it. The substances which are lipid soluble
can cross it more easily than others.
 Charged ions have difficulty to cross due to charged pores in the
membrane.
3) Transportation:
 Plays a vital role in the transportation of materials.
 Involve in the regulation of material flow.
•Peripheral Protein
•Integral Protein
Proteins
(60-80%)
•Phospholipids
•Cholestrol
Lipids
(20-40%)
•Glycolipids
•Glycoproteins
Carbohydrates
(small quantity)

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4) Conduction of nerve impulse:
 Transmit nerve impulse from one part of the body to other to
keep body coordination.
5) Homeostasis:
 Play a vital role to maintain the balance inside and outside the
cell.
Factors affecting the fluidity of membrane:
 Fatty acid --Increase in saturated fatty acid leads to rigidity while
increase in unsaturated fatty acid leads to fluidity).
 Temperature.
 Cholesterol -- (At low temperatures, cholesterol increases
membrane fluidity by preventing membrane lipids from packing
close together. At high temperatures, cholesterol decreases
membrane fluidity).

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Membrane Transport:
Anything that passes between a cell and the surrounding ECF.


Figure 6: Transport Membrane
Passive Process:
 Does not required energy.
 Substance moves along concentration/electric gradient.
 Moves from high concentration to low concentration.
Simple Diffusion
 Movement of substances from higher concentration to lower
concentration.
 Substances move freely across cell membrane.

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 Non polar, hydrophobic, small uncharged polar-oxygen, carbon
dioxide, nitrogen gases, fatty acids, steroids, fat soluble vitamins,
water, urea, small alcohols.
Net diffusion is when the flow of solute particle moving in one
direction is bigger than the flow of solute particles moving in the
opposite direction.

Figure 7: Factors Affecting Diffusion Rate
Facilitated Diffusion
 Facilitated diffusion is a type of passive transport that allows
substances (ions) to cross membranes with the assistance of
special transport proteins.
 Some molecules and ions such as glucose, sodium ions and
chloride ions are unable to pass through the lipid bilayer
of cell membranes.

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Types of Facilitated Diffusion
Channel Mediated Transport
 Throughout the central lipid layer of the cell membrane,
there are some pores (Integral protein) these pores form the
channels for the diffusion (protein channels).
 Moves down concentration gradient through a channel
protein (ion channel).
Carrier Mediated Transport
 Energy is directly required to move a substance against its
concentration gradient. The carrier splits ATP in order to power
the process.
 Carrier proteins are proteins involved in the movement of ions,
small molecules, or macromolecules, such as another protein,
across a biological membrane.
 In carrier-mediated transport, two different species can
be transported at the same time, giving a coupled transport, in
which the membrane contains a carrier which can only lead
to transport when two different species present themselves at the
same time.
Properties
Carrier-mediated transport exhibits the properties of
 Specificity
 Competition
 Saturation.

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Figure 8: Carrier Mediated Transport
Osmosis
 Special type of passive diffusion.
 Water moves from high concentration to low concentration by
using semi permeable membrane.
Exosmosis:
 Outward movement of water from inside to outside, higher to
lower concentration.
 Causes shrinkage of cell.
Endosmosis:
 Inward movement of water from outside to inside.
 Causes the turgidity of plant cell and burst in case of animal cell.

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Figure 9: Endosmosis & Exosmosis

Figure 10: Osmosis (left) Diffusion (right)

Water moves until equilibrium reached on both sides
of membrane by using hydrostatic and osmotic
pressure. Water Can Move In 2 Different Ways; 1)
Between lipid molecules . 2) Through aquaporin
channels (integral protein).

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Solution Tonicity
Measure of solution’s ability to change volume of cells by changing water
contents.
Isotonic: Same amount of water on both sides of membrane.
Hypotonic: More water, less solutes.
Hypertonic: Less water, more solutes.

Figure 11: Tonicity effect in animal and plant cell

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Figure 12: Transport Membrane Overview

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Figure 13: Transport Membrane Flowchart
Active Process
 Required energy to get substances across membrane.
 Substance moves against concentration gradient.
Primary Active Process
 Type of transport mechanism in which the
energy is liberated directly from the breakdown of ATP.
 The substances like sodium, potassium, calcium, hydrogen
and chloride are transported across the cell membrane.

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Figure 14: Primary Active Transport
Secondary Active Process
Secondary active transport is the transport of a substance with sodium
ion, by means of a common carrier protein.
Two types:
 Co-transport
 Counter transport.
Sodium Co-transport
 Substances carried by sodium co-transport are glucose, amino
acids, chloride, iodine, iron and urate.

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Figure 15: Secondary Active Transport – Sodium Cotransport


Figure 16: Primary & Secondary Active Process

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Figure 17: Difference Between Primary & Secondary Active Process

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Sodium Counter Transport
 Substances carried by sodium counter transport are
Sodium-calcium, Sodium-hydrogen, Sodium-magnesium,
Sodium-potassium.


Figure 18: Secondary Active Process
Bulk Movement/ Cytosis:
Movement of bulk material by membrane folding.
Types of Cytosis:
Exocytosis:
 Removal of materials from cell by the help of cell membrane.
 Reverse of endocytosis.
Endocytosis:
 Intake of material by infolding in the form of vacuoles.
Types of endocytosis:

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Phagocytosis:
 Movement of solid material inside cell by cell membrane
invagination, this is cell eating.
Pinocytosis:
 Movement of liquid by plasma membrane invagination, this is cell
drinking.

Figure 19: Endocytosis*
Receptor-Mediated Endocytosis:
 Receptor-mediated endocytosis (RME), also called clathrin-
mediated endocytosis, is a process by which cells absorb
metabolites, hormones, proteins – and in some cases viruses – by
the inward budding of the plasma membrane (invagination).
 Membrane of bulk material by using the membrane receptor.

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Figure 20: Receptor Mediated Endocytosis


Figure 21: Difference Between Active & Passive Transport

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Figure 22: Active Transport – Review


Figure 23: Passive Transport – Review

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References:
 Lauralee Sherwood-Human Physiology_ From Cells to
Systems-Cengage Learning USA (2014).
 Internet source.
 Class lecture.





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