Transcript Human-Physiology-Lecture-IV-CellMembranes-and-transport-by

Human Physiology: Unit-1
Cell Membranes transport across
cell and membrane
BY
DR BOOMINATHAN Ph.D.
M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel), Ph.D (NUS, SINGAPORE), PDF (USA)
PONDICHERRY UNIVERSITY
IV Lecture
9/August/2012
Source: Collected from various sources on the internet and modified by Dr Boominathan Ph.D.
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Cell Membranes
&
Movement Across Them
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2006-2007
Cell (plasma) membrane
 Cells need an inside & an outside…

separate cell from its environment

cell membrane is the boundary
IN
OUT
food
- sugars
- proteins
- Lipids
-salts
-O2
-H2O
waste
- ammonia
- salts
- CO2
- H2O
products
- proteins
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cell needs materials in & products or waste out
Building a membrane
 How do you build a barrier that keeps
the watery contents of the cell separate
from the watery environment?
 LIPIDS 
Remember:
oil & water
don’t mix!!
What substance
do you know
that doesn’t mix
with water?
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Lipids of cell membrane
 Membrane is made of special kind of lipid

phospholipids
“attracted to water”
 Membrane is a double layer

phospholipid bilayer
phosphate
inside cell
lipid
outside cell
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“repelled by water”
Semi-permeable membrane
 Cell membrane controls what gets in or out
 Need to allow some materials — but not all
— to pass through the membrane

semi-permeable
 only some material can get in or out
So what needs to get across the membrane?
sugar lipids
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aa
O2
H 2O
salt
waste
Crossing the cell membrane
 What molecules can get through the cell
membrane directly?

fats and oils can pass directly through
inside cell
waste
outside cell
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lipid
salt
sugar aa
H 2O
but…
what about
other stuff?
Cell membrane channels
 Need to make “doors” through membrane

protein channels allow substances in & out
 specific channels allow specific material in & out
 H2O channel, salt channel, sugar channel, etc.
inside cell
salt
wasteBiology
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H 2O
aa
sugar
outside cell
How do you build a semi-permeable
cell membrane?
 Channels are made of proteins

proteins both “like” water & “like” lipids
bi-lipid
membrane
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protein channels
in bi-lipid membrane
Protein channels
 Proteins act as doors in the membrane

channels to move specific molecules
through cell membrane
HIGH
LOW
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Movement through the channel
 Why do molecules move through
membrane if you give them a channel?
HIGH
?
LOW
?
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Molecules move from high to low
 Diffusion

move from HIGH to LOW concentration
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Diffusion
 Move from HIGH to LOW concentration
passive transport
 no energy needed

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diffusion
diffusion of water
osmosis
Diffusion (without energy-simple)
 Move from HIGH to LOW
inside cell
Lipid
Which way
will Lipid
substances
move?
Lipid
LOW
HIGH
outside cell
Lipid
Lipid
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Lipid
Lipid
Lipid Lipid
Facilitated Diffusion
 Move from HIGH to LOW through a channel
sugar sugar
sugar
sugar
inside cell sugar
sugar
LOW
Which way will
sugar move?
HIGH
outside cell
sugar
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sugar
sugar
sugar
sugar
sugar
Diffusion
 Move from HIGH to LOW concentration

directly through membrane
 simple diffusion
 no energy needed

help through a protein channel
 facilitated diffusion (with help)
 no energy needed
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HIGH
LOW
Simple vs. facilitated diffusion
simple diffusion
inside cell
lipid
facilitated diffusion
inside cell
H 2O
protein channel
outside cell
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outside cell
H 2O
Active transport
 Cells may need molecules to move
against concentration “hill”

need to pump “uphill”
 from LOW to HIGH using energy
protein pump
 requires energy
 ATP

ATP
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Transport summary
simple
diffusion
facilitated
diffusion
active
transport
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ATP
Osmosis
Movement of Water Across
Cell Membrane
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2006-2007
Osmosis
 Water is very important, so we talk about
water separately
 Osmosis

diffusion of water from HIGH concentration
of water to LOW concentration of water
 across a semi-permeable membrane
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Keeping water balance
 Cell survival depends on balancing
water uptake & water loss
freshwater
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balanced
saltwater
1
Keeping right amount of water in cell
 Freshwater
a cell in fresh water
 high concentration of water
around cell

Burst
freshwater
 cell gains water
 example: Paramecium
 problem: cells gain water,
swell & can burst
 water continually enters
No problem,
here
Paramecium cell
 solution: contractile vacuole
 transports water out of cell
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2
Keeping right amount of water in cell
 Saltwater
I’m shrinking,
I’m shrinking!
a cell in salt water
 low concentration of water
around cell

 cell loses water
example: shellfish
 problem: cell loses water

 in plants: plasmolysis
 in animals: shrinking cell

solution: take up water
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I will
survive!
saltwater
3
Keeping right amount of water in cell
 Balanced conditions

That’s
better!
no difference in
concentration of water
between cell & environment
 cell in equilibrium
 example: blood
 problem: none
 water flows across
membrane equally,
in both directions
 volume of cell doesn’t
change
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I could
be better…
balanced
CELLS
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Chemical compositions of extracellular and intracellular fluids
Downloaded from: StudentConsult (on 15 August 2012 04:30 AM)
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Na-K Channel: How it Works
•
•
•
•
A type of active transport.
3 sodium ions move out of cell
2 potassium ions move into cell.
ATP is needed as each of these ions are
moving against their conc. gradient.
• Mostly used in cardiac muscle and nervous
tissue. Maintains Na+K gradient
concentration.
• Huge amount of ATP goes into this NaK
channel.
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Sodium –Potassium Channel
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Figure 3.11
Sodium-Potassium Channel
A molecule of ATP is used with each “swap of Na/K ions
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Endocytosis (phagocytosis-Cell Eating)
 This is Vessicle
transport during
which the entire
plasma
membrane folds
inward allowing
large particles
into the cell.
 Ex; the cell is
ingesting
microbes ,
perhaps?
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Cell
Membrane
Function
Endocytosis
The cell membrane can also engulf structures that are much too large to fit
through the pores in the membrane proteins this process is known as
endocytosis. In this process the membrane itself wraps around the particle
and pinches off a vesicle inside the cell. In this animation an ameba engulfs a
food particle.
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AS Biology, Cell membranes and
33
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Exocytosis
 The opposite
of
ENDOcytosis.
Large particles
are leaving the
cell. (digested
microbes for
example).
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Receptor-mediated Endocytosis
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This actually uses specific proteins
to identify the substance to be
taken into the cell. This is how
your body gets rid of excess LDL
(cholesterol)from your blood.
Receptor- Mediated Endocytosis
 Viruses are species –
specific , and receptor
specific,
 transmitted via
receptor-mediated
endocytosis.
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Vesicle-mediated transport
Vesicles and vacuoles that fuse with the cell membrane may
be utilized to release or transport chemicals out of the cell or
to allow them to enter a cell. Exocytosis is the term applied
when transport is out of the cell.
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AS Biology, Cell
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Cell Membrane (Transport) Notes
Cell Membrane and Cell Wall:
• ALL cells have a cell membrane made of proteins and lipids
protein channel
Layer 1
Cell
Membrane
Layer 2
lipid bilayer
protein pump
• SOME cells have cell membranes and cell walls – ex: plants, fungi
and bacteria
Cell
Membrane
Cell Wall
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• Plant cells have a cell wall
made of cellulose – that
cellulose is fiber in our diet
• Bacteria and fungi also
have cell walls, but they
do not contain cellulose
• Cell membranes and cell
walls are porous allowing
water, carbon dioxide,
oxygen and nutrients to
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Biology
pass through
easily
Function of the Cell Membrane:
• Cell membrane separates the components of a cell
from its environment—surrounds the cell
• “Gatekeeper” of the cell—regulates the flow of
materials into and out of cell—selectively permeable
• Cell membrane helps cells maintain homeostasis—
stable internal balance
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Passive Transport
A process that does not require energy to move
molecules from a HIGH to LOW concentration
 Diffusion
 Facilitated Diffusion
 Osmosis
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• Diffusion is the movement of small particles across a
selectively permeable membrane like the cell membrane
until equilibrium is reached.
These particles move from an area of high concentration
to an area of low concentration.
outside of cell
inside of cell
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• Osmosis is the diffusion of water through a selectively
permeable membrane like the cell membrane
Water diffuses across a membrane from an area of high
concentration to an area of low concentration.
Semi-permeable
membrane is
permeable to water,
but not to sugar
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• Facilitated Diffusion is the movement of larger
molecules like glucose through the cell membrane –
larger molecules must be “helped”
Proteins in the cell membrane form channels for large
molecules to pass through
Proteins that form channels (pores) are called protein
channels
outside of cell
inside of cell
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Glucose molecules
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Hypertonic Solutions: contain a high concentration of solute
relative to another solution (e.g. the cell's cytoplasm). When
a cell is placed in a hypertonic solution, the water diffuses
out of the cell, causing the cell to shrivel.
Hypotonic Solutions: contain a low concentration of solute
relative to another solution (e.g. the cell's cytoplasm). When
a cell is placed in a hypotonic solution, the water diffuses
into the cell, causing the cell to swell and possibly explode.
Isotonic Solutions: contain the same concentration of solute
as another solution (e.g. the cell's cytoplasm). When a cell is
placed in an isotonic solution, the water diffuses into and
out of the cell at the same rate. The fluid that surrounds the
body cells is isotonic.
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Active Transport
Active transport is the movement of molecules from LOW to HIGH
concentration.
Energy is required as molecules must be pumped against the
concentration gradient.
Proteins that work as pumps are called protein pumps.
Ex: Body cells must pump carbon dioxide out into the surrounding
blood vessels to be carried to the lungs for exhale. Blood vessels are
high in carbon dioxide compared to the cells, so energy is required
to move the carbon dioxide across the cell membrane from LOW to
HIGH concentration.
outside of cell
inside of cell
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Carbon Dioxide
molecules
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ANALOGY:
ENERGY NEEDED:
Active Transport
NO ENERGY NEEDED:
Diffusion
Osmosis
Facilitated Diffusion
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• Endocytosis and Exocytosis is the mechanism by which
very large molecules (such as food and wastes) get into
and out of the cell
Food is moved into the
cell by Endocytosis
Wastes are moved out
of the cell by
Exocytosis
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Ex: White Blood Cells, which are part of the immune
system, surround and engulf bacteria by endocytosis.
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