Cellular Transport
Notes
The Purpose of the Plasma Membrane is to
Maintain Balance called “HOMEOSTASIS”
or “To Reach Dynamic Equilibrium””
Is traffic at equilibrium?
Why or why not?
Equilibrium occurs when molecules have
spread out evenly
When the concentration of a solute is equal
throughout the solution
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
• 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 pass through easily
Components of the Plasma Membrane
Phospholipids:
Proteins
Cholesterol
Phospholipids
Cell Membrane
Aka: PhosphoLipid Bilayer:
• 2 layers of phospholipids
• provides a barrier for the cell.
Allows for selective permeability
a. Phosphate head
(hydrophilic=water loving)
b. Fatty acid tails are
non-polar
(hydrophobic=water fearing)
Phospholipid
http://www.youtube.co
m/watch?v=Rl5EmUQd
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Lipid Bilayer
Beaker 1 Lipid Surface Monolayer
1.Draw a to scale 600ml beaker, and fill it
2/3 full of water.
2.By observe the phospholipid on the board
that your teacher has drawn
3.Define Hydrophilic and Hydrophobic
based on root words.
4.Finally imagine you have 10
phospholipids, draw how these molecules
would arrange themselves if they were
dropped from above their beaker of water.
Beaker 1
Beaker 2 Lipid Molecule
1.Draw a to scale 600ml beaker, and fill it
2/3 full of water.
2.You now have 10 more phospholipids
draw a representation of how they would
arrange themselves if they had to meet
the criteria that they had to be submerged
and surrounded by water.
3.Remember the molecules will work
together to solve the problem.
Beaker 2
Beaker 3
The Phospholipid Bilayer of a Cell
Membrane
1. For the third thought experiment student
are asked to draw their final
beaker 2/3 full of water.
2. You now have even more phospholipids,
how would they would arrange
themselves if they had to meet the criteria
that they had to be submerged and
surrounded by water, but also be able to
contain water.
Beaker 3
Some functions
functions of membrane
PROTEINS Figure
serve8.9many
for the proteins
plasma membrane
Cholesterol Molecules
Makes the bilayer stronger but still flexible
Holds two layers together
Cell to cell communication
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
http://www.
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02.sci.life.c
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Passive Transport
A process that does not require energy to move
molecules from a HIGH to LOW concentration
Diffusion
Osmosis
 Facilitated
Diffusion
• 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
Where does diffusion take place in the body?
• 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.
Types of Solution
Concentrations
1. Hypertonic
2. Hypotonic
3. Isotonic
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.
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.
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.
HYPO= “More”Figure 8.12
ISOThe
= “Equal”
= “More”
water balance ofHYPER
living cells
• 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
Glucose molecules
Facilitated diffusion
diffusion of specific particles through transport
proteins found in the membrane
Transport Proteins are specific – they “select” only certain
molecules to cross the membrane
Ex: channel or carrier proteins
a. Transports larger or charged molecules
a.
A
(Carrier
Protein)
Facilitated diffusion
(Channel Protein)
B
Diffusion
(Lipid
Bilayer)
ANALOGY:
NO
ENERGY
NEEDED:
Diffusion
Osmosis
Facilitated
Diffusion
ENERGY
NEEDED:
Active
Transport
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.
3 Types:
1. Protein Pumps
2. Endocytosis
3. Exocytosis
outside of cell
inside of cell
Carbon Dioxide
molecules
1. Protein Pumps -transport proteins that require
energy to do work
Protein changes shape to move molecules: this requires energy!
• Example: Sodium / Potassium Pumps are
important in nerve responses.
• Endocytosis and Exocytosis is the mechanism by which
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
2 Types of Endocytosis
1. Phagocytosis- “cell eating” Extensions of the cytoplasm
surround a particle and package it within the vacuole
2 Types of Endocytosis
2. Pinocytosis- “cell drinking” Pockets form along the cell
membrane, fill with liquid, and pinch off to form vacuoles within the cell