Transcript Cell Transport - Warren County Public Schools

Cell Transport
Cell Membrane:
 Function:


Maintain homeostasis.
 This is also called equilibrium.
Allow passage of some molecules while
preventing the passage of others
 This is called being “Selectively
permeable” or “semi-permeable”
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Semipermeable Membrane
Small molecules and larger hydrophobic
molecules move through easily.
e.g. O2, CO2, H2O
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Semipermeable Membrane
Ions-hydrophilic molecules larger than water,
and large molecules such as proteins do not
cannot pass through the membrane without
help.
Membrane structure:
Composed of a phospholipid
bilayer
 Have a phosphate head
which is polar- does react
with water
 Have a fatty acid
(lipid) tail that is non-polardoes not react with water
 Together these make up the
membrane
•
•
The inside of the
membrane is
hydrophilicwhich means it
does not react
with water
•
The outside of
the membrane
is hydrophobicwhich means it
does react with
water
•Contains proteins within its structure
1. Integral proteins (transport proteins)- which
allow the passage of molecules to large too
pass through the membrane without help
2. Peripheral proteins- aid in signaling for the cell
to communicate with other cells
Cell Structure:
 Make
up a metaphor for the phosphate
heads of the membrane and the lipid tails
of the membrane.
 The
cell’s structure allows it to maintain
homeostasis in different situations.
Concentration Gradient
 Concentration
gradients occur when
there is a higher amount of solutes in one
area of solution then in another.

Molecules will tend to travel from areas of
high concentration to areas of lower
concentrations
Passive transport
 Molecules
flow with or down a
concentration gradient
 No energy required
 Two types:

Diffusion
 Ex.

Osmosis
Facilitated Diffusion
Diffusion

Facilitated Diffusion
Diffusion for molecules
that are not lipid
soluble or are too large
to pass through the
membrane.
 Carrier proteins change
shape to aid these
molecules across the
membrane
 No Energy Required.
 Example: Glucose,
Fructose

Osmosis
 Diffusion
involving water moving from high
solute concentrations to low solute
concentration.


Water can move freely across the membrane
No energy required.
Osmosis
 There
are three different types of
osmotic solutions:



Hypotonic
isotonic
Hypertonic
Hypotonic Solution
 Higher
concentration of
solutes within the cell

More free water outside
the cell
 Water
moves into the
cell
 The cell becomes swells
or gets larger
 Hypo
Hippo- it gets big
and swells.
Hypertonic Solution

Higher concentration of
solute outside the cell



More free water in the cell
Water moves out of the cell
Cell shrinks
Isotonic solution
 Solutions
are equal
between the two areas
 Water moves both
directions to keep the
solutions at an
equilibrium.
What will happen to water in
the cell?
Three different Osmotic
Solutions
 Hypotonic-
higher concentration of
solutes in the cell
 Hypertonic- higher amount of water inside
the cell
 Isotonic – equal amount of solutes inside
and outside the cell
Example- Plants:
 In
a hypotonic solution plant cell’s
membrane is pushed against the cell wall

Turgor Pressure
 In
a hypertonic solution a plant cell’s
membrane will shrink within the cell wall


Plasmolysis
Causes wilting when plants dehydrate
Turgor Pressure
 Plant
cell become
engorged with
water
 Gives plant the
stiffness in their
stem
Plasmolysis
 Plant
cell membrane shrinks from the cell wall
 Causes plant to wilt.
Active Transport
 Molecules
are transported against the concentration
gradient by proteins
 Requires energy (ATP)
 Example: Sodium-Potassium Pump



A protein that transfer Na+ and K+ ions up the gradient
Cell has a high Na+ concentration outside the cell and
a high K+ concentration inside the cell
http://www.youtube.com/watch?v=GTHWig1vOnY
Active transport
Enodcytosis:
 cells engulf
substances that
are too large to
enter the cell by
passing through
the cell membrane
Exocytosis:
 cellular wastes are
removed from sacs
at the cell’s surface
Exocytosis-
moving things
out.
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• Molecules are moved out of the cell
by vesicles that fuse with the plasma
membrane.
• This is how
many
hormones are
secreted and
how nerve
cells
communicate
with one
another.
copyright cmassengale
Exocytosis
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Exocytic vesicle
immediately after
fusion with plasma
membrane.
copyright cmassengale
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Large molecules move materials into the cell by
one of three forms of endocytosis.
copyright cmassengale
Pinocytosis-
Most common form of endocytosis.
Takes in dissolved molecules as a vesicle.
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Pinocytosis Cell
forms an
invagination
 Materials dissolve in
water to be brought
into cell
 Called “Cell Drinking”
copyright cmassengale
Example of Pinocytosis
Transport across a capillary cell (blue).
mature transport vesicle
pinocytic vesicles forming
copyright cmassengale
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Receptor-Mediated Endocytosis
Some integral proteins have receptors
on their surface to recognize & take in
hormones, cholesterol, etc. copyright cmassengale
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copyright cmassengale
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Endocytosis – Phagocytosis
Used to engulf large particles such
as food, bacteria, etc. into vesicles
Called “Cell Eating”
copyright cmassengale
Phagocytosis
- Capture
of a Yeast
Cell (yellow)
by
Membrane
Extensions
of an
Immune
System Cell
(blue)
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copyright cmassengale
So to review the three types of
Endocytosis are:
• Phagocytosis
• Pinocytosis
• Receptor mediated Endocytosis.
Exocytosis
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The opposite of endocytosis is exocytosis.
Large molecules that are manufactured in the
cell are released through the cell membrane.
copyright cmassengale
Inside Cell
Cell environment
What are the three different
types of active transport?
 Protein
pumps
 Endocytosis
 Exocytosis
Cell Transport
 Passive
transport: molecules travel along
the concentration gradient

No energy required
 Active
Transport: molecules are
transported against the concentration
gradient

energy required