Transcript Membrane Transport Powerpoint

Cell Transport Mechanisms and Homeostasis
Cell Cytoplasm is full of
many different Substances.
Mostly WATER as the Solvent
making movement and
reactivity of the various
molecules possible.
≈ 80% Water!
Lots of dissolved Ions – but
different concentrations
than in the Blood.
Sugars and Proteins and
other molecules.
5%
If the
Balance is
wrong,
your blood
cells will
not
survive or
function.
Pre-Made!
Cells!
Precisely
Balanced!
An IV represents Balance with the
Cells of your Blood. Not the same
Stuff, but equal amounts!
5% Sugar (Dextrose or Ringer’s
Lactate) or 0.9% Salt = Cell.
Cell Transport Mechanisms and Homeostasis
OUTSIDE = Extracellular Fluid.
Contains all sorts of things that
cells need and that the
Organism Provides. Your
Digestive Tract is Choosy, but
not perfectly Picky!
Selective Permeability
allows Cells to Choose and
Move the RIGHT STUFF –
CONTROLLED!!
INSIDE = Cytoplasm.
THE RIGHT STUFF!
The Cell NEEDS Specific Things:
The right Ions, as many Amino Acids
as Possible, Glucose, “Its”
Proteins, etc…
Other things are Kicked OUT.
Contains a Precisely Balanced
Solution of all of the RIGHT
STUFF! This is Homeostasis!
Must be able to Transport the
RIGHT STUFF IN!
Cell Transport Mechanisms and Homeostasis
Transport Proteins can do their job because
they are specific in SHAPE! Only Proteins can
do this because they are so Variable!
R
R
?
R
R
?
r
But then the
Chain?
?
But Remember!!
Hydrophobic
Core
Hydrophilic
Edges
Inside
Membrane!
Outside
Membrane!
VARIABLE in SHAPE!!
Opening COULD BE:
OR OTHERS!
Water is the Solvent!
Water diffuses into the
Solute (High to low conc.)
and dissolves it!
H20
H20
H20
Dry Solutes cannot
move – they are
bound together as
a Solid.
If there is no Restriction to the Movement of the
Solutes (Remember – Water will move by itself!),
they will form a SOLUTION!
Water IS the SOLVENT and breaksup the SOLUTES from each other.
Once the SOLUTES are separate,
they WILL SCATTER until
completely distributed as a
Solution.
Solutes Stick Together!!
BUT! Solvents Stick to Solutes!
DIFFUSION leads to Equal Concentrations
Everywhere!
NORMAL CONDITION!
Cells DO NOT Really
WANT This! Must have
the RIGHT STUFF in the
RIGHT Place!
Cells will HAVE TO Choose and Separate what is
in the Cytoplasm. This Membrane is NOT doing
that here, but Cell’s Membrane will be
SELECTIVELY PERMEABLE!
INSIDE ≠ OUTSIDE
Cell Transport Mechanisms and Homeostasis
DIFFUSION is the most basic form of molecular movement. In
Diffusion, substances scatter as much as possible. As they
collide and scatter, they will spread out.
Diffusion
WILL MAKE
ALL
SOLUTIONS
THE SAME!!
Begin with packed
Solutes = High
Concentration
End with randomly
separated Solutes =
Lowest
Concentration =
SOLUTION!!
Always Moving!
Cell Transport Mechanisms and Homeostasis
BUT REMEMBER! The Cell is surrounded by a Plasma
Membrane that IS NOT just Open to Anything/Everything. The
Plasma Membrane Controls Access to the Cell!
Polar “Heads” line-up with
Aqueous Surface Inside and
Outside. Hydrophilic = Loves
Water!
Fatty Acid “Tails” are
Non-Polar and avoid
Water Inside the
Membrane = Fat
Sandwich!
Hydrophobic = Fears
Water.
Most Substances
CANNOT pass through
the membrane – would
need to be Polar AND
NonPolar -so the Bilayer is
a real boundary!
But they CAN Pass
through “their”
Transport Protein IF IT
IS OPEN!
Cell Transport Mechanisms and Homeostasis
SIMPLE DIFFUSION
The simplest process of molecular Transport.
Always High conc. To low conc. Always moves to make balance
on both sides. Diffusion is trying to force everything to be a
Solution. That is NOT always what the Cell wants!
High
Concentration
Outside
IF THIS Happened ALL
of the TIME:
Cytoplasm would be
the SAME as the
Outside of the Cell.
Low
Concentration
Inside.
It is NOT, so there have
to be ways to restrict
movement of various
molecules.
AND THERE ARE!!
Cell Transport Mechanisms and Homeostasis
Facilitated Diffusion: Passive Transport through a
Selectively Permeable Membrane.
Only a few substances can move through a Plasma
Membrane through Simple Diffusion. Everything else
will require a Transport Protein that forms an openable
and closeable Hole through the Lipids.
The Transport
Protein must
have an opening
that “suits” the
substance.
Shape, Charge,
Size, etc… all
must be Right!
Since each
substance
requires a
different
Transport
Protein – There
are LOTS in the
membrane of
every Cell!!
Can Move
Anything IF IT
FITS!!
Cell Transport Mechanisms and Homeostasis
Active Transport
Cells have very Specific Needs and sometimes need to “Pack”
molecules in and out of the membrane.
That would be moving AGAINST the Concentration Gradient and
is impossible in Diffusion. To move things from low to High
concentration requires Energy = ATP!
Wants In?! Why Not?!
Wants Out!
The substance will bind
with “its” Transport
Protein, but waits for?
Why?! But?!
But, The Cell NEEDS these
molecules and must “Pump”
them IN! That is “Work”!
Work requires?
ATP
ADP
Once “Energized”, the
substance is “pumped”
against the
Concentration Gradient
to make one side MORE
Concentrated! AntiDiffusion!
Cell Transport Mechanisms and Homeostasis
OSMOSIS: The reality of molecular Transport. Everything is Aqueous!!
Most Molecules CANNOT pass through the Cell Membrane directly. However, Water
is a small molecule and can “leak” through the various Transport Proteins and
CANNOT be completely Stopped! Water is Always Moving!!
But Water is everywhere as a solvent. It
is always sticking to the various Solutes
of the Environment. They have to Polar
if they are Dissolved!!
The Solutes
(Hearts) cannot
move (NOW!), but
Water can always
penetrate the
Membrane!
This can be a
Problem
because?
Low Conc.
Outside, but it
cannot
penetrate the
Membrane.
Not Equal.
High Conc. of the RIGHT
STUFF Inside! Wants OUT
(!), But cannot exit. It was
moved inside by the cell.
In Osmosis, water
moves to make both
sides Equal!
Cell Transport Mechanisms and Homeostasis
Endocytosis
The previous forms of Membrane Transport moved one molecule
at a time. Sometimes Cells want to engulf Large Amounts of a
substance – often Food Particles.
Endo = Inside, Cyto = Cell. This is often referred to as Bulk
Transport. Phopholipid Bilayers will merge and separate if the
Cytoskeleton attaches and pulls on them.
Membrane and Food
pinched into Cell.
F
O
O
D
In Animals, this is a
captured Food
Vacuole.
Transported on
to be
Digested/Used!
Cell Transport Mechanisms and Homeostasis
ExoCytosis
What goes in – Must come Out! After it has been used
and Processed by the Cell! Or Made for Export!
Exo = Outside, Cyto = Cell. This form of Bulk Transport
removes materials from the Cell. After the Food
Vacuole has been “used”, the waste that is still in the
“container” can be expelled.
Cell Transport Mechanisms and Homeostasis
Cells HAVE to be in “Balance” because of Osmosis. The Water
molecules cannot be completely stopped, so the Cytoplasm
WILL BE in equal concentration with the Extracellular Fluid in
Animal Cells.
However, the inside and Outside will be VERY DIFFERENT
because of Membrane Transport.
Cytoplasm
Extracellular Fluid
Many Substances are
Kept/Trapped Inside!
Cell Transport Mechanisms and Homeostasis
Animal Cells are Delicate and require very precise
Transport Processes to stay in Homeostasis. No Extra
Support.
Other Cells Possess a external Cell Wall that helps allow
them to survive changing external conditions.
WATER!
But this is OK because the
Vacuole holds the water
and keeps it separate from
the Cytoplasm!
Why is it Important to
keep the Water OUT of
the Cytoplasm?!