Download The Cell Membrane

The Cell Membrane
“The Gatekeeper”
Overview
• Cell membrane separates living cell from
nonliving surroundings
• Controls traffic in & out of the cell
It is called selectively permeable b/c it allows some
substances to cross more easily than others
• Made of phospholipids, proteins & other
macromolecules
Intro video
What’s so important about the
cell membrane?
• The cell membrane regulates what
enters and leaves your cells.
• You eat food, your stomach breaks it
into little pieces.
• The little pieces are brought to your
cells
• Your cell membrane lets those little
pieces into the cell.
• Without letting the bad stuff in.
• Your body can use these little
pieces of food for energy and to
make things the body needs.
• Example: release energy in
bonds of small sugars like
glucose
Cell Membrane
• The cell membrane is can also be called the
plasma membrane.
Structure of CM
• Phosopholipid bilayer
Tough flexible barrier
between the inside and
outside of the cell.
• Protein molecules
– Run completely through
lipid layer
– Form channels & pumps
Phospholipids
• Fatty acid tails
Are hydrophobic
• Phosphate group
head
Phosphate
Fatty acid
Are hydrophilic
• Arranged as a bilayer
I knew that!
carbohydrates
• The cell membrane also
has carbohydrates that
extend to the outside
of the cell.
• This carb is involved in
cell communication
• Its like a cell phone
that allows the cells to
communicate with each
other.
• It extends off of a
protein
• Not all proteins have
them though.
Proteins in the CM
Movement across
the Cell
Membrane
Movement Though the CM
• The cell membrane is said to be
Selectively Permeable
• This means it allows some things inside
but other things are rejected.
• Things coming in and out of the cell are
called transport.
Membrane Processes
Types of Cell Membrane transport include:
• 1. diffusion
(three types of diffusion)
– A. passive transport
– B. facilitated diffusion
– C. Osmosis
• 2. active transport
• Its based on whether ATP is needed or not.
Diffusion
• Diffusion
movement from high  low concentration
Diffusion
• Move from HIGH to LOW concentration
– “passive transport”
– no energy needed
diffusion
Diffusion across cell
membrane
• Cell membrane is the boundary between
inside & outside…
– separates cell from its environment
What diffuses in and out of the cell?
OUT
IN
food
carbohydrates
sugars, proteins
amino acids
lipids
salts, O2, H2O
OUT
IN
waste
ammonia
salts
CO2
H2O
products
cell needs materials in & products or waste out
Diffusion through phospholipid
bilayer
• What molecules can get through
directly?
– fats & other lipids
inside cell
NH3
lipid
salt
• What molecules
can NOT get
through directly?
– polar molecules
• H 2O
– ions
outside cell
sugar aa
H 2O
• salts, ammonia
– large molecules
• starches, proteins
Channels through cell
membrane
• Membrane becomes semipermeable with protein channels
– specific channels allow specific
material across cell membrane
inside cell
NH3
salt
H 2O
aa
sugar
outside cell
A. Passive Transport
• Passive transport: The movement of
material across the cell membrane
from areas of high concentration to
areas of low concentration.
• cell does not need energy or ATP
Passive transport is a type of
diffusion that requires a cell
membrane.
• Regular diffusion does not.
• http://videos.howstuffworks.com/hsw/23424-cell-diffusion-acrossthe-cell-membrane-video.htm
B. Facilitated Diffusion:
Protein helpers DIFFUSE
substances across the cell
membrane FASTER than
normal.
– Proteins are specific to the
substance they carry.
– Still is diffusion, meaning it
goes from high to low so no
ATP is needed.
Facilitated Diffusion
–no energy needed
facilitated = with help
open channel = fast transport
high
low
“The Bouncer”
C. Osmosis
• Osmosis is the diffusion of water.
• Water is very important to life,
so we talk about water separately
• Diffusion of water from
high concentration of water to
low concentration of water
– across a
semi-permeable
membrane
Concentration of water
• Direction of osmosis is determined by
comparing the concentration of solutes
dissolved on each side of the
membrane.
– Hypertonic - more solute, less water
– Hypotonic - less solute, more water
– Isotonic - equal solute, equal water
water
hypotonic
hypertonic
net movement of water
Hypertonic: "HYPER" means more
– there are more solutes (salt)
outside the cell than inside
– Osmotic pressure causes the
water to be sucked out.
– Plant cells: vacuole loses water;
the cells shrink, causing wilting.
– In animal cells, cells also shrink.
– In both cases, the cell may die.
– Water always goes in the
direction of the higher
solute.
– Higher solute=less water
Hypotonic: HYPO means less
– there are less solutes (salt)
outside the cell than inside
– Osmotic pressure causes,
water to move into the cell.
– The cell will gain water and
grow larger.
– In plant cells, vacuoles will
fill
– the cell wall keeps the plant
from bursting
– In animal cells, the cell is in
danger of bursting,
• Isotonic solution:
concentration of
solute (salt) is equal
on both sides,
• the water moves in
and out at an equal
rate
• Cell size will not
change.
• "ISO" means the
same
Remember
• During osmosis, the cell is permeable to
the water (water can pass) but not the
solutes (dissolved substances) such as
salt and sugar.
• Water moves across the membrane until
an equilibrium is reached
• Water concentration is equal on both
sides of cell membrane.
• The salts and sugars do not diffuse
osmosis
2. active transport: molecules move
from lower to higher concentration.
lower
higher
• Does not naturally occur.
http://videos.howstuffworks.com/hsw/23425-cell-active-transport-and-the-cellmembrane-video.htm
http://videos.howstuffworks.com/hsw/14765-simply-science-active-transportvideo.htm
2. Active Transport
• Cells move molecules against concentration
gradient
– Uses a protein “pump” which….
– “costs” energy = ATP
low
ATP
high
“The Doorman”
Transport summary
simple
diffusion
facilitated
diffusion
active
transport
ATP
Cell membrane and
homeostasis
• http://videos.howstuffworks.com/hs
w/23423-cell-homeostasis-and-thecell-membrane-video.htm
How about large molecules?
• Macromolecules are toooooo big to diffuse.
• They must be moved into the cell through
vesicles & vacuoles
A. endocytosis
•phagocytosis = “cellular eating”
•pinocytosis = “cellular drinking”
B. exocytosis
exocytosis
Endocytosis
phagocytosis
pinocytosis
fuse with
lysosome for
digestion
non-specific
process
review
Fluid mosaic model
• This model of the cell membrane is
called the fluid mosaic model.
• Do you know what a mosaic is?
• Think about art.
Mosaic
• A piece of artwork made up of little
pieces of tile lying close together but
not connected.
• It gives the illusion that it is all one
piece but it is not.
• Why is the cell membrane considered
a mosaic model?
• Because the pieces of the cell
membrane are not actually attached,
though the appear to be.
• The phospholipids are not attached
to each other.
• The proteins are not attached other.
Cell communication
• Cell-to-Cell communication is
important for multicellular
organisms.
• The billions of cells of a human or an
oak tree must communicate in order
to develop from a fertilized egg
• and then survive and reproduce in
turn.
•.
receptors
• Receptor molecules play
an important role in the
interactions and
communication between
cells.
• Two primary agents of
cellular communication
are hormones and
chemicals produced by
other cells
• The chemical has
instructions and tells
the cell what is needed
to be done..
Receptor molecule
Chemical released by
another celll
Blocked signal
• If those hormone signals are blocked,
cellular communication is stopped and
the organism’s homeostasis or health is
affected.
• Its like when you are out of range and
your cell phone cannot get a signal.
• You have no idea the other person is
even trying to call you
Receptors are specific
• Unlike your cell phone, each
receptor is specific to a a
specific type of signal.
• That’s kinda like trying to log
onto someone’s wifi and you
don’t have the password.
• You cant acess the info without
the correct password
• The cell cant access just any
chemical signal. It must fit the
receptor.
• Each cell has millions of
receptors.
Please explain how chemical
signals work
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Cell receptor animaton