Download Ch. 8 Cell membrane

Cell Membrane
C-8-1
Every cell has a cell membrane!
~ protects
~ helps move things in and out of cell
Homeostasis - maintaining internal conditions
regardless of surroundings
~ cell memb. controls this by being selectively
permeable - only lets certain things in/out
~ is made of lipids (fats) and has proteins in it
to allow things in or out
* cell memb. also:
~ provides structural support for the cell
~ recognizes foreign material
~ communicates with other cells
Structure of C.M.
~ made of phospholipids
*head is polar
* tails are nonpolar
Ex:
Membrane Proteins:
4 types embedded in the C.M.
1.) Cell surface markers - "name tags"
~ has a chain of sugars on it to help it tell
what cell it is!
ex:
2.) Receptor proteins - helps cell sense its
surroundings
* can bind to substances that cause a change
within the cell
ex:
3.) Enzymes - help with chemical reactions
ex:
4.) Transport proteins - move substances into or
ex:
out of the cell that would not otherwise
cross the membrane
Cell Transport
C-8-2
2 types of transport:
1.) Passive transport - does not use energy
*all things want to reach and be in equilibrium
- when a space is filled evenly
ex:
As the substance moves down the gradient, this is
called diffusion.
ex:
3 kinds of passive transport:
a.) Diffusion – movement of particles form areas of
high concentration to low concentration
*A concentration gradient will occur if one
area has more of the substance than another
Ex:
b.) Osmosis – movement of water across a
selectively permeable membrane in response to a
high solute concentration
Ex:
3 conditions of osmosis:
Hypertonic solution: more particles outside
the cell than inside
Solution is hypertonic
Cell solution is hypotonic
Water moves out of the cell
Cell will shrivel and shrink
Hypotonic solution: more particles inside the
cell than outside
Solution is hypotonic
Cell solution is hypertonic
Water moves into the cell
Cell will burst!
Isotonic solution: same solute concentration
inside and outside the cell
Solution is Isotonic
Cell solution is Isotonic
Water moves equally into and out of the cell
Cell will stay the same
c.) Facilitated diffusion: transport proteins help
molecules pass through the membrane
2 types of transport protein help with this
process:
1.) Channel proteins - allow ions, sugars, and AA's
through the membrane
~ are specific to the shape and charge of
the molecule
* This is how glucose gets into most cells!
2.) Carrier proteins - molecule must fit into its
binding site
~ kind of like enzymes!
2.) Active Transport - uses energy
2 ways: Pumps or Vesicles
a.) Pumps:
~ move substances against the concentration
gradient
*like fish swimming against a current!
Sodium-potassium pump - pumps 2 K+ in and 3 Na+
out! (pg. 182)
* goes against the concentration gradient
* prevent Na+ from building up inside the cell
* brings other molecules (glucose) in
ex:
b.) Vesicles: some substances are too large to go
through the membrane
Are brought in or released by these processes...
~ Endocytosis - cell engulfs or "eats" a substance
~ Exocytosis - cell releases a substance out of the
cell
* hormones, proteins
Cell Communication
C-8-3
Cells must communicate to coordinate activities
and share information! Just like you!
There are various ways that cells do this...
* the methods vary depending on whether the
target is specific or general, near or far.
A signaling cell produces some kind of signal,
usually a molecule, that is detected by a target
cell!
~ target cells then have proteins that
recognize and respond to the signal
Targets:
~ neighbors can communicate through their
membranes
ex: like you talking to the person next to
you
~ close cells use short distance signals
ex: talking across the room
~ far cells use hormones or nerve cells to
carry the message
ex: the telephone
* hormones - general release, few
receptors
~like a flyer distributed in all classes
*nerve cells - specific release, specific
receptors
~like a flyer released to a particular club
Some signals are environmental...
Ex: Light - can affect the action of hormones
in plants or when a plant flowers
Signal are received by receptor proteins in the cell
membrane
~ have specific binding sites like enzymes
~ once bound, the membrane changes shape
and relays the info to the inside of the cell
The cell can respond in 3 different ways:
1.) Permeability change - carrier proteins may open
or close
2.) Enzyme activation - trigger chemical reactions
in the cell
3.) Second messenger - the signal molecule triggers
an enzyme to form another messenger to deliver
the original message and cause the appropriate
change
~ like a note being brought from the office