The Cell Membrane: How the cell
maintains homeostasis
Cell
Homeostasis
Cats hate and are afraid of water.
What do you hate or fear? Think of one or two things
that you hate.
What do you love and what are you attracted to? Think
of one or two things that are attractive to you.
“phobia” means fear. Fear of water is hydrophobia.
Fear of snakes is Ophidiophobia . Fear of spiders?
“phile” means like. If you like water, you are an
hydrophile. If you like snakes you are an ophidiophile. If
you like spiders, you are an arachnophile.
The cell membrane is composed of two layers of
phospholipids. The Outer “heads” of the phospholipid
really like water and are called _________philic. The area
between the membrane layers is made of the
phospholipid “tails”. Tails are “afraid of water” and are
called: ____________phobic.
Hydrophylic head (PO4-) and
hydrophobic tail behavior
Cell membranes are composed of two
phospholipid layers. (bilayer)-draw the all
blue phospholipid model and label the
tails as “fatty acid tails” and label the
circle as the phosphate head:
Cell membranes are composed of two
phospholipid layers. (bilayer) Take a minute
to Label the cell membrane pictured on
your notes:
Think: Why does your cell need hydrophobic
parts of the membrane?
The components move!
The cell membrane has two
major functions.
1. Forms a boundary between
inside and outside of the cell
2. Controls passage of materials
into or out of the cell
outside cell
cell membrane
inside cell
Consult with a partner and come up with
an analogy for something that is like a
membrane in that it is “fatty and
phobic” on the inside, but “likes water”
on the outside (hint-something that
dissolves easily likes water ALOT)
Components move!
The fluid mosaic model describes the
membrane.
Think about definitions for the two words and then
we will discuss how this might relate to the cell
membrane:
FLUID –
bendable, movable, not solid
MOSAIC (puzzle)–
composed of many pieces
The fluid mosaic model describes the
membrane because the
molecule/compound components or pieces
are always moving
(http://www.susanahalpine.com/anim/Life/m
emb.htm
There are other compounds embedded in the
membrane: label the matching parts on your diagram:
example—where are the proteins?. https://www.wisconline.com/learn/natural-science/lifescience/ap1101/construction-of-the-cell-membrane
cell membrane
carbohydrate
chain
carbohydrate
chain
protein
cholesterol
protein
protein channel
Analogy
• So…what should the membrane proteins really look like?
Cell Homeostasis: Cell Membrane
components/parts
Macromolecule
compounds
Function
Proteins
Membrane proteins: Identification, holds cells together, sends
messages.
ChannelIdentification,
proteins transport
materials
intosends
and out
holds cells
together,
andof the cell.
Membrane
receptor
proteins: Are located in cell membranereceives
messages
Receive chemical signals/ligands from outside the cell.
Intracellular receptor proteins: Located inside the cell-Receive
chemical signals/ligands like hormones.
Protein
Channel
Protein
Carbohydrates
Carbohydrates Identification, signaling, and “sugary glue” that holds cell
membrane together.
Lipids/Fats
Lipids/Fats
(nonpolar-no
charge)
Do not mix with water-Cholesterol strengthens the cell
membrane and phospholipids form the fatty barrier between
cell and environment. Controls the passage of materials into
and out of the cell.
The cell membrane is selectively permeable.
Allows some, but not all molecules to cross
the membrane. Fig. 3.18
cell membrane
THINK: What molecules would you add to this
membrane to make it a more functional and a
complete “mosaic” ?
The cell membrane is selectively permeable.
Predict: Which way will the water molecules move?
Toward the inside or outside the cell? Why? Check this
out:
http://www.pbslearningmedia.org/resource/tdc02.sci.l
ife.cell.membraneweb/cell-membrane-just-passingthrough/
• Chemical signals are transmitted
across the cell membrane-Read page
84
– Receptor proteins bind with ligands
(chemicals) and change shape.
– A ligand is a specific “signaling” molecule
that binds with a receptor protein to
make something happen.
There are two types of
receptor proteins.
• One type: Intracellular
receptor protein
• *THINK: What does
Intracellular mean?
• Ligand moves through the
cell membrane to reach
receptor protein on inside
of cell.
• Example: hormones:
http://highered.mheducat
ion.com/sites/0072507470/
student_view0/chapter17/
animation__intracellular_re
ceptor_model.html
There are two types of
receptor proteins.
• The 2nd type of receptor
is: membrane protein
receptor (integral
protein)
• Ligand on outside of cell
binds with a receptor
within the cell
membrane.
• Ex: Neurotransmitters,
growth factors
There are two types of receptor proteins.
• The 2nd type of receptor is: membrane protein
receptor
• Label the missing parts:
Ligand
Receptor