Chapter 3:
Cell Biology
Unit 1
1
III. Plasma Membrane
• Terminology
–
–
–
–
–
–
Intracellular: (Intra- Inside) inside the cell
Extracellular: (Extra- Outside) outside of the cell
Intercellular: (Inter- Between) from 1 cell to another
Glycoproteins: carb’s + proteins
Glycolipids: Carb’s + Lipids
Membrane Potential: result of uneven distribution of ions on
the inside verses the outside of the cell
• Glycocalyx:
– Collection of glycoproteins, glycolipids, and carb’s that lies
2
on the outer surface ofUnit
the1 plasma membrane
IV. Membrane Lipids
Unit 1
3
IV. Membrane Lipids
• Phospholipids (PL’s):
– Predominant lipid in membrane
– Bipolar:
• Hydrophilic “head” is water
loving and polar and faces both
surfaces (inner & outer)
• Hydrophobic “tail” is water
hating and non-polar and crowd
together between the heads
• Cholesterol
– Makes up 1/3 of the membrane
and lie btwn PL’s
– Helps to limit PL’s mvmt
providing stability for the PM
– It is also bipolar and the “tail” is
embedded in head while the
ring is embedded in the tails
Unit 1
4
IV. Membrane Lipids
• *Fluid Mosaic Model*
– The lipid bilayer is mobile with things floating
w/in it
– Consequences of this:
a) Important for molecule distribution in the
membrane
b) Slight damage can be repaired because the
PL’s will move to cover it
c) It enables two different membranes to fuse
with each other
Unit 1
5
V. Membrane Proteins
A.
B.
C.
D.
E.
Marker Molecules
Attachment Proteins
Transport Proteins
Receptor Proteins
Enzymes
Unit 1
6
V. Membrane Proteins (MP)
• Many fxns of the plasma membrane are determined by
the combination of membrane proteins present.
• The ability of these proteins to fxn properly is
determined by their 3-D shape
• There are 2 major types:
1.
Integral/Intrinsic
•
2.
Peripheral/Extrinsic
•
•
•
(Transmembrane) contain hydrophobic and hydrophilic
regions to match the phospholipids characteristics & location
Surface proteins on inner or outer surface.
Can be bound to an integral protein or the phospholipids head
There are 5 major classes of MP’s
Unit 1
7
5 major classes of
Membrane proteins
c
b
Symporter
Uniporter
Gated
Channel
a
Antiporter
Receptors linked to
G-proteins
a
Voltage-gated
channel
Ligand-gated
channel
8
Unit 1
Receptors linked to
channel proteins
b
ATP powered
pump
Carrier
Proteins
Channel
Proteins
ii
B
Non-gated
Channel
i
A
C
B
A
V. Enzymes
IV. Receptor
Proteins
III. Transport
Proteins
II. Attachment
Proteins
I. Marker
molecules
Membrane Proteins:
I. Marker Molecules
• Glycoproteins or
glycolipids that allow for
cells to identify other
cells or other molecules
• Important because cells
aren’t isolated and must
function as a whole for
normal body function.
• May be integral or
peripheral proteins
• Ex/ immune cells
Unit 1
9
Membrane Proteins:
II. Attachment Proteins
• Integral proteins that
may attach to
intracellular
molecules.
• Integrins can also
function in cellular
communication.
Unit 1
10
Membrane Proteins:
III. Transport Proteins
All exhibit 3 characteristics
1. Specificity
–
Each binds to & transports
only 1 types of molecule/ion
2. Competition
–
Closely related substances
may bind to the same
binding site & the one w/
greater [ ] or higher affinity is
more readily moved across
the PM
3. Saturation
–
Unit 1
Movement is limited by the #
of transport proteins rate will
eventually plateau because
the # of proteins are going at
their maximum rate
11
Membrane Proteins:
III. Transport Proteins
A. Channel Proteins
•
Form passageways through the
plasma membranes that have both
hydrophobic and hydrophilic
regions.
B. Carrier Proteins
•
Move larger ions or molecules
across the membrane, when
bound it changes shape to allow it
to move from one side of the
membrane to the other then return
to its original shape to work again.
C. ATP-powered pumps
•
Moves ions or molecules across
the membrane using ATP.
Unit 1
12
Membrane Proteins:
III. Transport Proteins
A. Channel Proteins
a. Non-gated Channels
•
Always open responsible for the
permeability of the plasma
membrane when the cell
membrane at rest.
b. Gated Channels
•
i.
Can be opened or closed
Ligand Gated
–
ii.
Voltage Gated
–
Unit 1
Small molecules must bind in
order to open or close the channel
Change in voltage across the
plasma membrane causes the
gate to open
13
Membrane Proteins:
III. Transport Proteins
B. Carrier Proteins
a. Uniporter
•
Movement of 1 ion or molecule
across the plasma membrane.
b. Symporter
•
Movement of 2 ions or molecules in
the same direction (into the cell or
out of the cell).
c. Antiporter
•
Unit 1
Movement of 2 ions or molecules in
opposite directions (one in and one
out or vise versa).
14
Membrane Proteins:
III. Transport Proteins
C. Sodium-Potassium Pump
• These have 2 binding sites.
One is for the molecule to be
moved the other is for ATP
• Breakdown of ATP releases
e+ Ding shape of the “pump”
protein which moves the
molecule across the
membrane
Unit 1
15
Membrane Proteins:
IV. Receptor Proteins
• Proteins or
glycoproteins in the
plasma membrane that
have an exposed
receptor site on the
outer cell surface which
can attach to specific
chemical signals.
• Many are part of an
intercellular
communication system
that coordinates cell
activities.
Unit 1
16
Membrane Proteins:
IV. Receptor Proteins
A. Receptor linked to
channel proteins
–
These help form ligandgated channels & when
bound it changes the
channels shape to move
ions
B. Receptors linked to Gprotein complexes
–
•
Uses a second
messenger system,
binding of the receptor
externally causes to the
cell internally
3 ways a can stimulate a
cellular response
1.
2.
Unit 1
3.
Intracellular chemical
signals
Opening channels in the
plasma membrane
Activation of enzymes
associated with the
plasma membrane
17
Membrane Proteins:
V. Enzymes
• These may work on
the inner or outer
surface of the plasma
membrane.
• Some are always
active but others are
activated by things
like GPCR’s
Unit 1
18
VI. Movement through the
plasma membrane
Unit 1
19
V. Mvmt thru the PM
• Inside of the cell:
– Enzymes other proteins, glycogen, high potassium concentration
• Outside of the cell:
– High concentration of sodium, calcium, & chloride
• The cell has to be able to bring in nutrients inside and get waste
products out without changing the cell’s volume, because too
much can cause the cell the rupture (causing cell death) or to
shrivel (also causing cell death).
• Movement
1.
2.
3.
Molecules that are lipid soluble or very small water soluble
molecules will freely go across the plasma membrane.
Large lipid soluble molecules and water soluble molecules can’t
pass through the plasma membrane and may need to use transport
proteins.
Larger water soluble molecules or whole cells may be moved by
vesicles.
Unit 1
20
Membrane transport mechanisms
A. Passive Transport Mechanisms
• No energy required to
move molecules from one
side of the membrane to
another
B. Active Transport Mechanisms
• Energy required to move
molecules from one side
of the membrane to
another
Unit 1
21
Membrane transport mechanisms
Passive Transport Mechanisms
Active Transport Mechanisms
A. Diffusion
B. Osmosis
C. Facilitated Diffusion
A. Active Transport
B. Secondary Active
Transport
C. Vesicular Transport
a. Endocytosis
b. Exocytosis
Unit 1
22
Passive Transport Mechanisms
A. Diffusion:
– Movement of solutes from an area of high concentration
to an area of low concentration
– Concentration gradient: concentration difference between
2 points divided by the distance between the 2 points,
– Rate of Diffusion
1.
2.
3.
4.
Magnitude of the concentration gradient
Temperature of the solution
Size of the diffusion molecules
Viscosity of the solvent
23
Unit 1
Passive Transport Mechanisms
B. Osmosis
–
Diffusion of water across a
selectively permeable
membrane
Will allow water but not all
solutes with in the water
Important because it can
influence a cell’s function
when water moves.
Osmotic Pressure:
–
–
–
•
1)
2)
3)
Force required to prevent
water movement across a
selectively permeable
barrier via osmosis
Isosmotic
Concentration
Hyperosmotic
of solutions
Hyposmotic
Unit 1
24
Passive Transport Mechanisms
B. Osmosis
• Tonicity: refers to the cell’s shape remaining constant b/c it
maintains it’s internal pressure
1. Isotonic sol’n: no net mvmt of H2O, cell doesn’t D shape
2. Hypertonic sol’n: mvmt out of cell b/c sol’n has a greater [ ] of
solute thus a higher osmotic pressure (crenation)
3. Hypotonic sol’n: mvmt into cell b/c sol’n has a lower [ ] of
solute thus a lower osmotic pressure (Lysis)
Unit 1
25
Passive Transport Mechanisms
C. Facilitated Diffusion
– Amino acids & glucose go into the cell and area
going out of the cell can’t occur via direct diffusion
because they are too big. Thus there is
– Mediated transport (facilitated diffusion):
• Process by which transport proteins assist the movement
of water soluble molecules or electrically charged
molecules or ions across the plasma membrane.
26
Unit 1
Active Transport Mechanisms
A. Active Transport
• also a type of mediated
transport. Requires
energy provided by
ATP movement
dependent on the
number of pumps and
availability of ATP.
• Important because it
can move things
against their
concentration
gradients.
Unit 1
27
Active Transport Mechanisms
B. Secondary Active
Transport
• Passive transport of 1
molecule with its
concentration gradient
helps to energize the
carrier so that it can
transport the second
molecule against its
concentration gradient.
Unit 1
28
Active Transport Mechanisms
C. Vesicular Transport
• Movement of larger
volumes of substances
across the plasma
membrane through the
formation and release of
vesicles requiring ATP.
• BUT…the specificity seen
in others doesn’t occur in
this process.
a. Endocytosis
i.
ii.
iii.
Pinocytosis
Phagocytosis
Receptor mediated
endocytosis
b. Exocytosis
Unit 1
29
Active transport mechanisms
Phagocytosis
i.
Pinocytosis
a) Endocytosis: uptake
of material into the
cell.
• 3 types:
Pinocytosis
•
Molecules dissolved
in liquid
•
Cells and solid
particles
iii. Receptor mediated
endocytosis
•
Specificity for
substances
Receptor-mediated
ii. Phagocytosis
Unit 1
30
Active Transport Mechanisms
b. Exocytosis
– Materials
manufactured by the
cell are packaged in
secretory vesicles that
fuse w/the PM &
release their contents
outside of the cell
– ATP req’d
– Proteins & other water
soluble substances
Unit 1
31