WARM UP
How would you justify the scientific claim
that organisms share many conserved
core processes and features that evolved
and are widely distributed among
organisms today?
The following structural evidence supports the
relatedness of all eukaryotes: the cytoskeleton,
linear chromosomes, endomembrane system &
organelles (ex. mitochondria & chloroplasts).
All have the same structure and function despite
whether found in animal, plant, fungal, or
protist cells. This means these structures and
the genes that code for them existed in the
common ancestor to all eukaryotes.
Eukaryotes evolved due to endosymbiosis of
various prokaryotes.
Ch 7 continued
CELL
COATING
•
1)
2)
•
The exterior of animal cell membranes have short chains of
carbohydrates bound to proteins or lipids:
carb – proteins = glycoproteins.
carb – lipids = glycolipids.
Called glycocalyx or extracellular matrix (ECM)
FUNCTIONS OF THE glycocalyx / ECM:
1. recognition sites (cell to cell for tissue formation)- to hold cells
together.
2. identification markers (ex. MHC markers allow immune system
cells to distinguish self from foreign cells)
3. communication (hormone messenger receptors)
Glycocalyx/cell coating/ ECM
How are cells connected?
CELL TO CELL ADHESION
1) Intercellular matrix (ECMs of adjacent cells)
a) Collagen- the most abundant glycoprotein, protein fibers
that bind cells together
b) Elastin- protein fiber that binds cells together
2) Cell junctions
a) desmosomes = anchoring junctions (plaques & fibers)
“rivets”, fasten cells together in strong sheets (keratinintermediate filament)
b) tight junctions = proteins that tie cells together, leaving
no space between the cells- cells fused (ie. intestines)
c) communication junctions (2 kinds) allow flow of salt
ions, sugars, amino acids- cytoplasmic channels between
adjacent cells. (ie. heart muscle cells, cells of embryo)
1)
2)
gap junction (animal cells) membrane channels that allow
passage of material between cells.
Plasmodesmata (plant cells) openings in the cell wall where
adjacent membranes contact each other.
desmosome (anchoring junction)
(plaques & fibers)
“rivets”
fasten cells together
in strong sheets.
keratin- intermediate
filament.
tight junction
tight junctions =
proteins that tie
cells together,
leaving no space
between the cellscells fused (ie.
intestines)
Gap (communicating junction)
communication junctions
(2 kinds)
allow flow of salt ions, sugars, amino
acids- cytoplasmic channels
between adjacent cells.
ie. heart muscle cells, cells of embryo
1)
2)
gap junction (animal cells)
membrane channels that allow
passage of material between cells.
Plasmodesmata (plant cells)
openings in the cell wall where
adjacent membranes contact each
other.
Figure 7.30 Intercellular junctions in animal tissues
The End
Growth, reproduction and dynamic
homeostasis require that cells create and
maintain internal environments that are
different from their external environments.
Q: What structural component accomplishes
this?
A: cell membrane
membrane structure & function
Chapter 8
I. Cell membranes are selectively
permeable due to their structure.
a. Cell membranes separate the internal environment
of the cell from the external environment.
b. Selective permeability is a direct consequence of
membrane structure, as described by the fluid
mosaic model.
c. Cell walls provide a structural boundary, as well as a
permeability barrier for some substances to the
internal environments.
How is the structure of a
cell membrane similar to an
oreo cookie????
How is it different????? What property does this give cell membranes?
Phospholipids give the membrane
both hydrophilic and hydrophobic
properties (amphipathic).
The hydrophilic phosphate portions
of the phospholipids are oriented
toward the aqueous external or
internal environments,
while the hydrophobic fatty acid
portions face each other within the
interior of the membrane itself.
The membrane has a hydrophobic
region sandwiched between two
hydrophillic ones… just like the oreo.
• Phospholipids are
amphipathic moleculeshave both a nonpolar and
polar region.
• Small uncharged
particles can diffuse
through the phospholipid
bilayer…
ex. O2, CO2, N2
• But charged molecules
(ex. H20) are repelled.
How do they get in???
• The plasma membrane is filled with a group of proteins called
membrane proteins.
• Some of these membrane proteins show only contact surfaces with
either the inside or the outside of the cell (peripheral proteins).
• and some of them stick out at both ends (transmembrane proteins)
providing hydrophillic passageways for solutes repelled by the
bilayer’s hydrophobic tails.
• MISCONCEPTION: the lipid bilayer is just that, a lipid bilayer.
• The presence of proteins & the assortment of these proteins differs
from cell to cell making each “selectively” permeable to polar.
•
.
I. Cell membranes are selectively
permeable due to their structure.
Cell membranes consist of a structural framework of
phospholipid molecules, embedded proteins,
cholesterol, glycoproteins and glycolipids.
Singer & Nicolson’s
Fluid Mosaic Model
• Proteins molecules
“bobbing” in fluid bilayer
of phospholipids.
• FLUID MOSAIC MODEL
phospholipid bilayer =
grout
proteins=tiles
• Hydrophilic regions of
protein protrude into water
• Hydrophobic regions
embedded in nonaqueous
environment of “tails”
cholesterol
1. reduces fluidity of phospholipids
2. prevents solidification
Figure 8.5 Evidence for the drifting of membrane proteins
“fluid”
mosaic
Embedded proteins can be hydrophilic,
with charged and polar side groups, or
hydrophobic, with nonpolar side groups…
or both.
Membrane protein functions:
1. anchor the cells cytoskeletal components to neighboring cells.
2. actively transport various molecules over the plasma membrane.
3. receive signal molecules on the outside & relay the signal inside.
4. form the connection with the outside of the cell (cell-cell joining).
This is also documented in the membranes of cell organelles such
as the ER or the Golgi-complex.
TRAFFIC ACROSS MEMBRANES
Growth and dynamic homeostasis are maintained by the
constant movement of molecules across membranes.
• plasma membrane edge of
life 8 nm thick
• Primary functionseparates life from its
nonliving environment
and regulates interactions.
• Selective permeabilitycharacteristic due to
protein composition of
cell membrane.
plasma membranes are: SELECTIVELY
PERMEABLE- allow some materials to cross
based on transmembrane proteins present.
easy time crossing:
• N2, O2 & CO2
• Hydrophobic molecules
difficulty crossing (needs
specific protein tunnel):
• Polar/Hydrophillic
molecules
ex. (glucose & H2O)
• Ions
ex. (Na+, K+, Ca 2+, Cl-)
RECAP
•
•
•
Small, uncharged polar molecules and small
nonpolar molecules, such as N2, freely pass across
the membrane.
Hydrophilic substances such as large polar
molecules and ions move across the membrane
through embedded channel and transport proteins.
Water moves across membranes and through
channel proteins called aquaporins.
transport proteins = permeases
• provide a hydrophilic
channel across a
membrane
• are selective for a
particular solute
• Examples:
1. water channel
(aquaporin)
2. glucose not fructose
Permeases are
transport proteins
Integral membrane proteins that
facilitate the transport of a
specific molecule into or out
of a cell.
Similar to enzymes:
- specific “substrate”
- binding site
- can be saturated
- can be inhibited by mimics
- do not catalyze a chemical
reaction… just a physical
process.
Passive
Transport
No ATP
• Diffusion
• Osmosis
• Facilitated Diffusion
• Carrier Protein
• Gated Ion Channel
Active
Transport
ATP used
• PUMPS:
• Na+/K+
• H+
• ENDOCYTOSIS
• EXOCYTOSIS
Figure 8.16 Review: passive and active transport compared
Passive transport does not require the input of
metabolic energy; the net movement of molecules
is from high concentration to low concentration.
1. Passive transport plays a primary role in
the import of resources and the export of
wastes.
2. Membrane proteins play a role in
facilitated diffusion of charged and polar
molecules through a membrane.
– Glucose transport
– Na+ transport
– K+ transport
Growth and dynamic homeostasis are maintained by the
constant movement of molecules across membranes.
PASSIVE TRANSPORT
•
•
•
•
•
NO ENERGY (ATP) REQUIRED
diffusion of a substance across a biological membrane.
Molecules travel DOWN their concentration gradient
(difference)
[HIGH] --> [LOW]
Like walking down stairs
3 TYPES:
1. Diffusion
2. Osmosis
3. Facilitated diffusion
Transport Proteins & Gated Membrane Channels
Figure 8.10 The diffusion of solutes across membranes
1) diffusion
• kinetic energy/thermal
energy- molecules
spread out- space.
• atoms or molecules
move down a
concentration gradient.
• from areas of high to
low concentration
• “passive transport” is
diffusion across a
membrane (no ATP)
• ie. CO2, O2
Influenced by the temperature of the environment… kinetic energy.
2. OSMOSIS = the diffusion of water molecules
across a selectively permeable membrane
*[solute] = solute concentration
where will water move?
1) to the side with less water.
2) to the side with more
dissolved solute.
3) From the hypotonic side of
the membrane to the
hypertonic one.
osmotic solutions that a cell may
encounter:
1. Hypertonic = solution with
higher [solute]*
2. Isotonic = solution with the
same [solute]
3. Hypotonic = solution with
lower [solute]
if the environment is: / then inside the cell it is:
1.
2.
3.
Hypotonic
Hypertonic
Isotonic
1.
2.
3.
Hypertonic
Hypotonic
Isotonic
Figure 8.13 The contractile vacuole of Paramecium: an evolutionary adaptation for
osmoregulation
A PARAMECIUM’S ENVIRONMENT IS ___________
Figure 8.13 The contractile vacuole of Paramecium: an evolutionary adaptation for
osmoregulation
A PARAMECIUM’S ENVIRONMENT IS HYPOTONIC
SO IT NEEDS TO PUMP OUT THE WATER OR BURST
factors that influence osmosis:
1)
osmotic concentration- refers to the concentration of solutes
(dissolved substances) in the water.
•
Water will flow from the side with the low osmotic concentration
to the side of high concentration.
•
The solutes will flow from the side with high concentration to the
side with low osmotic concentration.
2) Osmotic Potential- tendency of water to move from one region to
another.
•
Measure of the potential of water molecules to move between
regions of differing concentrations across a water-permeable
membrane.
•
Water moves from the area of greater osmotic potential to the
area of lower osmotic potential.
•
Water moves from a hypotonic solution (more water, less
solutes) to a hypertonic solution (less water, more solutes)
across a semi permeable membrane.
3. Facilitated Diffusion (Transport) 2 kinds:
1. channel proteins provide hydrophylic passageways
ie. Water passes through “aquaporins”
ion channels
2. carrier proteins undergo a subtle change in shape that
translocates the solute-binding site across the membrane
ie. glucose, amino acids, nucleotides
4. Gated Membrane Channels
A stimulus (electrical or chemical) causes these
channel proteins to open or close.
ex. Stimulation of a nerve cell by a neurotransmitter
(ligand) causes gated sodium channels to open.
II. active transport
requires energy (ATP) to move molecules “uphill”
against their concentration gradient
[low] --> [high]
EXAMPLES:
1. Na+/K+ Pump
2. Proton (H+ ) Pump
3. Cooperative channels/Cotransport
4. Bulk Flow
5. Endo/Exocytosis
Active transport requires free energy to move
molecules from regions of low concentration to
regions of high concentration.
1. Active transport is a process where free
energy (often provided by ATP) is used by
proteins embedded in the membrane to
“move” molecules and/or ions across the
membrane and to establish and maintain
concentration gradients.
2. Membrane proteins are necessary for
active transport.
sodium potassium pump
• Animal cells utilize the
Na+/K+ pump
• 3 Na+ OUT but only 2 K+ IN
• Results in more positive ions
outside than inside cell
• maintains voltage (electrical
potential energy) across the
membrane- membrane
potential of -50 to -200
millivolts (the inside of cell is
negative) which in turn
creates an electrochemical
gradient
• Muscle and nerve cells.
2. The Proton Pump
Electrogenic pump
(voltage generating) for:
- plants
- bacteria &
- fungi
3. Cooperative Ion Channels
COTRANSPORT
ATP driven pump stores
energy by concentrating a
substance on one side of
the membrane.
As the substance diffuses
back it escorts another
substance against it’s
concentration gradient.
ex. Na+ and glucose
H+ and sucrose, amino
acids, other nutrients
4.Bulk Movement or Bulk Flow
• The collective movement
of substances in the same
direction in response to a
force or pressure over
great distances.
ex. Plants rely on the bulk
flow of water (based on
osmosis) to carry move
sugar from the leaves to
non-photosynthesizing
parts of the plant.
Ex. bulk flow of blood
through your blood
vessels.
The processes of endocytosis and exocytosis
move large molecules from the external
environment to the internal environment and
vice versa, respectively.
1. In exocytosis, internal vesicles fuse with
the plasma membrane to secrete large
macromolecules out of the cell.
2. In endocytosis, the cell takes in
macromolecules and particulate matter by
forming new vesicles derived from the
plasma membrane.
ENDOCYTOSIS
•
•
Cell takes in
macromolecules
and particulate
matter
By forming new
vesicles derived
from the plasma
membrane.
Figure 8.19 The three types of endocytosis in animal cells
exocytosis
Large molecules (proteins &
polysaccharides) are transported
to the cell membrane in transport
Vesicles from the Golgi App.
Membranes fuse and contents of
the vesicle spill out of the cell.
ex. Pancreas cells secrete insulin
Neurons secrete neurotransmitters
Cell membranes are selectively
permeable due to their structure.
Cell walls provide a structural boundary, as
well as a permeability barrier for some
substances to the internal environments.
1.Plant cell walls are made of cellulose and are
external to the cell membrane.
2. Other examples are cells walls of prokaryotes
and fungi (chitin).
THE END.
SUMMARY: Plasma Membrane
Fibers of Extra cellular Matrix:
Carbbohydrates
Collagen
Glycolipids
Phospholipid Bilayer
Cholesterol
PROTEINS:
Peripheral
Integral
Transmembrane
FLUID MOSAIC MODEL- SELECTIVELY PERMEABLE
1)Peripheral- not bound to bilayer
Are loosely bound to surface of membrane or integral proteins.
2)Integral- penetrate the hydrophobic core
Due to nonpolar amino acids in alpha helices.
3)Transmembrane proteins tunnel all the way through the PLBL
Act as PERMEASES.