Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Quiz next week on what we’ve
covered thru today!!!!!!
Hour exam in 2 weeks!!
Lab Practical in 3 weeks.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Prepare your bones!
Cell Theory
Last week studied the bones of the skull, wrist, and
ankle
The cell is the basic structural and functional unit
of life
This week study, in addition to the skull, the axial
skeleton.
Organismal activity depends on individual and
collective activity of cells
(Next week, study the appendicular skeleton)
(after that, the fetal skeleton)
Biochemical activities of cells are dictated by their
subcellular structures
Continuity of life has a cellular basis
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Chromatin
Nuclear envelope
Nucleus
Nucleolus
Cell Theory
Plasma
membrane
Smooth endoplasmic
reticulum
Cytosol
Lysosome
The Cell is the smallest “living” unit
Disease is the loss of cellular homeostasis
Over 200 cell types exist in the human body with
sizes ranging from 2 um to 1 meter (nerve cell)!
Shape (structure) reflects function. E.g. flat
epithelial cells act as barriers for protection.
Mitochondrion
Centrioles
Rough
endoplasmic
reticulum
Ribosomes
Centrosome
matrix
Golgi apparatus
Microvilli
Secretion being released
from cell by exocytosis
Microfilament
Microtubule
Intermediate
filaments
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Peroxisome
Figure 3.2
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Cell Theory
Plasma Membrane (Cell Membrane)
Cells are composed of three principle areas
(regions)
Defines the extent of the cell
Separates intracellular fluids from extracellular
fluids
Plasma Membrane
Cytoplasm
Encloses all of the cell organelles
Nucleus
Plays a dynamic role in cellular activity
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Fluid Mosaic Model
Plasma membrane is a double layer (bilayer) of
lipids with imbedded, dispersed proteins
A bilayer consists of phospholipids, cholesterol,
and glycolipids
Proteins are trapped in the bilayer:
Extra/intracellular regions are hydrophilic
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Fluid Mosaic Model
The Lipids of the Bilayer
Phospholipids have hydrophobic and hydrophilic
bipoles
Glycolipids are lipids with bound
carbohydrate
Cholesterol
Transdomain regions are hydrophobic
PLAY
Membrane Structure
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Fluid Mosaic Model
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Fluid Mosaic Model
The bilayer is self-orienting (forms by itself)
-self assembly into spheres
-seals quickly if torn
The majority of the membrane lipids are unsaturated
(phosphatidyl choline) which “kinks” the tails
This Increases
Membrane Fluidity!!
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.3
2
Functions of Membrane Proteins
Transport
PLAY
Intercellular adhesion
Cell-cell recognition
Attachment to
cytoskeleton and
extracellular matrix
Transport Protein
Enzymatic activity
PLAY
Functions of Membrane Proteins
Enzymes
Receptors for signal
transduction
PLAY
Receptor Proteins
PLAY
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Figure 3.4.1
Plasma Membrane Surfaces
Differ in the kind and amount of lipids they contain
Glycolipids are found only in the outer membrane surface
-5% of total membrane lipid
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20% of all membrane lipid is cholesterol
Figure 3.4.2
Lipid Rafts
Make up 20% of the outer membrane surface
Composed of sphingolipids and cholesterol
Create stable, less fluid, areas
Are concentrating platforms for cell-signaling
molecules
-Polarization via the sugar group
Structural Proteins
-Wedges it rings between the phospholipid
(nonpolar) tails
-Increases fluidity of the membrane
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Membrane Proteins
Two types: Integral & Peripheral
Integral: Span the lipid bilayer
Often are transmembrane proteins and
protrude on both sides of the membrane
Mainly involved in transport…says your
text book.
WRONG!!!!
Too general a statement
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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Peripheral Proteins
Glycoproteins
Not embedded in the lipid bilayer
Proteins supporting sugar groups
Attach to integral proteins or membrane lipids
Includes many of the integral proteins that extend
into the extracellular space
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Specializations of the Plasma Membrane:
Microvilli
Glycocalyx
Carbohydrate rich area at the cell surface
Formed from glycolipids and glycoproteins
Useful in identifying cell types on the basis of the
sugar types surrounding the cell
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Membrane Junctions
Bind cells together
Factors include:
Glycoproteins (e.g. adhesion proteins),
Tight junction – impermeable junction that
encircles the cell
Desmosome – anchoring junction scattered along
the sides of cells
Gap junction – a nexus that allows chemical
substances to pass between cells
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Minute extensions & recessions of the plasma
membrane that increase surface area
Found on the surface of absorptive cells, e.g.
intestine, kidneys, etc…
Have a core made of actin to support “villi”
structure
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Membrane Junctions: Tight Junction
-Integral membrane proteins in the plasma membrane of adjacent
cells that fuse together
-Help prevent molecules from passing through the extracellular
space between adjacent cells
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Figure 3.5a
4
Membrane Junctions: Desmosome
Membrane Junctions: Gap Junction
-Plaque on the cytoplasmic face of the plasma membrane
-Adjacent cells are held together by cadherins (thin filaments) that
extend from the plaques and interdigitate in the
intercellular space like a zipper
-E.g. connexons: transmembrane proteins that form a hollow
cylinder that connects adjacent cells
-Intermediate filaments form part of the cytoskeleton and extend
from the plaques on the opposite sides of a cell (e.g. guy wires)
-Varying connexons result in varying selectivity
-Things like ions, sugars, and small molecules can pass
-Abundant in tissues subjected to great mechanical stress
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Figure 3.5b
Function of the Plasma Membrane
Is bathed in Interstitial Fluid:
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Function of the Plasma Membrane
Plasma membrane is a selective (or differentially)
permeable barrier. E.g. allows some substances to
pass and blocks others
Plasma membrane moves things across by:
Derived from blood
Form of nutrition
Baths the cells
Contains: amino acids, sugars, fatty acids,
vitamins, hormones, neurotransmitters, salts,
waste
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Passive Membrane Transport: Diffusion
Figure 3.5c
Active processes: require ATP to cross P.M.
Passive processes: require no energy from cell
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Passive Membrane Transport: Diffusion
Diffusion is the tendency of molecules and ions to
scatter evenly throughout the environment
The plasma membrane is a physical barrier to free
diffusion due to its hydrophobic core.
Molecules move from areas of high concentration
to areas of low concentration
Molecules will diffuse through the plasma
membrane if the molecule is:
Kinetic energy is the driving force.
Thus, size and temperature influence rate of
diffusion
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lipid soluble
can pass through membrane channels
assisted by a carrier molecule
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5
Passive Membrane Transport: Diffusion
Passive Membrane Transport: Diffusion
Simple diffusion – nonpolar and lipid-soluble
substances
Diffuse directly through the lipid bilayer
E.g. O2 & CO2 (opposite gradients), fat-soluble
vitamins
Facilitated diffusion
Transported substance binds to protein carriers in
the plasma membrane and is ferried across or
moves through water filled protein channels
E.g. sugars, amino acids, ions
Diffuse through channel proteins
PLAY
Diffusion
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Carrier Proteins
Channels
Are integral transmembrane proteins
Show specificity for certain polar molecules,
including sugars and amino acids, too large for
simple diffusion and facilitated diffusion
Transmembrane proteins that transport ions &
water through aqueous channels across the plasma
membrane
Pore size and net charge of the amino acids lining
the channel determines selectivity
Leaky channels: always open
Gated channels: open & close by chemical or
electrical signals
Molecules move down a concentration gradient
Molecules are shielded from the hydrophobic
plasma membrane by integral membrane proteins
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Diffusion Through the Plasma Membrane
Extracellular fluid
Lipidsoluble
solutes
Lipid-insoluble
solutes
Small lipidinsoluble
solutes
Passive Membrane Transport: Osmosis
Occurs when the concentration of a solvent is
different on opposite sides of a membrane
Diffusion of water across a semipermeable
membrane
Osmolarity – total concentration of solute particles
in a solution
Tonicity – how a solution affects cell volume
[H2O] must be equal on both sides of membrane
Water
molecules
Lipid
bilayer
Cytoplasm
(a) Simple diffusion
directly through the
phospholipid bilayer
(b) Carrier-mediated facilitated
diffusion via protein carrier
specific for one chemical; binding
of substrate causes shape change
in transport protein
(c) Channel-mediated
facilitated diffusion
through a channel
protein; mostly ions
selected on basis of
size and charge
(d) Osmosis, diffusion
through a specific
channel protein
(aquaporin) or
through the lipid
bilayer
PLAY
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Figure 3.7
Osmosis
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Effect of Membrane Permeability on Diffusion
and Osmosis
Effect of Membrane Permeability on Diffusion
and Osmosis
[H2O] must be equal on both sides of membrane
Figure 3.8a
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Effect of Membrane Permeability on Diffusion and
Osmosis
In a cell, however, as water diffuses into the cell,
an equilibrium is reached where the hydrostatic
pressure (back pressure exerted by the water
against the membrane) within the cell is equal to
its osmotic pressure
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Effects of Solutions of Varying Tonicity
Isotonic – solutions with the same solute concentration as that of the cytosol
Hypertonic – solutions having greater solute concentration than that of the cytosol
Hypotonic – solutions having lesser solute concentration than that of the cytosol
RBC in Hypotonic Solution
RBC in Hypertonic Solution
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Figure 3.8b
Effect of Membrane Permeability on Diffusion and
Osmosis
Tonicity: the ability of a solution to change the
shape or tone of a cell by altering its internal water
volume
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RBC in Isotonic Solution
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Effects of Solutions of Varying Tonicity
Thus, water moves towards greater solute
concentration
Water moves towards lesser water concentration
Osmosis continues until osmotic and hydrostatic
pressures acting at the plasma membrane are equal
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