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Cells:
The Living Units
Chapter 3, PPT 1
Cells…What do you know?
Cells
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Cell History
•  Robert Hooke
–  Observation of plant cells in 1600s
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Cell History
•  Schleiden & Schwann
–  Said living things were composed of cells in 1830s
•  Virchow
–  Said cells only come from other cells
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Cell Theory
1.  All living things are composed of cells.
–  When you define the properties of a cell, you
define the properties of life.
2.  The cell is the basic structural and functional
unit of living organisms.
Cell Theory Additionally
4.  Organismal activity depends on individual
and collective activity of cells
5.  Biochemical activities of cells are dictated by
subcellular structure.
3.  All cells arise from pre-existing cells
–  Continuity of life has a cellular basis.
Cells
Generalized, Composite Cell
•  Vary in size, shape and function
–  Size = 2 micrometers to 40 inches
–  Shapes = see HW
–  Functions = so many!
1 micrometer =
1/12,000 of an inch
•  But even though they are different, they all
have similarities in common…
1.  Plasma/cell membrane
2.  Cytoplasm
3.  Nucleus
Plasma Membrane
•  Why does a cell have an outer
membrane?
–  Keep some things in,
keep some things out
•  Separate the two major fluid
compartments of the body
–  Intracellular fluid
–  Extracellular fluid
–  Both largely composed of H20
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Plasma Membrane Structure
Phospholipid Bilayer
•  Hydrophilic Head
–  Phospholipid
•  Hydrophobic Tail
–  Two fatty acid chains
Phospho =
Lipid =
Bi =
About Polarity
•  What do you know about “poles’?
•  What objects have “poles”?
•  What does the polarity of a magnet refer to?
–  Opposite charges … what do opposite charges do?
–  Opposites attract!
•  We said water was polar… what did that mean?
Hydro =
Phobic =
Philic =
Water is Polar
•  What does that mean?
•  What causes this?
•  Draw it…
Lipids are Nonpolar
•  What major organic biomolecule does NOT
disassociate in water?
•  Why??
–  It is non-polar, no charges to
pull/attract
•  Think back to bio…
what makes a duck’s feathers
waterproof?
NOTE:
§  With polar substances opposites attract
§  With non-polar substances, like attracts like
Let’s play a Game
•  If your last name starts with…
–  A to G; you are polar and have a negative charge
–  H to P; you are polar and have a positive charge
–  Q to Z; you are nonpolar
•  Look around the room for the neon green signs
•  Based on what you are, go to the place you
should hang out.
QUIZ
TIME
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Can you explain this to
someone?
The plasma membrane is composed of a
phospholipid bilayer. The hydrophilic head and
hydrophobic tail of this structure separates
intracellular and extracellular fluids.
Plasma Membrane Structure
Fluid Mosaic Model
•  Very thin structure
•  Phospholipid bilayer
–  A double layer of lipid molecules
•  Protein molecules dispersed among the bilayer
–  Protein molecules constantly change
–  Results in a constantly changing mosaic pattern
If not, you need to review the material
or come see me!!
Plasma Membrane Proteins
Two major types
•  Integral proteins
–  What does integral mean?
–  Steady Eddys
•  Peripheral proteins
Integral Protein Structure
•  Proteins firmly inserted into the phospholipid
bilayer
•  Transmembrane
–  Transatlantic flight?
–  Span the entire width of the membrane and protrude
on both sides
–  What does peripheral mean?
–  Rico Suaves
Integral Protein Function
Transport things into & out of cell
–  They all have hydrophobic and hydrophilic regions
•  Channels
–  Pores formed in membrane by a cluster of proteins
Integral Protein Function
Transport things into & out of cell
•  Signal transduction
–  Receptors that relay messages from hormones and other
chemical messengers
•  Carriers
–  Proteins bind to a substance and then move it through
membrane
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Peripheral Protein Structure
•  Attached loosely to integral proteins or
membrane lipids
Plasma Membrane Glycocalyx
The sugar coating of our cells!
•  Structure
–  Easily removed
–  Glycoproteins & Glycolipids
Peripheral Protein Function
•  Function
–  Recognition
•  Sperm, bacteria, etc.
•  Supporting filaments
•  Enzymes
•  Mechanical functions
–  Shape changers (cell division, muscles)
Fluid Mosaic Model
QUIZ
TIME
Figure 3.3
QUIZ TIME!!!
Graded or ungraded?
Individually or as a group?
1.  The plasma membrane separates what?
–  Intracellular fluid and extracellular fluid
2.  The intracellular and extracellular fluid are
composed of a large amount of what?
– H2O
3.  The head of a phospholipid is what?
–  Hydrophillic
4.  Bilayer means what?
–  Two layers
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5.  Who said cells come from other cells?
–  Virchow
6.  What are two of the three components of a
composite cell?
–  Plasma Membrane, Cytoplasm, Nucleus
7.  Is the head of the phospholipid on the inside or
outside of the plasma membrane?
Cell Theory
1.  All living things are composed of cells.
2.  The cell is the basic structural and functional
unit of living organisms.
3.  All cells arise from pre-existing cells
–  Outside hydrophobic tails line up inside
8.  And what are the proteins doing?
–  …
9.  Give one of the three parts of the cell theory.
Plasma Membrane
Specializations
•  Microvilli
•  Membrane Junctions
Microvilli Structure
Microvilli = “little shaggy hairs”
•  Minute fingerlike extensions of the plasma
membrane project from free or exposed cell
surface
•  Actin core
Microvilli Function
•  Increase surface area
•  Found on absorptive cells; intestinal cells
Microvilli in Celiac Disease
Membrane Junctions
Three types
•  Tight junction
•  Desmosome / Anchoring junction
•  Gap Junction / Nexus
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Tight Junctions
•  Impermeable junction
•  Series of integral
proteins fuse together
•  Prevents molecules
from passing through
extracellular space
between adjacent cells
•  Found in epithelial cells
lining the digestive tract
Desmosomes
•  Anchoring junctions
•  Spot welds between cells
•  Found in tissues subjected
to great mechanical stress;
skin, heart muscle
Gap Junction (aka “nexus”)
•  Communicating
junctions between
adjacent cells
•  Found in heart and
smooth muscle
•  What is that orange
thing?
We talked about composite cells. What are they?
Cells that have 3 components in common.
What are the two types of membrane proteins?
Integral (Steady Eddy)
Peripheral (Rico Sauve)
What three things?
1. Plasma Membrane 2. Cytoplasm
3. Nucleus
Remember what your cells’ sugar coating is called?
What is the plasma membrane composed of
A bilayer of phospholipids with hydrophilic heads
and hydrophobic tails.
We talked about specializations of the plasma
membrane. What are the projections called?
Microvilli.. Little shaggy hairs.
The tails are composed of what?
Two fatty acid chains
How do they help?
Increase surface area
Glycocalyx
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What are the three types of junctions?
1. Tight Junctions
2. Desmosomes
3. Gap Junctions
Why do cells need membrane junctions?
They can’t all just be floating out there wherever
they want; that would be silly. (Need to
communicate, keep things out, be held together)
Plasma Membrane Function
1.  Membrane Transport
–  Passive
–  Active
2.  Resting Membrane Potential
–  Generates
–  Maintains
Membrane Transport
•  Interstitial Fluid
–  “Blood bath”
–  Extracellular fluid that our cells are bathed in
–  “Feeds” our cells
•  Think about it…
–  What do our cells need to be fed?
•  Amino acids, sugars, fatty acids, vitamins,
hormones, neurotransmitters, salts
–  What might need to exit them?
•  Waste products
Selective Permeability
Cells have a selectively permeable membrane
–  (aka differentially permeable)
•  Allows some things to pass, but blocks others
Membrane Transport
•  Passive
– No cellular energy required
•  Active
– Require cellular energy
–  Allows nutrients, etc. to enter cell
–  Allows waste to exit cell
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Membrane Transport
Passive – no E
Active – need E
•  Diffusion
–  Simple
•  Osmosis
Diffusion
(Passive Transport)
•  Molecules and ions scatter evenly throughout the
environment
•  Molecules move from an area of higher
concentration to an area of lower concentration
–  Molecules move along (down) the concentration
gradient
–  Facilitated
•  Carriers
•  Can be simple or facilitated
•  Channels
•  Filtration
Simple Diffusion Examples
•  Molecules and ions scatter evenly throughout the
environment
•  Molecules move from an area of higher concentration to
an area of lower concentration
–  Molecules move along (down) the concentration gradient
Membrane Transport
Passive – no E
Active – need E
•  Diffusion
–  Simple
•  Osmosis
–  Facilitated
•  Carriers
•  Channels
•  Filtration
(Passive Transport)
Simple Diffusion
•  Unassisted diffusion of molecules that are:
–  Lipid-soluble
–  Small enough to pass through channels
•  Examples
–  Osmosis
•  Unassisted diffusion of a solvent (often water)
through membrane
–  Oxygen, carbon dioxide, fat-soluble vitamins
Osmosis
(A Special Simple Diffusion)
•  Osmos = pushing
•  Diffusion of a solvent
through a selectively
permeable membrane
•  Occurs when solvent
(usually water)
concentration differs on
both sides of cells
–  Solvent (water) moves
from area of high to low
concentration
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Osmosis
(A Special Simple Diffusion)
Osmosis
(A Special Simple Diffusion)
•  If the membrane is
impermeable to solute
molecules the volume of
the solution will change
–  Solute (particles) can’t
move, so solvent (water)
does
(A Special Simple Diffusion)
Osmosis Terms
•  Osmolarity
(A Special Simple Diffusion)
Osmosis Terms
•  Hydrostatic pressure
–  The number of atoms, ions or molecules present per
unit / The total concentration of all solute particles in
a solution
•  The greater the osmolarity, the greater the concentration
•  The lower the osmolarity, the lower the concentration
Tonicity
Ability of a solution to change shape (tone) of a cell by altering
internal water volume
•  Isotonic
–  Same osmolarity (solute conc) inside and outside cell
–  Intra- and Extra- cellular concentrations are equal
–  No net gain or loss of water in cell
–  Back pressure exerted by water against membrane
•  Osmotic pressure
–  Cell’s tendency to resist net water entry
•  Water will diffuse until hydrostatic pressure is
equal to osmotic pressure
(Osmosis)
Tonicity
(Osmosis)
•  Hypertonic
–  Hyper = high, above
–  Extracellular concentration is higher than intracellular
–  Cells lose water / shrink
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(Osmosis)
Tonicity
Osmosis, Osmolarity & Tonicity
•  Hypotonic
Review from last class…
–  Hypo = low, below
–  Extracellular concentration is lower than intracellular
–  Cells gain water / lyse (burst)
…any questions??
Human Tonicity
(Osmosis)
To be isotonic to a human, a solution must be:
–  0.9% saline
–  5% sucrose
Think…why does it matter??
Hypotonic
Hypertonic
Isotonic
What is the difference between active and passive
transport?
Active requires energy, passive doesn’t
Osmosis occurs when particles can or can’t pass through
the membrane?
Can’t… the solvent has to pass through
In diffusion particles move from an area of __________
concentration to an area of __________ concentration
High to low
If the osmolarity of a solution is high, then the solute
concentration is high or low?
High
What two things are required of molecules to enter a cell
via passive diffusion?
Lipid-soluble or small
If there is a large difference in the osmolarity on two sides
of a semipermeable membrane, the osmotic pressure
will be low or high?
High
Osmosis is a special type of what?
Passive diffusion (no energy, moving down
concentration gradient
If a cell is in a hypotonic solutions, what will happen to it?
Burst / Lyse
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(Passive Transport)
Membrane Transport
Passive – no E
Active – need E
•  Diffusion
Facilitated Diffusion
•  Molecules cannot pass through the membrane
because they are dissolved in water
–  Hydrophobic tails won’t allow them to pass
–  Simple
•  Still goes down concentration gradient
•  Osmosis
–  From high to low concentration
–  Facilitated
•  Examples
•  Carriers
–  Sugars, amino acids, ions
•  Channels
•  Filtration
(Passive Transport)
(Passive Transport)
Facilitated Diffusion
Facilitated Diffusion
Transport is facilitated (assisted) by
integral (transmembrane) proteins
•  Carrier Proteins
–  Molecule enters protein
–  Binding causes shape
change
–  Shape change opens “gate”
–  Shields it from non-polar
inner membrane
•  Channel Proteins
–  Aqueous channels
–  Some are always open
–  Some are gated and
controlled by chemical
and electrical signals
Membrane Transport
Passive – no E
•  Diffusion
–  Simple
•  Osmosis
–  Facilitated
•  Carriers
•  Channels
•  Filtration
Active – need E
Transport is facilitated by integral proteins
•  Carrier Proteins
– 
– 
– 
– 
•  Channel Proteins
Molecule enters protein
Binding causes shape change
Shape change opens “gate”
Shields it from non-polar inner
membrane
–  Aqueous channels
–  Some are always open
–  Some are gated and
controlled by chemical and
electrical signals
Filtration
(Passive Transport)
•  Process that forces water and solutes through a
membrane or capillary wall by hydrostatic
pressure
•  Uses pressure gradient - pushes fluid with
solute from a higher-pressure area to a lowerpressure area
•  Not selective
•  Example
–  From capillaries to tissues, makes urine
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