Transcript Chapter 5: Homeostasis and Transport

Bozeman
The plasma
Membrane
Bozeman
Diffusion Lab
Bozeman
Osmosis &
Diffusion Lab
The Cell Membrane
2007-2008
Arranged as a Phospholipid bilayer
• Serves as a cellular barrier / border= 8nm thick
sugar
H 2O
salt
polar
hydrophilic
heads
nonpolar
hydrophobic
tails
impermeable to polar molecules
polar
hydrophilic
heads
waste
lipids
Amphipathic: both hydrophobic and hydrophilic regions.
Cholesterol & Plasma Membrane
Why are
proteins the perfect
molecule to build structures
in the cell membrane?
2007-2008
Proteins domains anchor molecule
• Within membrane
Polar areas
of protein
– nonpolar amino acids
• hydrophobic
• anchors protein
into membrane
• On outer surfaces of
membrane in fluid
– polar amino acids
• hydrophilic
• extend into extracellular
fluid & into cytosol
Nonpolar areas of protein
Many Functions of Membrane Proteins
“Channel”
Outside
Plasma
membrane
Inside
Transporter
Enzyme
activity
Cell surface
receptor
Cell adhesion
Attachment to the
cytoskeleton
“Antigen”
Cell surface
identity marker
Membrane Proteins
• Proteins determine membrane’s specific functions
– cell membrane & organelle membranes each have unique
collections of proteins
• Classes of membrane proteins:
– peripheral proteins
• On the periphery of the cell
• ex: cell surface identity marker (antigens)
– integral proteins
• penetrate lipid bilayer, usually across whole membrane
• transmembrane protein
• ex: transport proteins
– channels, permeases (pumps)
Membrane is a collage of proteins & other
molecules embedded in the fluid matrix of the
lipid bilayer
Extracellular
fluid
Glycoprotein
Glycolipid
Phospholipids
Cholesterol
Peripheral
protein
Transmembrane
proteins
Cytoplasm
Filaments of
cytoskeleton
1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model
Membrane carbohydrates
• Play a key role in cell-cell recognition
– ability of a cell to distinguish one cell from
another
• antigens
– important in organ &
tissue development
– basis for rejection of
foreign cells by
immune system
– Blood type: codominance
Understanding
Cancer
Homeostasis and Transport
• How do substance enter and exit a cell?
• What is the difference between active and
passive transport?
• How does the chemical make-up of the
plasma membrane affect what can enter and
exit the cell?
Cell Size
Overview
The plasma membrane only
allows certain things to enter and
exit the cell. What is this called?
• Selectively permeable membrane or
selectively permeable
Bozeman
AP Lab 1
H2O Potential
What is passive transport? Name
and describe the 3 types.
• Passive Transport- movement of
substance of substances across the
plasma membrane without the use of
energy.
Passive
Transport
Pearson's
The Three Types
Diffusion: movement of substances across the
plasma membrane from high to low
concentration. aquaporins
Osmosis: diffusion of water across the plasma
membrane from high to low concentration
Facilitated Diffusion: carrier molecules
transport larger substances across the
membrane from high to low.
Filtration: Using a pressure gradient to move
particles through a plasma membrane.
What is active transport?
Describe the two major types.
• Active Transport: uses energy and
carrier molecules to move substances
across the plasma membrane from low
to high concentrations (against the
concentration gradient)
Active
Transport
Two Major types
• Bulk Transport
• Endocytosis: process by which large
particles are brought into the cell
Endo/
Exocytosis
– Pinocytosis
– Phagocytosis
– Receptor-mediated endocytosis
» familiar hypecholesterolemia causes high cholesterol levels.
Caused by defective cholesterol receptors, can’t get it out of the
blood. Receptor site binds to the ligand (in this case cholesterol)
and ceates a vessicle.
• Exocytosis: process by which large particles
leave the cell
– Contractile vacuoles
• Solute Pumping/ Protein Carriers
Types of Solute pumps/Protein
Carriers
• Sodium-Potassium Pump (nerve
cells)
• Plastoquinone (moves electrons in
photosynthesis)
• Electron Transport Chain
(mitochondria, photosynthesis)
Sodium Potassium Pump
Active transport
• Many models & mechanisms
ATP
ATP
antiport
symport
There are 3 types of solutions a
cell can be in.
• 1) Hypotonic
• 2) Hypertonic
• 3) Isotonic
Hypo/Hyper/
Iso Sollutions
Hypo/Hyper/
Iso
Scroll Down
Describe a cell in an isotonic
solution.
• Iso= the same. The concentration of
the solution is the same inside and
outside the cell.
• The cell stays the same size.
• There is no net movement across the
plasma membrane (things enter and
leave the cell at the same rate)
Describe a cell in an hypertonic
solution.
• Hyper= above. The concentration
of the solution is higher outside
the cell than inside.
• The cell shrivels in size.
• Water leaves the cell at a faster rate
then it enters.
Describe a cell in an hypotonic
solution.
• Hypo= below. The concentration of
solutions is lower outside the cell then
inside.
• The cell swells or pops in size.
hyPO=POP
• Water enters the cell at a faster rate
than it leaves
Cell Signaling
• Prokaryotic cells: Quorum sensing: bacteria
cells secrete molecules that allows them to
respond to changes in population density.
• Eukaryotic cells: Helps maintain homeostasis
– Tight Junctions: epithelial cells, prevent leakage,
Urinary bladder
– Desmosomes: spot welds rivet cells together,
mechanical stress, Skin and Uterus
– Gap Junctions: cytoplasmic flow from one cell to
another: heart (intercalated disks)
– Plasmodesmata: In Plants. Act as gap junctions.
Signal Transduction Pathways
Signal…Transduction…Responce
• Autocrine Signals: diffuse from one part of
a cell to another part of the same cell.
– Prostaglandins
• Synaptic Signaling: Used by nerves
• Paracrine Signals: Cells communicate with
each other by diffusion
– Prostaglandins
• Endocrine Signals: Hormones. (Hormone
is a chemical that effects another cell.
Produced at a specific site.)
Ligand= signaling
molecule. Can be
a hormone…. or
not. 
Steroid effect
Signal Transduction Pathway
• Ligand: signaling chemical…(hormone)
– Steroid: enters the nucleous becomes a transcription
factor switching genes on or off
– Non-steroid: cAMP causes reaction to effect DNA
• Target cell: Where Ligand must travel to
• Receptor: Spot on the target cell that the ligand
attaches to.(How cells know what proteins to
make, apoptosis, what to become.) …receptor
mediated endocytosis
The cascade effect
• Both hydrophobic and hydrophilic signaling
molecules may use a cascade effect because
it amplifies the signal.
• Evolution: All kingdoms use the cascade
effect and all steps/ proteins are similar. We
all have a common ancestor.
• Highly specific. Regulated
• One molecule can cause thousands of other
molecules to be made.
How do we control signals?
• Negative and Positive Feedback systems
– Negative feedback: one organ or gland negates
the effect of another. Maintains homeostasis.
– Positive feedback system: Amplifies the effect.
Childbirth, blood clots, allergic reactions.