lecture 5 membranes why does osmosis matter?
TRANSCRIPT
Lecture 5
Membranes
Why does osmosis matter?http://www.livescience.com/37227-man-overdoses-on-soy-sauce.html?cmpid=514645
Yesterday’s Exit Ticket
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Prokaryotes Animals Plants
No nucleus True nucleus True nucleus
Cell wall (featuring peptidoglycan)
No cell wall Cell wall(featuring cellulose)
No membrane-bound organelles
Membrane-bound organelles (including mitochondria, but NOT chloroplasts or vacuole)
Membrane-bound organelles (mitochondria, chloroplasts, vacuole)
DNA DNA DNA
Ribosomes Ribosomes Ribosomes
Cytoplasm Cytoplasm Cytoplasm
Cell Membrane Cell Membrane Cell Membrane
Sim
ilaritie
sD
iffere
nce
s
Key Themes
(2) “Think Like a Biologist”: Understand What Life Is. “Unity” of life: What are the common features of all life?
• Structure and function of biological membranes
• Maintenance of a suitable internal environment at the cost of energy input
Today’s agenda:
• Fun with membranes
• Review of the key concepts for the exam
Key Functions of Membranes
Membrane Structure and Function
1) Provide a barrier around cells & sub-cellular spaces
2) Provide controlled passageways for wanted & unwanted substances
Which macromolecules do which?
Phospholipid bilayer provides ±impenetrable barrier
Proteins provide selective & controllable passageways(“selective permeability”)
Phospholipid bilayer - as the basic membrane structure
Phospholipids have hydrophilic & hydrophobic regions.
Fig. 7.2
1. Be able to relate the basic structure of biological membranes to their principal functions
Fluid-Mosaic Membrane
• Membranes: typically “fluid” with consistency of salad oil (fluidity level varies with temperature!)
• Membranes: mosaic of phospholipids & proteins
Phospholipidbilayer
Hydrophobic regionsof protein
Hydrophilicregions of proteinFig. 7.3
The effect of unsaturated versus saturated phospholipids on membrane fluidity
In organisms that do not regulate body temperature (microorganisms, plants, & non-regulating animals)
Fluid Viscous
Unsaturated hydrocarbontails with kinks
Saturated hydro-carbon tails
Fig. 7.5 (b)
2. Be able to identify factors affecting membrane fluidity in various organisms
3. Be able to relate saturated and unsaturated fatty acids to the ecology of organisms
http://www.ecoworld.com/maps/world-ecoregions.html
Macademia nutAustralia & Hawaii
WalnutNortheast US & N Europe
Canola
TemperateTemperateMediterranean
&Olive oil
Tropical
versusPalm & coconut oil
Role of cholesterol in animal membranesActs as a “temperature buffer”
CholesterolFig. 7.5 (c)
Fig. 5.15
• Prevents hydrophobic chains from packing too closely together: increases fluidity at low temperatures• Limits lateral phospholipid movement & stabilizesmembranes at high temperatures
Passage of Molecules across the Plasma Membrane
Hydrophobic, non-polar molecules cross membranes with ease.
http://www.colorado.edu/ebio/genbio/07_11_MembraneSelectivity_A.html
4. Be able to predict the passage of hydrophilic (polar) and hydrophobic (nonpolar) molecules through biological membranes
Hydrophilic molecules cannot slip through hydrophobic core of membrane: Require help of proteins that span the entire membrane.
Passage of Molecules across MembranesHydrophilic, polar molecules cannot slip through membrane; their transport requires help of proteins that span entire membrane.
Fig. 7.15 (a)Cytoplasm
Extracellularfluid
Solute
Predict which portions of a membrane-spanning protein (allowing passage of polar or charged ions/molecules) are hydrophilic:
Fig. 7.15 (a)Hydrophilic regions (R groups!) of protein
Hydrophobic regions(R groups!) of protein
Predict which portions are hydrophobic:
5. Structure and function of membrane channels: Be able to predict where amino acids with hydrophilic versus
hydrophobic rest groups are found in transport proteins
Nonpolar R groups: hydrophobic
Glycine Alanine Valine Leucine Isoleucine
Methionine Phenylalanine Tryptophan Proline
Fig. 5.17(a)Amino acid R (rest) groups
Arginine HistidineAspartic acid Glutamic acid Lysine
ElectricallyCharged
R groups:hydrophilic
Fig. 5.17(b&c)
Polar R groups: hydrophilic
Asparagine GlutamineSerine Threonine Cysteine Tyrosine
http://www-als.lbl.gov/als/science/sci_archive/54aquaporin.html
Aquaporins: Membrane-spanning
protein channels allowing (polar) water to move
across (hydrophobic) lipid
membranes
5. Structure and function of membrane channels (example aquaporins)
Two aspects of movement across membranes:
• Predict when a protein is needed for movement:
For small non-polar, hydrophobic substances?
For polar, hydrophilic substances?
• Predict when ATP energy is needed for movement:
When substances move from high to low concentration, i.e. along their concentration gradient?
When substances are moved from low to high concentration, i.e. “uphill” against the concentration gradient?
No
Yes
No
Yes
6. Be able to predict when when ATP energy is needed to fuel active transport
Overview of the two possibilitiesPassive transport
Diffusion Facilitated diffusion
Active transport
ATP
Fig. 7.17
“Downhill”“Uphill”
ex. fructose, H2O
Predict how glucose moves from the gut into intestinal cells when the glucose concentration in the gut is higher than in the intestinal cells after a meal:
A) by passive transport
B) by active transport
Passive transport
Facilitated diffusion
Think-Pair-Share
Molecules of dye
Fig. 7-11a
Membrane (cross section)
WATER
Net diffusion Net diffusion
(a) Diffusion of one solute
Equilibrium
Water crosses membranes by
OSMOSISdown its
concentration gradient
7. Be able to predict the direction of water movement via osmosis
http://isite.lps.org/sputnam/Biology/U3Cell/Unit3Notes_cell.htm
Salt (Na+) retention & high blood pressure
Lowerconcentrationof solute (sugar)
Fig. 7-12
H2O
Higher concentrationof sugar
Selectivelypermeablemembrane
Same concentrationof sugar
Osmosis
Fig. 7-13
Hypotonic solution
(a) Animal cell
(b) Plant cell
H2O
Lysed
H2O
Turgid (normal)
H2O
H2O
H2O
H2O
Normal
Isotonic solution
Flaccid
H2O
H2O
Shriveled
Plasmolyzed
Hypertonic solution
Osmosis = passive (net!) movement of water across membranes along/down the concentration gradient
Net water movement follows only the water gradient (regardless of what kinds of dissolved
compounds are involved)
Intravenous saline solution (1) with similar concentration of all dissolved compounds, like salts & sugars, combined as the blood plasma
Net water movement into or out of red blood cells?
(2) Intravenous “solution” of pure water
Net water movement into or out of red blood cells?
(3) Intravenous solution more concentrated in salt & sugars
Net water movement into or out of red blood cells?
• The Crash Course for Membranes is particularly good!!
http://www.youtube.com/watch?v=dPKvHrD1eS4&list=PL3EED4C1D684D3ADF
3:07-3:43
5 minute break
30
Overview of the two possibilitiesPassive transport
Diffusion Facilitated diffusion
Active transport
ATP
Fig. 7.17
“Downhill”“Uphill”
K+/Na+ pump
K+
Na+
Na+/K+ Pump
• Cells want to pump Na+ out
• Cells want to pump K+ in
K+
Na+
ATP
Active transport and the sodium-potassium pump
Both Na+ and K+ are moved AGAINST their concentration gradient
http://www.colorado.edu/ebio/genbio/07_16ActiveTransport_A.html
See Fig. 7.16 for a six panel, blow-by-blowdescription of the sodium-potassium pump.
8. Be able to apply the principal features and functions of an ATP-fueled ion pump to the Na+/K+ pump
Fig.8.7
http://onlinephys.com/circuit1.html
ATP fuels the Na+/K+ pumpNa+ accumulates “on top of the hill” (against its concentration gradient)
Na+ flows downhill again
Releasing useful energy
Cotransport: Using potential energy
ATP
Na+
Cotransport: Using potential energy
This potential energy can be used… To transport other molecules
AGAINST their concentration gradient
The Na+ gradient built up by the Na+/K+ pump also fuels the secondary active transport
of glucose (& other substances) AGAINST their concentration gradient
Via Na+/glucose cotransport, whereNa+ flows back downhill & drags
glucose uphill AGAINST its concentration gradient
https://www.youtube.com/watch?v=LyvmM1lKtWs
https://www.youtube.com/watch?v=svAAiKsJa-Y
Predict how glucose moves into intestinal cells when glucose concentration is lower in the gut than in the intestinal cells:
A) through a glucose channel
B) directly through the lipid bilayer
C) via Na+-glucose cotransport fueled by the
Na+/K+ pump
D) directly through the ATP-fueled Na+/K+ pump
Think-Pair-Share
Predict how glucose moves into intestinal cells when glucose concentration is higher in the gut than in the intestinal cells after a meal: A) through a glucose channelB) directly through the lipid bilayerC) via Na+-glucose cotransport fueled by the Na+/K+ pumpD) through the ATP-fueled Na+/K+ pump
Passive transport
Facilitated diffusion
Think-Pair-Share
Membrane Bioflix Exo- and Endocytosis
Fig. 7.9Overview of functions of membrane proteins
(a) Transport
ATP
(c) Signal transduction
Signal transduction
Signaling molecule
Receptor
Let’s look at the two major classes of hormones: Protein hormones and steroid hormones
Predict which hormones can pass directly through the lipid bilayer of membranes:
A) Protein hormonesB) Steroid hormones
Think-Pair-Share
10. Be able to predict the principal differences in signal transduction of a protein hormone versus a steroid hormone
(a) Water-soluble protein hormones relay message via signal transduction pathway to a gene regulatory protein.
Eighth ed. = Fig. 45.5
(a) Water-soluble protein hormones relay message via signal transduction pathway to a gene regulatory protein.
Eighth ed. = Fig. 45.5
(b) Lipid-soluble (e.g. steroid) hormones move into nucleus & bind directly to gene regulatory protein.
See also Fig. 11.8
Open Forum
Questions leading up to Monday’s exam?
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