Cell Membranes and Transport1-2- Water and Polarity1-3 – Acids, Bases and Buffers 1-4 – Biological Molecules: Lipids1-5 – Cell Membranes1-6 – Surface Area-Volume Ratio
The unique properties of water make life as we know it possible.
Transport across membranes is just one process in our bodies that is greatly affected by WATER.
Water and It’s role in biological Systems
describe how the polarity of the water molecule results in hydrogen bonding
Polar bonding Unequal sharing of electrons (+) and (-) charges on the molecule
Polarity creates Hydrogen bonds H bonds are relatively
weak
Animation of Covalent and Polar bonds (scroll down on the page when it opens)
There’s strength in numbers!
Unique Properties of Waterdescribe the role of water as a solvent, temperature regulator, and lubricant
1. “Universal Solvent”
Dissolves all polar and ionic molecules.
HydrophobicVs Hydrophilic?
Hydrophobic Interactions:Oil cannot interact with the polar
regions of H2O and actually interfere with the H bonds between H2O molecules.
interfering (breaking) with the H bonds requires ENERGY
When given the chance, oil droplets will cluster, reducing the surface area exposed to the H2O. (therefore using less ENERGY to break the H bonds)
*** the H Bonds “force” the oil droplets to stay together.
2. Temperature Regulation by Water--another process our bodies use water for!
1. High specific heat (the amount of Energy needed to raise 1gm of water 1oC)
2. High heat of vaporization 3. High heat of fusion
“Water is Life” – Mr. Anderson
with Bozeman science.
Acids, Bases and pHdifferentiate among acids, bases, and buffers
pH measures the [ ] of the H+ compared with OH-
PURE H2O : Neutral, therefore pH 7
[H+] = [OH-]
** the pH scale is a log scale; a change in pH from 7 to 6 means there are 10x more H+ ions than in the neutral solution.
Acids
Dissociate to donate H+ ionspH < 7[H+] > [OH-]
Bases
molecules that release OH- ions
therefore pH > 7
(ex. NaOH)
[H+] < [OH-]
Controlling pH in the BodyBUFFERS are molecules that can either pick up or release
hydrogen (or hydroxide) ions Eg. pH is too low: HCO3
- + H+ --> H2CO3
(bicarbonate) (carbonic acid)
pH is too high: H2CO3 + OH- HCO3- + H2O
(excess of OH-)
Cell Membranes “gate keepers”
1. Isolate from outside
2. Control entry and exit
3. Communicate with others
4. Bare identification (I’m one of you!)
you tube cell membranes (lots of other links for passive/active transport, etc
Cell Walls NB** Cell walls are
different from cell membranes
Stiff, non-living Made of complex
carbohydrates Cellulose for plants Chitin for fungi Chitin-like frame for
bacteria Used for support and
protection Very porous; entry only
controlled by size
Which of these statements are true comparing cell walls with membranes?
Walls Membranes
A Non-living Living
B Plants and bacteria only
Animals only
C Control entrance by size only
Control entrance by many factors
D Made with cellulose Made with lipids
E Contain pores Contain pores
Fluid Mosaic Model A phospholipid
bilayer with proteins scattered through it
“fluid” because the proteins seem to “float” around the bilayer
Hydrophilic heads on the outside
Hydrophobic tails on the inside
PHOSPHOLIPIDS – one type of Lipid
Watch Mr. Anderson – Bozeman Science on LIPIDS
Lipids
Glycerol + Fatty Acids
Saturated fatty acids
Unsaturated
Fatty acids
Hydrophobic layer is a barrier to H2O soluble molecules (but makes it less fluid)
Cholesterol in the bilayer is even less permeable to H2O soluble molecules (but makes it less fluid)
“Protein Mosaic” Membrane proteins will interact with the
hydrophobic and hydrophilic layers of the bilayer Some proteins will protrude into the cytoplasm,
some into the extracellular space, others into both
Glycoproteins Membrane
proteins that have a carbohydrate chain attached
Often seen in proteins that protrude outside the cell
Glycolipids Membrane lipids
that have a carbohydrate chain attached
Both glycoproteins and glycolipids OFTEN function in cell-to-cell communication and/or recognition
What does the “fluid” in “fluid mosaic model” refer to? A. The structure of the cell membrane B. The structure of the cell wall C. The fact that the membrane is made up
mostly of water D. The fact that the membrane is always
changing, so it seems to be “fluid” E. The fact that the membrane is made up
of lipids, and they tend to “flow”
What does “mosaic” mean? A. a picture B. a lipid C. a bunch of different things clumped
together on a background D. a type of protein that lets things into
the cell E. No idea!
Which of the following is not true regarding this diagram?
A. 1a and 1b are fatty acids
B. 3 is a phosphate group
C. 5 is the hydrophobic end of the molecule
D. 6 is the hydrophobic end of the molecule
E. this is a type of lipid
Which one is a: 1. Phospholipid 2. Glycolipid 3. Cholesterol
3 major membrane Protein Categories: 1. Transport proteins Regulated, fast method for specific molecules to
enter and exit Channel proteins Carrier proteins
2. Receptor Proteins When activated, set off enzymatic
sequences inside the cell
3. Recognition Proteins “identification tags”
Membrane Transport - RATE Depends on:
Gradient (concentration, electrical or pressure)
Size of molecule Lipid solubility # of transporters
Diffusion The random net movement of molecules from an
area of high concentration to an area of low concentration.
(this is following the “concentration gradient”)
Osmosis The diffusion of WATER across a selectively
permeable membrane (this is also following the “concentration gradient”
and does not require energy)
Osmotic Effects Isotonic solution
Same solute concentration
Cell is happy (no net loss or gain of water)
HYPERtonic solutions
[Solute] is greater outside the cell than inside the cell
Cell is not happy It will crenate (shrink)
HYPOtonic solutions Solute concentation
is less outside the cell than inside
Cell is not happy Cell will lyse
Why are cells so small? (why don’t we grow them larger?)animation that shows
comparison of SA and Volume
calulating SA/V ratios WS
(that crazy guy with the pink shirt/yellow tie explains SA/Vol ratio)
Active transport Often against the
concentration gradient Therefore,
REQUIRES ENERGY
(ATP --> ADP + P) Uses transporter
proteins
Endocytosis - 3 types
PhagocytosisLarge particles
2. Pinocytosis Liquid and smaller particles
only
Receptor-mediated Endocytosis Uses receptors to
bind first to the desired molecules, then gathers them together before enclosing them in a membrane
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