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8/3/2019 RSF Lecture 1 Sides
1/23
LIPIDS
(Diverse class of compounds defined by their insolubility in water)
A. Fatty Acids
B. Neutral Fats (Triglycerides)
C. Steroids
D. Phospholipids
E. Micelles
F. The phospholipid Bilayer
Dr. Ross Feldberg
Tufts University,Medford, MA (near Boston)
Questions on the lectures? Send them to class e-mail so everyone can seethe answers
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8/3/2019 RSF Lecture 1 Sides
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CH3CH2CH2CH2CH2CH2CH2CH2CH2COOH
CH3(CH2)8COOH
The Building Blocks: Isoprene and the Fatty Acids
Charged at one end,but long nonpolar tail....
it this hydrophobic orhydrophilic?
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FattyAcids
(LONG HYDROCARBON CHAIN WITH CARBOXYLIC ACID AT ONE END)
CH2-CH
2-(CH
2)13
-CH2-CH
2-COOH
stearic acid C18 saturated (No double bonds)
CH2-CH2-(CH2)5-CH2-CH=CH-CH2-(CH2)5-CH2-COOH
oleic acid C18 1 cis double bond
A cis double bond introduces a kink inthe molecule - a bend in its structureThis is an unsaturated fatty acid
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Neutral Fats form when the carboxyl groups of three fatty acids
condense with the hydroxyl groups of glycerol.
Q. What do we call the functional group that is formed?
what does this zigzag line represent?
Neutral fats are your major long-term energy reservoir(stored in adipocytes a specialized fat storage cell that makes up fat tissue)
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Neutral Fats consist of three fatty acids linked to glycerol. This is
the storage form that excess calories take in your adipose tissue.
Saturated fatty acids have no double bonds and neutral fats with no double bonds form
solids (grease) found in animals
Unsaturated fatty acids with cis double bonds disrupt the compact structure and neutral
fats with such fatty acids form liquid structures (oils) - found in plants)
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8/3/2019 RSF Lecture 1 Sides
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H
O
H
+ -Water is a dipole, making it a goodsolvent for charged or polar solutes
Water Structure and solvent properties
8/3/2019 RSF Lecture 1 Sides
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Electronegativity
-C=O - -N-H + -C-H
+ - no in chargeacross bond
In biological systems, oxygen, nitrogen and sulfur have high electron affinity.
When they form bonds to C or H the covalent bond tends to have an unequalcharge across it (POLAR COVALENT BONDS)
In contrast, Bonds between C and H are NONPOLAR
Molecules that are made up mainly of Carbons and Hydrogens tend to beHYDROPHOBIC - they associate with one another when placed in waterrather than with the water molecules. They are insoluble in water.
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8
http://scholar.hw.ac.uk/site/chemistry/activity3.asp
Fats with cis double bonds cannot pack together to form solids
Fats with trans double bonds alsoshow close packing - these aresynthetic and used in baking, butnow thought to be unhealthy
Saturated fats and trans fats tend toform tightly packed solids(margarine)
Unsaturated cis fats form oils(olive oil, canola oil)
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8/3/2019 RSF Lecture 1 Sides
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CH3
CH3
H3C CH3
CH3
HO
STEROIDS
Steroids have a four-membered fused ring system
Cholesterol
Testosterone
Q. What does thisindicate?
Fused isoprene unitsmake up a steroid (a 4-membered ring system)
8/3/2019 RSF Lecture 1 Sides
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C
C
CH2
H
H
H
C CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
O
C CH2
CH2
CH2
CH2
CH
O
O
O
OP
O
O-
OR
CHCH2
CH2
CH2
CH3
PHOSPHOLIPIDS
GLYCEROL ESTERIFIED TO TWO FATTY ACIDS AND A PHOSPHORIC ACID
Where R = glycine,serine, ethanolamine,choline or a variety ofother small molecules
The cell membrane is made up of a phospholipid bilayer
charged head group
Hydrophobic tail groups
8/3/2019 RSF Lecture 1 Sides
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soaps form these!
(animal fat + lye to giveCH3(CH2)nCOO- Na+)insoluble fats will be trapped in thecenter of the micelles
Phospholipids associate to form micelles or lipid bilayers
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ARTIFICIAL MEMBRANES: 1. LIPOSOMES
Lipid Bilayers can also form small droplets called liposomes in which there isan aqueous interior.These fuse with cell membranes and can be used to carry into cellshydrophilic molecules that would not normally cross the membrane.
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Doxorubicin: An anticancer agent used in treatment of metastatic breast cancerand delivered to cells by being packaged in liposomes
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Q. What is the most fundamental characteristic of a cell ?
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Phospholipid bilayers are Selectively Permeable
These requireprotein carriers toget them across
the membrane
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In diffusion
1. The net movement of molecules is always down its concentration gradient
2. Since this is a spontaneous process, it is possible to capture some of the energydecrease in moving to equilibrium as work
3. The rate of diffusion is proportional to the concentration difference, thetemperature and the size of the molecules (Einstein was the first to derive anaccurate equation for diffusion!)
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Osmosis is the diffusion of water that takes place when a membrane impermeable
solute is present at different concentrations on either side of a membrane
We actually measure this bydetermining how much pressure wouldhave to be exerted on compartment 2
to keep its volume constant = OsmoticPressure
1 2
Molecules in compartment 2 can NOTcross the membrane
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Osmosis: The diffusion of water down its concentration gradient
high salt solution water balanced salt solution
During profound dehydration, you need to rehydrate with a balanced salt solution, not water
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What are some of the properties of biological membranes?
1. Are they rigid or fluid?2. What is the position of membrane proteins in the membrane?3. How do polar and charged molecules get across the membrane?
4. What roles do membrane proteins and carbohydrates play?
In addition to the membrane that defines a cells outer boundary (the plasma
membrane), in eukaryotic cells there are a number of membrane boundedinternal compartments.
The various cell membranes have different lipid components and different proteinsthat determine the structure and function of that membrane.
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Human Cell
Mouse Cell
Hybrid cellT = 0
Fuse the twocell types
Hybrid CellT = 60 min
Mouse Membrane Protein
Human Membrane Protein
Use specific fluorescent antibodies to identify mouse-specific and human -specificmembrane proteins
Q. What might you conclude from this experiment?
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The Fluid Mosaic Model of the Cell Membrane
Cholesterol
1. The lipid bilayer (fatty acids and groups attached to phosphate vary from membrane tomembrane)
2. Saturated Fatty Acids & Cholesterol (animal membranes) both reduce fluidity
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The Fluid Mosaic Model of the Cell Membrane
1. Proteins: Peripheral (easy to remove) and Integral (requires dissolving membrane to
remove)
2. Carbohydrates bound to proteins (glycoproteins) and to lipids on exterior surface. Thedifferent blood groups (A, B and O) reflect different sugars on the cell surface of bloodcells