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Lipids
-marginally soluble in H20 ; readily soluble in solvents
(chloroform and acetone)
2 main groups:
a.) Open chain compounds with polar head ; long
non-polar tails
a. FA
b. TAGS
c. Sphingolipids
d. Phosphoacyl glycerol
e. Glycolipids
b.) Fused ring compounds
a. Steroids (cholesterol)
*when organism uses Fas, the ester linkages of TAGS
are hydrolysed by enzymes called lipases (preferably @
C1/C3)
Saponification
-
Fatty Acids
-
Carboxyl group polar end ; hydrophilic
Hydrocarbon chain - non-polar tail; hydrophobic
Rarely found in nature
Unsaturated
-
C-C double bonds
Cis rather than trans
Double bonds are isolated from one another by
several singly bonded carbons
Lower melting points ; plant oils @ room temp
are liquid
Hydrogenation
-
Conversion of oils into fats
Adding of hydrogen in the double bond to
produce a saturated counterpart
Saturated
-
Single bonds
TriAcylGlycerol (tags)
Glyerol
-
All three hydroxyl groups form ester linkages
with Fas
3 ester groups are the polar part of the
molecule
o Tails of FA are non polar
Do not occur as components of membranes
Accumulate in adipose tissue
Provide means of storing Fas
Concentrated stores of metabolic energy
Produces glycerol and Na or Ksalts of Fatty
Acids
o These salts are soaps
o When soaps are used with hard H20, Ca
and Mg ions in the H20 react with FA to
form a precipitate
Base and NaOH or KOH is used
Glycerol product
o Used in creams and lotion
PhosphoacylGlycerol
Phosphatidic acid
-
2 FA esterified to the glycerol molecule
Phosphoric acid
-
Triprotic ; can form more than one ester
linkages
Phosphatidyl ester
-
One mol of phosphoric acid can form ester
bonds both to glycerol and to some other
alcohol
Most important
a.) Phosphatidyl ethanolamine
a. cephalin
b.) Phosphatidyl serine
c.) Phosphatidyl choline
a. choline
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d.) Phosphatidyl inositol
e.) Phosphatidyl glycerol
f.) Diphosphatidyl glycerol
a. Cardiolipin
*all these compounds have lol nonpolar, hydrophobic
tails and polar, highly hydrophilic head groups
*polar head group is charged because the phosphate is
ionized at neutral pH
*important components of biological membranes
Waxes and sphingolipids
Waxes
-
Complex mixtures of esters of long-chain
carboxylic acids and long chains of OH
Protective coatings for both plants and animals
Myricyl cerotate
-
Component of carnauba wax
o Carnauba wax is for floor wax and car
wax
Spermaceti
-
Wax produced by whales
Glycolipids
-
Cerebroside
-
Do not contain glycerol
Abundant in the nervous system
Ceramides
-
Simplest cpd of sphingolipids
o One FA linked to the amino group of
sphingosine by an amide
Parent cpd of glycolipids
Sphingomyelin
-
Primary OH group of sphingosine
o Esterified to phosphoric acid , esterified
again to another amino alcholol
choline
Ceramide and a sugar residue
Gangliosside
-
Contains more than 3 sugars
Neg.@ neutral ph
Steroids
-
3 six membered rings and 1 five membered ring
- sex hormones
Cholesterol
Cholesterol
-
Single hydroxyl group ; only hydrophilic group
Highly hydrophobic
Widespread in biological membranes
Does not occur in prokaryotic membranes
Precursor of other steroids and of vitamin D3
Artherosclerosis
-
Sphingolipids
-
A carbohydrate bound to an OH group of a lipid
by a glycosidic linkage
Lipid deposits block the blood vessels and lead
to heart disease
Biological membranes
Phosphoglycerides
-
Principal lipid component of membranes
-hydrophobic interior
- control the transport of small molecules and ions
Lipid Bilayers
-
Polar head groups are in contact with water
Non-polar tails lie in the interior
Held together by noncovalent interactions
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o Van der Waals
o Hydrophobic interactions
Surface : polar & charged
The non polar hydrocarbon interior is
composed of saturated and unsaturated chains
of Fas and cholesterol
Bulkier molecules tend to occur in the outer
layer smaller in the inner
Bilayers fluidity depends on its composition
Saturated FA : leads to close packing : rigidity
Unsaturated FA: kink in the hydrocarbon chain:
cause disorder in the packing of the molecules
o More open structute : Fluidity
Presence of cholesterol enhances order and
rigidity
o Stabilizes the extended straight-chain
arrangement of saturated FA by Van
Der Waals interactions
Integral proteins
-
a-helix * b-sheet
-
Help move substances in and out of the cell
Receptor protein
-
Important in the transfer of extracellular signals
Fluid-mosaic model
-
Can act as natural cholesterol blockers
Interfering with the uptake of dietary
cholesterol
Minimize contact of the polar parts of the
peptide backbone with the nonpolar lipids in
the interior of the bilayer
Transport Protein
Plant Sterol
-
Can be removed by using detergents or
extensive sonication
Most widely accepted description of the bio
membrane
Mosaic
-
-w/ heat, ordered bilayes become less ordered
2 components exist side by side w/o forming
some other substance of the intermediate
nature
-the transitions temperature is higher for more rigid
and ordered membranes than it is for relatively fluid
and disoredered membranes
-lipids are sorted into assemblages known as rafts ,
fundamental building blocks on which membrane
specificity is based
- when phase transition takes place different amount of
power is needed to maintain the temperature of two
cells
- the proteins float in the lipid bilayer and can move
along the plane of the membrane
Functions of Membranes
- inner layer are more tightly packed
-transport ; catalysis; receptor
-cerebrosides are located in the outer layer
Passive transport
-flip-flop migration
Kinds of membrane proteins
Peripheral proteins
-
Bound to the charged head groups of the lipid
bilayer by polar interactions, electrostatic
interactions
Higher concentration to lower concentration
-movement is the same as concentration
gradient
- Does not expend energy
a.) Simple diffusion
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a. Molecule moves directly through the
membrane w/o interacting w/ another
molecule
i. O2 N2 and CO2
- Rate of movement is controlled by
concentration difference
- Large molecules cannot pass through
b.) Facilitated Diffusion
a. Uses a carrier protein
b. No energy is expended
c. Hyperbolic curve
Active Transport
a.)
Lower concentration to higher concentration
Expends energy
-presence of carrier protein with energy source
Primary
a. Movement of molecules against a
gradient is directly linked to the
hydrolysis of a high energy molecule,
such as ATP
i. NA/K pump
Na/K pump
-
1.)
2.)
3.)
4.)
5.)
6.)
Concentration of K is higher inside a cell
Concentration of Na is lower inside the cell than
out
Energy reqd to move ions agains their gradients
comes from an exergonic reaction : hydrolysis
of ATP to ADP and P1
-no transport of ions w/o hydrolysis of ATP
Protein hydrolyzes ATP
Transfers phosphate group to an aspartate side
chain on another subunit
Binding of 3 Na ions from the interior of the cell
takes place
Opening of a channel / pore through w/c the 3
Na ions can be released to the extracellular fluid
Outside the cell, 2 K ions bind to the pump
enzyme
Conformational change occurs and phosphate is
hydrolysed
7.) Regeneration of the original form of the enzyme
and allows K ions to enter the cell
8.) Pumping process transports 3 Na ions out of the
cell for every 2K ions transported into the cell
- Operation of the pump can be reversed when
there is no K
o ATP is produced by the phosphorylation
of ADP
Secondary active transport
-
Example: galactoside permease in bacteria
Harnesses energy by letting hydrogen ions flow
through the permease into the cell
Proton pumps: creates h ion gradients
How do membrane proteins work?
-
1st step : binding the substance to a protein
receptor site on the exterior cell
o Binding site must provide a good fit fot
the substrate
Receptors are often large oligomeric protein
Important types of receptors:
a.) Low density lipoproteil (LDL)
a. Principal carrier of cholesterol in the
blood stream
b. Consists of cholesterol,
phosphoglycerides & protein
- The complex formed between LDL and the
receptor is pinched off into the cell
endocytosis
- Excess of cholesterol inhibits the synthesis of
LDL receptor -> level of cholesterol in the blood
increases -> artherosclerosis
Artherosclerosis
-
Blocking of arteries
Lipid Soluble Vitamins
Vitamin A
- Unsat hydrocarbon B-carotene is its precursor
- Retinol
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-
Carrots
o Opsin derivative of Vit A
Crucial role in vision
Cone cells
Responsible for vision
in bright light and for
color vision
Rod Cells- vision in dim light
Has an OH group, oxidized to an aldehyde ,
forming retinal
Retinal and opsin = rhodopsin
Fever-reducing
Leukotriene
-
Derived from arachidonic acid
Found in leukocytes
Also called eicosinoids
Thromboxanes
-
3rd class or derivatives of arachidonic acids
Vitamin D
-
Regulation of Calcium and phosphorus
metabolism
Rickets
-
Deficiency of vit. D
Bones become soft
Vitamin E
-
Prevention of muscular dystrophy
Most active form is a-tocopherol
Antioxidant
Removes free radicals
Vitamin K
-
Important factor in blood clotting process
Prostaglandins and Leukotrienes
Prostaglandin
-
Produced by the prostate gland
Controls blood pressure
For stimulation of smooth muscle contraction
Induction of inflammation
Inhibits aggregation of platelets
Antitumor and antiviral
Aspirin
-
Inhibits synthesis of prostaglandins
Anti-inflammatory
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