1. Chapter 12
LIPIDS
nysha
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2. What are lipids?
Lipids are a family of substances that are insoluble in
water but soluble in nonpolar solvents of low polarity.
Functions:
- to store energy within fat cells
- as part of membranes to separate
compartments of aqueous solutions
- to serve as chemical messengers
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3. Classification of Lipids by Structure
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4. Structure of Triglycerides
Animal fats and vegetable oils are
triglycerides. Triglycerides are tri-esters of
glycerol and long-chain carboxylic acids called
fatty acids.
The alcohol triglycerides is always glycerol.
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5. The acid component of fats may be any number of acid
which have certain things in common:
1. Fatty acids are practically all unbranched carboxylic
acids
2. They range in size from about 10 – 20 carbons.
3. They contain even number of carbon atoms.
4. They have no functional groups except that some do
have double bonds.
5. In most fatty acids that have double bonds, the cis
isomers predominate.
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6. Fatty acids can be divided into two groups:
saturated and unsaturated.
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7. Saturated Fat
→ Have single bonds in the hydrocarbon chain.
→ Solid at room temperature because their
aliphatic chain allows molecules to be packed in
a parallel alignment.
→ Interactions between neighboring chain are
weak.
Unsaturated Fat
→ Have at least one C=C in the chain
→ Liquid at room temperature because the cis
double bonds interrupt the packing of chains
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8. Lipids: Membranes
Complex lipids form the membranes around
body cells and around small structures
inside the cells.
Cell membranes separates cells from the
external environment and provide selective
transport for nutrients and waste products
into and out of the cells.
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9. - Membranes are made up of lipid bilayers
where 2 rows of complex lipid molecules
are arranged tail to tail
→ Hydrophilic: Projects to the inner and
outer layer of the membrane
→ Hydrophobic: Tail points toward each
other
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10. - The unsaturated fatty acids prevent the tight
packing of the hydrophobic chains in he
lipid bilayer, thereby providing a liquid-like
character to the membrane.
-The lipid part serves as barrier against any
movement of ions or polar compounds into
and out of the cells.
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11. In the lipid bilayer, protein molecules are
either suspended on the surface
(peripheral proteins) or partly or fully
embedded in the bilayer (integral proteins).
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12. Glycerophospholipids
- Also called “Phosphoglycerides” and is
very similar to that of fats.
- Two of three – OH groups are esterified by
fatty acids. The third is esterified by a
phosphate gruop, which is also esterified to
another alcohol.
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13. - If the other alcohol is choline, a
quaternary ammonium compound, the
glycerophospholipids are called
phosphatidycholines (common name:
Lecithin)
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14. Another example of glycerophospholipid is
cephalins. Instead od choline, they contain
other alcohol such as serine or
ethanolamine.
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15. - One important group of glycerophospholipids
is Phosphatidylinositols (PI). In PI, the
alcohol inositol is linked to the rest of the
molecule by phosphate ester linkage.
- This compound
serves as signaling
molecules in
chemical
communication.
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16. Note:
Glycerophospholipids are amphipathic —
glycerol and phosphate form the polar end
of the molecule, while hydrocarbon chains
form the nonpolar end.
They are insoluble in water, but their
unique geometry causes them to aggregate
into bilayers without any energy input.
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17. Steroids
Steroid is the 3rd major class of lipid and
contains this ring system:
They are not necessarily
esters (although some are).
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18. Cholesterol:
- The most abundant and imortant steroid in the
body.
- Serves as a plasma membrane component in all
animal cells.
- Serves as raw material for the synthesis of other
steroid.
- Exist both in the free form and esterified with fatty
acids.
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19. - The cholesterol in our body is in a dynamic
state which constantly circulates in the
blood.
- Being hydrophobic, it needs a water-soluble
carrier to circulate in the aqueous medium
of the blood.
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20. LIPOPROTEINS – Carrier of Cholesterol
- Cholesterol, along with fat, is transported by
lipoproteins. Most of them contain a core of
hydrophobic lipid molecules surrounded by a
shell of hydrophilic molecules.
Four kinds of lipoproteins
1. High-density lipoprotein
2. Low-density lipoprotein
3. Very-low-density lipoprotein
4. Chylomicrons
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21. Transport of Cholesterol in LDL
Step 1: Transport of cholesterol begins when the
liver secretes a VDL particle.
Step 2 : When a VLDL particle reaches the capillary
of muscle or adipose tissue, its triglyceride is
extracted leaving a Intermediate Density
Lipoprotien (IDL).
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22. Step 3: Half of the IDL particles are removed
from circulation by the liver within two
to six hours of their formation.
Step 4: The remaining IDL transform into
LDL which circulate fo approximately two
and a half days before binding to LDL
receptors in the liver and other tissues.
** The LDL carries cholesterol to
the cells, where specific LDL-
receptor molecules line the cell
surface in certain concentrated
areas called coated pits.
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23. Transport of Cholesterol in LDL
Step 1: HDL transports cholesterol from peripheral
tissues to the liver and transfers cholesterol
to LDL.
Step 2: While in the serum, the free cholesterols in
HDL are converted to cholesteryl esters.
Step 3: The esterified cholesterols
are delivered to the liver
for synthesis of bile acids
and steroid hormones.
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24. Step 4: In a selective lipid uptake, the HDL
binds to the liver cell surface and
transfers its cholesteryl ester to the cell.
Step 4: After, the HDL, depleted
from its lipid content, re-
enters the circulation
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25. Levels of LDL and HDL
LDL Cholesterol
LDL cholesterol can build up on the walls of
your arteries and increase your chances of
getting heart disease. That is why LDL
cholesterol is referred to as "bad"
cholesterol. The lower your LDL cholesterol
number, the lower your risk.
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26. HDL Cholesterol
When it comes to HDL cholesterol -- "good"
cholesterol -- the higher the number, the
lower your risk. This is because HDL
cholesterol protects against heart disease
by taking the "bad" cholesterol out of your
blood and keeping it from building up in
your arteries. The table below explains
what the numbers mean.
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27. Steroid Hormones
A. Adrenocorticoid Hormones
- Products of of the adrenal glands.
Two gruops:
→ Mineralocorticoids (regulate the
concentration of ions)
Aldosterone is one of the most important
mineralcorticoids. Increase secretion of
this enhances the reabsorption of sodium
and chlorine ions in the kidney tubules.
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28. → Glucocorticoids (control carbohydrate
metabolism).
Cortisol is the major glucocorticoid. Its function is
to increase glucose and glycogen concentration
in the body. Also, with its ketone derivative
(cortisone), it have a remarkable inflammatory
effects in the body.
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29. Sex Hormones
Testosterone
Promotes the normal growth of the male
genital organs.
Synthesized in the testes from cholesterol.
Leads to secondary male sexual
characteristics as deep voice and facial and
body hair.
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30. Estradiol
Female sex hormone synthesized from
testosterone by aromatization of the A ring.
Regulates the cyclic changes occuring in the
uterus and ovaries.
Together with progesterone, it promotes
further preparation of the uterine lining to
receive the fertilized ovum.
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31. Progesterone
Stimulates and regulates various functions.
Plays a role in maintaining pregnancy.
The hormone is produced in the ovaries, the
placenta (when a woman gets pregnant) and
the adrenal glands.
Cause the endometrium to secrete special
proteins during the second half of the
menstrual cycle
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