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الكيمـياء الحـيوية العامة Bioc211- Bioc101

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قديم 04-15-2007, 05:00 PM   #1
noartno
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افتراضي Cholesterol part 1

Cholesterol
[line]
Usually people when they start talking about cholesterol, the first thing that comes to their mind is the bad part of cholesterol, but let us talk about the good part of cholesterol

[line]
Cholesterol:

-contains 27 carbons

-it is white substance

-part of biological membranes, so it is very important constituent of all our cells
.
can be utilized or used by adernal cortex or gonads (tests or ovaries) to make steroids hormones such as corticosteroids
hormones, progestogen... etc

also can be used to make bile acids, Vitamen D (Whic is a fat soluble vitamen)

scientist found that its very important to for the process of learning and memory to have an adequate cholesterol in our food , specifically in the child hood.

[frame="1 80"]so memory and learning are directly related to the use of cholesterol[/frame]
[line]

The above diagram shows dite that can contain fats including cholesterol, which can be absorbed through the intestinal epithelium, of course cholesterol is not absorbed in the form of free cholesterol, it usually rather involved in metabolism of lipoproteins, and the major one here is chylomicrone which is formed in the intestine.

Chylomicrones are particles that contain largely triacyglycerols plus phospholipids and some cholesterol, so cholesterol is not the only lipid that found there, but when TAGs are hydrolyzed by lipoprotein lipase which is found in the capillaries, the remnant portion of chylomicrone is going to have high levels of cholesterol.

Lipprotein lipase, is very important enzyme and you have to remeber two things about this enzyme:
1- it is found in capillaries.
2- it is activated only by insulin action, so without insulin action the enzyme will be inactive

[frame="1 80"]People usually eat lipids with carbohydrates, this increase insulin secretion and lipoproteins lipase is activated, and the chylomicrone is hydrolyzed, leaving chylomicrone remnant which is utilized by many tissues, in a major way by receptors that expressed very will on the membranes of hepatocytes[/frame]

[line]
also from the diagram you can reveal that exogenous cholesterol that was found in the dite, will be apart of hepatic pool of cholesterol, these particles of cholesterol will inhibit the cholesterol biosyhtesis in the liver (cholesterol biosythesis accounts for 60 % of cholesterol found in the body)

[frame="1 80"] So the majority of cholesterol (total cholesterol) found in the body belongs to the endogenous cholesterol rather than the exogenous one[/frame]

[line]
Notes:
In the gut, exogenous cholesterol is digested
why we said digested???
because cholesterol usually is not eaten freely (you are not going to supermarket and get 1 kilo of cholesterol) rather than its eaten with together with fatty acids.
[line]
When cholesterol is attached to fatty acids, we call it cholesterol ester, and for this we have cholesterol esterase that cut the linkeage between the cholesterol and fatty acid, leading to free cholesterol that absorbed easily.
[line]
Cholesterol can diffuse through membranes easily because
* it is part of membranes.
* lipophilic (hydrophobic).
[line]
However cholesterol ester of lipoproteins (which containes cholesterol) can not cross the membranes smoothly because these particles are large.
[line]
Cholesterol in that is found in the liver, utilized to make bile acids which are used to digest lipids especially triacylglycerols rather than cholesterol.
[line]
[line]



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قديم 05-04-2007, 01:21 AM   #4
Buffer System
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Reference please ,,,



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قديم 05-17-2007, 05:48 AM   #5
DNA
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قديم 11-05-2007, 01:21 AM   #6
Medicine student
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افتراضي

thank you for this beneficial subject
biggrin:i have a question ...........if i may
is the cholesterol synthesized in all body cells without any exeption




   
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قديم 03-03-2008, 07:00 PM   #7
biochemist girl
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افتراضي رد: Cholesterol part 1

i can answer that question
yes , cholestrol is synthesized by viturally all tissue in humans,but mainly in liver,intestine and adrenal cortix

i hope that is clear to u


by the way, thanx 4 naortno



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قديم 03-21-2008, 04:20 PM   #8
mr.biochemistry
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افتراضي رد: Cholesterol part 1

great topic
thank u for sharing



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