Lipids ans sterols Flashcards
1
Q
What are the essential FA?
A
- Linoleic acid (C18:2 n-6)- omega 6
* Linolenic acid (C18:3 n-3)- omega 3
2
Q
Formula of linoleic aicd
A
C18:2n-6
3
Q
Are lipids soluble?
A
They are soluble in organic compounds such as acetone, ether and chloroform
4
Q
Name dietary lipidS
A
Sterols and phytosterols
triacylglycerols, make up by far the largest proportion of dietary lipids consumed by humans
5
Q
Describe TG FAs
A
generally nonbranched hydrocarbon chains with an even number of carbon atoms ranging in number from 4 to 26
6
Q
Each subsequent double bond almost invariably occurs __ carbon atoms farther along the carbon chain from the bond preceding it.
A
Each subsequent double bond almost invariably occurs three carbon atoms farther along the carbon chain from the bond preceding it.
7
Q
What is the maximum number of double bonds?
A
6
8
Q
Where will double bonds first occur in 18C FAs?
In 16 carbon FA?
A
FAs of 18 carbon atoms or greater that possess more than a single double bond will contain the first bond of their series only at the n-9, n-6, or n-3 position.
For a 16-carbon atom FA, the first double bond may be located at the n-7 position.
9
Q
Why FAs with double bonds at the n-6 and n-3 positions are considered to be essential in the diet?
A
During de novo FA formation by human biosynthetic enzymes, no double bonds are formed at any position closer to the methyl end than n-9.
10
Q
How can trans bonds be formed?
A
Through hydrogenation
through microbial metabolism in ruminants
11
Q
Most dietary trans FAs are __, __ carbons in length
A
Most dietary trans FAs are monoenes, 18 carbons in length
12
Q
What is conjugated linoelic acid
A
it contains both a cis and a trans double bond separated by only two, instead of three, carbon atoms
13
Q
What does zwitterionic mean?
A
Contains both positive and negative charge
14
Q
What are the possible polar head group of phospholipids
A
choline, serine, ethanolamine, and glycerol.
15
Q
Can sterols be founs in plants?
A
No
but phytosterols can
16
Q
What are sterols made of?
A
steroid nucleus and branched hydrocarbon tail
17
Q
How are phytosterols different ?
A
Phytosterols differ in their chemical side chain configuration and steroid ring-bonding pattern.
18
Q
What are the sources of fats in GI tract apart from the diet?
A
lipids enter the gastrointestinal tract both via release from mucosal cells and in bile and through bacterial contributions.
19
Q
What does intestinal digestion of lipids require?
A
Intestinal digestion requires bile salts (BSs) and pancreatic
lipase.
20
Q
What are the principal lipid components of bile?
A
Bile salts, pancreatic lipase and sterols
21
Q
What are primary bile salts?
A
These are bile salts synthesized directly from hepatic CH, include the trihydroxy and dihydroxy BSs
22
Q
What are secondary bile salts?
A
Secondary BSs, including deoxycholate and lithocholate,
are produced from primary BSs via bacterial conversion on cholate and chenodeoxycholate in the large intestine
23
Q
What is the function of pancreatic lipase?
A
It hydrolizes ester bonds at sn-1 and sn-3 positions
24
Q
What is the interaction between bile salts and pancreatic lipase?
A
BSs inhibit lipase activity through displacement of the enzyme from its substrate at the surface of the lipid droplet.
25
Do micelles have different proportion of digested products in them?
No, due to churning of intestine allows micelles to come in contact with each other and products of digestion, thus spreading the digestion products equally
26
Where do micelles go after the intestine
Micelles, but not lipid droplets approach and enter the water layer bordering the intestinal mucosal cells
27
What are enterocytes?
Intestinal absorptive cells
28
What helps in shuttling of digestion products FAs
Intestinal FA-binding proteins (FABPs) assist in transmucosal shunting of digestion product FAs, and possibly MGs and BSs. Elevated FABP activity in the distal bowel has been shown to be associated with higher FA
absorption
29
What is the relation between absorption efficiency and and FA chain length?
the longer the FA chain the lower the efficiency
30
Name aliphatic AA
Glycine, alanine, valine, leucine, isoleucine
31
Name aromatic AA
Phenylalanine, tyrosine, tryptophan
32
Name basic AA
Histidine
Lysine
Arginine
33
Name acidic AA
Aspartic acid
Glutamic acid
Asparagine
Glutamine
34
Define nutrigenetics
Nutrigenetics objective is to recognize in what way genetic difference affects response to nutrients
35
Define Nutrigenomics
how nutrients change the expression of genes (changes in the gene
36
Which FA is common in olive oil?
oleic (C18:1)
37
Which FA is common in safflower oil?
linoleic (C18:2)
38
Which FA is common in lard, beef tallow?
palmitic (C16:0) and stearic (C18:0)
39
Are trans fatty acids straight or bent
straight, thus they pack better
40
What are the different uses of fatty acids?
Energy source
Structural component
Covalent modifications of proteins
Substrate for the synthesis of signalling molcules
41
What are the major fatty acid species in coconut oil?
Lauric acid- 12 carbons
But also has a lot of palmitic acid which is highly active biologically that can have effect on many processes and control
42
Where are triglycerides synthesized
Triacylglycerides (triglycerides) are synthesized by virtually all cells. The major tissues for TAG synthesis are the small intestine, the liver, and adipocytes
43
Role of phospholipase A1
catalyzes the cleavage at the SN-1 position of phospholipids,
44
Role of phospholipase A2
cleave fatty acid in position two of phospholipids, hydrolyzing the bond between the second fatty acid “tail” and the glycerol molecule.
45
Role of phospholipase C
cleave phospholipids just before the phosphate group
46
Role of phospholipase d
hydrolyzes the bond between the polar head group and phosphate
47
What is the rate controlling enzyme in cholesterol synthesis?
HMG-CoA
48
Does cholesterol synthesis require energy?
Yes, a lot
49
Can cholesterol be oxidized to produce energy?
No
50
What are the different uses of cholesterol?
Substrate for the synthesis of steroid hormones and vitamin D
Substrate for synthesis of bile acids
Required to control membrane fluidity
51
Is cholesterol polar or non-polar
Hydroxyl group gives the cholesterol molecule a bit of polarity and it can interact with polar compounds
The rest of the molecule is non-polar
52
Do we know how much cholesterol we need?
No
53
Globules which transport fats are poor in __ but rich in __
Globules which transport fats are poor in cholesterol but rich in cholesterol esters
54
Describe solubility of fats and lipids
Fats and lipids are defined generally as a class of compounds soluble in organic solvents such as acetone, ether, and chloroform.
55
Name more polar lipids
phospholipids (PLs) and cardiolipins
56
Name dietary lipids
cholesterol (CH) and phytosterols
57
What is the most commonly dietary lipid consumed by humans?
triglycerides
58
Where can VLCFAs be foundÉ
Very-long-chain FAs (VLCFAs) occur in brain and specialized tissues such as retina and spermatozoa
59
Describe the characteristics of MUFAs
A monounsaturated FAs (MUFAs) must be at least 12 carbon atoms in length, typically with the double bond at the n-9
or n-7 position
60
What are the rules about the occurrence of double bonds (16C FA, 18C FA)
Each subsequent double bond almost invariably occurs three carbon atoms farther along the carbon chain
Therefore, the number of
double bonds within an FA is restricted depending on its chain length, but it will not exceed six.
FAs of 18 carbon atoms or greater that possess more than a single double bond will contain the first bond of their series only at the n-9, n-6, or n-3 position.
For a 16-carbon atom FA, the first double bond may be located at the n-7 position.
61
What does dietary essentiality of FA depends on?
The dietary essentiality of an FA depends on the position of the first double bond from the methyl terminus.
Humans cannot make FAs with double bonds any closer that at the 9th position
For this reason, FAs with double bonds at the n-6 and n-3 positions are, as individual classes, considered to be essential in the diet.
62
At what positions should FA contain their double bonds to be classified as essential?
only those of n-6 and n-3 classes are essential to the diet
63
Double bonds in dietary fats occur most commonly in the __ configuration
Double bonds in dietary fats occur most commonly in the cis configuration
64
What is the effect of having trans double bonds?
- Reduced rotation
- Decreased reactivity to electrophilic addition such
as halogenation, hydration, and hydrogenation
65
Can trans double bonds be found in FA containing more than one double bond?
Yes
An example is conjugated linoleic acid, which contains both a cis and a trans double bond separated by only two, instead of three, carbon atoms.
66
Are there a lot of dietary lipids in phospholipid form?
no, only limited quantities
67
What does zwitterionic mean?
Having both positive and negative charge
68
What are the components of sterols?
formed of a steroid nucleus and branched hydrocarbon
| tail
69
In what form can sterols be found in the diet?
both in free form and esterified
| to FAs
70
How can saturated phytosterols be formed? Name and describe them
The delta-5 hydrogenation
of beta-sitosterol, campesterol, and stigmasterol phytosterols forms saturated phytosterols, which includes campestanol and sitostanol (stanols), that are
found in very small amounts in normal diets but can be
commercially produced.
71
How can solubility and bioavailability of plant sterols and sterols be increased?
Plant sterols and stanols are often deliberately esterified to FAs such as C-18:2 n-6 and n-3
FAs to improve their solubility and bioavailability.
72
What is the main enzyme of triglyceride digestion?
pancreatic lipase
73
Where are secondary bile salts produced?
In the large intestine from primary bile salts
74
In what form is cholesterol present in bile
only in the unesterified form
75
What is the purpose of cholesterol esterification?
Esterification of cholesterol increases the efficiency of transport of both dietary and synthesized cholesterol
By converting cholesterol to cholesteryl esters more cholesterol can be packaged into the interior of lipoproteins. This vastly increases the capacity of lipoproteins, allowing for more efficient cholesterol transport through the blood stream.
76
What is the effect of incorporation of monoglycerides into the micelle?
incorporation of monoglycerides into the micelle increases the ability of the particle to solubilize free FAs and cholesterol
77
Describe the affinity properties of bile salt micelles
BS micelles generally possess the highest affinity for MGs and unsaturated long-chain FAs (LCFAs)
78
Bile acid vs cholesterol
Bile acid are made of cholesterol
79
Location of production of primary vs secondary bile acids
Primary bile acids are those synthesized by the liver. Secondary bile acids result from bacterial actions in the colon.
80
What are the sources of cholesterol
From chylomicrons
| From synthesis from Acetyl-CoA
81
What is cholesterol ester made of?
The ester bond is formed between the carboxylate group of a fatty acid and the hydroxyl group of cholesterol
82
What happens to mixed micelles made up of FAs, MGs, CH, PLs, and BSs after they are fomred
they migrate to the unstirred water layer adjacent to the surface of the enterocyte brush-border membrane.
83
When does the action of pancreatic lipase finish?
The 2-MGs and free FAs are released through the action
of pancreatic lipase until the saturation capacity of the
micelles is reached
84
Do lipid droplets and micelle enter the unstirred water layer adjacent to the surface of the enterocyte brush-border membrane?
Only micelles
85
What is the role of FABPs?
Intestinal FA-binding proteins assist in movement of FA (and possibly monoglycerides and bile salts) across a mucosal membrane
86
Which FA can be absorbed passively by gastric mucosal boundary?
FAs with chain length less than 12 carbon atoms
87
Where do absorbed FA go after being absorbed by mucosal boundary?
Portal vein
88
What happens to micellar BSs?
They are not absorbed with other fat digestion products
| They are taken up further along the gastrointestinal tract via passive absorption in the small intestine and colon
89
Are there a lot of PLs in bile?
yes
90
WHat is the role of phosphatidylcholine in bile?
it is essential in the stabilization of the micelle within the unstirred water layer
91
How are phospholipids digested?
PLs of both dietary and biliary origins are digested through cleavage by phospholipase A2, a pancreatic enzyme secreted in bile yielding lysophosphoglycerides
and free FAs. These products undergo absorption through a similar process, as described earlier.
92
phospholipase A2 vs pancreatic lipase
In contrast to pancreatic lipase, phospholipase A2 cleaves FAs at the sn-2 position of PLs, thus
yielding lysophosphoglycerides
and free FAs.
93
What are lysophosphoglycerides?
Lyso- is a prefix applied to the various phospholipids to indicate the removal of one of the two fatty acids
94
Is the digestion process of cholesterol well understood?
No
95
WHat is the rate limiting step of absorption and digestion of CH?
the major rate-limiting factor is the poor micellar solubility of CH
96
Describe digestion of CE
The digestion of dietary CE involves release of the esterified FAs through the
action of a BS-dependent CE hydrolase secreted by the
pancreas.
Free sterol then undergoes solubilization within mixed micelles in the upper small intestine
97
Is the amount of CH in circulation varied or stable? Is it controlled? if yes, then how?
Amount of CH in circulation is relatively stable
| Changes in absorption and biosynthesis help to control the amount of CH in the circulation
98
How doe absorption of plant sterols compare to absorption of cholesterol
it is much lower
99
Are all phytosterol types absorbed at the same proportion? What is the consqunce of that
Some types are absorbed better than other which is proportional to their amounts in circulation
100
Can bile acids be made out of CE?
No, from cholesterol only
101
Name essential AA
* Isoleucine
* Leucine
* Lysine
* Methionine
* Phenylalanine
* Threonine
* Tryptophan
* Valine
* Histidine
* Arginine (in children and special cases)
102
Why are some FA essential?
* Humans CANNOT themselves make FA with double bonds between carbons located at position 8 or less (counting from the methyl end).
* These FA are essential for normal function, and must be obtained from the diet.
103
Name essential water soluble vitamins
Vitamin B1 (thiamine), Vitamin B2 (riboflavin), Vitamin B3 (niacin), Vitamin B5 (pantothenic acid), Vitamin B6 (pyridoxine), Vitamin B7 (biotin), Vitamin B9 (folic acid), Vitamin B12 (cobalamin), Vitamin C (ascorbic acid), Choline
104
Name essential fat soluble vitamins
Vitamin A (retinol), Vitamin D (ergocalciferol, cholecalciferol), Vitamin E (tocopherol), Vitamin K (naphthoquinoids)
105
What are the functions of choline?
1. Substrate for phosphatidylcholine biosynthesis
o Without choline we cannot make phosphatidylcholine and therefore we cannot make membranes
2. Ensures the structural integrity and signaling functions of cell membranes
3. Source of methyl groups
4. Used to make a variety of very important metabolites (e.g., acetylcholine, platelet-activating factor, betaine)
106
What are the ways of making choline?
• Three successive methylation of the phosphatidylethanolamine head group generates phosphatidylcholine
o Choline can be released from phosphatidylcholine.
107
B1 name`
thiamine
108
B2
riboflavin
109
B3
niacin
110
B5
pantothenic acid
111
B6
pyridoxine
112
B7
biotin
113
B9
foilc acid
114
B12
cobalamin
