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Nutr 307 > Lipids ans sterols > Flashcards

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

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2
Q

Formula of linoleic aicd

A

C18:2n-6

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3
Q

Are lipids soluble?

A

They are soluble in organic compounds such as acetone, ether and chloroform

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4
Q

Name dietary lipidS

A

Sterols and phytosterols

triacylglycerols, make up by far the largest proportion of dietary lipids consumed by humans

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5
Q

Describe TG FAs

A

generally nonbranched hydrocarbon chains with an even number of carbon atoms ranging in number from 4 to 26

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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.

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7
Q

What is the maximum number of double bonds?

A

6

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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.

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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.

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10
Q

How can trans bonds be formed?

A

Through hydrogenation

through microbial metabolism in ruminants

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11
Q

Most dietary trans FAs are __, __ carbons in length

A

Most dietary trans FAs are monoenes, 18 carbons in length

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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

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13
Q

What does zwitterionic mean?

A

Contains both positive and negative charge

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14
Q

What are the possible polar head group of phospholipids

A

choline, serine, ethanolamine, and glycerol.

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15
Q

Can sterols be founs in plants?

A

No

but phytosterols can

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16
Q

What are sterols made of?

A

steroid nucleus and branched hydrocarbon tail

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17
Q

How are phytosterols different ?

A

Phytosterols differ in their chemical side chain configuration and steroid ring-bonding pattern.

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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.

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19
Q

What does intestinal digestion of lipids require?

A

Intestinal digestion requires bile salts (BSs) and pancreatic
lipase.

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20
Q

What are the principal lipid components of bile?

A

Bile salts, pancreatic lipase and sterols

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21
Q

What are primary bile salts?

A

These are bile salts synthesized directly from hepatic CH, include the trihydroxy and dihydroxy BSs

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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

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23
Q

What is the function of pancreatic lipase?

A

It hydrolizes ester bonds at sn-1 and sn-3 positions

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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.

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25
Q

Do micelles have different proportion of digested products in them?

A

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

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26
Q

Where do micelles go after the intestine

A

Micelles, but not lipid droplets approach and enter the water layer bordering the intestinal mucosal cells

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27
Q

What are enterocytes?

A

Intestinal absorptive cells

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28
Q

What helps in shuttling of digestion products FAs

A

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

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29
Q

What is the relation between absorption efficiency and and FA chain length?

A

the longer the FA chain the lower the efficiency

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30
Q

Name aliphatic AA

A

Glycine, alanine, valine, leucine, isoleucine

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31
Q

Name aromatic AA

A

Phenylalanine, tyrosine, tryptophan

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32
Q

Name basic AA

A

Histidine
Lysine
Arginine

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33
Q

Name acidic AA

A

Aspartic acid
Glutamic acid
Asparagine
Glutamine

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34
Q

Define nutrigenetics

A

Nutrigenetics objective is to recognize in what way genetic difference affects response to nutrients

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35
Q

Define Nutrigenomics

A

how nutrients change the expression of genes (changes in the gene

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36
Q

Which FA is common in olive oil?

A

oleic (C18:1)

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37
Q

Which FA is common in safflower oil?

A

linoleic (C18:2)

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38
Q

Which FA is common in lard, beef tallow?

A

palmitic (C16:0) and stearic (C18:0)

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39
Q

Are trans fatty acids straight or bent

A

straight, thus they pack better

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40
Q

What are the different uses of fatty acids?

A

Energy source
Structural component
Covalent modifications of proteins
Substrate for the synthesis of signalling molcules

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41
Q

What are the major fatty acid species in coconut oil?

A

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

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42
Q

Where are triglycerides synthesized

A

Triacylglycerides (triglycerides) are synthesized by virtually all cells. The major tissues for TAG synthesis are the small intestine, the liver, and adipocytes

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43
Q

Role of phospholipase A1

A

catalyzes the cleavage at the SN-1 position of phospholipids,

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44
Q

Role of phospholipase A2

A

cleave fatty acid in position two of phospholipids, hydrolyzing the bond between the second fatty acid “tail” and the glycerol molecule.

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45
Q

Role of phospholipase C

A

cleave phospholipids just before the phosphate group

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46
Q

Role of phospholipase d

A

hydrolyzes the bond between the polar head group and phosphate

47
Q

What is the rate controlling enzyme in cholesterol synthesis?

A

HMG-CoA

48
Q

Does cholesterol synthesis require energy?

A

Yes, a lot

49
Q

Can cholesterol be oxidized to produce energy?

A

No

50
Q

What are the different uses of cholesterol?

A

Substrate for the synthesis of steroid hormones and vitamin D
Substrate for synthesis of bile acids
Required to control membrane fluidity

51
Q

Is cholesterol polar or non-polar

A

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
Q

Do we know how much cholesterol we need?

A

No

53
Q

Globules which transport fats are poor in __ but rich in __

A

Globules which transport fats are poor in cholesterol but rich in cholesterol esters

54
Q

Describe solubility of fats and lipids

A

Fats and lipids are defined generally as a class of compounds soluble in organic solvents such as acetone, ether, and chloroform.

55
Q

Name more polar lipids

A

phospholipids (PLs) and cardiolipins

56
Q

Name dietary lipids

A

cholesterol (CH) and phytosterols

57
Q

What is the most commonly dietary lipid consumed by humans?

A

triglycerides

58
Q

Where can VLCFAs be foundÉ

A

Very-long-chain FAs (VLCFAs) occur in brain and specialized tissues such as retina and spermatozoa

59
Q

Describe the characteristics of MUFAs

A

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
Q

What are the rules about the occurrence of double bonds (16C FA, 18C FA)

A

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
Q

What does dietary essentiality of FA depends on?

A

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
Q

At what positions should FA contain their double bonds to be classified as essential?

A

only those of n-6 and n-3 classes are essential to the diet

63
Q

Double bonds in dietary fats occur most commonly in the __ configuration

A

Double bonds in dietary fats occur most commonly in the cis configuration

64
Q

What is the effect of having trans double bonds?

A
  • Reduced rotation
  • Decreased reactivity to electrophilic addition such
    as halogenation, hydration, and hydrogenation
65
Q

Can trans double bonds be found in FA containing more than one double bond?

A

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
Q

Are there a lot of dietary lipids in phospholipid form?

A

no, only limited quantities

67
Q

What does zwitterionic mean?

A

Having both positive and negative charge

68
Q

What are the components of sterols?

A

formed of a steroid nucleus and branched hydrocarbon

tail

69
Q

In what form can sterols be found in the diet?

A

both in free form and esterified

to FAs

70
Q

How can saturated phytosterols be formed? Name and describe them

A

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
Q

How can solubility and bioavailability of plant sterols and sterols be increased?

A

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
Q

What is the main enzyme of triglyceride digestion?

A

pancreatic lipase

73
Q

Where are secondary bile salts produced?

A

In the large intestine from primary bile salts

74
Q

In what form is cholesterol present in bile

A

only in the unesterified form

75
Q

What is the purpose of cholesterol esterification?

A

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
Q

What is the effect of incorporation of monoglycerides into the micelle?

A

incorporation of monoglycerides into the micelle increases the ability of the particle to solubilize free FAs and cholesterol

77
Q

Describe the affinity properties of bile salt micelles

A

BS micelles generally possess the highest affinity for MGs and unsaturated long-chain FAs (LCFAs)

78
Q

Bile acid vs cholesterol

A

Bile acid are made of cholesterol

79
Q

Location of production of primary vs secondary bile acids

A

Primary bile acids are those synthesized by the liver. Secondary bile acids result from bacterial actions in the colon.

80
Q

What are the sources of cholesterol

A

From chylomicrons

From synthesis from Acetyl-CoA

81
Q

What is cholesterol ester made of?

A

The ester bond is formed between the carboxylate group of a fatty acid and the hydroxyl group of cholesterol

82
Q

What happens to mixed micelles made up of FAs, MGs, CH, PLs, and BSs after they are fomred

A

they migrate to the unstirred water layer adjacent to the surface of the enterocyte brush-border membrane.

83
Q

When does the action of pancreatic lipase finish?

A

The 2-MGs and free FAs are released through the action
of pancreatic lipase until the saturation capacity of the
micelles is reached

84
Q

Do lipid droplets and micelle enter the unstirred water layer adjacent to the surface of the enterocyte brush-border membrane?

A

Only micelles

85
Q

What is the role of FABPs?

A

Intestinal FA-binding proteins assist in movement of FA (and possibly monoglycerides and bile salts) across a mucosal membrane

86
Q

Which FA can be absorbed passively by gastric mucosal boundary?

A

FAs with chain length less than 12 carbon atoms

87
Q

Where do absorbed FA go after being absorbed by mucosal boundary?

A

Portal vein

88
Q

What happens to micellar BSs?

A

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
Q

Are there a lot of PLs in bile?

A

yes

90
Q

WHat is the role of phosphatidylcholine in bile?

A

it is essential in the stabilization of the micelle within the unstirred water layer

91
Q

How are phospholipids digested?

A

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
Q

phospholipase A2 vs pancreatic lipase

A

In contrast to pancreatic lipase, phospholipase A2 cleaves FAs at the sn-2 position of PLs, thus
yielding lysophosphoglycerides
and free FAs.

93
Q

What are lysophosphoglycerides?

A

Lyso- is a prefix applied to the various phospholipids to indicate the removal of one of the two fatty acids

94
Q

Is the digestion process of cholesterol well understood?

A

No

95
Q

WHat is the rate limiting step of absorption and digestion of CH?

A

the major rate-limiting factor is the poor micellar solubility of CH

96
Q

Describe digestion of CE

A

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
Q

Is the amount of CH in circulation varied or stable? Is it controlled? if yes, then how?

A

Amount of CH in circulation is relatively stable

Changes in absorption and biosynthesis help to control the amount of CH in the circulation

98
Q

How doe absorption of plant sterols compare to absorption of cholesterol

A

it is much lower

99
Q

Are all phytosterol types absorbed at the same proportion? What is the consqunce of that

A

Some types are absorbed better than other which is proportional to their amounts in circulation

100
Q

Can bile acids be made out of CE?

A

No, from cholesterol only

101
Q

Name essential AA

A
  • Isoleucine
  • Leucine

  • Lysine
  • Methionine

  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine

  • Histidine

  • Arginine (in children and special cases)
102
Q

Why are some FA essential?

A
  • 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
Q

Name essential water soluble vitamins

A

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
Q

Name essential fat soluble vitamins

A

Vitamin A (retinol), Vitamin D (ergocalciferol, cholecalciferol), Vitamin E (tocopherol), Vitamin K (naphthoquinoids)

105
Q

What are the functions of choline?

A
  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
Q

What are the ways of making choline?

A

• Three successive methylation of the phosphatidylethanolamine head group generates phosphatidylcholine
o Choline can be released from phosphatidylcholine.

107
Q

B1 name`

A

thiamine

108
Q

B2

A

riboflavin

109
Q

B3

A

niacin

110
Q

B5

A

pantothenic acid

111
Q

B6

A

pyridoxine

112
Q

B7

A

biotin

113
Q

B9

A

foilc acid

114
Q

B12

A

cobalamin

Nutr 307 (8 decks)

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