Flashcards in sakai-Lipids Deck (21):
Describe the structure of palmitate and stearate. Why are free fatty acids
amphipatic and how are free fatty acids transported in blood? Which fatty acid
has a higher melting point: palmitic acid or stearic acid? Explain the concept!
Palmitic acid has 16 carbons and is a saturated fatty acid. Stearic acid is also a saturated fatty acid but has 18 carbons.
Fatty acids are amphipathic as they have a negatively charged hydrophilic carboxyl group and at the same time a long hydrophobic hydrocarbon chain.
Free fatty acids are transported in blood complexed to albumin.
Stearic acid is 18:0 and has a higher melting point than palmitic acid which is 16:0.
Concept: the melting point increases with increasing chain length and neither of the two fatty acids has a double bond.
Which fatty acid has the lowest melting point out of the group of oleic acid (18:1), linoleic acid (18:2) and -linolenic acid (18:3)? Explain the concept!
The lowest melting point is found for -linolenic acid.
All shown fatty acids have 18 carbons and -linolenic aid has most double bonds.
Concept: the melting point decreases with increasing double bonds.
Arachidonic acid (20:4, 6) contains four double bonds. Are all in the cis-configuration? where are they located (counting from the methyl end) and how are they separated from each other?
Double bonds in human fatty acids, including all four found in arachidonic acid, are in the cis-configuration.
Arachidonic acid is of the 6 family, so the first double bond that is found counting from the methyl group is found is position six.
The double bonds are spaced by three carbons intervals from each other.
Palmitoleic acid and oleic acid contain a double bond. Why are these fatty acids not grouped as dietary essential fatty acids? Explain!
Humans (animals) can introduce a fatty acid double bond between carbons 9 and 10, forming 9. The carbon of the carboxyl group is according to organic chemistry carbon #1.
Palmitoleic acid (16:1) can be formed from palmitic acid (16:0) and oleic acid (18:1) can be formed from stearic acid (18:0).
Both unsaturated fatty acids contain their double bond in 9 which can be formed in humans and with that palmitoleic acid and oleic acid are not dietary essential.
Name the two dietary essential fatty acids and describe the respective structures related to carbon number, amount of double bonds and -family. Which important fatty acid in humans is formed from linoleic acid or -linolenic acid, respectively?
The two dietary essential fatty acids are linoleic acid (18:2, 6) and -linolenic
acid (18:3, 3)
Linoleic acid is used to form arachidonic acid (20:4,6) in humans.
-linolenic acid is used to form eventually DHA (22:6,3) in humans.
Why do you find -3 fatty acids like EPA (20:5) in high concentration in cold water fish?
Lower plants form -3 fatty acids and these algae are food for fish. Cold water fish need more fluidity in their cell membranes at low temperatures.
Describe the structure of trans fatty acids!
Trans fatty acids contain double bonds in trans instead of cis configuration. They resemble in their structure saturated fatty acids.
Are triacylglycerols (TAGs) polar compounds? Are they amphipathic like fatty acids? Describe TAGs. Which fatty acid composition is found in oil?
Triacylglycerols are nonpolar compounds and they are not amphipathic. TAGs
contain a glycerol backbone with three esterified fatty acids and TAGs are totally
unpolar to the outside.
TAGs in oil contain mainly unsaturated and polyunsaturated fatty acids.
Explain the name phosphatidylcholine (PC)! Explain the abbreviation PE, PS, and PI! Which phospholipids have an overall negative charge?
Phosphatidylcholine gets its name from the fact that its structure contains phosphatidic acid bound to choline.
Phosphatidic acid contains a glycerol backbone with two esterified fatty acids and a phosphate group.
PE is phosphatidylethanolamine, PS is phosphatidylserine and PI is phosphatidylinositol. All of them are glycerophospholipids.
PS and PI contain an overall negative charge. [PC and PE are overall not charged, their neg. and pos. charges equal each other out.]
The demand for PC is high in the liver, how can PC be formed?
PC can be synthesized using choline, but it can also be formed from PE. In this case, PE is three times methylated using SAM (activated methionine).
What are plasmalogens and where are they mainly found?
Plasmalogens are ether analogues of PC or PE. Instead of an ester bond in position-1 of glycerol, they contain an alcohol linked with an ether (vinyl ether) bond. Instead of phosphatidyl- they are sometimes named phosphatidal-
PC related plasmalogens are found mainly in the heart, and plasmalogens related to PE are mainly found in nerve tissue.
What is the structure of the main lipid found in lung surfactant? Describe in detail the fatty acids that are esterified in position 1 and 2 of the glycerol backbone.
The lipid component of lung surfactant consists mainly of phosphatidylcholine,
most of it is disaturated dipalmitoylcholine DPPC with some monosaturated PC.
The normal fatty acid composition in glycerophospholipids, including “normal” PC shows only one saturated fatty acid in position-1 of the glycerol backbone (monosaturated), and an unsaturated fatty acid in position-2.
Specific for lung surfactant, normal PC is especially modified to DPPC, so that it contains two esterified palmitic acids, which are two saturated fatty acids of 16 carbon length.
Remember, that the fluidity of a phospholipid membrane can be regulated by the fatty acid composition. The change in lung surfactant to dipalmitoyl-PC (DPPC) makes the phospholipid “stiff”, and lung surfactant is not part of a phospholipid membrane and is instead released into the extracellular space.
Describe the location and action of lung surfactant. Which transporter type is involved with the release of lung surfactant?
Lung surfactant lines the alveoli of the lungs and prevents collapse during exhalation. It is synthesized in Type II alveolar cells and it is released into the alveoli using an ABC transporter.
What is the complete name for the abbreviation RDS? Is RDS only encountered in premature infants or can it be seen in adults? Explain!
RDS stands for Respiratory Distress Syndrome.
RDS is commonly found in premature infants but can also be seen in adults.
In premature infants, the synthesis of lung surfactant is not performed in sufficient quantity and often the lungs are not functioning adequately. The ratio of phosphatidylcholine to sphingomyelin >2 is an indicator of lung maturity.
RDS in infants and adults can also be due to deficient synthesis of dipalmitoyl-PC, or a defect in the ABC-transporter or also due to damaged Type II alveolar cells.
Describe the general structure and function of cardiolipin in humans! Is cardiolipin found only in the heart?
Cardiolipin contains four fatty acids, it is like a structure of two phosphatidic
acids linked via glycerol and cardiolipin is also known as diphosphatidylglycerol.
Cardiolipin is found in the inner mitochondrial membrane and is structurally
needed for the ETC and oxidative phosphorylation.
Cardiolipin was first analyzed in the heart, (cardio lipid) which has many
mitochondria. Later on it was shown to be in all cells as part of the inner
What are sphingolipids? Does the group of sphingolipids contain mainly phospholipids or are they mainly glycolipids?
Sphingolipids contain sphingosine instead of a glycerol backbone which leads to the name sphingolipids.
Sphingosine with a fatty acid (N-acyl sphingosine) is named ceramide.
The group of sphingolipids contains in humans one major sphingo-phospholipid and many different sphingo-glycolipids.
Name the major sphingophospholipid and describe the polar head group that is linked to ceramide! Which glycerophospholipid has a similar polar head group?
The major sphingophospholipid in humans is sphingomyelin. Its polar head group is phosphorylcholine linked to ceramide.
This polar head group is also found in phosphatidylcholine.
What are cerebrosides and gangliosides, and where in the human body are they mainly found?
Cerebrosides and gangliosides are glycosphingolipids, they are polar lipids but instead of phosphate, they contain sugar.
Cerebrosides are ceramide plus one sugar. Globosides are ceramide with more sugars and when NANA is linked, gangliosides are formed.
They are mainly found in the brain and the peripheral nervous system.
Describe the structure of cholesterol related to total carbon number, position of the hydroxyl group and letters of the sterol rings. Does cholesterol contain a double bond? Which molecule is amphipathic, cholesterol or cholesteryl ester?
Cholesterol contains 27 carbons, a hydroxyl group in position 3 and contains sterol rings A, B, C and D.
Cholesterol contains a double bond in sterol ring B. Cholesterol is amphipathic due to its hydroxyl group. Cholesteryl esters are esterified with a fatty acid and are totally nonpolar.
What is the biomedical importance of cholesterol?
Cholesterol is needed for the regulation of the membrane fluidity, mainly of the plasma membrane.
Cholesterol is the precursor for bile acid synthesis in the liver.[this synthesis takes place only in the liver]
In respective cells, like adrenal cortex or ovaries and testes, cholesterol is the precursor for steroid hormone synthesis.[note, the de-novo synthesis of steroid hormones does not take place in the liver. The liver can, however, modify already synthesized steroid hormones]
A precursor of cholesterol can be used for formation of vitamin D, but this needs UV light.