LIPIDS

Question 1

What is the different forms of lipids and their main character?

Answer 1

Fats, oils, phospholipids, steroids, & carotenoids, Characterized by not being soluble in polar substances “hydrophobic”

Question 2

What is the function of lipids?

Answer 2

Substances from living things that dissolve in non polar solvents they Store energy, important component of cell membrane, plays role in chemical signaling, vitamins, pigments

Question 3

What are the classes of lipids?

Answer 3

1) fatty acids

2) triglycerols

3) wax esters

4) Phospholipids

5) sphingolipids

6) isoprenoids (cholesterol)

7) lipoproteins

Question 4

What is the structure of fatty acids?

Answer 4

• Most naturally occurring fatty acid have an even number of carbons in an unbranded chain
• A mono-carboxylic acid containing hydrocarbon chains of variable lengths 12-20 or more but usually even number of carbons
• The terminal methyl group is named omega

Question 5

What is the most abundant fatty acid in nature?

Answer 5

16-carbon fatty acid palmitate

Question 6

What are the types of fatty acids?

Answer 6

1) saturated fatty acids (only single bonds)

2) unsaturated fatty acids (contains one or more double bonds ”mono-unsaturated & poly-unsaturated”) there is two conformation of double bonds cis- & trans- cis is more common in nature

Question 7

Example of fatty acids common names!

Answer 7

1) omega-3 fatty acid: a-linolenic acid

Question 8

Why is the cis conformation important?

Answer 8

Because it introduces a kink giving space between two phospholipids giving them the flexibility to move, while trans is a bad fatty acid as it behaves as a saturated fatty acid

Question 9

What is meant by nonessential fatty acids?

Answer 9

They are the fatty acid that can be synthesized by the body

Question 10

What is acylated proteins?

Answer 10

Fatty acids that are attached to proteins (palmitoylation (palmate added to protein))

Question 11

What is eicosanoids?

Answer 11

Group of fatty acids that are composed of 20 carbons (eicosa means 20), they are biologically important, plays a physiological role in inflammation, vasoconstriction, pain, fever control (they are like hormones but they are not steroids having short life, synthesized by specific cells that either acts as an autocrine or paracrine) their precursor is arachnoid acid

Question 12

What are the types of eicosanoids?

Answer 12

1) prostaglandins

2) throboxanes

3) leukotrienes

Question 13

How does eicosanoids act as pain reliever?

Answer 13

Drugs like aspirin, ibuprofen, voltaren, by inhibiting the enzyme which converts arachidonic acid to prostaglandin (which is associated with pain, fever)

Question 14

What is thromboxane?

Answer 14

They have a cyclic ether which are synthesize by polymorphonuclear lymphocytes, involved in platelet aggregation and vasoconstriction

Question 15

What is leukotrienes?

Answer 15

In WBC contains a triene group in their structure they function in edema, bronchodialation, & respiratory control

Question 16

What is Triacylglycerols?

Answer 16

It is the storage form of fatty acids, they are esters of glycerols with three fatty acids with different lengths and some can be saturated and others not, they are neutral having no charge they are synthesized by the reaction of glycerol with three fatty acids forming ester bonds we can have mono/di/ & tri-acylglycerol this eliminates the polarity of the fatty acids making it totally non-polar depending on the composition of the fatty acid they can be termed oil (liquid at room temperature containing high concentration of unsaturated fatty acids) or fats (solid at room temperature containing a high concentration of saturated fatty acids”)

Question 17

What is the importance of triglycerols?

Answer 17

• Totally hydrophobic conserving space, and it is more reduced so when breaking it don it will release high amount of energy
• Insulates at low temperatures
• Water repellent found in some animals feathers and fur

Question 18

What is wax esters?

Answer 18

Especially in the ear, they are mixtures of nonpolar lipids, synthesized by the reaction of a long chain fatty acid and a long chain alcohol forming an ester (like carnuba and beeswax)

Question 19

What is phospholipids?

Answer 19

They contain a phosphate group, they are amphipathic with a polar head and a nonpolar tail, rearranging into an ordered structure when suspended in water, they act in membrane formation, emulsification and as a surfactant

Question 20

How many groups of phospholipids are there?

Answer 20

Two groups:

1) phosphoglycerides (same structure as triglycerides but instead of a fatty acid in carbon 3 they will have a phosphate attached to a X group based on X we will have different compounds, it is the most numerous phospholipid found in cell membrane, 16-20 carbons
- phophatidic acid (glycerol-3-phosphate Esterification with two fatty acids) is the simplest phosphoglyceride molecule and the precursor for all other phosphoglycerides)

2) sphingomyelin (contain sphingocyne instead of glycerol)

Question 21

What are the X groups of phosphoglycerides?

Answer 21

X can be:

1) water (phosphatidic acid)

2) choline (phosphatidylcholine “lecithin”)

3) ethanolamine (phosphatidylethanolamine “cephalin”)

4) serine (phosphatidylserine)

5) glycerol (phosphatidylglycerol)

6) phosphatidylglycerol (di-phosphatidylglycerol “cardiolipin”)

7) inositol (An important example is GPI anchor protein, which anchors certain proteins to the membrane surface via amide linkage “cell signaling, etc”, phosphatidylinositol)

Question 22

What is phospholipases?

Answer 22

An enzyme that cuts phosphoglycerides, (PLA1 & PLA2 (hydrolyzed ester bonds at C1 & C2 respectively), PLB (hydrolyzed ester bonds at C1 & C2), PLC & PLD (phosphodiesterases yielding diacylglycerol and phosphatidic acid)) they are important in membrane remodeling (by adjusting the ratio of saturated to unsaturated fatty acids in the membrane), signal transduction (required by hormones), and digestion (degrading dietary phospholipids in the small intestine)

• they have a toxic effect which is occurring by their use via many organisms to degrade the membrane inflicting damage like the bacterial a-toxin and necrosis from snake venom (PLA2)

Question 23

What is sphingolipids?

Answer 23

• Important component of animal and plants membrane
• Contain long-chain amino alcohol (mainly sphingosine in animals)
• their core is ceramide

Question 24

What are the types of sphingolipids?

Answer 24

• Sphingosine
• sphingomyelin
• Ceramides
• Cerebroside

Question 25

What is a sphingosine?

Answer 25

Sphingosine (long-chain amino alcohol, (core of sphingolipids))

Question 26

What s a sphingomyelin?

Answer 26

Sphingomyelin, found in most cell membrane especially in the myelin sheath of the nerve cells

The first hydroxyl group of ceramide is Esterified to the phosphate group of phosphorylcholine or phosphorylethanolamine

Question 27

What is ceramides?

Answer 27

ceramide (sphingosine + fatty acid), they are also precursors of glycolipids (lipids with monosaccharides attached to it)

Question 28

What is a cerebroside?

Answer 28

A monosaccharide (in their head group) attached to a sphingolipid, examples include:

• Galactocerebroside a galactose attached to a sphingolipid (found in brain cell membranes)
• Sulfatides (Sulfate attached to a sphingolipid, they are negatively charged at physiological pH)
• Ganglioside (similar to cerebroside having a sialic acid and a oligosaccharide instead of one monosaccharide, which occurs in most of our tissues involved in Tay-Sachs disease)

Question 29

What are the diseases involved in sphingolipids?

Answer 29

Sphingolipids has storage diseases, involving sphingolipids metabolism (sphingolipidoses) like:

1) Tay-Sachs disease which evolves around the deficiency of b-hexosaminidase A, an enzyme responsible for the degradation of ganglioside Gm2, this disease results in blindness, weakness, seizures & mental retardation causing death by the age of 3

Question 30

What is isoprenoids?

Answer 30

• Biomolecules containing repeating five-carbon structural unit (isoprene unit)
• We can synthesize them starting from (IPP) from acetyl-CoA
• They consists of terpenes and steroids
• Precursors of steroids and cholesterol

Question 31

What is a Terpene? & list there types

Answer 31

• Classified by the number of isoprene units like:

1) Monoterpene (“2 isoprene units” used in perfumes like geraniol)
2) Sesquiterpines (Farnesene)
3) Diterpene (Phytol)
4) Triterpene (squalene)
5) Tetraterpene (B-carotene “carotenoids which is a orange pigments in plants”)
5) Polyterpene (Dolichol)
6) Thousand of isoprene units (rubber)

• Mixterpene (contains terpene and non-terpene components, like Vitamin E,K, UQ, CytQ)

Question 32

What is steroids?

Answer 32

An important group derived from triterpenes with four fused rings (cholesterol), they are found in all eukaryotes and some bacteria, and differentiate by a double bond placement and various substituents

Question 33

What is the structure of cholesterol?

Answer 33

• 27 carbons
• four fused rings (3-6 member rings, 1-5member ring)
• only one double bond at the second six ring
• a hydrophobic molecule with a polar head (the OH attached to the first ring at carbon number 3)

FYI: since it contains a OH which requires water for it to be store, in our body there is an enzyme (found inside the cell “ACAT” & in the blood “LCAT”) that attaches a fatty acid to the OH via an ester bond producing a cholesterol ester (cholesterol + fatty acid), which is broken by cholesterol esterase when the body needs cholesterol

Question 34

How can we degrade cholesterol?

Answer 34

By converting it to bile salts which will be secreted in the stool

Question 35

What is a cholesterol?

Answer 35

An important molecule in animal cells that is classified as a sterol due to the fact that the C-3 is oxidized to a hydroxyl group,

• It is essential in animal membranes
• Precursor of all steroid hormones, Vitamin D, & bile salts

It is usually stored as a fatty acid ester

Question 36

What are some of the cholesterol derivatives?

Answer 36

1) Progesterone
2) Testosterone
3) 17-b-Estradiol
4) Aldosterone
5) Cortisol
6) Cholic acid
7) Cardiac glycosides (increases cardiac muscle contraction, ouabain is its toxic “inhibits the NA+/K+ ATPase” form and digitalis is medically important)

Question 37

What is lipoproteins?

Answer 37

• A way to transport lipids between organs to the adipose
• Its surface is hydrophilic (phospholipid) and core hydrophobic (cholesterol ester)
• They add protein on the surface to be recognized by the target cell (Apolipoprotein B100, etc) synthesized in the liver or intestine
• Classified according to their densities

Question 38

What is a chylomicron?

Answer 38

Large lipoproteins of extremely low density that transports triglycerols & cholesteryl ester, which is synthesized in the intestine, they contain the highest percentage of triacylglycerol (triglyceride) & lowest in cholesterol, protein & phospholipids

Question 39

What is HDL?

Answer 39

High density lipoprotein containing the highest amount of protein (protein-rich “apolipoproteins”), produced in the liver and intestine that scavenges excess cholesterol and cholesteryl esters produced by lecithin from membranes which is converted into bile acids by the liver
- The good protein because it goes to peripheral tissues taking the excess cholesterol from the membrane and its a source for the important apolipoprotein

Question 40

What is LDL?

Answer 40

Low density protein containing with the highest percentage of cholesterol & cholesterol ester, they transport cholesterol and cholesteryl ester to tissues

• bad cholesterol highly correlated to cardiovascular diseases

Question 41

What is VDL?

Answer 41

Very low density lipoproteins, synthesized in the liver and transports lipids into tissues

Question 42

What are the reactions of fatty acid?

Answer 42

1) reacts with alcohols to form esters + water

2) unsaturated fatty acids can undergo hydrogenation reactions forming saturated fatty acids

3) unsaturated fatty acids can undergo oxidation reactions

4) Myristoylation & palmitoylation (protein acylation) which can be covalently attached to proteins, which helps in the facilitation of the interaction between membrane proteins and their hydrophobic environment & transports hydrophobic fatty acids from fat cells to body cells to yield energy

Question 43

How is trans fatty acids produced?

Answer 43

By products of hydrogenation reaction of margarine

Question 44

How are eicosanoids named?

Answer 44

• First two letters indicate its type (PG, TX, LT)
• Third letter indicates the type of medication made (A = hydroxyl group and an ether ring, B = two of the hydroxyl group)
• The number in the end indicates the number of double bonds

Question 45

What is a glycolipid?

Answer 45

A ceramide derivative, mono/di/oligosaccharide attached to a ceramide through an O-glycosidic bond, includes glycosphingolipids and GPI anchors they have classes (cerebrosides, sulfatides, & ganglioside)