Biomolecules - Lipids

Question 1

Functional features of lipids?

Answer 1

– Relatively insoluble in water
– Soluble in nonpolar solvents (eg- ether, chloroform)

Question 2

Presence of lipids in the human body?

Answer 2

Humanbody
– Compartmentalized (membrane-associated lipids, triacylglycerol in adipocytes or in association with protein (lipoprotein particles) or on albumin.

Question 3

Lipids in the diet?

Answer 3

Important dietary constituent. 20%-35% total energy intake for a healthy adult.
– Determine the taste and palatability of food
– Provide energy 9 kcal/g
– Storage - Energy storage – lipids deposited in adipose tissues

Question 4

Biomedical importance of lipids?

Answer 4

1. Transport
   - (gut)-Facilitate absorption of fat-soluble vitamins.
   - Transport function in the blood
2. Structural
   - Contain essential fatty acids (EFA) important for normal growth and development
   - Cell membrane
3. Insulator:
   - Thermal Insulator
   - Electric Insulator in neurones
4. Signalling molecule proteins
5. Protects internal organs
6. Lipoproteins
7. Obesity

Question 5

Classification of Lipids?

Answer 5

1. Simple Lipids
2. Complex Lipids
   - Phospholipids: Sphingophospholipids and Glycerophophospholipids.
   - Glycolipids
   - Sulfolipids and Amino lipids
3. Derived Lipids

Question 6

Where do we find fatty acids?
Importance of fatty acids?

Answer 6

• Exist in free (unesterified) or esters (eg. Triacylglycerols).
• Free fatty acids can be oxidized by many tissues to provide energy

Question 7

Factors affecting physical properties of fatty acids?

Answer 7

1. Length of the Hydrocarbon chain
2. Degree of unsaturation

Question 8

Classification of Fatty acids?

Answer 8

Two groups – Saturated and Unsaturated
* Unsaturated- mono (MUFA) and poly unsaturated (PUSFA)
* Unsaturated – two types of configurations cis and trans

Question 9

What are essential fatty acids?
Examples?

Answer 9

Lenoleic Acid (LA), the precursor of omega 6
and α Lenolenic Acid (ALA), the precursor of omega 3 cannot be synthesized by mammals. Thus known as essential FA.

Question 10

Explain DHA regarding pregnancy and infancy.

Answer 10

DHA plays a major role in development of the brain and retina during foetal development and the first two years of life
* An intake of at least 300mg/day EPA+DHA, of which 200 mg/day are DHA is recommended for pregnant and lactating mothers.
* Brest milk provides adequate amount to infants.

Question 11

LA, ALA and their derivatives play a significant role in the …

Answer 11

structure of biological membranes.

Question 12

Health benefits of omega 3 FAT?

Answer 12

• Anti inflammatory effects of ALA, EPA and DHA
• For certain chronic diseases where the inflammation is a contributory cause, the diets rich in ω3 fatty acids are beneficial
• eg cardiovascular disease and for other chronic degenerative diseases such as cancer, rheumatoid arthritis, and Alzheimer disease.

Question 13

Biomedical importance of hydrogenated food?

Answer 13

– Partial hydrogenation converts a part of cis-isomers
into trans-unsaturated fats
– Consumption of transfats (TFA) increases the risk of coronary heart disease, and other diseases such as diabetes mellitus, and cancer by raising the levels of LDL cholesterol and lowering levels of HDL cholesterol.

Question 14

Relationship between TFAs and Negative pregnancy outcomes.

Answer 14

TFA (in partially hydrogenated vegetable oils) are transmitted from mother to foetus and from mother to infant in breast milk. Negative outcomes related to conception, foetal loss, and growth. Thus it is recommended that industrially-derived trans fatty acids should be as low as practical for pregnant and lactating women.

Question 15

Structure of Triacylglycerols.
What is their nature and how soluble are they?

Answer 15

3 FAs linked to a single glycerol with ester linkages.
* Simplest lipids.
* Non polar, hydrophobic, essentially insoluble in water

Question 16

function of TAGs

Answer 16

TAG provides stored energy (adipose) serving as metabolic fuel & insulator.
* The main storage form of fatty acids.

Question 17

biomedical significance of TAGs

Answer 17

• high levels of triglycerides in the bloodstream have been
  linked to atherosclerosis
• Diets that are rich CHO with a high glycemic load elevates TAG in blood
• Moderate exercises may reduce TAG levels in blood

Question 18

structure of phospholipids

Answer 18

• Compound Lipid (Simple lipids + other groups)
• Amphipathic in nature
• The predominant lipids of plasma
  membranes
• Two groups ;
  glycerophospholipids and sphingophospholipids

Question 19

What are glycerophospholipids?

Answer 19

Alcohol +PA → Glycerophospholipids

Question 20

What are Sphingophospholipids (sphingomyelin)?

Answer 20

• The backbone of sphingomyelin is the amino alcohol sphingosine
• A long-chain fatty acid is attached to the amino group of
  sphingosine producing a ceramide
• Sphingosine in combination with phosphorylcholine produces
  sphingomyelin
• Sphingomyelin is an important constituent of the myelin sheath of
  nerve fibers

Question 21

Comparison of glycerophospholipid and sphingophospholipid structures?

Answer 21

• In glycerophospholipids, two (2) hydrophobic tails
  and both are fatty acid chains * in sphingolipids,
  Two (2) hydrophobic tails but only one is a fatty acid chain and the other is part of the sphingosine moiety.
• Both have polar head groups.

Question 22

Phosphatidylcholines (Lecithins) as a surfactant?

Answer 22

Choline + PA → phosphatidylcholine (PC) (lecithin) produced by type II cells.
* form a stiff layer between air and water interphase
* Reduces surface tension
* Reduces the pressure needed to re inflate
* Prevent alveoli collapse
* Respiratory distress syndrome (RDS) in preterm infants is associated with insufficient surfactant production and/or secretion

Question 23

Functions of selected phospholipid?

Answer 23

1.Phosphatidylcholines (Lecithins) as a surfactant.
2. Acts as a choline reservoir

• The predominant lipids of plasma membranes
• blood coagulation- required for the conversion of Prothrombin to thrombin by active factor X
  (Cephalin)
• lipid absorption-lowers the surface tension of water & aids in the emulsification of lipids
• Plays a role in the enzymatic action:- Some mitochondrial enzymes require tightly bound PL for their action eg- cardiolipin, a phospholipid found in mitochondria, is essential for mitochondrial function. (mitochondrial dysfunction in aging and in pathologic conditions including heart failure).

Question 24

Neutral glycosphingolipids?

Answer 24

Cerebrosides- simplest form. Contains galactose or glucose.
Predominantly in the brain and peripheral nervous tissue, with high concentrations in the myelin sheath
Globosides- ceramide oligosaccharides (addition of monosaccharides or other substituted sugars such as N- acetylgalactosamine.

Question 25

Acidic glycosphingolipids?

Answer 25

* Gangliosides- derivatives of ceramide oligosaccharides with the addition of one or more sialic acids (eg Neuraminic acid). They function in cell–cell recognition and communication. as receptors for hormones and bacterial toxins such as cholera toxin.

Question 26

Lysosomal lipid storage diseases?

Answer 26

* Enzymes required for the degradation of sphingolipids are present in lysosomes. * Any defect in enzymes causes accumulation of sphingolipid (Lysosomal lipid storage diseases) * Early death due to neurologic deterioration * Most of them are autosomal-recessive diseases,

Question 27

Importance of DHA in the first two years of life.

Answer 27

DHA plays a major role in development of the brain and retina during foetal development and the first two years of life. Consumption of an adequate amount of DHA together with EPA is recommended even after 2 years due to the probable evidence of reduce risk of cardiovascular mortality and anti-inflammatory effects. But no evidence of mental or physical benefits during this age range.

Question 28

What are Eicosanoids?

Answer 28

* 20 carbon units * Derive from ARA or other C 20 PUFA. * Prostaglandins (PG), thromboxanes (TX) and leukotrienes (LT)

Question 29

Function of Eicosanoids?

Answer 29

* Physiologically and pharmacologically active compounds * Physiologically, they are considered to act as local hormones * Family of very potent biological signaling molecules. * Mainly acts as a short-range messenger affecting tissues near the cells that produces them.

Question 30

Production and metabolism of eicosanoids?

Answer 30

* produced in very small amounts in almost all tissues * Eicosanoids are not stored, and they have an extremely short half-life, being rapidly metabolized to inactive products.

Question 31

Biosynthesis of some important eicosanoids from Arachidonic acid?

Answer 31

* Synthesis of prostaglandins and thromboxanes * Synthesis of leukotrienes

Question 32

Synthesis of prostaglandins and thromboxanes?

Answer 32

* prostaglandin endoperoxide synthase (PGH synthase). * This enzyme has two catalytic activities: – fatty acid cyclooxygenase (COX), which requires two molecules of O2, – peroxidase,whichisdependent on reduced glutathione * PGH2 is converted to a variety of prostaglandins and thromboxanes.

Question 33

Isozymes of prostaglandin endoperoxide synthase (PGH) synthase?

Answer 33

Two isozymes of PGH synthase ( COX-1 and COX-2) * COX-1 in most tissues and is required for maintenance of healthy gastric tissue, renal homeostasis, and platelet aggregation. * COX-2 is inducible in a limited number of tissues mediates the pain, heat, redness, and swelling of inflammation and the fever of infection.

Question 34

Functions of different prostaglandins?

Answer 34

Prostaglandins: 1. Vasoconstriction 2. Contraction of smooth muscles 3. Stimulates uterine contractions 4. Used to induce labor

Question 35

Functions of different thromboxjnes?

Answer 35

1. Platelet aggregation 2. Vasoconstriction 3. Contraction of smooth muscle

Question 36

Functions of different leukotrines?

Answer 36

1. Contraction of smooth muscle 2. Bronchoconstriction 3. Pathophysiology of asthma

Question 37

Applications of Eicosanoids- Anti-inflammatory drugs?

Answer 37

* a steroidal anti-inflammatory agent (cortisol) inhibits s phospholipase A2 activity * Non-Steroidal Anti-Inflammatory Drugs (NSAIDs). Aspirin, indomethacin, and phenylbutazone inhibit both COX-1 and COX-2. * COX-2 inhibitors eg-coxibs (celecoxib) reduce pathologic inflammatory processes mediated by COX-2 while maintaining the physiologic functions of COX-1. But they increased risk of heart attacks. * Explain the biochemical basis of Aspirin-induced asthma

Question 38

Biochemical basis of low-dose aspirin therapy used to lower the risk of stroke and heart attacks?

Answer 38

* Aspirin inhibits both COX-1 and COX-2 – COX-1 in platelets responsible for production of TXA2 that promotes platelet aggregation. – COX-2 in endothelial responsible for production of PGI2 that inhibits platelet aggregation. * Platelets- no nuclei thus cannot regenerate COX 1 * Endothelial cells contains nuclei and can regenerate COX 2 synthesis then continue to produce PGI2 * Thus [PGI2] > [TXA2] * Then the over all balance favored inhibition of platelet aggregation.

Question 39

Applications- Leukotriene?

Answer 39

* Leukotrienes are mediators of allergic response and inflammation. * Their synthesis is not inhibited by NSAIDs. * Use of – Inhibitors of 5-lipoxygenase – leukotriene receptor antagonists in the treatment of asthma.

Question 40

What are the characteristics of muscle cells?

Answer 40

1. Excitability 2. Conductivity 3. Contractility 4. Extensibility 5. Elasticity