lipid 1

Question 1

Explain the functions of lipids.

Answer 1

Major storage form of energy.
* Structural components of biomembranes (phospholipids and cholesterol).
* Metabolic regulators (steroids hormones and prostaglandins).
* Act as a surfactants, detergents and emulsifying agents (amphipathic lipids).
* Protect internal organs (pads of fat).
* Help in absorption of fat-soluble vitamins.
* Act as electric insulator in neurons.
* Provide insulation against changes in external temperature.
* Give shape and contour to the body.

Question 2

Clinical significance of lipids

Answer 2

• Obesity
• Diabetes mellitus
• Atherosclerosis
• Fatty liver
• Lipid storage diseases
• Hyperlipoproteinemia

Question 2

Lipids classification

Answer 2

1. Simple lipids
2. Compound lipids
3. Derived lipids
4. Lipids complexed to other compounds

Question 3

Simple lipids

Answer 3

-esters of fatty acids with glycerol or other higher alcohols. two types :
1. Fats
Fatty acids + glycerol
E.g: Triacylglycerol or Triglycerides or neutral fat
2. Waxes
Esters of fatty acids (usually long chain) with alcohols OTHER than
glycerol. alcohols may be aliphatic or alicyclic. E.g: Cetyl alcohol.

Question 4

2. Compound lipids

Answer 4

Fatty acids esterified with alcohol AND contain other groups such as phosphate, nitrogenous base, carbohydrate, protein, etc.
They are subclassified as :
(a) Phospholipids ; Lecithin (phosphatidylcholine), Cephalin, Phosphatidylserine , Phosphatidylinositol, Sphingomyelin.
(b) Non-phosphorylated lipids ; Glycosphingolipids, Sulpholipids or sulfatides

Question 5

Derived lipids

Answer 5

Compounds which are derived from lipids or precursor of lipids :
-steroids
Fatty acids
Prostaglandin
Leukotrienes
Terpenes
Dolichols

Question 6

Lipids complexed to other compounds

Answer 6

Macromolecular complexes of lipids with proteins. E.g :
* Lipoprotein
* Proteolipids

Question 7

Is lipid similar to fat?

Answer 7

Lipid is a broad group of biomolecules.
Fat is a type of lipids. Fat is stored as triacylglycerol in the adipose tissue and under the skin. It is the main energy-storage molecule in the body.

Question 8

Triacylglycerol (TAG)

Answer 8

An ester formed from glycerol and three fatty acid groups.
* Also called as neutral lipids.
* Formed by esterification of fatty acids with glycerol.
* Highly concentrated energy reserve.
* Excess fatty acids in the diet and fatty acids synthesized from excess dietary CHO and protein are converted to TAG and stored in adipose cells.

Question 9

What makes adipose triacylglycerol an efficient fuel store?

Answer 9

Triacylglycerol contains more calories per gram than carbohydrate or protein (9 kcal/g vs. 4 kcal/g).
➢Adipose tissue does not contain much water.

Question 10

Phospholipids

Answer 10

-compound lipids.
* Ionic compound composed of an alcohol (e.g: choline, inositol) that attached by a phosphodiester bond to either diacylglycerol (DAG) or sphingosine.
* Predominant lipids of cell membrane.
* Nonmembrane phospholipids serve additional functions in the body (e. g : lung surfactant and essential components of bile).

Question 11

Structure of a Phospholipid Molecule

Answer 11

• hydrophobic and a hydrophilic component.
• has a phosphate group on one end, called the “head,” and two side-by-side chains of fatty acids that make up the lipid “tails. ”
• The phosphate group is negatively charged, making the head polar and hydrophilic, thus attracted to the water molecules in their environment.
• The lipid tails, on the other hand, are uncharged, nonpolar, and hydrophobic. Some lipid tails consist of saturated fatty acids and some contain unsaturated fatty acids.

Question 12

Classes of Phospholipids

Answer 12

1. Glycerophospholipids : those that have glycerol (from glucose) as a backbone.
2. Sphingophospholipids (Sphingomyelin) : Those that have sphingosine (from serine and palmitate).

Question 13

Glycerophospholipid

Answer 13

• phospholipids containing glycerol.
• Major class
• All contain of phosphatidic acid (PA).
• PA is the simplest phospholipid and the precursor of other members in this group.
• PA consist of DAG (diacylgyceride)
  with a phosphate group on carbon 3.

Question 14

Function of Phosphatidic acid (PA)

Answer 14

• Precursor for the biosynthesis of many other lipids.
• second messenger with direct biological function.
• important role in cellular signaling and membrane dynamics in all eukaryotes.
• influence membrane curvature.
• lipid ligand that gates ion channels (lipid-gated ion channels).

Question 15

Derivatives of PA

Answer 15

PA + Serine= Phosphatidylserine (PS)
PA + Ethanolamine= Phosphatidylethanolamine (PE)
PA+ Choline= Phosphatidylcholine(PC)
PA + Inositol= Phosphatidylinositol (PI)

Question 16

Function of phosphatidylcholine (lecithin)

Answer 16

• (DPPC) or dipalmitoyl lecithin is important in lung functioning.
• Secreted by lung pneumocytes II.
• major component ofl ung surfactant.
• Extracellular fluid layer lining the alveoli.serves to decrease the surface tension of this fluid layer reducing the pressure needed to reinflate alveoli, thereby preventing alveoli
  collapse(actelactesis)

Question 17

Respiratory Distress Syndrome

Answer 17

• AKA hyaline membrane disease
• most common in preterm infants
• due to structural and functional immaturity of lungs- underdeveloped parenchyme
• surfactant deficiency
• unstable alveoli

Question 18

Function of Phosphatidylinositol (PI)

Answer 18

-important role in mediation (Vasopressin & Oxytocin) on biomembranes.
* Cell growth, proliferation differentiation, motility , survival and intracellular trafficking
* Regulate immune responses.
* Key component of insulin signaling pathway.

Question 19

Sphingophospholipids : Sphingomyelin

Answer 19

*only sphingophospholipid that contain phosphate and have no sugar moiety.
* Backbone-amino alcohol sphingosine, rather than glycerol.
* Alcohol group at carbon 1 sphingosine is esterified to phosphorylcholine.

Question 20

Function of Sphingomyelin

Answer 20

1. Central nervous system (CNS)
   * Important constituent of the myelin sheath of nerve fibers.
2. Maintain skin’s water permeability
   * Sphingomyelin combined with fatty acid formed ceramide.

Question 20

Function of Sphingomyelin

Answer 20

1. Central nervous system (CNS)
   * Important constituent of the myelin sheath of nerve fibers.
2. Maintain skin’s water permeability
   * Sphingomyelin combined with fatty acid formed ceramide.

Question 21

PROSTAGLANDINS (PG)
(Derived lipids)

Answer 21

• Eicosanoids (polyunsaturated FAs with 20 carbons)
• Synthesised from arachidonic acid (a 20:4 FA) via COX (cyclooxygenase)
  Cell signaling (pain pathway)
• Potent with short half life (seconds)
• Multiple roles
  – Inflammatory
  – Platelethomeostasis

Question 22

NSAID(cyclooxygenase inhibitors)

Answer 22

-Two types of COX enzymes, COX-1 and COX-2.
-PGs promote inflammation, pain, and fever.
NSAIDs(COX inhibitors) block the COX enzymes and reduce production of prostaglandins.
Therefore, inflammation, pain, and fever are reduced
-Only COX-1 produces prostaglandins that activate platelets and protect the stomach and intestinal lining.
-COX-2 inhibitors do not block COX-1, they do not cause ulcers or increase the risk of bleeding and platelet reduction.

Question 23

Prostaglandins inhibitors

Answer 23

COX-1 & COX-2 inhibitor