Lipids Flashcards
Definition
Classes of biological compounds that are generally insoluble in water but soluble in organic solvents.
Functions
- Storage of energy
- Insulation from environment
- Protection of organs
- Water repellent
- Buoyancy control and acoustics in water mammals
- Membrane structure
- Cofactors for enzymes
- Signalling molecules
- Pigments
- Antioxidants
- Inflammation
- Digestion
Fatty acids
Usually a component of other lipids.
They referred to as a free fatty acids.
Fatty component: Hydrocarbon chain
Acid component: Carboxyl group (negatively charged at physiological pH so it can interact with water.
SFA vs MUFA/PUFA
- Saturated fatty acid
no double bonds in the hydrocarbon chain - Unsaturated fatty acid
1. Monounsaturated fatty acids (MUFA) have a single double bond between 2 carbons in the chain
2. Polyunsaturated fatty acids (PUFA) have a multiple double bonds between different carbons.
Nomenclature
Carbon in carboxyl group is carbon 1.
* Second carbon (or first in chain not part of the carboxyl) is carbon 2 or the α carbon.
* Nomenclature reflects number and location of double bonds.
* Chemical names are also used.
Arachidonic Acid Derivatives
- Prostaglandins (mucosal protection, renal blood flow, inflammation an fever)
- Thromboxanes (formation of blood clots)
- Leukotrienes (smooth muscle contraction in lungs and inflammation)
Triacylglycerois
Two components: 3 fatty acids linked to Glycerol.
Each of the 3 OH groups in glycerol forms an ester bonds with the carboxyl group of a fatty acid. Ester bonds can be hydrolysed by enzymes called lipases or esterases.
Fats need to be digested because TGAs cannot cross cell membranes, but FAs and glycerol can with the help of specific transporters.
FAs are then reconverted in TGAs within the cell and exported into the blood as part of Lipoprotein Pathway.
They are stored in the ADIPOSE TISSUE formed of adipocytes.
Chylomicrons
TAGs are digested into FA and monoacylglycerol components in the SI.
After that the TAGs are re-constituted within enterocytes, they are packaged in the ER into chylomicrons.
They enter the lymphatic system via the lacteal where they join lymph fluid become chyme fluid. Chyle returns to vascular system through venous return.
Lipoprotein Pathway
major pathway for supply of FA and cholesterol:
- same components as chylomicrons
- transport TAGs and cholesterol
- Higher cholesterol component -> name by density.
Ligenesis
SYNTHESIS OF FA/ TAG.
glucose is converted to fatty acids and TAGs for long-term storage in adipocytes.
Process:
1. Acetyl CoA (from glycolysis and Pyruvate).
2. NADPH is required for each additional Acetyl CoA.
3. Plus Glycerol (from glucose) to form TAGs.
4. Happens mainly in the liver.
5. Main pathway for getting rid of excess glucose.
6. TAGs are exported from the liver cell as VLDL to other tissues.
Lipolysis
Breakdown of stored TAGs to FAs and glycerol, induced by SEVERAL HORMONES.
Free fatty acids and glycerol are transported by the blood to other organs:
- skeletal muscle
- cardiac muscle
- liver
Metabolisation via beta-oxidation
beta-oxidation occurs in mitochondria.
Fatty acids cannot cross the mitochondrial double membrane. Fatty acids are transported into mitochondria by the carnitine shuttle:
1. Fatty acid bound to CoA → fatty acyl CoA
2. CoA exchanged for carnitine → acyl carnitine
3. Acyl carnitine translocated by facilitated diffusion with unbound carnitine
4. Carnitine on acyl carnitine exchanged for CoA
Each step requires a specific enzyme:
* Fatty acyl CoA synthetase
* Carnitine palmitoyltransferase I and II
* Carnitine-acylcarnitine translocase
The breakdown of FA: 2 carbons at a time in the from of acetyl CoA. Also, NADH and FADH2 produced – (ETC to regenerate ATP).
Acetyl CoA can go on to enter the TCA cycle.
When f.a. and acetyl CoA in excess – acetyl CoA enters pathway called ketogenesis.
Ketogenesis
excess of acetyl CoA is converted into ketone ( Acetoacetate, beta-hydroxybutyrate, Acetone.
Acetoacetate and beta-hydroxybutyrate, can be used buy brain and muscle.
Acetone has no metabolic function and is excreted in the breath.
Structure of Phospholipids
Hydrophobic and hydrophilic components allow spontaneous formation of bilayers
Structure of Glycerophospholipids
4 components:
- 2 fatty acids, one saturated and one unsaturated
- glycerol
- phosphate -> negatively charged so hydrophilic
- polar head group
Examples:
- Phosphatidylcholine
* Most common phospholipid of plasma membrane
-Phosphatidylinositol 4,5-bisphosphate
* Involved in cell signalling processes
-Cardiolipin
* Found in cardiac tissue and mitochondria
* Often used as a biomarker for apoptosis (programmed cell death)
* Head group is another phospholipid so there are four fatty acids
