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
Structure of Sphingolipids
similar to phospholipids.
Components:
- hydrophobic and hydrophilic components
- one fatty acid, linked to sphingosine (ceramide)
Structure of Sphingomyelin
Consists of:
- phosphocholine head group
- sphingosine
- fatty acid
Functions:
- found in myelin sheath that surrounds and insulates many nerves cell axons
- plays a role action potential transduction
- involves in apoptosis
Structure of Sterols
Aids with the structural support of the plasma membrane, they are components of many proteins as well.
Examples:
- Cholesterol is the starting point fro many sterols
- High carbon content makes sterols very hydrophobic
- Conserved ring structure
- Cholesterol needed fro steroid hormone synthesis and proper membrane function
- Animals can obtain cholesterol from diet or synthesis from Acetyl CoA.
Types of Hormones
- Sex hormones -> Testosterone and Estradiol
- Cortisol -> Stress response, Starvation response including gluconeogenesis, Excessive production in Cushing’s disease
- Aldosterone -> Sodium retention and potassium excretion in the kidneys, Water retention as a secondary result, Reduced or no production in Addison’s disease
- Steroid drugs -> Prednisone, Prednisolone Brassinolide.
Cholesterol and Dietary fats ‘ Digestion
detergent:
solibulises lipids and makes them water-soluble.
Break fats up into smaller droplets to aid digestion, due to:
- Hydrophobic and hydrophilic components
- Bile acids coat the lipid droplets
- Pancreatic lipases break fats into its constituent parts.
Vitamin D
Multi-step process of synthesis involving skin, liver and kidneys.
Necessary for calcium absorption from the small intestine.
Vitamin A
aka Retinol.
- Hydrophobic vitamin
- Retinol produced from beta-carotene
- Retinol can be converted in 11 cis-retinal
- Basis of vision when light converts 11 cis-retinal to all-trans-retinal
- Isomerisation
- Causes a conformational change in the rhodopsin protein which activates an associated G-protein leading to a neuronal signal
- 11-cis-retinal can also be converted into retinoic acid
- Important in certain gene transcription involved in embryological development.
Vitamin A required for osteoblastic and osteoclastic activity in bone turnover. Excess Vit A results in loss of bone from skeleton, hypercalcaemia and deposition of new bone in inappropriate locations.
Vitamin A is hydrophobic, so needs to be converted to a more hydrophilic product for excretion.
Vitamin A is also stored in adipose tissue as not accessible to drug metabolism enzymes
Vitamin E
- hydrophobic vitamin
- antioxidant properties
- important antioxidant in hydrophobic environments such as within cell membranes
- protects fatty acids from oxidation
Vitamin K
- Hydrophobic vitamin
- Cofactor in blood coagulation pathway
It is required as a cofactor for the enzyme Vit K-dependent corboxylase.
The Carboxylase adds a carboxyl group to glutamate residues in certain clotting factors.
The carboxyglutamate residues can chelate Ca2+ which enables the factors to bind to cell membranes and form the clot.
Vitamin K is oxidised in this process so must be reduced = some drugs inhibit the enzymes that reduces inactive Vitamin K -> Anti-Vit K poisons
Types of Misc. Lipids
- Waxes
Two components joined by an ester bond:
1. long chain fatty acid
2. long chain alcohol
Functions:
Storage of fuel in plankton.
Protection and pliability for hair and skin
Waterproofing of feathers
Beeswax - Polyketides
produced by plants and fungi. - Pigments
