WK 5: Lipids and biomembranes Flashcards
1. Understand the classification of lipids, based on their biological roles (e.g., energy storage, structural, signaling). 2. Become familiar with the structure and nomenclature of lipids, by recognising different lipid structures (e.g., fatty acids, triglycerides, phospholipids, sterols), understand their chemical composition, and correctly apply common nomenclature of fatty acids. 3. Gain knowledge on the major biological functions of lipids, explain the key roles of lipids in energy storage, (16 cards)
LO1: What is a lipid
Lipids are molecules that are soluble in organic solvents.
- Insoluble in water (hydrophobic)
- Do not form polymers (in contrast with other biomolecules)
- Possess different forms, properties and functions
LO1: name the lipid classifications with examples
Energy Storage: Fatty acids, Triacylglycerols, Waxes
Structure: Phospholipids, Sphingolipids, Sterols
Signaling: Steroid hormones, Eicosanoids, Vitamins
Biomembranes: Lipid bilayer organisation and properties, Structure & function
LO1: what are the biological functions of a lipid
- Energy storage (highly efficient form to store energy): fatty acids, triacylglycerols & waxes
- Structural components of biological membranes (i.e. form barriers): phospholipids, sphingolipids & sterols
- Signalling (intra and extracellular): steroid hormones, eicosanoids, plant hormones & vitamins
LO2: What is a fatty acid
Fatty acids are carboxylic acids with hydrocarbon chains
* Normally have an even number of carbons (4 – 36 carbons)
* Saturated (all carbons are saturated, full hydrogenated, only single bonds,
* Unsaturated (some carbons have double bonds, C=C)
* Monounsaturated (one double bond)
* Polyunsaturated (more than one double bond)
LO2: How do you name a fatty acid (nomenclature)
- Carbons are numbered from the carboxyl (COOH) end
- ∆ is used to denote double bond
LO2: What is a triglyceride
storage lipid: triglyceride
Triacylglycerol (triglyceride, or just fat): glycerol esterified with 3 fatty acids
LO2: Difference b/w saturated and unsaturated fats
Saturated Fats = triacylglycerols with saturated fatty acids (no double bonds)
if saturated, fatty acid tails are straight and packed tightly (stronger van der Waals interactions)- e.g. butter
Unsaturated Fats = triacylglycerols with unsaturated fatty acids (with double bonds)
If unsaturated, fatty acid tails have kinks and cannot pack tightly (weaker van der Waals interactions)- e.g. olive oil and fish at room temp
LO2: Triglycerides- what is cis and trans CONFIGURATION
Double bonds in naturally occurring unsaturated fatty acids are in cis configuration and get a kink
when liquid at room temp: Double bond with Cis configuration (i.e. the 2 H are in the same side, and induce a kink)
when solid at room temp: Double bond with Trans configuration (i.e. the 2 H are in opposite side, the molecule has no kink)
LO2: What is hydrogenation (trans fat)
Some manufacturers developed a process called hydrogenation (add H to the double bonds to convert some of the double bonds into single bonds):
* Improve shelf life of vegetable oils
* More solid and more spreadable (e.g. cooking margarine)
* More resistant to high temperatures (e.g. blended oils used for deep-
frying)
Side products, some cis double bonds become trans double bonds from partial hydrogenation Trans fats increase the incidence of cardiovascular disease
what are waxes.
Storage lipid: Waxes
Structure:
* long chain of saturated or unsaturated fatty acids (C14 to C36)
* long chain alcohol (C14 to C30)
* Linked by an ester bond
Function:
* Energy Storage (e.g. plankton)
* Water repellent (e.g. beeswax)
LO2: What are Structural lipids and their role in biomembranes
- Phospholipids(e.g.phosphatidylcholine) * Sphingolipids(e.g.sphingomyelin)
- Sterols(e.g.cholesterol)
LO2: What are phospholipids and different types
Also known as glycerophospholipids
* Most abundant lipid in cell membranes
* Amphipathic (polar & non-polar regions)
(Hydrophilic & hydrophobic)
Structure contains:
* Glycerol
* Phosphate often linked to a polar group (R)
* 2 fatty acids (linked via ester bond)
The head group in the phospholipids varies * Size
* Charge
Head group defines the class of phospholipid:
Phosphatidic acid (PA): very small, negative Phosphatidylethanolamine (PE): small, zwitterion Phosphatidylcholine (PC): zwitterion
Phosphatidylserine (PS): negative, multiple charged groups Phosphatidylglycerol (PG): negative
Phosphatidylinositol (PI): negative, carbohydrate
The fatty acids in the phospholipids also vary
* Length (C12-24)
* Saturated vs unsaturated (1, 2 and 3 double bonds)
* Modulate fluidity of the phospholipid
LO2: What are sphingolipids
structural lipids:
* Derivatives of sphingosine (long-chain amino alcohol)
* No glycerol
* Amphipathic (polar & non-polar regions)
(Hydrophilic & hydrophobic
Structure contains:
* sphingosine
* long chain fatty acid
* Polar head group (via glycosidic or phophoester bond)
Head group defines the class of sphingolipid:
* Ceramide (sphingosine + fatty acid)
* Sphingomyelin (the most common sphingolipid in membranes)
* Glycolipids (carbohydrate instead of a phosphate group
what is a glycolipid
Glycosylated Phospholipids or Sphingolipids
* Have sugar groups attached
* Found on the non-cytosolic side of a cell membrane bilayer
* Function in cell recognition
what are sterols
structural lipid
Sterols are structural lipids present in membranes of most eukaryotic cells
* The most common sterol in mammalian cells is cholesterol
* Similar sterols exist in plants and fungi
* Bacteria cannot synthesise sterols
Cholesterol structure contains:
* 4 fused rings: 3 with 6C, 1 with 5C
* Hydrocarbon side chain (non-polar)
* Polar head group
Hydrophobic but with a small polar group
Function:
* Integral part of biological membranes
* Increases the rigidity of membranes
* Increases the impermeability of membranes
* Very important to maintain the integrity of cells
LO4: What is lipid composition
Lipid bilayer:
Phospholipids, sphingolipids and cholesterol are virtually insoluble in water But they are amphipathic.
When mixed with water they cluster together and from aggregates:
- Fatty acid chains are hidden in the interior of the lipid membrane via Hydrophobic effect (reduction of contact
with water), and once in close proximity can establish van der Waals interactions
* The polar group are exposed to water and can establish H-bonds with water molecules
Lipid composition modulates bilayer properties
