Lipids and Bilayers Flashcards
Describe lipids?
They are not polymeric bu they do aggregate
Very varied
Largely hydrophobic, therefore insoluble in water
Soluble in organic solvent e.g. chloroform and methanol
They can be separated chromatographically and identified by mass spec
What are the general biological functions of lipids?
- Lipids form lipid bilayers that are essential components of biological membranes
- Lipids containing hydrocarbon chains = energy stores
- Many intra/intercellular signalling events involve lipid molecules
What are the main types of lipids?
Triacylglycerols/triglycerides
Glycerophospholipids
Steroids
Describe fatty acids?
Long hydrocarbon unbranched chains with a carboxylic acid at the end
Usually in between 14-20 carbons in the chain
Most common: palmitic, oleic, linoleic and stearic acids
They can be saturated - only single bonds
OR
They can be unsaturated - contains at least one double bond
What are some features of saturated fatty acids?
Contains only single C-C bonds, fitting closely together in a regular pattern
Have strong interaction between long carbon chains
Have higher melting points
Usually solids at room temperature
What are some features of unsaturated fatty acids?
Double bonds = kinks in the chain Don't pack closely together Fewer attractions between chains Lower melting point Liquids at room temp
Polyunsaturated Fatty acids = more than one C=C bond
Monounsaturated Fatty acid = one C=C bond
What are the types of double bond within unsaturated fatty acids?
Cis and Trans
Cis - two H atoms on the same side of the double bond = rigid 30° kink
This is the most common
Trans - H atoms on opposite sides
Formed when polyunsaturated fatty acids from plants are ‘partially hydrogenated’
Consumption of trans fats causes cardiovascular disease
Describe triacylglycerols?
Glycerol + 3 fatty acids (esterfied)
Fats and oils in plants/animals mainly consists of triacylglycerols
Nonpolar and water insoluble
Function as enery reserves (adipocytes - fat cells)
Fats provide six times the metabolic energy of equal weight of hydrated glycogen
What are the types of triacylglycerols?
Simple - 3 fatty acids esterified to glycerol are the same
Mixed - different fatty acid chains are connected to glycerol
Most contain 2-3 different types
-ate at the end of a fatty acid becomes -oyl in fatty acid ester
What are Glycerophospholipids?
Glycerol-3-phosphate
C1 and C2 are esterified with fatty acids
C3 has a phosphoryl group usually linked to another polar group (X)
X helps determine the name
= Amphiphilic
Non-polar aliphatic tails
Polar phosphoryl-X heads
What are some glycerophospholipid names based on different X groups?
Water - Phosphaditic acid Ethanolamine - Phosphatidylethanolamine Choline - Phosphatidylcholine Serine - Phosphatidylserine Myo-inositol - Phosphatidylinositol
What are some facts of the different glycerophospholipids?
Phosphatidylcholine - most abundant in cell membranes
Phosphatidylethanolamine - 2nd most abundant, helps proteins to be positioned in the membrane
Phosphatidylserine - presence on the outer membrane ofdying cells signalsmacrophages to digest them
Phosphatidylinositol - abundant in thebrain
Give an example where glycerophospholipids are used to prevent a medical condition?
DPPC - major lipid of lung surfactant
Surfaces of alveoli covered in surfactant
Collapse of alveolar space is prevented by surfactant, as tightly packed DPPC (due to saturated, straight chains) resist compression
Premature infants have low surfactant production pre-birth = at risk for respiratory distress syndrome
Treated by exogenous surfactant to the lungs
What are phospholipases?
Phospholipases hydrolyse glycerophospholipids
E.g. Phospholipase A2 removes the fatty acid at C2 leaving a lysophospholipid
Lysophospholipid = powerful detergent (disrupt cell membranes and lyse cells) e.g. bee/snake venom
What are plasmalogens?
Glycerophospholipids, where C1 chain is linked by either and a or b unsaturated ether linkage is the cis configuration (rather than ester linkage)
Function isn’t well understood as the vinyl ether group is easily oxidised
They react with O2 free radicals - preventing free-radical damage to other organelles
What are sphingolipids?
Major membrane components
Derivatives of amino alcohol sphingosine (= bond in trans)
General structure: sphingosine, fatty acid, PO4, amino alcohol
The N-acyl fatty acid derivatives of sphingosine are known as ceramides
Ceramides are the parent compounds of the more abundant sphingolipids
What are some types of sphingolipids?
Sphingomyelins
Cerebrosides
Gangleosides
Describe sphingomyelins?
Can have choline instead of amino alcohol but can have ethanolamine as well
Make up 10-20% of plasma membrane lipids
Rich in the myelin sheath
Describe cerebrosides?
Lack a phosphate and are non-ionic
They are ceramides with a head consisting of a single sugar residue
e.g. galactocerebrosides and glucocerebrosides
Describe gangliosides?
Ceramides with attached oligosaccharides that include at least one sialic acid residue
Primarily components of cell surface membranes and 6% of brain lipids
Receptors for pituitary glycoprotein hormones and the cholera toxin
Likely involved in cell growth and differentiation & carcinogenesis
What is a disease of gangliosides?
Tach Sachs disease
A fatal neurodegenerative disorder
The inability to catabolise gangliosides
What are steroids?
Eukaryotic origin - contains 4 fused rings (A-D)
A-C has 6C and D has 5C
Can be further classified as a sterol due to C3-OH group e.g. in cholesterol
Describe cholesterol?
Forms 30-40% of plasma membrane lipid
Provides integrity and fluidity to the membrane - fluidity allows cells to change shape rapidly
Weak amphiphilic character due to OH group - this interaction with the head of the phospholipids also holds the membrane together
At high temperatures, they attract each other and prevent the membrane from breaking down
Fused ring provides great rigidity
What is cholesterol the precursor of in mammals?
Steroid hormones
They control a variety of physiological functions through regulation of gene expression
They are classified according to the physiological responses the evoke
