BCHM-3050 Lecture Notes - Lecture 10: Membrane Lipids, Membrane Structure, Amphiphile
15 Jun 2018
School
Department
Course
Professor
Lipid Introduction
Characteristics:
Not water soluble
Due to large portion of chain being hydrocarbon
§
Lipids are rarely found free in solution
§
○
Lipids do not form large covalent polymers
Associate with each other through non covalent interactions
§
○
•
Major functions:
Energy storage
○
Membrane structure
○
Signaling
Hormones
§
○
•
Limited solubility in aqueous media
Unlike amino acid, nucleotide, and carbs
○
Amphipathic: hydrophobic and hydrophilic
○
•
Construct from long chain carboxylic acids
Fatty acids
○
•
Fatty acids
Simplest lipids
•
Can be considered monomer for lipids
•
Saturated FA's: all C-C single bonds
•
unsaturated FA's: at least one C-C double bond
Naturally occurring unsaturated fatty acids have cis orientation about
the double bond
○
Polyunsaturated: multiple double bonds
○
Monounsaturated: one double bond
○
Cause kink
○
•
Systematic description of double bond:
# of carbons: dbl bond #, C(cis) or T(trans), ∆, # at which dbl bond
starts
○
Ex. Oleic acid = 18:1c∆9
Oleic acid has 18 carbons, 1 double bond that is cis and the
double bond starts on the 9th carbon
§
○
•
Tm of fatty acid increases with the number of carbons
Due to van der Waal forces
○
•
Fatty acid and diet
Essential nutrient: Fatty acid req. for optimal metabolism that can not be
synthesized by the organims
Ex. Omega -3 fatty acids
EPA and DHA
§
○
•
Esterification of Glycerol and fatty acids
Esterification: condensation of rxn b/w an OH and a carboxylic acid
•
Rxn = reversible
Via hydrolysis
Break ester bond
§
○
•
Glycerol = tri-ol
3 Oh groups available for esterification
○
•
Fat or triglycerides: glycerol esterified with 3 FA's
Fat = suited for metabolic energy storage
C atoms are highly reduced
○
Bio thermal insulator
○
•
Fat storage and composition of some natural fats
Unsaturated fatty acids = one or more cis double bond
Saturated has no double bonds
○
•
"fluidity" of fatty acid decreases as chain length increases and number of
cis bonds decrease
•
Tm trend: linoleic < oleic<stearic
•
Fluidity: linoleic>oleic>stearic
•
Waxes and Soaps *
Natural waxes: lone chain of fatty acid is esterified to long chain of OH
Insoluble in water
○
Small polar region
○
Two long hydrocarbon chains
Completely water insoluble
§
○
•
Soap: treatment of fatty acid with a strong base
Saponification: hydrolyzation of fat with a strong base
○
Form soluble sodium or potassium salt
Precipitate w mg2+/ ca2+
§
○
Form micelles around oil
Emulsify oil
§
○
•
Synthetic detergents: not precipitated by calcium or magnesium ions
•
Membrane lipid composition
Composition: large role in function of membrane
Also denotes fluidity of the membrane
○
•
Composed of bilayer
•
All fatty acids from micelles
•
Major classes of lipids:
Glycerophospholipids
○
Sphingolipids
○
Glycosphingolipids
○
Glycoglycerolipids
○
•
Hydrophobic interior = twice as thick as polar hydrophilic head groups
•
Glycerophospholipids
Glycerophospholipids: major class of naturally occurring phospholipids
Lipid w phosphate containing group
○
•
Has two fatty acid chains
•
Names derived from phosphatidic acid
•
Sphingolipids
Cousin to phospholipids
•
Built on sphingosine
Synthesized from a palmitoyl CoA + serine residue
○
Used to make sphingolipid derivatives:
Simple:
Sphingomyelin
□
§
Complex: glycosphingolipids
Cerebroside
□
Ganglioside
□
§
○
Amino alcohol
○
•
Major component of cell membranes
Particularly in neuro membranes
○
•
Glycosphingolipids
Have glycans attached to sphingosine
Can be any sugar
○
Use for cell ID
○
•
Have long chain OH
•
Constituents of ABO blood antigens
•
Include
Cerebrosides and gangliosides
○
Common in membranes of brain and nerve cells
○
•
Glycosphingohospholipid v sphingolipids
Glycosphingophospholipid: involve glycerol
•
Sphingolipid: involve sphingosine
•
Both:
Fatty acid
○
Phosphate group
○
Hydrophilic R group
○
○
•
Cholesterol
Major portion of membrane lipids in most organisms
•
Disrupts regular fatty acid chain packing in membranes
Bulky and rigid
○
Increase membrane fluidity at low temperature
Good thing
§
○
•
Weakly amphipathic
Small hydroxyl group
○
Fatty acid esters of cholesterol = very apolar
○
•
Evidence of fluidity of membrane
Fluorescent-labeled membrane proteins: induced to fuse
From mouse to human cells
○
Protein gradually mix over time via lateral shifts (10^-6 s)
○
•
Groups of bilayer can flip flop from one side to the other
Much slower ~1 day
○
•
Membrane goes from gel to crystal state*
Gel is ordered while liquid crystal is disordered
•
Longer fatty acid chain and increased saturation of fatty acid in membrane
= higher value Tm
•
Increase concentration of cholesterol broadens transition point
But cholesterol is primarily found in eukaryotes
○
•
Bacteria: relate membrane fluidity to growth temp
Regulate fatty acid synthesis
○
Decrease in growth temp = increase unsaturation fatty acid %
Prevent transition of membrane to the gel state
§
○
•
Asymmetry of membrane lipid structure
Inner and outer leaflets can be considered asymmetrical in composition
•
Membrane proteins
Intermembrane region of membrane protein: apolar amino acid to the fatty
acyl tail of phospholipid
Regions in the membrane may be:
Beta barrels or alpha helices
§
○
•
High proportion of hydrophobic amino acids
•
Transmembrane helices = 20-25 residues
Predominantly hydrophobic
○
•
Bacteriorhodopsin: integral membrane protein*
Transmembrane protein that contains all alpha helices
Membrane spanning regions = highly hydrophobic
Typical of membrane spanning protein
§
○
•
Insertion of proteins into membranes
Cotranslational process
Require ribosome and translocon
Translocon: acts as a protein conduction channel
§
○
•
Translocon: facilitate insertion of hydrophobic region of protein in bilayer
•
Membrane rafts*
Membrane rafts: short lived dynamic structures that transiently associate
with each other to form larger platforms
Happens in response to stimuli
○
•
Rich in cholesterol, sphingolipids and glycosylphosphatidylinositol
•
Role in cell signaling and sorting of proteins into organelles
•
Sterol to liquid ratio: critical in determining raft formation
•
Membrane transport process
Nonmediate transport
Slow
○
Diffusion: more rapid for hydrophobic solutes
Slower for polar charged solutes
§
○
•
Facilitated transport
Diffusion of certain solutes accelerated by specific pores, carriers or
"permeases"
○
•
Active transport
Couple thermodynamically favorable process like ATP hydrolysis to
achieve transport against a concentration gradient
○
•
Thermodynamic of membrane transport
[C1] = extracell
•
[C2] = intracell
•
If [C1]> [C2] a solute will diffuse across the membrane until the
concentrations are equal and the process has reached equilibrium
UNLESS:
The solute is bound by macromolecules on one side of the
membrane
Reduce concentration of free solute on that side of the
membrane
§
○
The solute is an ion and diffusion is influenced by the electrical
potential
○
•
Transport of saccharides by GLUT fam
Use permease or transporters
Membrane spanning protein tht recognize specific molecules
○
•
Cotransport: symport v antiport
Symport: transport two solutes across the membrane in the same direction
•
Antiport: transport two solutes across the membrane in opposite directions
•
Sodium glucose cotransport system
Unfavorable movement is coupled with favored movement
•
Na gradient drives unfavorable transport of glucose
•
Aquaporins
Water channels that increase water transport in some tissue
Erythrocyte, salivary gland, kidney
○
•
Rapid transport of water is critical to prevent rupture of cell membrane
Plasma concentration varies
○
•
Facilitate rapid transport of water and maintain osmotic balance in cell
while keeping critical ion gradients
•
Chapter 10: Lipids
Friday, June 8, 2018
4:47 PM
Lipid Introduction
Characteristics:
Not water soluble
Due to large portion of chain being hydrocarbon
§
Lipids are rarely found free in solution
§
○
Lipids do not form large covalent polymers
Associate with each other through non covalent interactions
§
○
•
Major functions:
Energy storage
○
Membrane structure
○
Signaling
Hormones
§
○
•
Limited solubility in aqueous media
Unlike amino acid, nucleotide, and carbs
○
Amphipathic: hydrophobic and hydrophilic
○
•
Construct from long chain carboxylic acids
Fatty acids
○
•
Fatty acids
Simplest lipids
•
Can be considered monomer for lipids
•
Saturated FA's: all C-C single bonds
•
unsaturated FA's: at least one C-C double bond
Naturally occurring unsaturated fatty acids have cis orientation about
the double bond
○
Polyunsaturated: multiple double bonds
○
Monounsaturated: one double bond
○
Cause kink
○
•
Systematic description of double bond:
# of carbons: dbl bond #, C(cis) or T(trans), ∆, # at which dbl bond
starts
○
Ex. Oleic acid = 18:1c∆9
Oleic acid has 18 carbons, 1 double bond that is cis and the
double bond starts on the 9th carbon
§
○
•
Tm of fatty acid increases with the number of carbons
Due to van der Waal forces
○
•
Fatty acid and diet
Essential nutrient: Fatty acid req. for optimal metabolism that can not be
synthesized by the organims
Ex. Omega -3 fatty acids
EPA and DHA
§
○
•
Esterification of Glycerol and fatty acids
Esterification: condensation of rxn b/w an OH and a carboxylic acid
•
Rxn = reversible
Via hydrolysis
Break ester bond
§
○
•
Glycerol = tri-ol
3 Oh groups available for esterification
○
•
Fat or triglycerides: glycerol esterified with 3 FA's
Fat = suited for metabolic energy storage
C atoms are highly reduced
○
Bio thermal insulator
○
•
Fat storage and composition of some natural fats
Unsaturated fatty acids = one or more cis double bond
Saturated has no double bonds
○
•
"fluidity" of fatty acid decreases as chain length increases and number of
cis bonds decrease
•
Tm trend: linoleic < oleic<stearic
•
Fluidity: linoleic>oleic>stearic
•
Waxes and Soaps *
Natural waxes: lone chain of fatty acid is esterified to long chain of OH
Insoluble in water
○
Small polar region
○
Two long hydrocarbon chains
Completely water insoluble
§
○
•
Soap: treatment of fatty acid with a strong base
Saponification: hydrolyzation of fat with a strong base
○
Form soluble sodium or potassium salt
Precipitate w mg2+/ ca2+
§
○
Form micelles around oil
Emulsify oil
§
○
•
Synthetic detergents: not precipitated by calcium or magnesium ions
•
Membrane lipid composition
Composition: large role in function of membrane
Also denotes fluidity of the membrane
○
•
Composed of bilayer
•
All fatty acids from micelles
•
Major classes of lipids:
Glycerophospholipids
○
Sphingolipids
○
Glycosphingolipids
○
Glycoglycerolipids
○
•
Hydrophobic interior = twice as thick as polar hydrophilic head groups
•
Glycerophospholipids
Glycerophospholipids: major class of naturally occurring phospholipids
Lipid w phosphate containing group
○
•
Has two fatty acid chains
•
Names derived from phosphatidic acid
•
Sphingolipids
Cousin to phospholipids
•
Built on sphingosine
Synthesized from a palmitoyl CoA + serine residue
○
Used to make sphingolipid derivatives:
Simple:
Sphingomyelin
□
§
Complex: glycosphingolipids
Cerebroside
□
Ganglioside
□
§
○
Amino alcohol
○
•
Major component of cell membranes
Particularly in neuro membranes
○
•
Glycosphingolipids
Have glycans attached to sphingosine
Can be any sugar
○
Use for cell ID
○
•
Have long chain OH
•
Constituents of ABO blood antigens
•
Include
Cerebrosides and gangliosides
○
Common in membranes of brain and nerve cells
○
•
Glycosphingohospholipid v sphingolipids
Glycosphingophospholipid: involve glycerol
•
Sphingolipid: involve sphingosine
•
Both:
Fatty acid
○
Phosphate group
○
Hydrophilic R group
○
○
•
Cholesterol
Major portion of membrane lipids in most organisms
•
Disrupts regular fatty acid chain packing in membranes
Bulky and rigid
○
Increase membrane fluidity at low temperature
Good thing
§
○
•
Weakly amphipathic
Small hydroxyl group
○
Fatty acid esters of cholesterol = very apolar
○
•
Evidence of fluidity of membrane
Fluorescent-labeled membrane proteins: induced to fuse
From mouse to human cells
○
Protein gradually mix over time via lateral shifts (10^-6 s)
○
•
Groups of bilayer can flip flop from one side to the other
Much slower ~1 day
○
•
Membrane goes from gel to crystal state*
Gel is ordered while liquid crystal is disordered
•
Longer fatty acid chain and increased saturation of fatty acid in membrane
= higher value Tm
•
Increase concentration of cholesterol broadens transition point
But cholesterol is primarily found in eukaryotes
○
•
Bacteria: relate membrane fluidity to growth temp
Regulate fatty acid synthesis
○
Decrease in growth temp = increase unsaturation fatty acid %
Prevent transition of membrane to the gel state
§
○
•
Asymmetry of membrane lipid structure
Inner and outer leaflets can be considered asymmetrical in composition
•
Membrane proteins
Intermembrane region of membrane protein: apolar amino acid to the fatty
acyl tail of phospholipid
Regions in the membrane may be:
Beta barrels or alpha helices
§
○
•
High proportion of hydrophobic amino acids
•
Transmembrane helices = 20-25 residues
Predominantly hydrophobic
○
•
Bacteriorhodopsin: integral membrane protein*
Transmembrane protein that contains all alpha helices
Membrane spanning regions = highly hydrophobic
Typical of membrane spanning protein
§
○
•
Insertion of proteins into membranes
Cotranslational process
Require ribosome and translocon
Translocon: acts as a protein conduction channel
§
○
•
Translocon: facilitate insertion of hydrophobic region of protein in bilayer
•
Membrane rafts*
Membrane rafts: short lived dynamic structures that transiently associate
with each other to form larger platforms
Happens in response to stimuli
○
•
Rich in cholesterol, sphingolipids and glycosylphosphatidylinositol
•
Role in cell signaling and sorting of proteins into organelles
•
Sterol to liquid ratio: critical in determining raft formation
•
Membrane transport process
Nonmediate transport
Slow
○
Diffusion: more rapid for hydrophobic solutes
Slower for polar charged solutes
§
○
•
Facilitated transport
Diffusion of certain solutes accelerated by specific pores, carriers or
"permeases"
○
•
Active transport
Couple thermodynamically favorable process like ATP hydrolysis to
achieve transport against a concentration gradient
○
•
Thermodynamic of membrane transport
[C1] = extracell
•
[C2] = intracell
•
If [C1]> [C2] a solute will diffuse across the membrane until the
concentrations are equal and the process has reached equilibrium
UNLESS:
The solute is bound by macromolecules on one side of the
membrane
Reduce concentration of free solute on that side of the
membrane
§
○
The solute is an ion and diffusion is influenced by the electrical
potential
○
•
Transport of saccharides by GLUT fam
Use permease or transporters
Membrane spanning protein tht recognize specific molecules
○
•
Cotransport: symport v antiport
Symport: transport two solutes across the membrane in the same direction
•
Antiport: transport two solutes across the membrane in opposite directions
•
Sodium glucose cotransport system
Unfavorable movement is coupled with favored movement
•
Na gradient drives unfavorable transport of glucose
•
Aquaporins
Water channels that increase water transport in some tissue
Erythrocyte, salivary gland, kidney
○
•
Rapid transport of water is critical to prevent rupture of cell membrane
Plasma concentration varies
○
•
Facilitate rapid transport of water and maintain osmotic balance in cell
while keeping critical ion gradients
•
Chapter 10: Lipids
Friday, June 8, 2018 4:47 PM
Document Summary
Due to large portion of chain being hydrocarbon. Associate with each other through non covalent interactions. Saturated fa"s: all c-c single bonds unsaturated fa"s: at least one c-c double bond. Naturally occurring unsaturated fatty acids have cis orientation about the double bond. # of carbons: dbl bond #, c(cis) or t(trans), , # at which dbl bond starts. Oleic acid has 18 carbons, 1 double bond that is cis and the double bond starts on the 9th carbon. Tm of fatty acid increases with the number of carbons. Essential nutrient: fatty acid req. for optimal metabolism that can not be synthesized by the organims. Esterification: condensation of rxn b/w an oh and a carboxylic acid. Fat or triglycerides: glycerol esterified with 3 fa"s. Fat storage and composition of some natural fats. Unsaturated fatty acids = one or more cis double bond. fluidity of fatty acid decreases as chain length increases and number of cis bonds decrease.
