Podcast
Questions and Answers
Which characteristic is common to lipids in cells?
Which characteristic is common to lipids in cells?
- Solubility in polar solvents
- Solubility in water
- Insolubility in organic solvents
- Insolubility in water (correct)
What is the primary role of triacylglycerols?
What is the primary role of triacylglycerols?
- Immediate energy source for cells
- Structural component of cell membranes
- Important energy storage (correct)
- Catalyzing biochemical reactions
Which lipid is most likely found in higher concentration in mammalian cell membranes?
Which lipid is most likely found in higher concentration in mammalian cell membranes?
- Phosphatidylglycerol
- Triacylglycerol
- Cholesterol (correct)
- Phosphatidic acid
Which membrane lipid is found in internal membranes?
Which membrane lipid is found in internal membranes?
Which lipid is commonly replaced by ergosterol in fungal cell membranes?
Which lipid is commonly replaced by ergosterol in fungal cell membranes?
Lipopolysaccharide (LPS) is a characteristic component of the membranes of which bacteria?
Lipopolysaccharide (LPS) is a characteristic component of the membranes of which bacteria?
What is a key feature of the membrane lipids in Staphylococcus aureus?
What is a key feature of the membrane lipids in Staphylococcus aureus?
Which characteristic distinguishes glycerophospholipids from triacylglycerols?
Which characteristic distinguishes glycerophospholipids from triacylglycerols?
What is the basic structure of glycerophospholipids compared to triacylglycerols?
What is the basic structure of glycerophospholipids compared to triacylglycerols?
If a researcher identifies a lipid containing sphingosine, a fatty acid, and a carbohydrate, how should this lipid be classified?
If a researcher identifies a lipid containing sphingosine, a fatty acid, and a carbohydrate, how should this lipid be classified?
Which of the following is characteristic of sphingomyelin?
Which of the following is characteristic of sphingomyelin?
What distinguishes cerebrosides from other glycolipids?
What distinguishes cerebrosides from other glycolipids?
What role does cholesterol play in animal cell membranes?
What role does cholesterol play in animal cell membranes?
What is the effect of increasing the proportion of unsaturated fatty acids in a cell membrane?
What is the effect of increasing the proportion of unsaturated fatty acids in a cell membrane?
Which physical characteristic is associated with lipids containing predominantly saturated fatty acids?
Which physical characteristic is associated with lipids containing predominantly saturated fatty acids?
Which type of molecule is most permeable through a lipid bilayer?
Which type of molecule is most permeable through a lipid bilayer?
What is the primary function of flippases in cell membranes?
What is the primary function of flippases in cell membranes?
Which of the following lipids is exclusively found in the outer leaflet of the plasma membrane?
Which of the following lipids is exclusively found in the outer leaflet of the plasma membrane?
How does the presence of cis double bonds in fatty acid tails affect membrane packing?
How does the presence of cis double bonds in fatty acid tails affect membrane packing?
Which factor primarily determines the transition temperature of a lipid bilayer?
Which factor primarily determines the transition temperature of a lipid bilayer?
Which lipid modification would be expected to raise the melting temperature ($T_m$) of a phospholipid bilayer composed primarily of palmitic acid?
Which lipid modification would be expected to raise the melting temperature ($T_m$) of a phospholipid bilayer composed primarily of palmitic acid?
How do bacteria adapt their membrane composition in response to decreasing environmental temperature?
How do bacteria adapt their membrane composition in response to decreasing environmental temperature?
What is the role of sterols in a cell membrane?
What is the role of sterols in a cell membrane?
What effect does cholesterol have on membrane fluidity at high temperatures?
What effect does cholesterol have on membrane fluidity at high temperatures?
What is the effect of cholesterol on membrane fluidity at low temperatures?
What is the effect of cholesterol on membrane fluidity at low temperatures?
What is a characteristic feature of membrane domains?
What is a characteristic feature of membrane domains?
Which statement accurately describes membrane asymmetry?
Which statement accurately describes membrane asymmetry?
If a phospholipid has one saturated and one unsaturated fatty acid, how does this arrangement affect its shape and packing in a membrane?
If a phospholipid has one saturated and one unsaturated fatty acid, how does this arrangement affect its shape and packing in a membrane?
What is the effect of increasing the chain length of saturated fatty acids in membrane lipids?
What is the effect of increasing the chain length of saturated fatty acids in membrane lipids?
How does unsaturation affect the physical properties of fatty acids in glycerophospholipids?
How does unsaturation affect the physical properties of fatty acids in glycerophospholipids?
Why are triacylglycerols an important energy storage molecule?
Why are triacylglycerols an important energy storage molecule?
If a patient is diagnosed with Tay-Sachs disease that affects ganglioside GM2, which process is most likely impaired?
If a patient is diagnosed with Tay-Sachs disease that affects ganglioside GM2, which process is most likely impaired?
The antibiotic daptomycin inserts into bacterial membranes and forms pores causing rapid depolarization, resulting in loss of membrane potential and cell death. If bacteria are grown in the presence of daptomycin, what change would be most likely found to increase its survival?
The antibiotic daptomycin inserts into bacterial membranes and forms pores causing rapid depolarization, resulting in loss of membrane potential and cell death. If bacteria are grown in the presence of daptomycin, what change would be most likely found to increase its survival?
Which of the following is the correct order of how fast a molecule can cross a lipid bilayer?
Which of the following is the correct order of how fast a molecule can cross a lipid bilayer?
Given the following melting points, which fatty acid is most likely to be found in higher abundance in organisms that live in colder temperatures?
Given the following melting points, which fatty acid is most likely to be found in higher abundance in organisms that live in colder temperatures?
Which outcome would most likely be accelerated in a cell deficient in flippases?
Which outcome would most likely be accelerated in a cell deficient in flippases?
Which of the following lipids is based on a sphingosine backbone rather than glycerol?
Which of the following lipids is based on a sphingosine backbone rather than glycerol?
In the context of membrane lipids, what is the defining characteristic of a cerebroside?
In the context of membrane lipids, what is the defining characteristic of a cerebroside?
Which of the following best explains how cholesterol affects membrane fluidity?
Which of the following best explains how cholesterol affects membrane fluidity?
What is a key structural difference between glycerophospholipids and sphingolipids?
What is a key structural difference between glycerophospholipids and sphingolipids?
How does the presence of multiple cis double bonds in the fatty acid tails of membrane lipids affect membrane packing and fluidity?
How does the presence of multiple cis double bonds in the fatty acid tails of membrane lipids affect membrane packing and fluidity?
Which of the following lipids is uniquely found in the myelin sheaths of neurons and is crucial for proper nerve function?
Which of the following lipids is uniquely found in the myelin sheaths of neurons and is crucial for proper nerve function?
A researcher is studying a membrane lipid and determines that it contains sphingosine, a fatty acid, and a complex oligosaccharide. How should this lipid be classified?
A researcher is studying a membrane lipid and determines that it contains sphingosine, a fatty acid, and a complex oligosaccharide. How should this lipid be classified?
How would you best describe membrane asymmetry in biological membranes?
How would you best describe membrane asymmetry in biological membranes?
Consider a mutation that impairs the function of enzymes responsible for synthesizing polyunsaturated fatty acids in a cell. What would be the most likely consequence regarding membrane fluidity?
Consider a mutation that impairs the function of enzymes responsible for synthesizing polyunsaturated fatty acids in a cell. What would be the most likely consequence regarding membrane fluidity?
Imagine a novel synthetic lipid that contains two saturated fatty acid tails, a glycerol backbone, a phosphate group, and a modified sugar alcohol that sterically hinders hydrogen bond formation. How would this lipid affect membrane properties compared to a standard glycerophospholipid?
Imagine a novel synthetic lipid that contains two saturated fatty acid tails, a glycerol backbone, a phosphate group, and a modified sugar alcohol that sterically hinders hydrogen bond formation. How would this lipid affect membrane properties compared to a standard glycerophospholipid?
Flashcards
Lipids
Lipids
Molecules in cells that are water-insoluble (hydrophobic) but soluble in organic solvents
Triacylglycerols
Triacylglycerols
Dietary and storage lipids, composed of glycerol and three fatty acids.
Glycerophospholipids
Glycerophospholipids
Class of polar membrane lipids based on glycerol. The most common type of polar membraine lipids.
Amphipathic molecules
Amphipathic molecules
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Phosphatidylcholine
Phosphatidylcholine
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Sphingosine-based phospholipids
Sphingosine-based phospholipids
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Sphingomyelin
Sphingomyelin
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Glycolipids/Glycosphingolipids
Glycolipids/Glycosphingolipids
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Cerebrosides
Cerebrosides
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Gangliosides
Gangliosides
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Cholesterol
Cholesterol
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Saturated fatty acids
Saturated fatty acids
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Mono-unsaturated fatty acids
Mono-unsaturated fatty acids
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Polyunsaturated fatty acids
Polyunsaturated fatty acids
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Sterols
Sterols
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Membrane Fluidity
Membrane Fluidity
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Longer chain FAs
Longer chain FAs
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Unsaturated FAs
Unsaturated FAs
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Cholesterol
Cholesterol
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Flip-flop
Flip-flop
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Lateral Diffusion
Lateral Diffusion
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Study Notes
Lipids and Fats
- Lipids are water-insoluble (hydrophobic) but soluble in organic solvents.
- Examples of lipids:
- Triacylglycerols (fats and oils)
- Glycerophospholipids
- Steroids and cholesterol
Dietary and Storage Lipids
- Triacylglycerols are hydrophobic molecules.
- They form droplets in water or aqueous environments.
- Triacylglycerols are important energy storage molecules.
Membrane Lipids
- Membranes contain cholesterol.
- Membranes' external leaflet is zwitterionic in healthy cells.
- PS exposure occurs in some transformed cells.
- Some membranes have internal membranes.
- Red blood cells are rich in cholesterol.
- In parasitized cells, cholesterol is reduced.
- There is possible PS exposure post infection.
- Plasmodium falciparum has low cholesterol content.
- Candida albicans replaces cholesterol with ergosterol in most fungi.
- Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii do not have sterols.
- They contain a mixture of zwitterionic (PE) and anionic (PG) lipids.
- They also contain Lipopolysaccharide (LPS).
- Staphylococcus aureus, Streptococcus spp., Enterococcus, Listeria monocytogenes, and Clostridium difficile do not have sterols.
- They contain anionic lipids only (PG and cardiolipin).
- They contain peptidoglycan, lipoteichoic acid, and capsule polysaccharides.
- HIV-1 virion (I) is an enveloped virus rich in PS, cholesterol, and sphingolipids.
- SARS-CoV-2 (r) is an enveloped virus rich in PS and/or Pl
Asymmetry in Cell Membranes
- Cell membranes exhibit asymmetry in their composition.
Membrane Permeability
- Cell membranes are selectively permeable.
- Hydrophobic molecules (O₂, N₂, benzene, short-chain fatty acids) can permeate.
- Small uncharged polar molecules (H₂O, CO₂, urea, glycerol) can permeate.
- Large uncharged polar molecules (glucose, sucrose) can permeate.
- Ions (H+, Na+, Mg2+, HCO3-, K+, Ca2+, Cl-) can permeate.
- Charged polar molecules (amino acids, ATP) can permeate.
- The lipid bilayer's permeability is higher for uncharged, non-polar, and small molecules.
Membrane Proteins
- Proteins play important roles in membrane function like transporters, anchors, receptors, and enzymes
Membrane Lipids (cont.)
- Polar amphipathic molecules.
- Phospholipids are the most common class of polar membrane lipids, based on glycerol (glycerophospholipids).
- Glycerophospholipids have a basic structure compared to triacylglycerols.
- Instead of a third fatty acid, they have a phosphate attached to a polar head group.
Glycerophospholipids
- Glycerophospholipids have a polar head group and nonpolar tails.
- Choline, phosphate, and glycerol compose of head.
- Fatty acids are the tail.
Polar Head Groups of Phospholipids
- Amino alcohols include ethanolamine, choline, and serine.
- Cyclic alcohols or sugar alcohols include inositol.
Glycerophospholipid Nomenclature
- Phosphatidylcholine is the most common glycerophospholipid.
Phospholipid Nomenclature
- DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) has acyl chains 14:0 x 2 (1,2-ditetradecanoyl-sn-glycero-3-phosphocholine).
- POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) has acyl chains 16:0, 18:1 (1-hexadecanoyl-2--(9Z-octadecenoyl)-sn-glycero-3-phosphocholine).
Glycerophospholipid Summary
- Ethanolamine has the formula HOCH₂CH₂NH₃+ and forms Phosphatidylethanolamine ('cephalin').
- Choline has the formula HOCH₂CH₂N⁺(CH₃) and forms Phosphatidylcholine ('lecithin').
- Serine has the formula HOCH₂CHNH₃+COO and forms Phosphatidylserine.
- Inositol has the formula (-CHOH-)₆ and forms Phosphatidylinositol.
Sphingosine-Based Phospholipids
- Other phospholipids are based on sphingosine rather than glycerol.
- Sphingosine has a backbone quite like glycerol.
- It also has a permanent hydrocarbon chain (C15).
Sphingomyelin
- Sphingomyelin is found in myelin sheaths of neurons.
- Sphingomyelin is formed from sphingosine backbone.
- Additions to the structure: a fatty acid, a phosphate, and a polar head group (choline).
Membrane Lipids Summary
- Phospholipids:
- Glycerol-based (glycerophospholipids)
- Sphingosine based (sphingomyelin)
- Glycolipids/glycosphingolipids:
- Sphingosine-based, containing no phosphate, but with a carbohydrate polar head group.
Glycolipids
- Glycolipids are based on sphingosine (e.g., cerebrosides).
- Glycolipids have no phosphate.
- They have a single sugar head group (glucose or galactose).
- Glycolipids are important in brain cell membranes.
Gangliosides
- Glycolipids that contain no phosphate.
- They contain an oligosaccharide head group.
- ABO blood group determinants are examples.
Cholesterol
- Cholesterol is a necessary component of animal cell membranes.
- Its rigid structure inserts between phospholipids, modulating membrane fluidity.
- Cholesterol is hydrophilic and hydrophobic.
Fatty Acids and Membrane Properties
- Saturated fatty acids have only single C-C bonds.
- Palmitic acid (C16) is the most common FA in animals, plants, and microorganisms.
- Named from PALM oil, with a melting point of 62 - 63° C.
- Stearic acid (C18) gets its name 'Waxy' from the Greek word for tallow.
- It has a melting point of 69 - 70° C.
Unsaturated Fatty Acids
- Mono-unsaturated FAs have one double C=C bond.
- Oleic acid is a C18 mono-unsaturated FA.
- It is named from OLIVE oil with a melting point of 13 - 14° C.
- Naturally occurring FAs is nearly always in cis configuration.
- Polyunsaturated FAs have two or more C=C bonds.
- Linoleic acid and Linolenic acid are examples.
- Melting points are even lower such as:
- Linoleic acid, -9°C
- Linolenic acid, -17°C
- These two are essential in diet (cannot be synthesized).
- Arachidonic acid (20:4 Δ5,8,11,14) has an important function in cell signaling.
Membrane Formation
- Bilayer formation is energetically favorable.
- Vesicle formation is energetically favorable.
- New membrane is formed in the ER and carried by vesicles.
Lipid Shape
- Differences in lipid shape enable curvature.
- DOPE has a wedge shape.
- Lyso-lauryl PC has a cone shape.
Membrane Shape
- Shape helps manipulate membrane curvature.
- Lipids are flexible with fluid motion in the layers (but rare on other layers)
Membrane Fluidity
- Cell membranes must stay in 'liquid crystal' form for cell function.
- Longer chain FAs increase transition temperature.
- They increase Van der Waals interactions and decrease membrane fluidity.
- Unsaturated FAs reduce transition temperature.
- They increase membrane fluidity
- Kinks introduced by cis double bonds cause looser packing of fatty acid tails, reducing Van der Waals interactions.
- Bacteria respond to changing environment by varying the proportion of unsaturated fatty acids in the membrane.
- Animals maintain a stable body temperature.
Cholesterol and Membrane Fluidity
- Cholesterol acts as a key regulator of fluidity in animal cell membranes.
- At high temperatures, it 'stiffens' the membrane by filling space between unsaturated FAs.
- At low temperatures, it increases fluidity by preventing FA tails from packing too closely.
- Cholesterol acts as a ‘fluidity buffer' by 'blurring' the membrane transition temperature.
Membrane Order
- Sterols increase membrane order and can promote domain formation.
- Membrane domains are more mosaic and less fluid.
Tay-Sachs Disease
- Lysosomal storage disorder.
- Mutation affects processing of ganglioside GM2 in the brain.
Liposomes
- Liposomes are used for drug delivery.
- “Theranostic” is therapeutic and diagnostic.
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