29 Questions
What is the major sterol found in animal cell membranes?
Cholesterol
What type of molecules can readily diffuse through the hydrophobic regions of the membrane?
Gases
Which type of FA is represented by 'S' in the amphipathic structure?
Saturated FA
What type of molecules is the lipid bilayer impermeable to?
Charged and water-soluble molecules
What is the slowest molecule to pass through the membrane?
Sodium (Na+)
Which type of lipids are considered amphipathic?
Phospholipids
What is the backbone for Glycerophospholipids?
Glycerol-phosphate
Which compound is NOT a type of Glycolipid?
Cardiolipin
What type of lipids are Galactolipids?
Not present in mammalians, present in plants
Which alcohol group gives a phospholipid the name Phosphatidic acid?
Glycerol
Which lipid is NOT found in mammalian cell membranes?
Sulphatides
What is the most common sterol in animal cell membranes?
Cholesterol
What type of molecule is a glycoconjugate?
A biologically active molecule formed by the covalent joining of a carbohydrate to a protein or lipid
Which type of membrane protein is loosely bound to the membrane and can move through it?
Peripheral proteins
What is the function of glycophorin in human erythrocytes?
Increases the flip-flop frequency of membrane phospholipids
Which process do oligosaccharides play a central role in?
Blood clotting
How are carbohydrates typically attached to the plasma membrane according to the text?
Attached to the amino-terminal portion outside the external surface
What is the major function of membrane proteins?
Transporting molecules, acting as channels, and serving as receptors
What is the term used to describe the temperature at which membrane structure transitions from an ordered to a disordered state?
Transition temperature (Tm)
How do unsaturated fatty acids affect the fluidity of a membrane?
Increase fluidity
What effect does the chain length of a fatty acid have on hydrophobicity?
Increases hydrophobicity
How does unesterified cholesterol affect membrane fluidity at temperatures below the transition temperature?
Increases fluidity
What role do glycoconjugates play in eukaryotic cell membranes?
Form a carbohydrate layer (glycocalyx)
What is the significance of the carbohydrate layer (glycocalyx) on eukaryotic cell membranes?
Serves as an information-rich surface
Which glycolipid can be converted to sulfogalactosylceramide (sulfatide) by adding a sulfo group to galactose?
Sulfatides
What is the principal sialic acid found in human tissues?
Neuraminic acid
Which component of gangliosides binds to galactose or N-acetyl galactosamine?
Oligosaccaride
What property of cholesterol allows it to modify the fluidity of membranes?
Amphipathic nature
What is directly proportional to temperature regarding membrane fluidity?
Fluidity
Study Notes
Cell Membranes
- Triacylglycerols (TAGs) and cholesterol-esters are pure hydrophobic molecules, not present in membranes.
- Individual lipid and protein units in a membrane form a fluid mosaic model with amphipathic structure.
Properties of Cell Membranes
- Lipid bilayer is impermeable to most water-soluble molecules due to its hydrophobic core.
- Gases like oxygen, CO2, and nitrogen can readily diffuse through the hydrophobic regions of the membrane.
- Permeability coefficient measures a molecule's ability to diffuse across a permeability barrier.
- H2O can easily pass through the membrane, while Na+ is the slowest to pass.
Plasma Membrane Composition
- Membranes consist of lipid, carbohydrate, and protein parts.
- Major lipids in mammalian membranes are phospholipids, glycosphingolipids, and sterols.
- Cholesterol is the most common sterol in animal cell membranes.
Lipid Types
- Phospholipids:
- Glycerophospholipids (phosphatidate derivative)
- Examples: phosphatidic acid, cardiolipin, plasmalogens, platelet-activating factor
- Glycolipids:
- Glycosphingolipids (GSLs): cerebrosides, sulphatides, globoside, gangliosides
- Galactolipids (not present in mammals, found in plants)
- Sterols: cholesterol is the most common sterol in animal cell membranes.
Phospholipid Structure and Function
- Phospholipids have a glycerol-phosphate backbone and a fatty acid tail.
- Phosphatidic acid is derived from phosphatidate and an alcohol.
- Phospholipids can be named based on the attached alcohol group (e.g., choline, ethanolamine).
Glycolipids
- Glycosphingolipids (GSLs) have a sphingosine backbone and a ceramide derivative.
- Examples: sulfatides, gangliosides
- Sulfatides have a sulfo group attached to the galactose.
- Gangliosides are complex glycosphingolipids with one or more sialic acid molecules.
Sterol Function
- Cholesterol is amphipathic and intercalates among phospholipids in the membrane.
- Cholesterol acts as a buffer to modify the fluidity of membranes.
Factors Affecting Membrane Fluidity
- Temperature: directly proportional to fluidity
- Unsaturated fatty acids: directly proportional to fluidity
- Fatty acid chain length: inversely proportional to fluidity
- Cholesterol: decreases fluidity at high concentrations, increases fluidity at low concentrations
Carbohydrates in Cell Membranes
- Glycoconjugates: proteoglycans, glycoproteins, and glycolipids
- Oligosaccharide chains attached to components of the plasma membrane form a carbohydrate layer (glycocalyx).
- Carbohydrates are covalently joined to proteins or lipids to form biologically active molecules.
- Carbohydrate presence on the outer surface of the plasma membrane has been shown using plant lectins.
Membrane Proteins
- Proteins are the major functional molecules of membranes, including enzymes, pumps, transporters, channels, and receptors.
- Membrane proteins are asymmetrically distributed in the lipid bilayer and can move through it.
- Integral and peripheral proteins are classified based on their binding to the membrane.
Test your knowledge on glycolipids, focusing on glycosphingolipids, sulfatides, and gangliosides. Learn about the structures and functions of these important membrane lipids.
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