Chapter 6- Lipids, Membranes, and the First Cells
Molecules that contain only carbon and hydrogen are known as hydrocarbons.
Fatty acid is a simple lipid consisting of a hydrocarbon chain bonded to a polar carboxyl functional group
Hydrocarbon chains that consist of only single bonds between the carbons are called saturated.
If one or more double bonds exist in the hydrocarbon chains, then they are unsaturated.
Saturated lipids that have extremely long hydrocarbon tails, like waxes, form particularly stiff solids at room temperature
Highly unsaturated lipids are liquid at room temperature and called oils
Steroids a family of lipids distinguished by the bulky, four-ring structure
Fats are nonpolar molecules composed of three fatty acids that are linked to a three-carbon molecule called glycerol.
In organisms, energy storage is the primary role of fats.
The glycerol and fatty acid molecules become joined by what is called an ester linkage.
An ester linkage occurs when two atoms ( one of them carrying a double-bonded oxygen, often a carbonyl group) are linked together by an oxygen.
Phospholipids consist of a glycerol that is linked to a phosphate group and two hydrocarbon chains of either isoprenoids or fatty acids.
Substances that contain both hydrophilic and hydrophobic regions are amphipathic.
A lipid bilayer is created when lipid molecules align in paired sheets.
Micelles tend to form from free fatty acids or other simple amphipathic lipids with single hydrocarbon chains.
Micelles and phospholipid bilayers form spontaneously in water-no input of energy is required.
Vesicles are small bubble-like structures consisting of lipid bilayers surrounding a small amount of aqueous solution.
Artificially generated membrane-bound vesicles like these are called liposomes.
Liposomes provide a three-dimensional model that mimics a membrane-bound cell.
The permeability of a structure is its tendency to allow a given substance to pass through it.
Selective permeability means that some substances cross a membrane more easily than other substances do.
A membrane’s permeability is closely related to its level of fluidity, which is a measure of molecular mobility. As temperature drops, molecules in a bilayer move more slowly and become less fluid.
Spontaneous movement of molecules and ions is known as diffusion.
A difference in solute concentrations creates what is called a concentration gradient.
Solutes move randomly in all directions, but when a concentration gradient exists, there is a net movement from regions of high concentration to regions of low concentration.
When substances diffuse across a membrane in the absence of an outside energy source, it is known as passive transport.
The movement of water is a special case of diffusion that is given its own name: osmosis.
Osmosis occurs only when solutions are separated by a membrane that permits water to cross, but holds back some or all of the solutes-that is, a selectively permeable membrane
If the solution outside the vesicle has a higher concentration of solutes than the interior has, the solution outside is said to be hypertonic relative to the inside of the vesicle.
If the solution outside the vesicle has a lower concentration of solutes than the interior has, the outside solution is said to be hypotonic relative to the inside of the vesicle.
If solute concentrations are equal on both sides of the membrane, the outside is said to be isotonic.
Simple vesicle-like structures that harbor nucleic acids are referred to as protocells.
Their hypothesis was called the fluid-mosaic model. Singer and Nicolson suggested that membranes are a dynamic and fluid mosaic of phospholipids and different types of proteins.
The method is called freeze-fracture electron microscopy because the steps involve freezing and fracturing the membrane before examining it with a scanning electron microscope (SEM), which produces images of an object’s surface
Some proteins span the membrane and have segments facing both the interior and the exterior of the cell which are called integral membrane proteins or transmembrane proteins.
Proteins that bind to membrane lipids or integral membrane proteins without passing through it are called peripheral membrane proteins.
In cells, ions routinely cross membranes by way of specialized transmembrane proteins called ion channels.
When considered together, concentration and electrical gradients are called an electrochemical gradient.
Cells have many different types of pore-like channel proteins in their membranes.
Gated channels open or close in response to a signal, such as the binding of a particular substance or a change in the electrical voltage across the membrane
When transmembrane proteins assist the passive transport of substances that otherwise would not cross a membrane readily, the process is called facilitated diffusion.
The movement of water and K+ are examples of facilitated diffusion through channel proteins, but facilitated diffusion can also occur through specialized membrane proteins called carrier proteins.
Transport against a gradient is called active transport.
A classic example of how structural changes can lead to active transport is provided in the sodium-potassium pump,
Gradients are crucial to the function of the cell, in part because they make it possible for cells to engage in secondary active transport-also known as cotransport.
Molecules that contain only carbon and hydrogen are known as hydrocarbons.
Fatty acid is a simple lipid consisting of a hydrocarbon chain bonded to a polar carboxyl functional group
Hydrocarbon chains that consist of only single bonds between the carbons are called saturated.
If one or more double bonds exist in the hydrocarbon chains, then they are unsaturated.
Saturated lipids that have extremely long hydrocarbon tails, like waxes, form particularly stiff solids at room temperature
Highly unsaturated lipids are liquid at room temperature and called oils
Steroids a family of lipids distinguished by the bulky, four-ring structure
Fats are nonpolar molecules composed of three fatty acids that are linked to a three-carbon molecule called glycerol.
In organisms, energy storage is the primary role of fats.
The glycerol and fatty acid molecules become joined by what is called an ester linkage.
An ester linkage occurs when two atoms ( one of them carrying a double-bonded oxygen, often a carbonyl group) are linked together by an oxygen.
Phospholipids consist of a glycerol that is linked to a phosphate group and two hydrocarbon chains of either isoprenoids or fatty acids.
Substances that contain both hydrophilic and hydrophobic regions are amphipathic.
A lipid bilayer is created when lipid molecules align in paired sheets.
Micelles tend to form from free fatty acids or other simple amphipathic lipids with single hydrocarbon chains.
Micelles and phospholipid bilayers form spontaneously in water-no input of energy is required.
Vesicles are small bubble-like structures consisting of lipid bilayers surrounding a small amount of aqueous solution.
Artificially generated membrane-bound vesicles like these are called liposomes.
Liposomes provide a three-dimensional model that mimics a membrane-bound cell.
The permeability of a structure is its tendency to allow a given substance to pass through it.
Selective permeability means that some substances cross a membrane more easily than other substances do.
A membrane’s permeability is closely related to its level of fluidity, which is a measure of molecular mobility. As temperature drops, molecules in a bilayer move more slowly and become less fluid.
Spontaneous movement of molecules and ions is known as diffusion.
A difference in solute concentrations creates what is called a concentration gradient.
Solutes move randomly in all directions, but when a concentration gradient exists, there is a net movement from regions of high concentration to regions of low concentration.
When substances diffuse across a membrane in the absence of an outside energy source, it is known as passive transport.
The movement of water is a special case of diffusion that is given its own name: osmosis.
Osmosis occurs only when solutions are separated by a membrane that permits water to cross, but holds back some or all of the solutes-that is, a selectively permeable membrane
If the solution outside the vesicle has a higher concentration of solutes than the interior has, the solution outside is said to be hypertonic relative to the inside of the vesicle.
If the solution outside the vesicle has a lower concentration of solutes than the interior has, the outside solution is said to be hypotonic relative to the inside of the vesicle.
If solute concentrations are equal on both sides of the membrane, the outside is said to be isotonic.
Simple vesicle-like structures that harbor nucleic acids are referred to as protocells.
Their hypothesis was called the fluid-mosaic model. Singer and Nicolson suggested that membranes are a dynamic and fluid mosaic of phospholipids and different types of proteins.
The method is called freeze-fracture electron microscopy because the steps involve freezing and fracturing the membrane before examining it with a scanning electron microscope (SEM), which produces images of an object’s surface
Some proteins span the membrane and have segments facing both the interior and the exterior of the cell which are called integral membrane proteins or transmembrane proteins.
Proteins that bind to membrane lipids or integral membrane proteins without passing through it are called peripheral membrane proteins.
In cells, ions routinely cross membranes by way of specialized transmembrane proteins called ion channels.
When considered together, concentration and electrical gradients are called an electrochemical gradient.
Cells have many different types of pore-like channel proteins in their membranes.
Gated channels open or close in response to a signal, such as the binding of a particular substance or a change in the electrical voltage across the membrane
When transmembrane proteins assist the passive transport of substances that otherwise would not cross a membrane readily, the process is called facilitated diffusion.
The movement of water and K+ are examples of facilitated diffusion through channel proteins, but facilitated diffusion can also occur through specialized membrane proteins called carrier proteins.
Transport against a gradient is called active transport.
A classic example of how structural changes can lead to active transport is provided in the sodium-potassium pump,
Gradients are crucial to the function of the cell, in part because they make it possible for cells to engage in secondary active transport-also known as cotransport.