Chapter 6: Lipids and Membranes
What particles struggle to move across lipid bilayers quickly?
-Small, uncharged, polar molecules (H2O, Glycerol) -Large, uncharged, polar molecules (Glucose, Sucrose)
What do membranes do?
1) Compartmentalization: Membranes separate material serving as barriers to keep things inside the cell in, and things outside the cell out. 2) Allow the exchange of material through the use of receptors found on the plasma membrane.
What is a lipid bilayer?
A lipid bilayer is created when lipid molecules align in 2 closely, paired sheets. This results in the hydrophilic heads in each layer facing and interacting with the surrounding solution, while the hydrophobic tails face and interact with each other inside the bilayer.
What is fluidity?
A measure of molecular mobility
How does temperature affect the fluidity and permeability of membranes?
A membranes permeability is closely related to its level of fluidity. So, when temperature drops, molecules in a bilayer move more slowly and become less fluid. At very low temperatures, lipid bilayers even begin to solidify.
What is an amphipathic molecule?
A molecule that has both a hydrophilic region and a hydrophobic region. This being said phospholipids are amphipathic.
What is the composition of biological membranes?
Biological membranes are composed of amphipathic lipids, mainly phospholipids.
What are the properties of biological membranes?
Biological membranes are fluid, amphipathic, and have selective permeability.
How does bond saturation affect hydrocarbon chains?
Bond saturation in hydrocarbon chains, affects the molecular structure of lipids. Saturation also profoundly changes the physical state of lipids.
What is the structural formula of a fatty acid?
a simple lipid consisting of a hydrocarbon chain bonded to a polar carboxyl functional group (-COOH)
What is the composition of fats?
Fats are nonpolar molecules composed of three fatty acids that are linked to glycerol, a 3-carbon molecule.
What are fats?
Fats are nonpolar molecules, used in organisms primarily for energy storage.
How are fats formed?
Fats form by an ester linkage between glycerol and 3 fatty acid molecules.
Explain why fatty acids are not considered monomers of fats.
Fatty acids are not considered monomers since they are not linked into chains and for this same reason fats are not polymers.
How do hydrocarbons affect solubility of lipids?
Hydrocarbons are nonpolar (electrons are shared equally in carbon to hydrogen (C-H) bonds) and do not dissolve in water. Therefore, lipids are mostly hydrophobic due to their significant hydrocarbon component.
What does hypotonic mean?
less solute, more water
Why are there 3 different types of lipids found in cells?
There are 3 different types of lipids found in cells since the structure of lipids vary widely, due to the many different ways their hydrocarbon skeletons can be put together.
What is a physical characteristic of unsaturated lipids?
Unsaturated lipids have relatively low melting points, so they are liquid at room temperature. Oils are an example of unsaturated lipids.
Why is the type of bond between carbons in hydrocarbon chains a key factor in lipid structure and function?
When 2 carbon atoms form a double bond, they are locked into place and cannot rotate freely. As a result, certain double bonds between carbon atoms produce a "kink" in an otherwise straight hydrocarbon chain. This causes hydrocarbon chains to be saturated or unsaturated.
Why is a concentration gradient important for diffusion?
When a concentration gradient exists, there is a net movement from regions of high concentration to regions of low concentration.
What is an ester linkage?
When a dehydration reaction occurs between a hydroxyl group (-OH) of glycerol and the carboxyl group (-COOH) of a free fatty acid.
What does osmosis (the movement of water) look like?
When a solute cannot pass through a separating membrane, then water moves by osmosis, the solutions on both sides of the membrane experience a change in volume as well as a change in solute concentration.
What is passive transport?
When substances diffuse (move) across a membrane in the absence of an outside energy source (so, no energy is invested)
How is life affected by osmosis?
When water moves across the membranes of cells and vesicles, the volume and concentration of solutes enclosed within the membrane will change. A rapid change in amount of water can be catastrophic for cells.
What is a concentration gradient?
A difference in the solute concentration of a substance from one location to another
What are steroids?
A family of lipids characterized by a carbon skeleton consisting of a bulky, 4-ring structure
What is a fatty acid?
A fatty acid is the monomer of a lipid; that is a key building block of important lipids found in organisms
What does it mean that a hydrocarbon chain is saturated?
A hydrocarbon chain is saturated since the maximum number of hydrogen atoms that can attach to the carbon skeleton. As a result, hydrocarbon chains consist of only single bonds between the carbons, so hydrocarbon chains do not contain a double bond.
What does it mean that a hydrocarbon chain is unsaturated?
A hydrocarbon chain is unsaturated since fewer than the maximum number of attached hydrogen atoms can attach to the carbon skeleton. As a result, hydrocarbon chains consist of one or more double bonds between the carbons.
How does cholesterol affect the behavior of the membrane?
Cholesterol orients in the membrane with hydrophobic steroid rings buried deeply in hydrocarbon tails. As a result of this, the bulky cholesterol rings force the phospholipid tails closer to each other, increasing their packing density, causing the membranes to become less permeable.
What 2 types of structures do amphipathic lipids form when placed in an aqueous solution?
In an aqueous solution, fats spontaneously form: 1) Micelles 2) Lipid bilayer
Why are lipid bilayers important?
Lipid bilayers are highly selective about which particles in solution cross the membrane barrier.
How are lipid bilayers formed?
Lipid bilayers form spontaneously (no input of energy needed) in water, from longer and bulkier lipids; 2-flat sheets of lipids that came together
What are lipids?
Lipids are a wide-range term for carbon-containing compounds that are defined by their physical property rather than chemical structure.
What is the composition of lipids?
Lipids are composed of carbon, hydrogen and oxygen atoms. As a result, they have a large hydrocarbon component.
Why are lipids insoluble in water?
Lipids are insoluble in water due to their high proportion of hydrocarbons, nonpolar carbon to carbon (C-C) and carbon to hydrogen (C-H) bonds, relative to polar functional groups.
What is the structure of lipids?
Lipids do not posses a shared chemical structure. So, the structure of lipids varies widely because their hydrocarbon skeletons can be put together in may different ways.
What is the function of lipids?
Lipids found in organisms have a wide array of functions: -storing chemical energy -acting as pigments that capture or respond to sunlight -serving as signals between cells -forming waterproof coatings (eg. on leaves and skin) -acting as vitamins used in many cellular processes -the most notable function is their role in cell membranes
What is the significant physical property of lipids?
The significant physical property of Lipids their insolubility to water.
What is membrane fluidity?
Membrane fluidity is a degree of movement of the lipids in a membrane
What is the composition of membrane-forming lipids?
Membrane-forming lipids have a polar, hydrophilic region ("head") and a nonpolar, hydrophobic region ("tail")
What is a micelles?
Micelles are tiny droplets created when the hydrophilic heads of a set of lipids face outward and interact with the water and form hydrogen bonds, while the hydrophobic tails face the interior and interact with themselves, away from water.
How are micelles formed?
Micelles form spontaneously (no input of energy needed) in water, from short and small lipids
Explain what hydrocarbons are.
Molecules that only contain carbon and hydrogen.
When diffusion down a concentration gradient (from high to low concentration), is energy needed?
No, since diffusion down a concentration gradient (from high to low concentration) happens through passive transport.
Are all steroids the same?
No. Steroids differ from each other by the functional or side groups attached to different carbons in the hydrophobic bulky, 4-ring structure.
What happens after diffusion occurs down a concentration gradient (from high to low concentration)?
Once the molecules or ions are randomly distributed throughout a solution, there is no longer a net movement of solutes across the membrane because they are equally likely to move in any direction (equilibrium is established).
Why does bond saturation, in hydrocarbon chains, matter for lipids?
The type of bond between carbons in hydrocarbon chains is a key factor in lipid structure and function.
What is osmosis?
Osmosis occurs only when solutions are separated by a selectively permeable membrane that permits the movement of water to cross; diffusing from the side with a lower concentration of solute to the side with a higher concentration of solute.
What are phospholipids?
Phospholipids consist of a glycerol that is linked to phosphate group and 2 hydrocarbon chains in its molecule.
How does bond saturation affect the behavior of the membrane?
Phospholipids containing unsaturated hydrocarbon tails form bilayers that have more gaps and are more permeable than bilayers formed from phospholipids with saturated hydrocarbon tails.
What is a physical characteristic of saturated lipids?
Saturated lipids have relatively high melting points, so they are solid at room temperature. Such as butter and waxes.
Why is selective permeability important?
Selective permeability is a critical in organisms because it controls what passes between the exterior and interior environments.
What is selective permeability in lipid bilayers?
Selective permeability means that some substances cross a membrane more easily than other substances do.
What is the composition of a saturated lipid?
Since saturated lipids only have single bonds, the composition of hydrocarbon chains are straight.
What is the composition of an unsaturated lipid?
Since unsaturated lipids have one or multiple double bonds, the composition of hydrocarbon chains has bent areas, or "kinks", in an otherwise straight hydrocarbon chain.
Why do unsaturated fats have a relatively low melting points that they are liquid in room temperature?
Since van der Waals interactions allow nonpolar molecules to stick together, but the composition of unsaturated lipids are bent in hydrocarbons, then they will have fewer interactions, allowing the lipids to move freely, and form a liquid.
Why do saturated fats have a relatively high melting points that they are solid in room temperature?
Since van der Waals interactions allow nonpolar molecules to stick together, the composition of saturated lipids cause many of these interactions to form, allowing the lipids to pack together tightly to form a solid
What does it mean that lipid bilayers are "semi-permeable"
Small hydrophobic molecules can diffuse across lipid bilayers rather easily, while large polar molecules and charged molecules (ions) cannot cross lipid bilayers without "help".
What particles cannot move across lipid bilayers?
Small, charged ions (Na+, K+, Cl-) do not effectively cross lipid bilayers without "help" from membrane proteins
What particles are able to move across lipid bilayers quickly?
Small, nonpolar molecules (eg. O2, CO2, N2)
What is diffusion?
The spontaneous movement of molecules and ions. That is, permeable solutes moving across a membrane, down their concentration gradient, until they reach equilibrium.
Why is it important that lipids are an amphipathic molecule?
The amphipathic nature of many lipids is their most important biological feature and is responsible for life's defining barrier, the plasma membrane.
If membranes do not filter solutes based on size, what is responsible for the differences in permeability?
The differences of permeability is that charged substances and polar molecules above a certain
What is the relationship between a change in volume and solute concentration by osmosis (the movement of water)?
The greater the initial difference in solute concentration, the greater the volume change will be.
How does lipid structure affect membrane permeability?
The length and bond saturation state of the hydrocarbon tails, in addition to the presence of cholesterol molecules, profoundly influences the physical properties of a membrane and it s permeability.
Why is a membrane-forming lipid said to have a hydrophilic region?
The molecule of membrane-forming lipids have a "head" region in which this region is charged and has polar covalent bonds that interact with water molecules when it is placed in solution.
Why is a membrane-forming lipid said to have a hydrophobic region?
The molecule of membrane-forming lipids have a region with long hydrocarbon tails in which this region has nonpolar covalent bonds. As a result, water molecules cannot form hydrogen bonds with the hydrocarbon tails, so they do not interact extensively with water molecules when it is placed in solution.
What lipids do we find in cells?
The most important types of lipids found in cells are steroids, fats, and phospholipids.
What is permeability in regard to lipid bilayers?
The permeability of a structure is its tendency to allow a given substance to pass through it
Why is a plasma membrane important for biological organisms to have?
The plasma membrane separates life from nonlife; serving as a selective barrier, by a layer of molecules, that surrounds and separates the cell interior from the environment; keeping damaging substances out of the cell and allowing entry of substances needed by the cell.
What is the significance of these 2 amphipathic lipid structures?
The shape of these 2 amphipathic lipid structures minimizes the exposure of the hydrophobic domain and the lipid to the water.
What does Isotonic mean?
both solutions have an equal concentration
What does hypertonic mean?
more solute, less water
