Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
62 Cards in this Set
- Front
- Back
|
What are seven functions of cellular membranes? |
1. Compartmentalization 2. Selectively permeable barrier 3. Transport of solutes and molecules 4. Response to signals 5. Intercellular Interactions 6. Locus for biochemical activities 7. Energy Transduction |
|
|
What is meant by compartmentalization? |
Enclosure of the entire cell, as well as membrane-bound organelles.
|
|
|
What is meant by having a selectively permeable barrier? |
Membranes prevent the free interchange of materials from one side to another, but provide passage of appropriate substances.
|
|
|
What is meant by transport of solutes and molecules? |
Membranes contain machinery for transport both down and against concentration gradients. Vesicles transport both soluble and insoluble substances. |
|
|
What is meant by response to signals? |
External and internal membranes contain receptors, allowing the cell to respond to specific ligands, hormones, neurotransmitters, light, and mechanical stimuli.
|
|
|
What is meant by intercellular interactions? |
Recognition by membranes allow cells to adhere, fuse when appropriate, and exchange information and materials.
|
|
|
What is meant by being a locus for biochemical activities? |
Membranes may recruit molecules permanently or transiently, or provide a scaffolding as a locus for reactions.
Membranes act as a locus for lipid and some protein synthesis. |
|
|
What is meant by energy transduction? |
Membranes are the locus for the conversion of one form of energy to another. (ATP Synthesis from a proton gradient!)
|
|
|
List the features of the Fluid Mosaic Model. |
1. The basic structure is a lipid bilayer (two sheets of phospholipids arranged tail to tail). 2. Proteins are dispersed throughout the membrane in a mosaic patter. Proteins contribute to the structure and function. Some span the membrane, others confined to inner or outer leaflets. 3. The membrane is fluid! Most proteins and lipids can move freely within each leaflets, but not between them. 4. The lipid bilayer serves as a hydrophobic barrier, confining hydrophilic molecules to the inside or outside of a cell. |
|
|
What does it mean to be amphipatic? What is the difference between the amphipatic structure of soap bubbles and lipid vesicles? |
Amphipatic describes a molecule that possesses both hydrophilic and hydrophobic components. In a soap bubble, the hydrophobic tails face outward, while the hydrophilic heads face each other inward. In a lipid vesicle, the hydrophobic tails are sandwiched in the middle, while the hydrophilic heads face outward. |
|
|
What is the basic structure of a phospholipid molecule? |
Hydrophilic Head Group (Choline, Phosphate, Glycerol), and Hydrophobic Tails (containing a cis double bond). *Phosphotidylcholine |
|
|
What are four major phospholipids in mammalian plasma membranes? Write out the different head groups. Which one has an overall negative charge? Which one has one different fatty chain tail? |
Phosphotidylethenolamine (NH3+,CH2,CH2,O) Phosphotidylserine (NH3+H,C,COO-,CH2,O; negative charge on the COO- gives overall negative charge) Phosphotidylcholine (CH3, CH3, N+,CH3, CH2,CH2,O) Sphingomyelin (Same head group as phosphotidylcholine, with one OH,CH,CH=CH tail instead of CH2,O,C=O like the others) |
|
|
What is the basic structure of cholestrol? |
Polar head group, rigid steroid ring structure, and non-polar hydrocarbon tail. |
|
|
What does the addition of cholestrol between phospholipid molecules do? |
They add rigidity to the fluid structure, keeping a consistent fluidity. |
|
|
What happens when a polar molecule such as acetone (partial positive and partial negative charges) is placed in water? |
The polar molecule is able to form hydrogen bonds with the water molecules, along with other favorable electrostatic interactions. |
|
|
What happens when a nonpolar molecule such as 2-methyl-propane is placed in water? |
The nonpolar molecule is hydrophobic and cannot form favorable interactions with water, so it forces adjacent water molecules to reorganize into icelike cage structures surrounding the molecule (increases free energy). |
|
|
What happens when multiple nonpolar molecules are placed in water? |
The more favorable organization would be to place the nonpolar molecules together and have that group be surrounded by the water molecules (instead of having individual nonpolar molecules being surrounded). |
|
|
What is the general shape of a lipid molecule? How do lipid molecules arrange themselves in an aqueous environment? |
Lipid molecules are cone-shaped, and they spontaneously form spherical forms called micelles. |
|
|
What is the general shape of a phospholipid molecule? How do phospholipid molecules arrange themselves in an aqueous environment? |
Phospholipid molecules are cylinder-shaped, and they spontaneously form lipid bilayers.
|
|
|
What is the more energetically favorable structure of a phospholipd bilayer in water? |
The phospholipid bilayer spontaneously closes into a sealed compartment, which is energetically favorable as it avoids exposure of the hydrophobic hydrocarbon tails in the exposed edges to water. |
|
|
What are synthetic phospholipid vesicles called? |
Liposomes. |
|
|
What generally allows better permeability of a molecule across a synthetic lipid bilayer? |
The smaller the molecule, and the more weakly it associates with water, the more rapidly the molecule will diffuse across the bilayer. |
|
|
What is the mobility of phospholipid molecules in a lipid bilayer? What is possible but rarely occurs. |
There is lateral diffusion (movement from side to side within one leaflet side) and rotation about the molecule. Flip-flop (switching of molecule from one side to another) rarely occurs. |
|
|
What is the difference between the portions of the membrane containing saturated hydrocarbon chains and unsaturated hydrocarbon chains (cis-double bonds). |
The saturated hydrocarbon chains allow for tighter packing which makes these portions more rigid and thicker. The unsaturated hydrocarbon chains contain cis-double bonds that make it more difficult to pack together and they are more spread apart, so these portions are thinner, more fluid, and more difficult to freeze. |
|
|
What are lipid droplets? How do they form? |
It is a lipid surrounded by a single monolayer of phospholipids and associated proteins. They are organelles from from neutral lipids that were deposited between the two monolayers of the ER membrane, which aggregated into a droplet that budded off. |
|
|
In an asymmetrically distributed lipid bilayer, which side contains polar head groups with a negative charge? |
The polar head groups facing towards the cytosol. |
|
|
What are glycolipids? |
Lipids with a carbohydrate attached by a glycosidic bond. |
|
|
What can occur with lipid mixtures in artificial bilayers? |
Phase segregations can occur in which specific lipids come together in separate domains. |
|
|
What are lipid rafts? |
Specialized domains rich in cholestrol, sphingolipids, glycolipids, glycosylphosphatidylinositol-anchored proteins, and some transmembrane proteins due to weak protein-protein and protein-lipid and lipid-lipid interactions that help to partition the interacting components together. |
|
|
Why is galactocerebroside a "neutral glycolipid"? |
The sugar that forms its head group is uncharged. |
|
|
Where does the charge on a ganglioside come from? |
There is always one or more negatively charged sialic acid component. |
|
|
What type of sialic acid is in human cells? |
N-acetylneuraminic acid (NANA). |
|
|
From what are glycolipids derived in bacteria and plant cells? |
Glycerol. |
|
|
From what are glycolipids in animal cells derived from? |
Sphingosine. |
|
|
What are the three general ways proteins can associate with a lipid bilayer? |
1. Extend across the bilayer. 2. Exposed at only one side of the membrane. 3. Attached to the membrane by noncovalent interactions with other membrane proteins. |
|
|
What are three ways a transmembrane protein can extend across the bilayer? |
1. As a single alpha helix. 2. As multiple alpha helixes. 3. As a beta barrel. |
|
|
What are two ways membrane proteins might attach and be only exposed on one side? |
1. Anchored to the cytosolic surface by an amphiphilic alpha helix that separates into the cytosolic monolayer of the lipid bilayer through the hydophobic face of the helix. 2. Attached to the bilayer by a covalently bound lipid chain (fatty acid or prenyl group) or an oligosaccharide linker (GPI anchor). |
|
|
What is one other way membrane-associated proteins attach to the membrane, without directly attaching to the membrane? |
They can attach to the membrane by noncovalent interactions with other membrane proteins.
|
|
|
What are three types of covalent attachment of a membrane protein by a fatty acid chain or a prenyl group? |
1. Amide linkage between terminal amino group and myristic acid. 2. Thioester linkage between cysteine and palmitic group. 3. Thioester linkage between cysteine and prenyl group. |
|
|
What are the three fatty acid chain anchors that correspond to the linkage groups previously mentioned? |
1. Myristoyl anchor 2. Palmitoyl anchor 3. Farnesyl anchor |
|
|
What are hydropathy plots? |
An analysis used to characterize or identify possible structure or domains of a protein. |
|
|
What is measured in a hydropathy plot? |
The free energy needed to transfer successive segments of a polypeptide chain from a nonpolar solvent to water. |
|
|
How is a hydropathy plot shown on a graph? |
The "hydropathy index" is plotted on the Y axis and the amino acid number is plotted on the X axis. (Hydropathy is plotted as a function of its location in the chain) |
|
|
What does a positive value indicate? What does the value represent? |
Free energy is required to transfer it into water, so the segment must have been hydrophobic. The value is an index of the amount of energy needed. |
|
|
Considering these indications, how is this hydropathy plot interpreted? |
Positive peaks in the hydropathy index represent positions of hydrophobic segments in the amino acid sequence. |
|
|
What is the basic structure of an aquaporin water channel? |
A tetramer, with a hydrophilic pore at the center of each monomer, which allows water molecules to cross the membrane. There are two short alpha helixes inside, each of which spans only halfway through the lipid bilayer (formed by protein-protein interactions). |
|
|
What happens as a newly synthesized multipass transmembrane protein folds? |
The contacts between the helices displace some of the lipid molecules surrounding the helices. |
|
|
What is the basic structure (3) of a single-pass transmembrane protein? |
Polypeptide chain traverses the lipid bilayer as a right-handed alpha helix. Oligosaccharide chains and disulfide bonds on the noncytosolic surface of the membrane. |
|
|
Why don't the sylfhydryl groups in the cytosolic domain of the protein form disulfide bonds? |
The reducing environment in the cytosol maintains the groups in their reduced form. |
|
|
What type of layer is surrounding the cell's extracellular surface? |
Thick carbohydrate-rich layer made up of the oligosaccharide chains of membrane glycoproteins and the polysaccharide chains on membrane proteoglycans. Adsorbed glycoproteins and proteoglycans also contribute to the carbohydrate layer. |
|
|
What are three commonly used detergents? |
Sodium dodecyl sulfate (SDS) Triton-X-100 Beta-octylglucoside |
|
|
What is the organization of detergent molecules in solution at low concentrations? At what point do they form micelles? What happens to the concentration of detergent molecules past that? |
At low concentration, detergent molecules are monomeric in solution. Once the concentration has increased above the critical micelle concentration (CMC), the detergent molecules start to form micelles. The concentration of detergent molecules remain constant after CMC. |
|
|
What happens when a mild nonionic detergent solubilizes a membrane protein? What kind of detergent complexes are formed? |
The detergent disrupts the bilayer, brings the protein into solution, and also solubilizes the phospholipids. Water-soluble protein-lipid-detergent complexes, and water-soluble lipid-detergent micelles. |
|
|
How can this solubilizing act be applied? |
Mild nonionic detergents can be used to purify and reconstruct functional membrane protein systems. (Ex: Na+/K+ pump) |
|
|
What is a nanodisc? What is its basic structure? How is it water-soluble? |
Nanodiscs are synthetic model membrane systems which assist in the study of membrane proteins. Nanodiscs have a transmembrane protein embedded in a small patch of lipid bilayer surrounded by a belt made of a protein subunit of the high-density lipoprotein (HDL). Since the protein belt shield the hydophobic portion of the lipid bilayer, the assembly is water-soluble. |
|
|
What is bacteriorhodopsin? Where is it found? |
A protein pump in the plasma membrane that transports protons across the membrane when activated by light. It is found in the patches of purple membrane of archaeon called Halobacterium salinarum, which live in saltwater pools where they can be exposed to sunlight. |
|
|
What is the basic structure of the bacteriorhodopsin molecule? |
This polypeptide chain crosses the lipid bilayer in seven alpha helices, inside which the purple chromophore called retinal is found. |
|
|
Describe the pathway taken by the H+ during the light-activated pumping cycle. |
1. Retinal absorbs a photon of light, and one of its double bonds isomerizes from a trans into a cis configuration, causing conformation rearrangements in the surrounding protein. 2. In its excited state, retinal is positioned to transfer a proton to an Aspertine sidechain, Asp 85, which is positioned towards the extracellular side of the protein. 3. Asp 85 passes off the proton through a bucket brigade of water molecules into the extracellular space. 4. The newly negatively charged retinol takes a proton from Asp 96, which is positioned towards the cytosolic face of the protein. The retinol returns to the ground state. 5. Asp 96 retrieves a proton from the cytosol. The cycle is ready to repeat. |
|
|
What is the net result of the bacteriorhodopsin pathway? |
One photon in, one proton pumped out of the cell. Overall, this pathway allowed one proton to be pumped outside the cell. |
|
|
What is rhodopsin? |
A G Protein Coupled Receptor that responds to light stimluli. |
|
|
What are three types of rhodopsins? Describe their general transport function. |
Archaerhodopsins and Bacteriorhodopsins (Transport protons to the extracellular side) Halorhodopsins (Transport chlorine into the cell) Channelrhodopsins (Transport H+, Na+, K+, Ca+ into the cell) |
|
|
What is retinal? |
A long unsaturated hydrocarbon covalently bonded to a Lyseine sidechain, Lys 216 (of one of the seven alpha helices), and gives the protein and the cell its purple color. |
