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57 Cards in this Set
- Front
- Back
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The most significant macromolecular structure of a cell. |
Biomembrane (plasma membranes) |
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All cell membranes share what common structural characteristics? |
Composed of lipids and proteins. Lipids are arranged in two sheets forming a bilayer. |
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What defines the characteristics of a specific membrane vs another |
The number and kinds of membrane bound proteins. |
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Fundamental structure of all membranes |
Lipid bilayer constitution |
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Most abundant lipids within cell membranes |
Phospholipids |
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Why are lipids arranged into bilayers within the cell membrane in an aqueous environment |
Bilayer formation is a product of the amphipathic nature of phospholipids. Bilayer is the most energetically favorable confirmation. |
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What factor allows for a plasma membrane or any lipid bilayer to be self-sealing following puncture? |
any tear in the sheet will create an unfavorable interaction between the surrounding water and the hydrophobic tails of phospholipids. The molecules of the bilayer will thus spontaneously rearrange back together. |
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Give three examples of ampipathic molecules |
Phospholipids, Cholesterols, glycolipids |
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What is the most common phospholipid in biomembranes |
Phosphatidylcholine |
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What is a phosphoglyceride? |
Alternative way to say phospholipid. |
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What 5 lipids comprise 65-85% of all Biomembranes? |
1. Phosphatidylethanolamine 2. phosphatidylserine 3. phosphatidylcholine 4. sphingomyelin 5. Cholesterol |
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Which of the 5 most common lipids in biomembranes is negatively charged at neutral pH? |
phosphatidyllserine |
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Why is sphingomyelin not considered a phospholipid? |
Sphingomyelin does not contain a glycerol backbone |
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What is the structure and occurrence of liposomes. |
A closed spherical vesicle consisting of lipid bilayers. They are formed by purified phospholipids spontaneously upon introduction to aqueous environment. |
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What phospholipid structure has potential use in drug delivery systems? |
Liposomes. |
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What is considered to be the rare form of movement carried out by a single phospholipid molecule within a bilayer? |
Flip-Flop, in which a phospholipid tumbles from one half of the bilayer to the other. |
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What are common forms of movement carried out by the consituent phospholipids within a bilayer? |
Lateral exchange between phospholipids and vertical axis rotation by molecules. |
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What factors affect the fluidity of a phospholipid bilayer? |
Phospholipid's hydrocarbon tail: length, number of double bonds present, and the cis- vs trans- nature of those double bonds. Temperature of external environment |
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Shortened hydrocarbon tail length of membrane phospholipids has what effect on membrane fluidity? |
It causes an increased fluidity because it decreases the number of intermolecular interactions between phospholipids. |
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What effect does a higher degree of unsaturation of phospholipid tails have on the membrane fluidity? |
Leads to increased fluidity because unsaturation leads to "kinks" between phospholipid molecules. |
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What effect does increased incorporation of cholesterol have on the membrane fluidity? |
Decreases membrane fluidity. |
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At what temperature does the lipid bilayer "melt" ? |
Critical Temperature |
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Where are new phospholipids synthesized within the cell? |
On the cytosolic-surface of the endoplasmic reticulum |
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What conversion do scramblases carry out? |
Remove randomly selected phospholipids from one half of the lipid bilayer and insert them in the other. |
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Why are scramblases necessary for membrane integrity? |
Newly made phospholipids are only deposited on the cytosolic half of the lipid bilayer. scrambalases allow for equal distribution of the new phospholipids among each of the sides. |
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What enzyme is responsible for maintaining asymmetry of cell membranes? |
Flippases, produced in the Golgi Apparatus |
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How do flippases function? |
Flippase catalyze the transfer of specific phospholipids from the side of the bilayer facing the exterior space to the monolayer that faces the cytosol. |
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What is the composition of lipid rafts relative to normal plasma membrane? |
three-five times the amount of cholesterol in lipid rafts. Enriched with sphingolipids and contain lesser phosphotidylcholine. |
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What is the role/function of lipid rafts? |
compartmentalize cellular processes by serving as organization centers for the assembly of signaling molecules, influencing membrane fluidity, and membrane-protein trafficking. |
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What minor phospholipid, localized to cytosolic leaflet is important docking and signaling molecule? |
Phosphatidylinositol |
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What membrane lipids are strictly oriented on the noncytosolic side of membranes? |
Glycolipids forming part of the Glycolax. |
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How are the newly synthesized lipid membrane components distributed throughout the endomembrane system? |
By Vesicular transport from membrane-enclosed organelle (ER or Golgi) to the plasma membrane. |
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What conversion does the enzyme phosphatidylinositol 3-kinase carry out? |
Converts phosphatidylinositol(4,5) bis-phosphate to Phosphatidylinositol (3,4,5) triphosphate |
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What is the role of Phosphatidylinositol Bis-phosphate? |
Important signaling molecule incorporated in the plasma membrane |
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What is the role of Phosphatidylinositol Tri-phosphate? |
acts as substrate for enzymes but also serve as docking phospholipids that bind specific domains that promote the recruitment of proteins to the plasma membrane and subsequent activation of signaling cascades. E.g. Pleckstrin Homology *(PH)* Domain. |
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What are the essential functions carried out by membrane proteins? |
1. Receiving of information from extracellular environment. 2. Import / Export of molecules 3. Capacity for movement and expansion 4. Enzymatic activity 5. Anchoring |
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Name the 4 Functional Classes of membrane proteins. |
Transporters, Anchors, |
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What trait classifies a protein as being an integral membrane protein. |
If the protein may only be removed from the membrane by disrupting the bilayer with detergents. |
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What are the three general types of Integral membrane proteins? |
1. Transmembrane proteins 2. Monolayer associated Alpha-helix 3. Lipid-linked proteins |
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What defines a membrane protein as a peripheral membrane protein? |
They can be released from the membrane by gentle extraction procedures that interfere with Protein-protein interactions but leave the lipid bilayer intact. They are non-covalently bound to proteins. |
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Example of an Ionic Detergent |
Sodium Dodecyl Sulfate (SDS) |
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Example of non-ionic detergent |
Triton X-100 |
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What is Bacteriorhodopsin? |
A protein used by Archaea, most notably by Halobacteria, a class of the Euryarchaeota.It acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane out of the cell. The resulting proton gradient is subsequently converted into chemical energy. |
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The vast majority of membrane-spanning segments of polypeptide chains traverse the bilayer as what secondary structure? |
Alpha-helices Bc water is absent from the interior of the bilayer and thus hydrogen bonds within the polypeptide and side chain interaction with bilayer is most favorable. |
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What is the retinal? |
Each molecule of bacteriorhodopsin contains a single light-absorbing molecule which is called the Retinal. |
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The plasma membrane of animal cells is stabilized by a meshwork of fibrous proteins that are attached to the underside of the cell membrane. The structure is called? |
The Cell Cortex |
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What is the main component of red blood cell's cell cortex? |
Spectrin, a long, thin, flexible rod |
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How is the spectrin meshwork of red blood cells connected to the membrane |
Via intracellular attachment proteins that link the spectrin to specific transmembrane proteins |
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The cell cortex of most cells is especially rich in what two molecules? |
Actin and the motor protein myosin |
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What is FRAP and what does it accomplish? |
Fluorescence Recovery after Photobleaching It irreversibly bleaches fluorescent molecules within an area of the membrane. The amount of time it takes for unbleached fluorescent proteins to migrate into the bleached region is measured and evidence of degree of membrane fluidity. |
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What are membrane domains? |
Confined proteins to localized areas within the bilayer membrane, leading to functionally specialized regions. |
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What are the Four Methods to restrict the distribution of membrane proteins? |
1. Tether protein to cell cortex 2. Tether protein to Extracellular Matrix molecules 3. Stabilize by tethering protein-protein via cell-cell junctions 4. Restrict to a domain by tight junctions |
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All the carbohydrates on the glycoproteins, proteoglycans, and glycolipids are located on the outside of the plasma membrane forming a sugar coating called the: |
Glycocalyx |
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What are the various functions of the Glycocalyx? |
Protect cell from mechanical damage, give cell slimy surface, aid cells motility, prevent cells from sticking to eachother or other membranes. Play role in cell-cell recognition. |
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How is glycosylation of membrane proteins restricted to ECF facing side of membrane? |
Cell cytosol is a reducing environment which keeps cysteine residues from forming disulfide bonds which are critical to stabilizing glycosylated proteins. |
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What cell organelles are defined as having a structure of Double membranes? |
1. Nuclear envelope 2. Mitochondria 3. Chloroplasts |
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What are the organelles of the Endomembrane System of Eukaryotes? |
1. Nuclear Envelope 2. Endoplasmic Reticulum 3. Golgi apparatus 4. Endosomes 5. Lysosomes 6. Transport Vesicles 7. Plasma membrane |
