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98 Cards in this Set
- Front
- Back
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What is liquid-liquid demixing?
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Two liquids with different properties separate from each other.
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What examples of liquid-liquid demixing involving membranes and the cytosol are given in the article "Beyond Oil and Water--Phase Transitions in Cells"? (2)
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Lipids and proteins in membranes separate into dynamic liquid membrane rafts, distinct from the surrounding bilayer. There are mutual interactions between sterols, sphingolipids, and raft proteins. |
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True or false: cell membranes are inflexible.
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false, flexible
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True or false: cell membranes are self-healing. |
true
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True or false: cell membranes are static structures. |
false
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What are ruffles and spikes in membranes required for? |
movement and phagocytosis
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What is the structure of membranes?
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sheet-like, two molecules thick (two leaflets)
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What are membranes composed of? |
lipids and proteins, either of which can be decorated with carbohydrates
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What do membrane lipids form?
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closed bimolecular sheets that prevent the movement of polar or charged molecules
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lessen the impermeability of membranes
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proteins
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allow movement of molecules and information across the cell membrane
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proteins
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What hold membranes together? |
noncovalent bonds
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How are membranes asymmetric?
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outer leaflet is always different from the inner leaflet
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True or false: membranes are fluid structures. |
true
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What percentage of the mass of biological membranes consists of proteins embedded in or associated with a lipid bilayer? |
50-75
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What percentage of the mass of biological membranes consists of lipids?
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25-50
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What do biological membranes contain? (3)
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phospholipids sphingolipids sterol |
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glycerolipids and glycolipids |
phospholipids
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What are sphingolipids sometimes called? |
glycosphingolipids
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What spontaneously form lipid bilayers in aqueous solutions?
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phospholipids
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What are the structural basis for all biological membranes? |
lipid bilayers
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What are aqueous compartments enclosed by a lipid membrane? |
liposomes, or liquid vesicles
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What are formed by sonicating (ultrasound causing it to vibrate) a mixture of phospholipids in aqueous solution?
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liposomes
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What may be useful as drug-delivery systems? |
liposomes
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What is the formation of membranes powered by?
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hydrophobic effect increase in entropy |
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What make lipid bilayers flexible and self-sealing?
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noncovalent interactions among lipid molecules
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How thick are typical lipid bilayers? |
5-6 nm
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What is the ability of small molecules to cross a membrane a function of? |
hydrophobicity
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Why can't ions cross membranes? |
because of the energy cost of shedding their associated water molecules
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What is membrane fluidity controlled by?
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fatty acid composition and cholesterol content
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What do membrane processes depend on? |
fluidity of the membrane
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What helps to maintain proper membrane fluidity in the membranes of animals? |
cholesterol
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How does cholesterol help maintain proper membrane fluidity? |
It breaks up tight packing. The fused rings in cholesterol are rigid, so it breaks up the interactions between other lipids.
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establish a permeable barrier
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membrane lipids
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embedded in the hydrocarbon core of the membrane
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integral membrane proteins
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bound to polar head groups of membrane lipids or to the exposed surfaces of integral membrane proteins |
peripheral membrane proteins
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How are proteins other than integral and peripheral proteins associated with membranes?
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lipid anchors
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What are common structural features of integral membrane proteins? |
membrane-spanning alpha helices
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What is a means of embedding integral membrane proteins other than membrane-spanning alpha helices? |
Beta strands to form a pore in the membrane or by embedding part of the protein into the membrane.
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What does COX stand for? |
cyclooxygenase
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What is the COX activity of prostaglandin H2 synthase-1 dependent on?
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a channel connecting the active site to the membrane interior
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How does aspirin inhibit cyclooxygenase activity? |
by transferring an acetyl group to a serine residue in cyclooxygenase and blocking the channel
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Where are lipid anchored membrane proteins mostly found? |
outside of cells
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How are proteins bound to lipids to anchor the protein to the cell membrane? |
covalently
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What are two examples of lipid anchors that proteins can be tethered to? |
fatty acid group isoprenoid group |
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What are prenylated proteins bound to? |
isoprenoid/prenyl group
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True or false: lipid anchored membrane proteins are bound to one lipid.
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false, usually in pairs to ensure a tight hold
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What does GPI stand for?
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glycosylphosphatidylinositol
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Where are GPI-anchored proteins present? |
only in the outer leaflet of the membrane
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True or false: transverse diffusion or flip-flopping is slow and very rare without the assistance of enzymes.
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true
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True or false: lateral diffusion of lipids occurs slowly in membranes. |
false, rapidly
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What does the prohibition of transverse diffusion account for?
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the stability of lipid asymmetry in membranes (different lipids in inner and outer leaflets)
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What are three types of integral membrane protein transporters? |
passive transporters channels and pores active transporters |
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True or false: there are two types of passive transporters, primary and secondary. |
false, active
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When will a small molecule spontaneously cross a membrane by diffusion?
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If the concentration of the molecule is higher on one side of the membrane than the other (there is a concentration gradient) or if the molecule is lipophilic or soluble in nonpolar solutions.
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How can polar molecules diffuse across a membrane down their concentration gradient?
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with the assistance of a particular protein called a channel or pore
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What is the use of channels or pores called?
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facilitated diffusion or passive transport
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movement of molecules against a concentration gradient requiring a source of energy |
active transport
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What does movement of oxygen from one side of a membrane to the other depend on?
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Only concentration gradient: it is able to simply diffuse.
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What move solutes in bulk flow?
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channels and pores
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What do bulk flow channels require? |
protein
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True or false: bulk flow channels are saturable. |
false, if you increase the concentration of solute you increase the rate of transport
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What is a saturable channel or pore and what does this mean? |
facilitated diffusion carrier can't go any faster at a certain concentration, it's also more specific than an open channel |
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uses ATP to move molecules across the concentration gradient
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active transport pump
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What occurs when a molecule moves down its concentration gradient through a transport protein?
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passive transport or facilitated diffusion
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facilitate the flow of small molecules across the cell membrane |
transport proteins functioning as pumps or channels
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What is the process of active transport?
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protein pumps use energy to move a molecule against its concentration gradient
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What are ion channels? |
specific passive transport systems
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How can channels be activated? (3)
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changes in the voltage across a membrane (voltage-activated) binding of specific ligand (ligand-activated) stresses (stress-activated) |
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What among the four ion binding sites in the selectivity filter of the potassium channel accounts for the rapid transport of K+ ions down their concentration gradient? |
charge repulsion
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What is an important pump in many cells and an example of primary active transport?
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Na+-K+ ATPase
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What does the Na+-K+ ATPase or Na+-K+ pump utilize energy from?
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ATP hydrolysis
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True or false: ATPase is the extracellular domain of the Na+-K+ pump.
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false, cytosolic
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What is the K+ gradient?
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higher inside the cell
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What is the Na+ gradient?
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higher outside the cell
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What is multidrug resistance protein or P-glycoprotein an example of? |
primary active transporter
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contain a domain that binds ATP, called the ATP-binding cassette |
ABC transporters
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What are two examples of ABC transporters?
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multidrug resistance protein cystic fibrosis transmembrane conductance regulator |
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pumps drugs out of a cell and is one reason anti-cancer drugs stop working |
multidrug resistance protein
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What is the problem with multidrug resistance protein?
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Pump isn't substrate specific, can take most hydrophobic things out of cell.
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power the transport of a molecule against its concentration gradient by coupling the movement to the movement of another molecule down its concentration gradient, with both molecules moving in the same direction |
symporters
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use one concentration gradient to power the formation of another, but the molecules move in opposite directions |
antiporters
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What are the two types of secondary active transporters? |
symporters antiporters |
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How is glucose moved into some animal cells against its concentration gradient? (2)
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Symporter type of secondary transporter protein powered by Na+ ions moving down a concentration gradient. The Na+ gradient is generated by active transporter. |
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How do cells import/export molecules too large to be transported via pores, channels or proteins? |
endocytosis/exocytosis
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macromolecules are engulfed by plasma membrane and brought into the cell |
endocytosis
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How does endocytosis bring macromolecules into the cell? |
inside a lipid vesicle
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How are materials excreted from the cell? |
Exocytosis: outgoing materials are enclosed in vesicles that bud from the Golgi and fuse with the plasma membrane.
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What specifically did Choi et al. predict would happen in the brain of zebrafish fed a vitamin E deficient diet? |
increased lipid peroxidation
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What change in lipid structure/composition was predicted to occur in zebra fish fed a diet deficient in vitamin E (abstract of Choi et al)? |
Lipids with unsaturated double bonds (e.g. polyunsaturated fatty acids) would be less abundant.
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What does lipid peroxidation usually involve? |
polyunsaturated fatty acids (can also involve mono, but prefers poly)
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What do radicals do to double bonds? |
donate one electron
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What cause chain reactions? |
peroxide
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What keeps peroxides from spreading?
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vitamin E
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What solvent is most likely to promote formation of a lipid bilayer?
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water
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What would a medium (versus a low) concentration of cholesterol do to the Tm of a biological membrane? |
decrease the Tm
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What are three compounds that could anchor a protein to a membrane? |
fatty acid glycosylphosphatidylinositol isoprenoid group |
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Which type of membrane transport does not require a protein carrier, is not saturable, and does not require energy?
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simple diffusion
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