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Membrane characteristics
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Sheet like structures, two molecules thick, form closed boundaries
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composed of lipids and proteins,
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noncovalent assemblies
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covalent assesmblies
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are fluid structures
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are fatty structures
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Most are electrically polarized
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Membranes are asymmetric in that the outer surface is always different from the inner surface
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- True
- False
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Membrane lipids are
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small amphipathic molecules that form closed bimolecular sheets that prevent the movement of polar or charged molecules.
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large amphipathic molecules that form closed bimolecular sheets that prevent the movement of polar or charged molecules.
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small amphipathic molecules that form closed molecular sheets that prevent the movement of polar or charged molecules.
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large amphipathic molecules that form closed molecular sheets that prevent the movement of polar or charged molecules.
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Proteins serve to mitigate the impermeability of membranes and
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allow movement of molecules and information across the cell membrane
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don't allow movement of molecules and information across the cell membrane
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Fatty acid names are based on their parent hydrocarbons
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- True
- False
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Fatty acids
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are chains of hydrogen bearing carbon atoms that have a carboxylic acid at one end and a methyl group at the other end
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are chains of hydrogen bearing carbon atoms that have a ketone at one end and a methyl group at the other end
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may be saturated or unsaturated
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usually numbered beginning with the carboxyl terminal carbon atom
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When double bonds present, they are commonly in the cis position
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Properties are dependent on chain length and degree of unsaturation
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Fatty acids can also be numbered from the methyl carbon atom which is called the omega (ω) carbon.
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- True
- False
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Carbon atoms [blank_start]2[blank_end] and [blank_start]3[blank_end] are also referred to as α and β, respectively.
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2
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3
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Fatty acids in biological systems usually contain an [blank_start]even[blank_end] number of carbon atoms, with the [blank_start]16[blank_end]- and [blank_start]18[blank_end]-carbon atom chains the most common.
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even
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odd
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16
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15
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18
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17
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In polyunsaturated fatty acids, the double bonds are separated by at least one
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methylene group
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carboxylic acid
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ketone
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aldehyde
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Long chain length and the presence of cis double bonds enhances the fluidity of fatty acids
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- True
- False
Frage 12
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What are the major class of membrane lipids
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Phospholipids
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Glycolipids
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Cholesterol
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Phospholipids are composed of four components:
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fatty acids (1 or more), a platform, a carbon, and an alcohol.
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fatty acids (1 or more), a platform, a phosphate, and an alcohol.
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fatty acids (1 or more), a platform, a phosphate, and an nitrogen.
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Two common platforms are [blank_start]glycerol[blank_end] and [blank_start]sphingosine[blank_end]
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glycerol
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glycogen
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sphingosine
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sphinose
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Phospholipids with a glycerol platform are called
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phosphoglycerides
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phosphoglycerols
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phosphoglycogen
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The common types of membrane lipids are
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Phospholipids
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Glycolipids
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Cholesterol
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Carbohydrates
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The major phospholipids are derived from
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Phosphatidate (diacylglycerol 3-phosphate)
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Phosphatidate (diacylglycerol 2-phosphate)
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Phosphoglycerides are derived from phosphatidate by the formation of an ester bond between the phosphate and an alcohol
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- True
- False
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Glycolipids are
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carbohydrate-containing lipids derived from sphingosine.
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carbohydrate-containing lipids derived from glycerol.
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The carbohydrate in the glycolipid is linked to the secondary alcohol of sphingosine
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- True
- False
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What are the simplest glycolipids, containing only a single sugar
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Cerebrosides
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Gangliosides
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Monosaccharides
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Gangliosides contain a branched chain of as many as
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seven sugar molecules
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five sugar molecules
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three sugar molecules
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eight sugar molecules
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The [blank_start]carbohydrate[blank_end] components of glycolipids are on the [blank_start]extracellular[blank_end] surface of the cell membrane, where they play a role in cell-cell recognition
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carbohydrate
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lipid
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extracellular
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intracellular
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Cholesterol is a lipid based on a steroid nucleus
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- True
- False
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Cholesterol is a
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a steroid that is modified on both ends by the attachment of a fatty acid chain and at the other end by a methyl group
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a steroid that is modified on one end by the attachment of a fatty acid chain and at the other end by a hydroxyl group
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In membranes, the hydroxyl group interacts with phospholipid head groups
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- True
- False
Frage 27
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A membrane lipids is an
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an amphipathic molecule containing a hydrophilic and hydrophobic moiety
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an amphipathic molecule containing a hydrophilic moiety
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an amphipathic molecule containing a hydrophobic moiety
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The fatty acid components provide the
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hydrophobic properties
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hydrophilic properties
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The alcohol and phosphate components are called the
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polar head group, hydrophilic properties
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polar head groups, hydrophobic properties
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Phospholipids and Glycolipids Readily form Bimolecular sheets in Aqueous Media
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- True
- False
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Membrane formation is a consequence of the amphipathic nature of the constituent lipid molecules.
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- True
- False
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Phospholipids are
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too large to form micelles
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too small to form micelles
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like glycolipids spontaneously form lipid bilayers in aqueous solutions
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like glycolipids nonspontaneously form lipid bilayers in aqueous solutions
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The hydrophobic effect powers membrane formation, and van der Waals interactions between the [blank_start]hydrophobic[blank_end] tails stabilize membranes
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hydrophobic
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hydrophillic
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Integral membrane proteins
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composed of β strands that form a pore in the membrane.
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composed of α helices that form a pore in the membrane
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What is an example of β strand–rich integral membrane protein.
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bacterial protein porin
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Membrane spanning
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The [blank_start]outside[blank_end] surface of porin, which interacts with the [blank_start]hydrophobic[blank_end] interior of the membrane, is composed of [blank_start]hydrophobic[blank_end] amino acids. The [blank_start]inside[blank_end] is [blank_start]polar[blank_end] and filled with water.
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outside
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inside
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hydrophobic
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hydrophillic
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hydrophobic
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hydrophillic
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inside
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outside
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polar
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nonpolar
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Membrane-spanning α helices are a common structural feature of integral membrane proteins.
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- True
- False
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Bacteriorhodopsin, a light-powered proton pump, is an integral membrane protein composed of eight membrane- spanning helices.
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- True
- False
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Only a portion of the enzyme prostaglandin H2 synthase-1 is embedded in the membrane.
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- True
- False
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The cyclooxygenase (COX) activity of prostaglandin H2 synthase-1 is dependent on a channel connecting the [blank_start]active site[blank_end] to the membrane interior.
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active site
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terminator site
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What inhibits cyclooxygenase activity by obstructing the channel
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Aspirin
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Xanax
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Klonopin
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Naproxen
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Hydrophobic proteins can be made to associate with the membrane by attaching a hydrophillic group.
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- True
- False
Frage 43
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The fluid mosaic model allows
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lateral movement but not rotation through the membrane
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rotation through the membrane
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vertical movement
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The fluid mosaic model describes
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membranes as two-dimensional solutions of oriented lipids and globular proteins
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membranes as two-dimensional solutions of oriented lipids and quartnary proteins
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membranes as two-dimensional solutions of oriented lipids and primary proteins
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The lipids serve as a solvent and a permeability barrier
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- True
- False
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Lipids rapidly diffuse vertically in membranes, although transverse diffusion or flip-flopping is very rare without the assistance of enzymes
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- True
- False
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The prohibition of [blank_start]transverse[blank_end] diffusion accounts for the stability of membrane asymmetry.
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transverse
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Membrane fluidity is controlled
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by fatty acid composition and carbohydrate content
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by fatty acid composition and cholesterol content
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by fatty acid composition and amino acid content
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Cholesterol helps to maintain proper membrane fluidity in membranes in animals
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- True
- False
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No Biological membranes are asymmetric
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- True
- False
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The Na+-K+ pump illustrates
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the principle of membrane asymmetry.
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Pumps 3 Na+ out of the cell and 2 K+ into the cell by hydrolyzing ATP on the intracellular side of the membrane
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Pumps 2 Na+ out of the cell and 3 K+ into the cell by hydrolyzing ATP on the extracellular side of the membrane
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Some bacteria are enclosed by a single membrane surrounded by a cell wall.
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- True
- False
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Other bacteria are surrounded by two membranes, with a cell wall lying between them
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- True
- False
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Other bacteria are surrounded by two membranes, with a cell wall lying between them.The space between the two membranes is called the
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periplasm
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cytoplasm
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mitochondria
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With exception of plants, what cells do not have cell walls and area surrounded by a single membrane, the plasma membrane
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Eukaryotic cells
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Prokaryotic cells
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Cells can acquire molecules from their environment by receptor-mediated endocytosis.
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- True
- False
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The protein clathin helps to
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internalize receptors bound to their cargo
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receptor-mediated endocytosis
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facilitate membrane fusion by forming tightly coiled four-helical bundles
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Fusion of internal membranes with the plasma membrane allows the [blank_start]release[blank_end] of molecules, such as [blank_start]neurotransmitters[blank_end], from the cell
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release
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absorabance
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neurotransmitters
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serotonin
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9. The internalization of iron-bound transferrin in association with the transferrin receptor is a example of
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SNARE proteins
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receptor-mediated endocytosis
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protein clathrin
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[blank_start]SNARE[blank_end] proteins facilitate membrane fusion by forming tightly coiled four-helical bundles.
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SNARE
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