Cellular Structures and Functions - GRE
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Which polymer is the primary component of plant cell walls?
Which polymer is the primary component of plant cell walls?
Cell walls can vary in composition based on what organism is being discussed. In the case of plant cells, cellulose is the primary component. Bacteria use peptidolgycan in their cell walls, and fungi use chitin.
Cell walls can vary in composition based on what organism is being discussed. In the case of plant cells, cellulose is the primary component. Bacteria use peptidolgycan in their cell walls, and fungi use chitin.
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Which of the following encloses a plant cell in a rigid framework and cannot be digested by humans?
Which of the following encloses a plant cell in a rigid framework and cannot be digested by humans?
The cell wall is composed of cellulose and encloses a plant cell in a rigid framework. Plant cells have both cell membranes and cell walls. Plant cell walls cannot be digested by humans due to the beta glycosidic bond in its structure. The cell membrane forms the outer boundary of a cell and isolates cell contents from the environment. The cell membrane regulates movement of materials into and out of the cell. The cell membrane is also referred to as the plasma membrane. The nuclear envelope regulates movement into and out of the nucleus. The cytoskeleton gives shape and support to cells and is typically involved in cell movement.
The cell wall is composed of cellulose and encloses a plant cell in a rigid framework. Plant cells have both cell membranes and cell walls. Plant cell walls cannot be digested by humans due to the beta glycosidic bond in its structure. The cell membrane forms the outer boundary of a cell and isolates cell contents from the environment. The cell membrane regulates movement of materials into and out of the cell. The cell membrane is also referred to as the plasma membrane. The nuclear envelope regulates movement into and out of the nucleus. The cytoskeleton gives shape and support to cells and is typically involved in cell movement.
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An unknown molecule is identified by a researcher. He notices that the structure is abundantly found in cell walls of bacteria. Upon further analysis, which of the following will be observed by the researcher?
An unknown molecule is identified by a researcher. He notices that the structure is abundantly found in cell walls of bacteria. Upon further analysis, which of the following will be observed by the researcher?
The most abundant molecule in bacterial cell walls is peptidoglycan. Recall that peptidoglycan contains repeating NAG-NAM units, which are made from glucose. In addition, peptidoglycan also has peptides attached to these oligosaccharides. These units form bonds with each other to create a strong and a robust cell wall. Peptidoglycan is synthesized in cytoplasm and on cell membrane before finally being transported to the cell wall.
Recall that phosphate head groups are found on phospholipids, which make up cell membranes (not cell walls).
The most abundant molecule in bacterial cell walls is peptidoglycan. Recall that peptidoglycan contains repeating NAG-NAM units, which are made from glucose. In addition, peptidoglycan also has peptides attached to these oligosaccharides. These units form bonds with each other to create a strong and a robust cell wall. Peptidoglycan is synthesized in cytoplasm and on cell membrane before finally being transported to the cell wall.
Recall that phosphate head groups are found on phospholipids, which make up cell membranes (not cell walls).
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Gram positive bacteria have
cell wall(s) and Gram negative bacteria have
cell wall(s).
Gram positive bacteria have cell wall(s) and Gram negative bacteria have cell wall(s).
Gram stain is a laboratory technique used to distinguish bacteria. Gram positive and Gram negative bacteria are distinguished based on their cell walls. Gram positive bacteria have a single thick cell wall (outside its cell membrane). Upon Gram staining, these bacteria will hold the Gram stain because of their thick cell wall. The Gram negative bacteria also have only one cell wall; however, it is a lot thinner and is sandwiched between two cell membranes. The thin nature of the cell wall makes it easier for the Gram stain to leak out of the bacterial cell.
Gram stain is a laboratory technique used to distinguish bacteria. Gram positive and Gram negative bacteria are distinguished based on their cell walls. Gram positive bacteria have a single thick cell wall (outside its cell membrane). Upon Gram staining, these bacteria will hold the Gram stain because of their thick cell wall. The Gram negative bacteria also have only one cell wall; however, it is a lot thinner and is sandwiched between two cell membranes. The thin nature of the cell wall makes it easier for the Gram stain to leak out of the bacterial cell.
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Which of the following is true regarding cell walls?
I. They are only found in bacteria that can be Gram stained
II. Some organisms that have cell walls can undergo photosynthesis
III. They expand when a cell is placed in a hypoosmolar environment
Which of the following is true regarding cell walls?
I. They are only found in bacteria that can be Gram stained
II. Some organisms that have cell walls can undergo photosynthesis
III. They expand when a cell is placed in a hypoosmolar environment
Cell walls are robust structures found in most bacteria, fungi, and plants. Gram stain depends on the properties of the cell wall. Some bacteria don’t stain well with Gram stain (such as Mycobacterium that causes tuberculosis) because of unique cell walls (not lack thereof). Fungal and plant cell walls are also made up of polysaccharides. Fungal cell walls contain a special molecule called chitin whereas plant cell walls contain cellulose. Recall that plants obtain energy from sunlight via photosynthesis; therefore, photosynthetic organisms do contain cell walls.
One of the biggest function of a cell wall is to prevent cellular swelling. Recall that a cell placed in a hypoosmolar solution will swell due to the influx of water; however, this cellular swelling will not occur in a cell containing cell wall because the robust cell wall prevents contents of the cell from expanding, thereby preventing cellular lysis.
Cell walls are robust structures found in most bacteria, fungi, and plants. Gram stain depends on the properties of the cell wall. Some bacteria don’t stain well with Gram stain (such as Mycobacterium that causes tuberculosis) because of unique cell walls (not lack thereof). Fungal and plant cell walls are also made up of polysaccharides. Fungal cell walls contain a special molecule called chitin whereas plant cell walls contain cellulose. Recall that plants obtain energy from sunlight via photosynthesis; therefore, photosynthetic organisms do contain cell walls.
One of the biggest function of a cell wall is to prevent cellular swelling. Recall that a cell placed in a hypoosmolar solution will swell due to the influx of water; however, this cellular swelling will not occur in a cell containing cell wall because the robust cell wall prevents contents of the cell from expanding, thereby preventing cellular lysis.
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How are glucose monomers linked in the cellulose polymers present in a plant cell wall?
How are glucose monomers linked in the cellulose polymers present in a plant cell wall?
Cellulose is a polymer of glucose linked by beta (1-4) linkages. Humans lack the enzyme that catalyzes the cleavage of this bond; thus cellulose (dietary fiber) is indigestible and passes through the digestive system unchanged.
Cellulose is a polymer of glucose linked by beta (1-4) linkages. Humans lack the enzyme that catalyzes the cleavage of this bond; thus cellulose (dietary fiber) is indigestible and passes through the digestive system unchanged.
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Which of the following typically describes molecules that easily diffuse through the plasma membrane (lipid bilayer) of animal cells?
Which of the following typically describes molecules that easily diffuse through the plasma membrane (lipid bilayer) of animal cells?
The correct answer is nonpolar, small in size, and have a large lipid solubility coefficient. The center of the lipid bilayer is nonpolar and composed of fatty acid chains; therefore, nonpolar molecules diffuse through more easily. Diffusion does not use transport proteins to shuttle molecules through the lipid bilayer, so smaller molecules are able to diffuse more easily between the phospholipids that comprise the bilayer. Finally, a higher lipid solubility coefficient means that the molecule is more soluble in lipids and less soluble in aqueous solutions. A low lipid solubility means that the molecule is more aqueous-soluble than lipid-soluble.
The correct answer is nonpolar, small in size, and have a large lipid solubility coefficient. The center of the lipid bilayer is nonpolar and composed of fatty acid chains; therefore, nonpolar molecules diffuse through more easily. Diffusion does not use transport proteins to shuttle molecules through the lipid bilayer, so smaller molecules are able to diffuse more easily between the phospholipids that comprise the bilayer. Finally, a higher lipid solubility coefficient means that the molecule is more soluble in lipids and less soluble in aqueous solutions. A low lipid solubility means that the molecule is more aqueous-soluble than lipid-soluble.
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Dense specialized plasma membrane microdomains that cluster cholesterol, sphingolipids, and protein receptors, and are also sites of receptor trafficking and assembly of signal molecules, are called
.
Dense specialized plasma membrane microdomains that cluster cholesterol, sphingolipids, and protein receptors, and are also sites of receptor trafficking and assembly of signal molecules, are called .
The correct answer is lipid rafts. Lipid rafts are more dense, less fluid domains of the plasma membrane. In addition to clustering cholesterol and sphingolipids, large transmembrane-domain proteins also localize here.
Integrins are transmembrane receptors, micelles are small lipid spheres, and phosphoinositides are a family of lipid molecules.
The correct answer is lipid rafts. Lipid rafts are more dense, less fluid domains of the plasma membrane. In addition to clustering cholesterol and sphingolipids, large transmembrane-domain proteins also localize here.
Integrins are transmembrane receptors, micelles are small lipid spheres, and phosphoinositides are a family of lipid molecules.
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Which type of membrane protein spans the entire width of the membrane?
Which type of membrane protein spans the entire width of the membrane?
Integral proteins are proteins that connect the inside of the cell to the outside by traversing the phospholipid bilayer. Carrier proteins, for example, allow substances to pass the membrane by letting them cross through channels.
Integral proteins are proteins that connect the inside of the cell to the outside by traversing the phospholipid bilayer. Carrier proteins, for example, allow substances to pass the membrane by letting them cross through channels.
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Many retroviruses, including (human immunodeficiency virus) HIV and other lentiviruses, generally bind what structure on the plasma membrane of vertebrate cells?
Many retroviruses, including (human immunodeficiency virus) HIV and other lentiviruses, generally bind what structure on the plasma membrane of vertebrate cells?
The correct answer is glycoprotein. HIV and many lentiviruses, which are also retroviruses, bind the CD4 glycoprotein. Lipopolysaccharides are found in bacteria, not vertebrates. Oligosaccharides are sugar polymers and generally function in cell-cell signaling. Cholesterol and phosphatidylcholine are components of the plasma membrane, not necessarily extracellularly exposed. The latter two help define the shape and rigidity of the plasma membrane.
The correct answer is glycoprotein. HIV and many lentiviruses, which are also retroviruses, bind the CD4 glycoprotein. Lipopolysaccharides are found in bacteria, not vertebrates. Oligosaccharides are sugar polymers and generally function in cell-cell signaling. Cholesterol and phosphatidylcholine are components of the plasma membrane, not necessarily extracellularly exposed. The latter two help define the shape and rigidity of the plasma membrane.
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What is the name for dense microdomains of the plasma membrane that are enriched in cholesterol and sphingolipids and are centers for signal molecule assembly and receptor trafficking?
What is the name for dense microdomains of the plasma membrane that are enriched in cholesterol and sphingolipids and are centers for signal molecule assembly and receptor trafficking?
The correct answer is lipid rafts. These are dense portions of the phospholipid bilayer that are slightly thicker due to the increased presence of cholesterols and sphingolipids and are hubs for many processes. Micelles are single layer phospholipids that form spheres. Endosomes are intracellular compartments that are often important for transport of materials to the plasma membrane.
The correct answer is lipid rafts. These are dense portions of the phospholipid bilayer that are slightly thicker due to the increased presence of cholesterols and sphingolipids and are hubs for many processes. Micelles are single layer phospholipids that form spheres. Endosomes are intracellular compartments that are often important for transport of materials to the plasma membrane.
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Which of the following can freely diffuse through the cell membrane?
I. Oxygen
II. Potassium ions
III. Glucose
IV. Hydrogen ions
Which of the following can freely diffuse through the cell membrane?
I. Oxygen
II. Potassium ions
III. Glucose
IV. Hydrogen ions
Only small, nonpolar molecules can freely diffuse through the plasma membrane. From this group, only oxygen fits this description. Hydrogen and potassium ions are charged and, therefore, carry a polar element that cannot diffuse through the membrane. Glucose is too large, and also contains a polar aldehyde group. Oxygen atoms generally contribute to molecular polarity due to their abundance of valence electrons. When arranged symmetrically, however, such as in the oxygen molecule, the oxygen atoms result in zero net polarity.
Transmembrane proteins and channels are used for facilitated diffusion of glucose and small ions.
Only small, nonpolar molecules can freely diffuse through the plasma membrane. From this group, only oxygen fits this description. Hydrogen and potassium ions are charged and, therefore, carry a polar element that cannot diffuse through the membrane. Glucose is too large, and also contains a polar aldehyde group. Oxygen atoms generally contribute to molecular polarity due to their abundance of valence electrons. When arranged symmetrically, however, such as in the oxygen molecule, the oxygen atoms result in zero net polarity.
Transmembrane proteins and channels are used for facilitated diffusion of glucose and small ions.
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Which of the following is false with regard to the LDL-receptor?
Which of the following is false with regard to the LDL-receptor?
The LDL-receptor enters the cell via clathrin-mediated endocytosis, not COPII. COPII is involved in budding off of the endoplasmic reticulum.
All of the other given answer options are true.
The LDL-receptor enters the cell via clathrin-mediated endocytosis, not COPII. COPII is involved in budding off of the endoplasmic reticulum.
All of the other given answer options are true.
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Which of the following is false concerning facilitated diffusion?
Which of the following is false concerning facilitated diffusion?
Facilitated diffusion is used to move polar or charged substances down their electrochemical gradients. Although this does require the use of integral membrane proteins, no energy is used during this process, as it is still a form of diffusion.
Facilitated diffusion is used to move polar or charged substances down their electrochemical gradients. Although this does require the use of integral membrane proteins, no energy is used during this process, as it is still a form of diffusion.
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When will water have a net flow into a cell?
When will water have a net flow into a cell?
The direction for the diffusion of water, or osmosis, can be predicted by comparing the tonicities of the cell and its surroundings. When the cell has more solute in it than the external environment, water will flow into the cell in order to help even out the concentrations.
As a result, water will flow into the cell when it is found in a hypotonic solution.
The direction for the diffusion of water, or osmosis, can be predicted by comparing the tonicities of the cell and its surroundings. When the cell has more solute in it than the external environment, water will flow into the cell in order to help even out the concentrations.
As a result, water will flow into the cell when it is found in a hypotonic solution.
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A person is found to have a defect in his ATP synthase gene. Which of the following will be halted in his cells?
A person is found to have a defect in his ATP synthase gene. Which of the following will be halted in his cells?
ATP synthase is a molecule used to generate energy for the cell (in the form of ATP). Lack of ATP synthase will halt many active processes that require energy. Recall that sodium-potassium pump is found on multitude of cells in the body and functions to maintain the intracellular concentration of ions. This pump transports sodium and potassium ions against its concentration gradient (sodium out of and potassium into the cell). Since it is transporting against a concentration gradient, the sodium-potassium pump carries out active transport and, therefore, requires energy. Decreased ATP synthase activity will lead to decreased ATP levels and, subsequently, affect the sodium-potassium pump.
Potassium channels are selective molecules (selective for potassium) that transport potassium ions along its concentration gradient (from inside of cell to outside); therefore, this is a type of passive transport and does not require energy.
ATP synthase is a molecule used to generate energy for the cell (in the form of ATP). Lack of ATP synthase will halt many active processes that require energy. Recall that sodium-potassium pump is found on multitude of cells in the body and functions to maintain the intracellular concentration of ions. This pump transports sodium and potassium ions against its concentration gradient (sodium out of and potassium into the cell). Since it is transporting against a concentration gradient, the sodium-potassium pump carries out active transport and, therefore, requires energy. Decreased ATP synthase activity will lead to decreased ATP levels and, subsequently, affect the sodium-potassium pump.
Potassium channels are selective molecules (selective for potassium) that transport potassium ions along its concentration gradient (from inside of cell to outside); therefore, this is a type of passive transport and does not require energy.
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A researcher observes that a molecule is brought inside the cell via membrane transporters. What can the researcher conclude about this type of transport?
A researcher observes that a molecule is brought inside the cell via membrane transporters. What can the researcher conclude about this type of transport?
Membrane transporters are molecules found on plasma membranes that act as gateway for several molecules that enter and exit cells. These transporters are usually specific for one or two molecules and transport them across the cell membranes. The membrane transporters can transport ions/molecules along or against the concentration gradients; therefore, membrane transporters perform both passive and active transport. Transporters that move molecules along concentration gradient carry out a special type of passive transport called facilitated diffusion whereas transporters that move against concentration gradient carry out active transport (requires energy).
The question doesn’t state whether the molecule is brought along or against its concentration gradient; therefore, the membrane transporter could be a facilitated transporter or an active transporter.
Membrane transporters are molecules found on plasma membranes that act as gateway for several molecules that enter and exit cells. These transporters are usually specific for one or two molecules and transport them across the cell membranes. The membrane transporters can transport ions/molecules along or against the concentration gradients; therefore, membrane transporters perform both passive and active transport. Transporters that move molecules along concentration gradient carry out a special type of passive transport called facilitated diffusion whereas transporters that move against concentration gradient carry out active transport (requires energy).
The question doesn’t state whether the molecule is brought along or against its concentration gradient; therefore, the membrane transporter could be a facilitated transporter or an active transporter.
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In a normal individual, which of the following molecule(s) always enter(s) the cell via passive transport?
I. Calcium
II. Potassium
III. Sodium
In a normal individual, which of the following molecule(s) always enter(s) the cell via passive transport?
I. Calcium
II. Potassium
III. Sodium
There are two types of membrane transport: passive and active transport. Passive transport involves movement of molecules along its concentration gradient. This is a spontaneous process and does not require energy. Examples of passive transport include simple diffusion of lipophilic molecules and facilitated transport of molecules involving a membrane transporter (such as an ion channel). Active transport, on the other hand, moves molecules against their concentration gradient. This is not a spontaneous process and, therefore, requires energy.
To answer this question we need to recall the relative concentrations of the three ions presented in the question. Potassium ions are found in higher concentrations inside the cell whereas calcium and sodium are found in higher concentrations outside the cell. This means that moving calcium and sodium ions inside the cell will involve moving along their respective concentration gradients (from high to low concentration) whereas moving potassium ions inside the cell will involve moving against the concentration gradient; therefore, sodium and calcium come into the cell via passive transport whereas potassium enters via active transport.
There are two types of membrane transport: passive and active transport. Passive transport involves movement of molecules along its concentration gradient. This is a spontaneous process and does not require energy. Examples of passive transport include simple diffusion of lipophilic molecules and facilitated transport of molecules involving a membrane transporter (such as an ion channel). Active transport, on the other hand, moves molecules against their concentration gradient. This is not a spontaneous process and, therefore, requires energy.
To answer this question we need to recall the relative concentrations of the three ions presented in the question. Potassium ions are found in higher concentrations inside the cell whereas calcium and sodium are found in higher concentrations outside the cell. This means that moving calcium and sodium ions inside the cell will involve moving along their respective concentration gradients (from high to low concentration) whereas moving potassium ions inside the cell will involve moving against the concentration gradient; therefore, sodium and calcium come into the cell via passive transport whereas potassium enters via active transport.
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Which of the following transport mechanisms requires ATP hydrolysis to move a molecule against its concentration gradient?
Which of the following transport mechanisms requires ATP hydrolysis to move a molecule against its concentration gradient?
Secondary active transport and cotransport are the same thing, and while solutes can be moved against their concentration gradient, ATP is not used. Passive and facilitated diffusion do not require ATP either. Active transport is the only transport mechanism that uses ATP to move molecules against their concentration gradient.
Secondary active transport and cotransport are the same thing, and while solutes can be moved against their concentration gradient, ATP is not used. Passive and facilitated diffusion do not require ATP either. Active transport is the only transport mechanism that uses ATP to move molecules against their concentration gradient.
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Which of the following is not a method used to transport substances into a cell?
Which of the following is not a method used to transport substances into a cell?
Endocytosis is the process by which substances from the external environment are encapsulated in vesicles and brought into the cell. Receptor-mediated endocytosis uses membrane receptors to help localize the formation of the trasnport vesicle. Pinocytosis uses vesicles to transport fluids into the cell, while phagocytosis uses vesicles to bring pathogenic debris into the cell for digestion.
Exocytosis, in contrast, is the expulsion of substances from the cell via a transport vesicle.
Endocytosis is the process by which substances from the external environment are encapsulated in vesicles and brought into the cell. Receptor-mediated endocytosis uses membrane receptors to help localize the formation of the trasnport vesicle. Pinocytosis uses vesicles to transport fluids into the cell, while phagocytosis uses vesicles to bring pathogenic debris into the cell for digestion.
Exocytosis, in contrast, is the expulsion of substances from the cell via a transport vesicle.
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