Cell Biology - GRE Subject Test: Biology
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A researcher finds a large amount of an unusual sugar in the cells of a recently discovered species. Which of the following are potential mechanisms the cell is using to import the sugar?
I. Passive diffusion
II. Receptor-mediated endocytosis
III. Symport
A researcher finds a large amount of an unusual sugar in the cells of a recently discovered species. Which of the following are potential mechanisms the cell is using to import the sugar?
I. Passive diffusion
II. Receptor-mediated endocytosis
III. Symport
Because the molecule is a sugar, it is too large to passively diffuse across the plasma membrane and contains polar regions that would make this impossible.
There are several other mechanisms by which the sugar could enter the cell. One of these is receptor-mediated endocytosis. In this process the sugar would bind to receptors on the plasma membrane, which stimulates a budding event and eventually leads to the formation of a vesicle inside the cell.
Symport is another potential mechanism. In symport, the import of a molecule is coupled with the import of another molecule through the same transmembrane protein. For example, glucose has a symport mechanism with sodium ions.
Because the molecule is a sugar, it is too large to passively diffuse across the plasma membrane and contains polar regions that would make this impossible.
There are several other mechanisms by which the sugar could enter the cell. One of these is receptor-mediated endocytosis. In this process the sugar would bind to receptors on the plasma membrane, which stimulates a budding event and eventually leads to the formation of a vesicle inside the cell.
Symport is another potential mechanism. In symport, the import of a molecule is coupled with the import of another molecule through the same transmembrane protein. For example, glucose has a symport mechanism with sodium ions.
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What type membrane protein changes its shape when allowing substances to cross the membrane?
What type membrane protein changes its shape when allowing substances to cross the membrane?
Of the given choices, only channel and carrier proteins allow substances to cross the membrane. While channel proteins create an open pore through which substances can cross, carrier proteins will change their shape in order to allow substances to cross the membrane.
Of the given choices, only channel and carrier proteins allow substances to cross the membrane. While channel proteins create an open pore through which substances can cross, carrier proteins will change their shape in order to allow substances to cross the membrane.
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Which of the following conditions would result in a more fluid membrane?
Which of the following conditions would result in a more fluid membrane?
There are many factors that determine the fluidity of cell membranes. Membranes that are composed of fully saturated, long fatty acid tails are generally less fluid then the opposite conditions. In addition, lower temperatures result in a less fluid membrane.
Membranes that have fatty acid tails with double bonds are more fluid because the double bonds make it difficult for multiple phospholipids to float next to one another. The shape of the double bond adds a another dimension to the lipid, preventing the tails from packing together. Unsaturated fatty acids are thus more fluid than saturated fatty acids.
There are many factors that determine the fluidity of cell membranes. Membranes that are composed of fully saturated, long fatty acid tails are generally less fluid then the opposite conditions. In addition, lower temperatures result in a less fluid membrane.
Membranes that have fatty acid tails with double bonds are more fluid because the double bonds make it difficult for multiple phospholipids to float next to one another. The shape of the double bond adds a another dimension to the lipid, preventing the tails from packing together. Unsaturated fatty acids are thus more fluid than saturated fatty acids.
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Which of the following factors would you expect to see in a cell membrane for an animal living in a very hot environment?
Which of the following factors would you expect to see in a cell membrane for an animal living in a very hot environment?
In higher temperatures, the cell membrane is going to become increasingly fluid due to the increased movement of the phospholipids. The cell membrane can control its fluidity in high temperatures by both increasing the saturated fatty acid tail content of the phospholipids, as well as making the fatty acid tails longer. Cholesterol can also help by acting as a buffer at high temperatures.
In higher temperatures, the cell membrane is going to become increasingly fluid due to the increased movement of the phospholipids. The cell membrane can control its fluidity in high temperatures by both increasing the saturated fatty acid tail content of the phospholipids, as well as making the fatty acid tails longer. Cholesterol can also help by acting as a buffer at high temperatures.
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What polymer is commonly found in the cell walls of fungi?
What polymer is commonly found in the cell walls of fungi?
Although cell walls often serve very similar functions for different species, the composition of the cell walls can vary significantly. Plant cell walls employ cellulose, while bacteria use peptidoglycan. Fungal cell walls use the polymer chitin.
Although cell walls often serve very similar functions for different species, the composition of the cell walls can vary significantly. Plant cell walls employ cellulose, while bacteria use peptidoglycan. Fungal cell walls use the polymer chitin.
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In bacteria, what is the polymer that makes up the cell wall?
In bacteria, what is the polymer that makes up the cell wall?
The correct answer is peptidoglycan. Cellulose composes the cell walls of plants, whereas chitin composes the cell walls of fungi. Starch and glycogen are stored polymers of glucose in plants and animals, respectively.
The correct answer is peptidoglycan. Cellulose composes the cell walls of plants, whereas chitin composes the cell walls of fungi. Starch and glycogen are stored polymers of glucose in plants and animals, respectively.
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Which statement correctly describes a Gram-positive bacterial cell?
Which statement correctly describes a Gram-positive bacterial cell?
A Gram-positive cell has the following basic structural characteristics: stains dark purple in the Gram stain, has a thick peptidoglycan layer, and possesses no outer membrane beyond this layer. Thus, there is also no periplasmic space. Acid-fast stains are only used for specific bacteria that have waxy cell walls.
A Gram-positive cell has the following basic structural characteristics: stains dark purple in the Gram stain, has a thick peptidoglycan layer, and possesses no outer membrane beyond this layer. Thus, there is also no periplasmic space. Acid-fast stains are only used for specific bacteria that have waxy cell walls.
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Which of the following is not true of lysosomes?
Which of the following is not true of lysosomes?
Lysosomes have the function of digesting foreign materials and large structures, such as organelles. They do this by maintaining an acidic pH of approximately 5 and utilizing special proteins called acid hydrolyases, which are specifically designed to function at low pH levels. In order to maintain this low pH, lysosomes must be membrane-bound and have a highly regulated flow of protons.
Prokaryotes do not have membrane-bound organelles, including lysosomes.
Lysosomes have the function of digesting foreign materials and large structures, such as organelles. They do this by maintaining an acidic pH of approximately 5 and utilizing special proteins called acid hydrolyases, which are specifically designed to function at low pH levels. In order to maintain this low pH, lysosomes must be membrane-bound and have a highly regulated flow of protons.
Prokaryotes do not have membrane-bound organelles, including lysosomes.
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If a cell is incapable of catabolizing very long fatty acid chains, it most likely has a problem with which of the following organelles?
If a cell is incapable of catabolizing very long fatty acid chains, it most likely has a problem with which of the following organelles?
Peroxisomes are primarily responsible for the breakdown of very long chain fatty acids and D-amino acids, as well as the synthesis of special types of phospholipids known as plasmalogens. If the cell cannot catabolize very long chain fatty acids, the issue is most likely within the peroxisomes.
The Golgi apparatus is very important for protein packaging. Mitochondria are crucial to generating energy for the cell. The smooth endoplasmic reticulum has various functions, including lipid and carbohydrate metabolism.
Peroxisomes are primarily responsible for the breakdown of very long chain fatty acids and D-amino acids, as well as the synthesis of special types of phospholipids known as plasmalogens. If the cell cannot catabolize very long chain fatty acids, the issue is most likely within the peroxisomes.
The Golgi apparatus is very important for protein packaging. Mitochondria are crucial to generating energy for the cell. The smooth endoplasmic reticulum has various functions, including lipid and carbohydrate metabolism.
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Which organelle is used for the degradation of macromolecules in the cell?
Which organelle is used for the degradation of macromolecules in the cell?
The function of breaking down cellular contents is done by the lysosome. Lysosomes have an acidic interior, which is useful for breaking down macromolecules that are no longer being used in the cell.
The smooth endoplasmic reticulum, in contrast, helps to break down foreign material, such as toxins. Mitochondria primarily serve to produce ATP for cellular energy. The Golgi apparatus works in tandem with the rough endoplasmic reticulum and helps to group and package proteins for vesicular transport.
The function of breaking down cellular contents is done by the lysosome. Lysosomes have an acidic interior, which is useful for breaking down macromolecules that are no longer being used in the cell.
The smooth endoplasmic reticulum, in contrast, helps to break down foreign material, such as toxins. Mitochondria primarily serve to produce ATP for cellular energy. The Golgi apparatus works in tandem with the rough endoplasmic reticulum and helps to group and package proteins for vesicular transport.
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Lysosomes are organelles that contain acid hydrolase enzymes, such that materials that are taken up by lysosomes can be degraded into their basic components, and these components can be reused by the cell. Due to the presence of these enzymes, interior of the lysosome is very acidic, with a pH around 4.7 or 4.8. The cell cytoplasm has pH typically around 7.2, making it slightly basic. What type of membrane component is likely responsible for maintaining the acidic environment within the lysosome?
Lysosomes are organelles that contain acid hydrolase enzymes, such that materials that are taken up by lysosomes can be degraded into their basic components, and these components can be reused by the cell. Due to the presence of these enzymes, interior of the lysosome is very acidic, with a pH around 4.7 or 4.8. The cell cytoplasm has pH typically around 7.2, making it slightly basic. What type of membrane component is likely responsible for maintaining the acidic environment within the lysosome?
Proton pumps use ATP to continuously pump hydrogen ions into the interior of the lysosome, thus maintaining an acidic environment in which the enzymes are most optimally efficient at breaking down the debris/macromolecules. The membrane of the lysosome is selectively permeable due to these types of transporters, and protects the rest of the cell from the very acidic environment. Recent journal articles suggest that the lysosome's membrane will be deliberately disrupted, releasing the acid and the hydrolases into the cytosol during apoptosis.
Proton pumps use ATP to continuously pump hydrogen ions into the interior of the lysosome, thus maintaining an acidic environment in which the enzymes are most optimally efficient at breaking down the debris/macromolecules. The membrane of the lysosome is selectively permeable due to these types of transporters, and protects the rest of the cell from the very acidic environment. Recent journal articles suggest that the lysosome's membrane will be deliberately disrupted, releasing the acid and the hydrolases into the cytosol during apoptosis.
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Chloroplasts are found primarily in which cell type?
Chloroplasts are found primarily in which cell type?
Chloroplasts are found primarily in the mesophyll cells. Mesophyll cells are the green colored tissue that is found within the leaf. It is the abundance of chloroplasts containing chlorophyll that give the mesophyll cells their green coloring. Parenchyma, sclerenchyma, and collenchyma cells are all found within the shoot and root of the plant, not in the leaves. These cell types have little to no chloroplasts within their membranes.
Chloroplasts are found primarily in the mesophyll cells. Mesophyll cells are the green colored tissue that is found within the leaf. It is the abundance of chloroplasts containing chlorophyll that give the mesophyll cells their green coloring. Parenchyma, sclerenchyma, and collenchyma cells are all found within the shoot and root of the plant, not in the leaves. These cell types have little to no chloroplasts within their membranes.
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The inner mitochondrial membrane is organized into cristae, which essentially results in a series of folds within the mitochondria. Which of the following best describes the primary advantage to having cristae in inner compartments of mitochondria?
The inner mitochondrial membrane is organized into cristae, which essentially results in a series of folds within the mitochondria. Which of the following best describes the primary advantage to having cristae in inner compartments of mitochondria?
ATP synthase and cytochromes stud the inner membrane, and more surface area means that more of them can be present in each mitochondrion. This increases the capacity to generate ATP.
ATP synthase and cytochromes stud the inner membrane, and more surface area means that more of them can be present in each mitochondrion. This increases the capacity to generate ATP.
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Which of the following is true about eukaryote ribosomes?
Which of the following is true about eukaryote ribosomes?
Eukaryotic ribosomes are 80S with one large 60S subunit and one small 40S subunit. Prokaryotic ribosomes are 70S, with one large 50S subunit and one small 30S subunit. "S" refers to the sedimentation coefficient (Svedberg), which is a particles sedimentation velocity for a given applied acceleration.
Eukaryotic ribosomes are 80S with one large 60S subunit and one small 40S subunit. Prokaryotic ribosomes are 70S, with one large 50S subunit and one small 30S subunit. "S" refers to the sedimentation coefficient (Svedberg), which is a particles sedimentation velocity for a given applied acceleration.
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Which of the following best describes the ribosome in terms of its structural components?
Which of the following best describes the ribosome in terms of its structural components?
Ribosomes can be classified as ribonucleoproteins because the proteins are associated with ribonucleic acids (RNA). Thus, RNA-protein complex is the best descriptor.
Ribosomes can be classified as ribonucleoproteins because the proteins are associated with ribonucleic acids (RNA). Thus, RNA-protein complex is the best descriptor.
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Ribosomes are the organelle responsible for the translation of mRNAs into proteins. To do this, ribosomes translate the mRNA codons into amino acids which are joined to form a long polypeptide. The ribosome has a catalytic domain that is responsible for the formation of the peptide bonds between these amino acids. What is the name, i.e. the enzymatic classification, of this domain in the ribosome?
Ribosomes are the organelle responsible for the translation of mRNAs into proteins. To do this, ribosomes translate the mRNA codons into amino acids which are joined to form a long polypeptide. The ribosome has a catalytic domain that is responsible for the formation of the peptide bonds between these amino acids. What is the name, i.e. the enzymatic classification, of this domain in the ribosome?
Interestingly, ribosomes are one of the only examples of an RNA structure that has enzymatic activity. The primary enzymatic function of the ribosome is one of a peptidyl transferase; that is, the catalysis of peptide bond formation between amino acids as those acids are brought to the nascent strand.
Interestingly, ribosomes are one of the only examples of an RNA structure that has enzymatic activity. The primary enzymatic function of the ribosome is one of a peptidyl transferase; that is, the catalysis of peptide bond formation between amino acids as those acids are brought to the nascent strand.
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__________ is a protein/complex that helps nucleate G-actin.
__________ is a protein/complex that helps nucleate G-actin.
On its own, G-actin (globular actin) is not likely to nucleate and begin to form chains of F-actin (fibrous actin); therefore, it is useful to have proteins to help the nucleation process. One of these protein complexes is Arp2/3. Arp2/3 is especially known for its function of nucleating actin chains that branch off of previously established actin chains. Myosins are motor proteins that interact with actin chains to perform various functions, such as muscle contraction and transporting vesicles. Cofilin is a protein that binds G-actin monomers and helps them dissociate from F-actin.
On its own, G-actin (globular actin) is not likely to nucleate and begin to form chains of F-actin (fibrous actin); therefore, it is useful to have proteins to help the nucleation process. One of these protein complexes is Arp2/3. Arp2/3 is especially known for its function of nucleating actin chains that branch off of previously established actin chains. Myosins are motor proteins that interact with actin chains to perform various functions, such as muscle contraction and transporting vesicles. Cofilin is a protein that binds G-actin monomers and helps them dissociate from F-actin.
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Which of the following are functions of the cytoskeleton?
I. Support organelles
II. Form motile structures
III. Create cell junctions
IV. Vesicle trafficking
Which of the following are functions of the cytoskeleton?
I. Support organelles
II. Form motile structures
III. Create cell junctions
IV. Vesicle trafficking
Each choice describes a distinct function of the cytoskeleton. The cytoskeleton is involved in supporting various organelles, helping to anchor them in various locations around the cell and maintaining their shape and integrity. It also has the important function of helping with vesicle trafficking by associating with various motor proteins that carry vesicles from one part of the cell to another. The cytoskeleton is also a part of several different types of cell junctions (e.g. adherens junctions). Finally, the cytoskeleton is also an important part of various motile structures, such as cilia and flagella.
Each choice describes a distinct function of the cytoskeleton. The cytoskeleton is involved in supporting various organelles, helping to anchor them in various locations around the cell and maintaining their shape and integrity. It also has the important function of helping with vesicle trafficking by associating with various motor proteins that carry vesicles from one part of the cell to another. The cytoskeleton is also a part of several different types of cell junctions (e.g. adherens junctions). Finally, the cytoskeleton is also an important part of various motile structures, such as cilia and flagella.
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Which of the following structures is made from microfilaments?
Which of the following structures is made from microfilaments?
The three major components of the cytoskeleton in cells are microtubules, intermediate filaments, and microfilaments. Microtubules are the larger filaments and make up the mitotic spindle, as well as flagella and cilia. Intermediate filaments are used in structural maintenance.
Microfilaments are the smaller filaments and make up the polymerized actin filament in muscle fibers.
Microfilaments and microtubules are both polarized, and can be used in vesicular transport. Intermediate filaments lack polarity and serve only structural functions.
The three major components of the cytoskeleton in cells are microtubules, intermediate filaments, and microfilaments. Microtubules are the larger filaments and make up the mitotic spindle, as well as flagella and cilia. Intermediate filaments are used in structural maintenance.
Microfilaments are the smaller filaments and make up the polymerized actin filament in muscle fibers.
Microfilaments and microtubules are both polarized, and can be used in vesicular transport. Intermediate filaments lack polarity and serve only structural functions.
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Which of the following is a function of intermediate filaments?
Which of the following is a function of intermediate filaments?
Intermediate filaments form a veil right next to the nuclear membrane, are of intermediate thickness with respect to the other two cytoskeletal filaments, and they almost exclusively play structural roles. Actin filaments brace cells against surfaces and allow contractions in striated muscle. Also, actin filaments provide structural support and have a role in determining cell shape. Microtubules form the mitotic spindle and comprise cilia and flagella. They are also the "freeways" on which motor proteins move and transport vesicles throughout the cell.
Intermediate filaments form a veil right next to the nuclear membrane, are of intermediate thickness with respect to the other two cytoskeletal filaments, and they almost exclusively play structural roles. Actin filaments brace cells against surfaces and allow contractions in striated muscle. Also, actin filaments provide structural support and have a role in determining cell shape. Microtubules form the mitotic spindle and comprise cilia and flagella. They are also the "freeways" on which motor proteins move and transport vesicles throughout the cell.
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