Cytoskeletal Element Quiz Questions

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Cytoskeletal Element Quiz Questions - Quiz

This is to prpare for exam 3


Questions and Answers
  • 1. 

    The building blocks of a nucleoside are _____

    • A.

      A pentose sugar and a phosphate group

    • B.

      A pentose sugar and a nitrogenous base

    • C.

      A phosphate group and a nitrogenous base

    • D.

      A pentose sugar, a phosphate group and a nitrogenous base

    • E.

      A pentose sugar, a phosphate gruop and an amino acid

    Correct Answer
    B. A pentose sugar and a nitrogenous base
    Explanation
    The building blocks of a nucleoside are a pentose sugar and a nitrogenous base. Nucleosides are composed of a five-carbon sugar molecule (pentose sugar) and a nitrogen-containing base. These two components are linked together to form the nucleoside structure. The phosphate group is not a part of the nucleoside structure, but it is present in the nucleotide, which is formed when a phosphate group is attached to the nucleoside. An amino acid is not involved in the structure of a nucleoside.

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  • 2. 

    You incubate liposomes with a series of purified proteins nomrally found in the coats of cell transport vesicles. after adding one of them to the liposome mixture, budding of vesicles fromt he liposomes began. what does this mean?

    • A.

      Liposomes cause the protein to denature

    • B.

      The protein is involved in the intiation of vesicle formation

    • C.

      The protein is involved in liposome denaturation

    • D.

      The protein triggers protein synthesis

    • E.

      The protein causes the entry of water into the liposomes

    Correct Answer
    B. The protein is involved in the intiation of vesicle formation
    Explanation
    The correct answer suggests that the protein added to the liposome mixture is involved in the initiation of vesicle formation. This means that the protein plays a role in the process of vesicles budding from the liposomes.

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  • 3. 

    How and where is the asymmetry of the phospholipid bilayers initially established?

    • A.

      It is initially established in the Golgi complex during lipid and protein modification

    • B.

      It is initially established in the ER during lipid and protein synthesis

    • C.

      It is initially established in the secretory vesicles during lipid and protein modification

    • D.

      It is initially established in the in the mitochodnria by random insertion into the membranes.

    • E.

      All of the above

    Correct Answer
    B. It is initially established in the ER during lipid and protein synthesis
    Explanation
    The asymmetry of the phospholipid bilayers is initially established in the ER during lipid and protein synthesis. During this process, specific enzymes and proteins are involved in the selective incorporation of different phospholipids into the inner and outer leaflets of the bilayer. This results in the establishment of an asymmetric distribution of phospholipids, with different compositions and functions on each side of the bilayer.

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  • 4. 

    In general, how are proteins targeted to specific destinations?

    • A.

      Sorting signals is located on the gene

    • B.

      Sorting signals is located on the proteins

    • C.

      Receptors in trasport vesicle walls that recognize them

    • D.

      Sorting signals is located on the cellular compartments

    • E.

      B and c

    Correct Answer
    E. B and c
    Explanation
    Proteins are targeted to specific destinations through a combination of sorting signals located on the proteins themselves and receptors in transport vesicle walls that recognize these signals. The sorting signals on the proteins act as a molecular address, guiding the protein to its intended location within the cell. The receptors in transport vesicle walls recognize these sorting signals and facilitate the transport of the protein to the appropriate cellular compartment. Therefore, the correct answer is b and c.

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  • 5. 

    The __-carbon of the sugar of a nucleotide participates in the formation of the phosphodiester bond?

    • A.

      1

    • B.

      2

    • C.

      3

    • D.

      5

    • E.

      C and d

    Correct Answer
    E. C and d
    Explanation
    The answer is c and d because both the 3'-carbon and the 5'-carbon of the sugar in a nucleotide participate in the formation of the phosphodiester bond. The 3'-carbon forms a bond with the phosphate group of the next nucleotide, while the 5'-carbon forms a bond with the phosphate group of the previous nucleotide, creating a chain of nucleotides in DNA or RNA.

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  • 6. 

    Which of the following are pathways of vesicle trafficking through the cytoplasm that have been discovered?

    • A.

      Biosynthetic pathway

    • B.

      Secretory pathway

    • C.

      Endocytic pathway

    • D.

      Hydrolytic pathway

    • E.

      A, b and c

    Correct Answer
    E. A, b and c
    Explanation
    The correct answer is a, b and c. Vesicle trafficking through the cytoplasm has been discovered to occur through the biosynthetic pathway, secretory pathway, and endocytic pathway. The biosynthetic pathway involves the transport of newly synthesized proteins and lipids from the endoplasmic reticulum to the Golgi apparatus and then to the plasma membrane. The secretory pathway involves the release of proteins and other molecules from the cell through exocytosis. The endocytic pathway involves the internalization of substances from the extracellular environment into the cell through endocytosis. The hydrolytic pathway is not a recognized pathway of vesicle trafficking.

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  • 7. 

    Which of the models below suggests that the Golgi cisternae are transient structures that form at the cis face of the stack by fusion of membranous carriers from the ER and ERGIC and that each cisterna travels through the Golgi complex from the cis to the trans end of the stack, changing in composition as it progresses?

    • A.

      The cisternal maturation model

    • B.

      The cargo carrying model

    • C.

      The vesicular transport model

    • D.

      The secretory transport model

    • E.

      The chemiosmotic model

    Correct Answer
    A. The cisternal maturation model
    Explanation
    The cisternal maturation model suggests that the Golgi cisternae are transient structures that form at the cis face of the stack by fusion of membranous carriers from the ER and ERGIC. Each cisterna then travels through the Golgi complex from the cis to the trans end of the stack, changing in composition as it progresses. This model proposes that the Golgi cisternae mature and transform into the next cisterna in the stack, rather than vesicles transporting cargo between the cisternae.

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  • 8. 

    What determines the sequence of sugar addition to glycoprteins traveling through the gogli complex?

    • A.

      Nothing- the sequence is random.

    • B.

      The spatial arrangement of specific glycosyltransferases that contact proteins as they pass through the Golgi complex

    • C.

      The concentration of sugars in the Golgi complex

    • D.

      The sequence of sugars in the Gogli complex

    Correct Answer
    B. The spatial arrangement of specific glycosyltransferases that contact proteins as they pass through the Golgi complex
    Explanation
    The sequence of sugar addition to glycoproteins traveling through the Golgi complex is determined by the spatial arrangement of specific glycosyltransferases that come into contact with the proteins as they pass through the Golgi complex. These glycosyltransferases are responsible for adding specific sugars to the proteins in a specific order, resulting in the formation of complex sugar structures on the glycoproteins. The spatial arrangement of these enzymes ensures that the correct sugars are added in the correct sequence, leading to the proper glycosylation of the proteins.

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  • 9. 

    Which molecule below is a GTP-binding protein that is requred for the release of a clatherin-coated vesicle from the membrane on which it was formed?

    • A.

      AP2

    • B.

      GGA

    • C.

      Clathrin

    • D.

      Dynamin

    • E.

      Opscrin

    Correct Answer
    D. Dynamin
    Explanation
    Dynamin is a GTP-binding protein that plays a crucial role in the release of clathrin-coated vesicles from the membrane. It functions by constricting and pinching off the vesicle from the membrane, allowing it to be transported to its destination within the cell. The other options, AP2, GGA, Clathrin, and Opscrin, are not directly involved in the release of clathrin-coated vesicles and do not possess GTP-binding activity.

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  • 10. 

    In a pulse-chase procedure, if the chase is longer, which statement below correctly describes the location of the radioactively labeled proteins in the cell?

    • A.

      Closer to the synthesis site

    • B.

      Farther from the nucleus

    • C.

      Farther from the synthesis site

    • D.

      Closer to the nucleus

    Correct Answer
    C. Farther from the synthesis site
    Explanation
    In a pulse-chase procedure, radioactively labeled proteins are initially synthesized at a specific site in the cell. The pulse involves adding a labeled precursor to the cell, allowing it to be incorporated into newly synthesized proteins. The chase involves removing the labeled precursor and replacing it with an unlabeled precursor. The chase period allows for the labeled proteins to be further distributed within the cell. Therefore, if the chase is longer, the labeled proteins will have more time to move away from the synthesis site, resulting in them being farther from the synthesis site.

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  • 11. 

    Which of the following is (are) made on free ribosomes?

    • A.

      Proteins that are to remain in the cytosol

    • B.

      Peripheral proteins of the inner cell membrane surface

    • C.

      Peripheral proteins of the outer cell membrane surface

    • D.

      Proteins to be transported to the nuclelus

    • E.

      A, b and d

    Correct Answer
    E. A, b and d
    Explanation
    Proteins that are to remain in the cytosol, peripheral proteins of the inner cell membrane surface, and proteins to be transported to the nucleus are all made on free ribosomes. Free ribosomes are ribosomes that are not attached to the endoplasmic reticulum and are responsible for synthesizing proteins that function within the cytosol or are destined for other organelles such as the nucleus. Therefore, options a, b, and d are all correct answers.

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  • 12. 

    How are proteins normally resident in the ER retrieved when they escape the ER?

    • A.

      Proteins that normally reside int he ER lumen have short amino acid sequences at their C-terminus that serve as retrieval sequences.

    • B.

      Proteins that normally reside int he ER lumen have short amino acid sequences at their N-terminus that serve as retrieval sequences.

    • C.

      Proteins that normally reside int he ER membrane have short amino acid sequences at their C-terminus that serve as retrieval sequences.

    • D.

      Proteins that normally reside int he ER membrane have short amino acid sequences at their N-terminus that serve as retrieval sequences.

    • E.

      A and c

    Correct Answer
    E. A and c
    Explanation
    Proteins that normally reside in the ER lumen or membrane have short amino acid sequences at their C-terminus that serve as retrieval sequences. These retrieval sequences help in retrieving the escaped proteins and directing them back to the ER.

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  • 13. 

    To what site does Sar1 bind after it binds to GTP?

    • A.

      The luminal leaflet of the ER membrane

    • B.

      The cytosolic leaflet of the Golgi membrane

    • C.

      The luminal leaflet of the Gogle membrane

    • D.

      The cytosolic leaflet of the ER membrane

    Correct Answer
    D. The cytosolic leaflet of the ER membrane
    Explanation
    After Sar1 binds to GTP, it binds to the cytosolic leaflet of the ER membrane. This is because Sar1 is a small GTPase protein involved in vesicle trafficking between the endoplasmic reticulum (ER) and the Golgi apparatus. It functions as a molecular switch, where it is activated by binding to GTP and then recruits coat proteins to form transport vesicles. The cytosolic leaflet of the ER membrane is the site where Sar1 binds to initiate the formation of these transport vesicles.

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  • 14. 

    Which type of cytoskeletal element is characterized as a hollow, rigid cylindrical tube with walls coposed of tubulin subunits

    • A.

      Microfilaments

    • B.

      Microtubules

    • C.

      Intermediate filaments

    • D.

      All of the above

    Correct Answer
    B. Microtubules
    Explanation
    Microtubules are characterized as a hollow, rigid cylindrical tube with walls composed of tubulin subunits. They are a type of cytoskeletal element involved in various cellular processes such as cell division, intracellular transport, and maintenance of cell shape. Microfilaments, on the other hand, are made up of actin subunits and are involved in cell movement and contraction. Intermediate filaments provide structural support to the cell and are composed of various proteins. Therefore, the correct answer is microtubules.

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  • 15. 

    What endosome serves as a sorting station that directs different types of receptors and ligands along diferent pathways?

    • A.

      Medial endosomes

    • B.

      Late endosomes

    • C.

      Early lysosomes

    • D.

      Medial lysomes

    • E.

      Early endosomes

    Correct Answer
    E. Early endosomes
    Explanation
    Early endosomes serve as a sorting station that directs different types of receptors and ligands along different pathways. They receive cargo from the plasma membrane through the process of endocytosis and then sort and direct this cargo to different destinations within the cell. This sorting process helps regulate the cellular trafficking of receptors and ligands, ensuring that they are transported to the appropriate locations for further processing or degradation. Late endosomes and lysosomes are involved in later stages of the endocytic pathway, while medial endosomes and medial lysosomes are not commonly recognized components of the endocytic pathway.

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  • 16. 

    The heads of kinesin like proteins have farily closely related amino acid sequences but diverse tail sequences. what ist he explation for this seeming contradiction?

    • A.

      The similarity of kinesin like protein heads and the variation in their tails are purely random

    • B.

      The similarity of the heads is explained by their similar roles in interacting with microtubules; the variation in the tails reflects the variation of cargoes to which they bind

    • C.

      The similarity of the heads is explained by their different roles in interacting with microtubules; the variation in the tails reflects the similar cargoes to which they bind.

    • D.

      The similarity of the heads is explained by their similar roles in interacting with microtubules; the variation in the tails reflects the similar of cargoes to which they bind

    • E.

      The similarity of the heads is explained by their different roles in interacting with microtubules; the variation in the tails reflects the variety of cargoes to which they bind.

    Correct Answer
    B. The similarity of the heads is explained by their similar roles in interacting with microtubules; the variation in the tails reflects the variation of cargoes to which they bind
    Explanation
    The similarity of the heads of kinesin like proteins can be explained by their similar roles in interacting with microtubules. This suggests that the heads have evolved to perform a specific function in the cell, which requires a conserved amino acid sequence. On the other hand, the diversity in the tails reflects the variation of cargoes to which they bind. This implies that the tails have evolved to interact with different types of cargoes, leading to a greater diversity in their amino acid sequences. Overall, this explains the seeming contradiction between the similarity of the heads and the diversity of the tails in kinesin like proteins.

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  • 17. 

    Why is the Er so well-suited and ideally constructed for its role as a port of entry for secretory proteins?

    • A.

      It has a large surface area allowing the attachment of many ribosoems

    • B.

      The ER cisternae lumen favors the folding and disassembly of proteins

    • C.

      The RER segregates secreotry, lysosomal and plant-cell vacuclar proteins from toher newly made proteins, allowing their modication, and sends them to their destination

    • D.

      A and c

    • E.

      A, b and c

    Correct Answer
    E. A, b and c
    Explanation
    The ER is well-suited and ideally constructed for its role as a port of entry for secretory proteins because it has a large surface area allowing the attachment of many ribosomes, which are responsible for protein synthesis. Additionally, the ER cisternae lumen provides an environment that favors the folding and disassembly of proteins. Furthermore, the RER segregates secretory, lysosomal, and plant-cell vacuolar proteins from other newly made proteins, allowing their modification, and sends them to their destination. Therefore, all of these factors make the ER highly efficient in processing and transporting secretory proteins.

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  • 18. 

    The vesicle is targeted to the appropriate compartment by

    • A.

      Endocytosis

    • B.

      Rabs

    • C.

      GTP binding proteins

    • D.

      T-snares

    Correct Answer
    B. Rabs
    Explanation
    Rabs are GTP-binding proteins that play a crucial role in targeting vesicles to the appropriate compartments within the cell. They act as molecular switches, cycling between an active GTP-bound state and an inactive GDP-bound state. By interacting with specific effector proteins, Rabs help to tether and fuse vesicles to the correct target membrane, ensuring accurate delivery of cargo. Thus, the presence of Rabs facilitates the targeting of vesicles to their appropriate compartments, making them the correct answer in this context.

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  • 19. 

    Avery, MacLead, and McCarty (1944) demonstrated that DNA was the molecule of heredity by treating heat killed Streptaccacus pneumonia A (smooth) strain with DNase, thereby preventing transfer of the transforming substance from the killed S straight to the live R (rough) straight when the two were mixed together and injected into mice. Another way that one could demonstrate transformation in bacteria would be to extract DNA from

    • A.

      A R straight and mix it with S cells

    • B.

      A S strain and mix it with R cells

    • C.

      A S strain and mix it with heat-killed S cells

    • D.

      None of the above

    Correct Answer
    B. A S strain and mix it with R cells
    Explanation
    By mixing a S strain (which does not have the ability to cause disease) with R cells (which do have the ability to cause disease), one can demonstrate transformation in bacteria. This is because the S strain contains the transforming substance, which is DNA, that can be transferred to the R cells, causing them to acquire the ability to cause disease. This experiment would replicate the same principle that Avery, MacLeod, and McCarty demonstrated in their experiment, further supporting the idea that DNA is the molecule of heredity.

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  • 20. 

    The uptake (both specific and nonspecific) of fluid, dissolved solutes and suspended macromolecules is called ____

    • A.

      Endocytosis

    • B.

      Phagoctyosis

    • C.

      Autophagy

    • D.

      Exoctyosis

    • E.

      Pinocytosis

    Correct Answer
    E. Pinocytosis
    Explanation
    Pinocytosis refers to the process of the uptake of fluid, dissolved solutes, and suspended macromolecules by cells. It involves the formation of small vesicles at the cell membrane, which then engulf and internalize the extracellular material. This process is non-specific, meaning it can take up a variety of substances from the surrounding environment. Unlike phagocytosis, which involves the engulfment of solid particles, pinocytosis primarily focuses on the uptake of fluids and dissolved substances. Autophagy refers to the degradation of a cell's own components, while exocytosis involves the release of substances from the cell.

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  • 21. 

    A small subfamily of kinesines moves toward the minus end of a microtubules, while the rest move toward the plus end. when the neck and stalk of a minus-directed kinesin is joined to the head of ap lus-directed kinesin, in what direction will the hydrid motor protein travel along a microtubule?

    • A.

      In a retrograde direction

    • B.

      Toward the plus-end of the microtubule

    • C.

      In an anterograde direction

    • D.

      Towards the fastest growing end of the microtubule

    • E.

      C and d

    Correct Answer
    A. In a retrograde direction
    Explanation
    When the neck and stalk of a minus-directed kinesin are joined to the head of a plus-directed kinesin, the resulting hybrid motor protein will have a minus-directed component. This means that the protein will move in the opposite direction of the normal plus-directed kinesin, which is towards the minus end of the microtubule. Therefore, the hybrid motor protein will travel in a retrograde direction along the microtubule.

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  • 22. 

    What recognizes the signal sequence as it exits the ribosomes and of what is it made?

    • A.

      Signal recognition particle, DNA and protein

    • B.

      Signal recognition particle, carbohydrate and protein

    • C.

      SRP and its components, RNA and protein

    • D.

      Signal recognition protein, carbohydrate and lipid

    Correct Answer
    C. SRP and its components, RNA and protein
    Explanation
    The signal recognition particle (SRP) and its components, RNA and protein, recognize the signal sequence as it exits the ribosomes. The SRP is a ribonucleoprotein complex composed of both RNA and protein subunits. Together, they form a complex that binds to the signal sequence of newly synthesized proteins. This binding helps to target the protein to the endoplasmic reticulum, where it can be properly folded and processed. Therefore, the correct answer is SRP and its components, RNA and protein.

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  • 23. 

    Which of the following are components of Chargaff's rules of bases?

    • A.

      Amount of G= Amount of C

    • B.

      Amount of purines= Amount of pyrimidines

    • C.

      %C+T=%A+G

    • D.

      Amount of A= Amount of T

    • E.

      All of the above

    Correct Answer
    E. All of the above
    Explanation
    Chargaff's rules of bases state that the amount of G (guanine) is equal to the amount of C (cytosine), the amount of purines (G and A) is equal to the amount of pyrimidines (C and T), the sum of the percentages of C and T is equal to the sum of the percentages of A and G, and the amount of A (adenine) is equal to the amount of T (thymine). Therefore, all of the given statements are components of Chargaff's rules of bases.

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  • 24. 

    In addition to microtubule motor proteins ____ are also involved in vesicular transport.

    • A.

      Actin

    • B.

      Non-muscle myosins

    • C.

      Tubulin

    • D.

      Dynein

    • E.

      Kinesin-like proteins

    Correct Answer
    B. Non-muscle myosins
    Explanation
    Non-muscle myosins are a type of motor proteins that are involved in vesicular transport, along with microtubule motor proteins. These proteins are responsible for moving vesicles and other cellular cargo along the actin cytoskeleton. They generate force by interacting with actin filaments, enabling the transport of vesicles to their intended destinations within the cell.

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  • 25. 

    Most vesicles budding from the Golgi body have a fuzzy, electron-dense coat on their ______ surface. The coat appears to be made of _______.

    • A.

      Luminal, lipid

    • B.

      Cytosolic, lipid

    • C.

      Cytosolic, carbohydrate

    • D.

      Luminal, protein

    • E.

      Cytosolic, protein

    Correct Answer
    E. Cytosolic, protein
  • 26. 

    Which coated vesicles move materials in a retrograde direction from the ERGIC and Golgi stack toward the ER?

    • A.

      Cadmium-coated vesicles

    • B.

      COPI-coated vesicles

    • C.

      Clathrin-coated vesicles

    • D.

      COPII-coated vesicles

    Correct Answer
    B. COPI-coated vesicles
    Explanation
    COPI-coated vesicles are responsible for moving materials in a retrograde direction from the ERGIC and Golgi stack back to the ER. This is achieved through the binding of COPI proteins to cargo molecules and the subsequent formation of COPI-coated vesicles. These vesicles then bud off from the Golgi stack and transport the cargo molecules back to the ER.

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  • 27. 

    All of the following statements about cellular trafficking are true EXCEPT

    • A.

      COPI-coated vesicles move materials from Gogli to the secretory vesicle

    • B.

      Tethering proteins mediate docking between target and vesicle

    • C.

      COPII-coated vesicles move materials from ER to Golgi

    • D.

      Movement may be mediated by microtubules

    Correct Answer
    A. COPI-coated vesicles move materials from Gogli to the secretory vesicle
    Explanation
    The given correct answer is incorrect. COPI-coated vesicles do indeed move materials from the Golgi to the ER, not from the Golgi to the secretory vesicle. The other statements are true: tethering proteins mediate docking between target and vesicle, COPII-coated vesicles move materials from the ER to the Golgi, and movement may be mediated by microtubules.

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  • 28. 

    How do protein coats select the contents of vesicles they help to form?

    • A.

      They electromagnetically attract the correct cargo proteins

    • B.

      The coats have a specific affinity for the cytosolic tails of integral membrane receptors for cargo proteins that reside in the donor membrane

    • C.

      The coats have a specific affinity for the luminal tails of integral membrane

    • D.

      Receptors for cargo proteins that reside in the donor membrane

    • E.

      The coat proteins directly attach to the cargo proteins in the lumen of the forming vesicles

    Correct Answer
    B. The coats have a specific affinity for the cytosolic tails of integral membrane receptors for cargo proteins that reside in the donor membrane
    Explanation
    Protein coats select the contents of vesicles they help to form by having a specific affinity for the cytosolic tails of integral membrane receptors for cargo proteins that reside in the donor membrane. This means that the protein coats are able to recognize and bind to specific receptors on the membrane, ensuring that the correct cargo proteins are packaged into the vesicles.

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  • 29. 

    What GTP-binding protein plays a regulatory role in the formation and disassembly of the COPII coat?

    • A.

      Sar1

    • B.

      Gar1

    • C.

      ARF1

    • D.

      Ras

    • E.

      Src

    Correct Answer
    A. Sar1
    Explanation
    Sar1 is a GTP-binding protein that plays a regulatory role in the formation and disassembly of the COPII coat. The COPII coat is responsible for vesicle formation and transport of proteins from the endoplasmic reticulum to the Golgi apparatus. Sar1 is involved in the initial step of COPII coat assembly by recruiting other proteins to the ER membrane. It functions by binding to GTP, which induces a conformational change and allows Sar1 to associate with the ER membrane. This interaction leads to the recruitment of other COPII coat proteins and the subsequent formation of transport vesicles.

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  • 30. 

    What is the supposed function of the small subfamily of kinesins that is incapable of movement

    • A.

      They stabilize microtubules

    • B.

      They encouraging depolymerization

    • C.

      They cause polymerization

    • D.

      They block other kinesins from moving along microtubules

    • E.

      They add phosphate groups to tubulin

    Correct Answer
    B. They encouraging depolymerization
    Explanation
    The small subfamily of kinesins that is incapable of movement is believed to encourage depolymerization. This means that they promote the breakdown of microtubules, which are important structures within cells. By encouraging depolymerization, these kinesins play a role in regulating the dynamics and stability of microtubules.

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  • 31. 

    When the rate of loss of actin subunits from the pointed end of an actin filament is balanced by the rate of their addition to the barbed end, __________

    • A.

      The filaments are said to be steady state

    • B.

      The length of the filaments remains the same

    • C.

      Treadmilling occrus

    • D.

      A, b and c

    Correct Answer
    D. A, b and c
    Explanation
    When the rate of loss of actin subunits from the pointed end of an actin filament is balanced by the rate of their addition to the barbed end, the filaments are said to be in a steady state. In this state, the length of the filaments remains the same, and treadmilling occurs. Treadmilling refers to the simultaneous addition of subunits at one end of the filament and the loss of subunits at the other end, resulting in no net change in filament length. Therefore, all options a, b, and c are correct.

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  • 32. 

    Which end of a microtubule is the slow growing end

    • A.

      The minus end

    • B.

      The end with beta-tubulin at the tip

    • C.

      The end with alpha-tubulin at the tip

    • D.

      A and c

    • E.

    Correct Answer
    D. A and c
    Explanation
    The correct answer is "a and c" because the slow growing end of a microtubule is the minus end, which is also the end with alpha-tubulin at the tip. This is because microtubules are polar structures with distinct plus and minus ends, and the minus end is known to grow at a slower rate compared to the plus end. Additionally, alpha-tubulin is found at the minus end of the microtubule, while beta-tubulin is found at the plus end. Therefore, both options "a" and "c" correctly identify the slow growing end of a microtubule.

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  • 33. 

    The accumulation of misfolded proteins in the ER is a potentially lethal situation and thus causes the triggering of what process?

    • A.

      The polysomal response

    • B.

      The posttranscriptional resopnse

    • C.

      The unfolded protein response (UPR)

    • D.

      The proleasomal response

    Correct Answer
    C. The unfolded protein response (UPR)
    Explanation
    The accumulation of misfolded proteins in the endoplasmic reticulum (ER) is a potentially lethal situation because it disrupts normal cellular function. In response to this, the unfolded protein response (UPR) is triggered. The UPR is a cellular stress response pathway that aims to restore ER homeostasis by increasing the production of chaperone proteins, enhancing protein folding capacity, and reducing protein synthesis. It also promotes the degradation of misfolded proteins and can induce cell death if the stress cannot be resolved. Therefore, the UPR is the correct answer as it is the specific process that is triggered in response to the accumulation of misfolded proteins in the ER.

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  • 34. 

    Which protein below is often a component of intermediate filaments?

    • A.

      Keratin

    • B.

      Lubulin

    • C.

      Actin

    • D.

      Primentin

    • E.

      A and d

    Correct Answer
    A. Keratin
    Explanation
    Keratin is often a component of intermediate filaments. Intermediate filaments are a type of cytoskeletal protein that provide structural support to cells. Keratin is a fibrous protein that is found in the skin, hair, and nails of animals, including humans. It forms intermediate filaments in epithelial cells, which help to maintain the integrity and strength of these tissues. Therefore, keratin is the correct answer as it is commonly associated with intermediate filaments.

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  • 35. 

    Kinesin movement along a microtubule is said to be ______ meaning that it can move long distances along an individual microtubule without falling off

    • A.

      Excessive

    • B.

      Progressive

    • C.

      Excessive

    • D.

      Processive

    • E.

      Aggresive

    Correct Answer
    D. Processive
    Explanation
    Kinesin movement along a microtubule is said to be processive, meaning that it can move long distances along an individual microtubule without falling off. This indicates that kinesin molecules are able to maintain a stable attachment to the microtubule and continue their movement in a coordinated and efficient manner. This processive movement is crucial for kinesin's role in transporting cargo within cells.

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  • 36. 

    What circumstantial evidence supports the proposed role of the Rabs-in recruiting cytosolic tethering proteins to specific membrane surfaces?

    • A.

      With over 60 Rab genes identified in humans, Rabs constitute the most diverse group of proteins involved in membrane trafficking

    • B.

      Rabs have the potential of giving each cell compartment a unique surface identity

    • C.

      Different Rabs have been found to be associated with different membrane compartments

    • D.

      The preferential localization of Rabs would allow them to recruit the various proteins involved in targeting specificity

    • E.

      All others are correct

    Correct Answer
    E. All others are correct
    Explanation
    The proposed role of the Rabs in recruiting cytosolic tethering proteins to specific membrane surfaces is supported by several pieces of circumstantial evidence. Firstly, the fact that there are over 60 Rab genes identified in humans suggests that Rabs play a significant role in membrane trafficking, making them potential candidates for recruiting tethering proteins. Additionally, Rabs have the ability to give each cell compartment a unique surface identity, indicating their involvement in recruiting specific proteins. Moreover, different Rabs have been associated with different membrane compartments, further supporting their role in recruiting tethering proteins to specific surfaces. Lastly, the preferential localization of Rabs would enable them to recruit the various proteins involved in targeting specificity.

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  • 37. 

    Hich of the proteins below is (are) not made on the membrane-bound ribosomes of the RER?

    • A.

      Inner peripheral membrane proteins

    • B.

      Soluble lysosomal proteins

    • C.

      Vacuolar enzymes

    • D.

      Proteins of the extracellular matrix

    • E.

      All of the above

    Correct Answer
    A. Inner peripheral membrane proteins
    Explanation
    Inner peripheral membrane proteins are not made on the membrane-bound ribosomes of the RER. The RER is responsible for synthesizing proteins that are either secreted or membrane-bound. Inner peripheral membrane proteins are proteins that are associated with the inner leaflet of the plasma membrane but are not embedded within it. These proteins are typically synthesized by free ribosomes in the cytoplasm and then targeted to the plasma membrane. Therefore, inner peripheral membrane proteins are not made on the membrane-bound ribosomes of the RER.

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  • 38. 

    Ring-shaped complexes in the centrosome contain ______ in combination with _____

    • A.

      Gamma tubulin; tubulin GTP

    • B.

      Gamma tubulin; tubulin ATP

    • C.

      Beta tubulin, tubulin GTP

    • D.

      Gamma tubulin, myosin I ATP

    • E.

      None of the above

    Correct Answer
    E. None of the above
  • 39. 

    When microtubules grow out of a centrosome, which end is associated with the centrosome?

    • A.

      The plus end

    • B.

      The minus end

    • C.

      The end with beta-tubulin at the tip

    • D.

      The end with alpha-tubulin at the tip

    • E.

      A and d

    Correct Answer
    E. A and d
    Explanation
    Microtubules grow out of a centrosome in a polarized manner, with one end known as the plus end and the other end known as the minus end. The plus end is associated with the centrosome and contains beta-tubulin at the tip, while the minus end does not. Therefore, both option a (the plus end) and option d (the end with alpha-tubulin at the tip) are correct.

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  • 40. 

    What led Avery, MacLead and McCarty to conclude that DNA was the transformation principle reported by Griffith and others?

    • A.

      The transformation principle exhibited a host of chemical properties shared by DNA and protein

    • B.

      When exposed to various enzymes, the transforming principle was only inactivated by DNAse

    • C.

      When exposed to various enzymes, the transforming principle was inactivated by all enzymes except DNAse

    • D.

      When exposed to various enzymes, the transofrming principle was only inactivated by protease

    • E.

      B and c

    Correct Answer
    B. When exposed to various enzymes, the transforming principle was only inactivated by DNAse
    Explanation
    Avery, MacLeod, and McCarty concluded that DNA was the transformation principle reported by Griffith and others because when exposed to various enzymes, the transforming principle was only inactivated by DNAse. This suggests that the transforming principle is a substance that shares chemical properties with DNA, as DNAse specifically targets and breaks down DNA. This finding supports the idea that DNA is responsible for the transformation observed in Griffith's experiment.

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  • 41. 

    The current model for the nucleation of microtubules is that a helical array of y-tubulin subunit forms an open, nng-shaped template on which the first row of alphabeta-tubulin dimers assembles. how does this model account for the polarity of microtubules?

    • A.

      Only the alpha-tubulin of a heterodimner can bind to the ring of y-subunits

    • B.

      Only the beta-tubulin of a heterodimner can bind to the ring of y-subunits

    • C.

      The ring structure straightens out the microtuble

    • D.

      The ring structure interacts with a homodimer instead of a heterdimer

    Correct Answer
    A. Only the alpha-tubulin of a heterodimner can bind to the ring of y-subunits
    Explanation
    In the current model for the nucleation of microtubules, a helical array of y-tubulin subunits forms a template in the shape of an open, nng structure. This template allows the first row of alphabeta-tubulin dimers to assemble. The model suggests that only the alpha-tubulin of a heterodimer can bind to the ring of y-subunits, which explains the polarity of microtubules. This means that the alpha-tubulin subunit is oriented towards the minus end of the microtubule, while the beta-tubulin subunit is oriented towards the plus end. Thus, the model accounts for the polarity of microtubules by specifying which tubulin subunit can bind to the y-subunit ring.

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  • 42. 

    ____ refers to the fact that the sequence of one DNA strand specifies the sequence of the other strand in the double helix?

    • A.

      Indirectionality

    • B.

      Complexity

    • C.

      Complementary

    • D.

      Similarity

    • E.

      Compulsivity

    Correct Answer
    C. Complementary
    Explanation
    Complementary refers to the fact that the sequence of one DNA strand specifies the sequence of the other strand in the double helix. This means that the two strands are paired together in a way that the bases on one strand can only form hydrogen bonds with their complementary bases on the other strand. This complementary base pairing allows for the accurate replication of DNA during cell division and is essential for maintaining the genetic code.

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  • 43. 

    Typically, receptors for hormones or growth factors are destroyed during endocytosis, leading to a reduction in the cell sensitivity to further stimulation by that particular hormone or growth factor. this is a mechanism by which cells regulate their ability to respond to extracellular messengers. what is it called?

    • A.

      Receptor up-regulation

    • B.

      Receptor annihilation

    • C.

      Endocytic assignation

    • D.

      Receptor down-regulation

    • E.

      Super signaling

    Correct Answer
    D. Receptor down-regulation
    Explanation
    Receptor down-regulation refers to the process in which receptors for hormones or growth factors are destroyed during endocytosis, resulting in a decrease in the cell's sensitivity to further stimulation by that specific hormone or growth factor. This mechanism allows cells to regulate their ability to respond to extracellular messengers.

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  • 44. 

    Which type of cytoskeletal element is described as a solid, thinner structure, often organized into a branching network, and composed of actin subunits?

    • A.

      Microfilaments

    • B.

      microtubules

    • C.

      Intermediate filaments

    • D.

      All of the above

    • E.

      Macrofilaments

    Correct Answer
    A. Microfilaments
    Explanation
    Microfilaments, also known as actin filaments, are described as solid, thinner structures composed of actin subunits. They form a branching network within the cell and play a crucial role in cell shape, movement, and contraction. Microtubules, on the other hand, are larger, hollow structures composed of tubulin subunits and are involved in cell division and intracellular transport. Intermediate filaments provide structural support to the cell and are made up of various proteins. Therefore, the correct answer is microfilaments.

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