Block 1 Cell Biology Dr Moore
- 1.
Which of the following types of proteins are translated on ribosomes bound to the rough endoplasmic reticulum (RER) instead of being completely translated on ribosomes free in the cytosol?
- A.
Cytoskeletal proteins
- B.
Mitochondrial proteins
- C.
Lysosomal proteins
- D.
Peroxisomal proteins
- E.
Nuclear proteins
Correct Answer
C. Lysosomal proteinsExplanation
Lysosomal proteins are translated on ribosomes bound to the rough endoplasmic reticulum (RER) instead of being completely translated on ribosomes free in the cytosol. This is because lysosomal proteins have a specific signal sequence that targets them to the RER, where they are synthesized and then transported into the lumen of the RER. From there, they are further processed and transported to the lysosomes, where they perform their functions in cellular digestion.Rate this question:
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- 2.
Many targeting and sorting processes in the cell require a pH difference between one compartment and another to occur efficiently. Of the choices below, pick the process that DOES NOT require a difference in pH between two compartments to occur.
- A.
Correct trafficking of the mannose-6-phosphate (M6P) receptor
- B.
Correct trafficking of the LDL receptor and its ligand during receptor-mediated endocytosis
- C.
Movement of protons into the mitochondrial matrix through ATP synthase
- D.
Correct trafficking of newly synthesized integral plasma membrane proteins from the rough endoplasmic reticulum to the plasma membrane
- E.
Activation of lysosomal enzymes in the lumen of lysosomes compared to their relative inactivity in the trans Golgi
Correct Answer
D. Correct trafficking of newly synthesized integral plasma membrane proteins from the rough endoplasmic reticulum to the plasma membraneExplanation
The correct answer is "correct trafficking of newly synthesized integral plasma membrane proteins from the rough endoplasmic reticulum to the plasma membrane". This process does not require a difference in pH between two compartments to occur. The other processes mentioned in the choices involve movement of molecules or proteins between compartments that require a pH difference for efficient functioning, such as the movement of protons into the mitochondrial matrix through ATP synthase or the activation of lysosomal enzymes in the lumen of lysosomes compared to their relative inactivity in the trans Golgi.Rate this question:
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- 3.
You have engineered a protein construct mRNA that will encode for a protein not normally found in nature. To a soluble protein that is normally a cytoplasmic protein you have added an ER signal sequence to its amino terminus, and an NLS to its carboxy terminus. There are no other targeting signals present in this protein. The final protein will be 100 kD in size. After transfection into the cell, what is the final destination of the translated construct protein?
- A.
Cytoplasm
- B.
Lumen of the ER
- C.
Lumen of the Golgi
- D.
Secreted into the extracellular space
- E.
The nuclear interior
Correct Answer
D. Secreted into the extracellular spaceExplanation
The presence of an ER signal sequence at the amino terminus indicates that the protein will be targeted to the endoplasmic reticulum (ER). The addition of a nuclear localization signal (NLS) at the carboxy terminus suggests that the protein will be transported to the nucleus. However, since there are no other targeting signals present, the protein will not be retained in either the ER or the nucleus. Instead, it will be secreted into the extracellular space. Therefore, the final destination of the translated construct protein is the extracellular space.Rate this question:
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- 4.
Which of the following is a site of mRNA transcription?
- A.
Ribosome
- B.
Nucleolus
- C.
Heterochromatin
- D.
Rough ER
- E.
Euchromatin
Correct Answer
E. EuchromatinExplanation
Euchromatin is the correct answer because it is a region of the chromosome that is less condensed and more accessible for transcription. Transcription is the process by which mRNA is synthesized from DNA, and it occurs in the nucleus of the cell. Euchromatin is the type of chromatin that allows for gene expression, making it the site where mRNA transcription takes place.Rate this question:
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- 5.
Of the following cellular compartments, which one maintains the most acidic pH?
- A.
Lumen of early endosome
- B.
Mitochondrial matrix
- C.
Lumen of lysosome
- D.
Lumen of trans-Golgi
- E.
Peroxisomal matrix
Correct Answer
C. Lumen of lysosomeExplanation
The lysosome is responsible for degrading and recycling cellular waste. It contains various hydrolytic enzymes that function optimally at an acidic pH. The acidic pH is maintained by the proton pumps present in the lysosomal membrane, which actively transport protons into the lysosome, resulting in a low pH. This acidic environment is crucial for the proper functioning of the enzymes within the lysosome, allowing them to break down macromolecules effectively. Therefore, the lumen of the lysosome maintains the most acidic pH compared to the other cellular compartments listed.Rate this question:
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- 6.
Which of the following WOULD NOT be found on the half of the plasma membrane bilayer facing the cytoplasm?
- A.
Phosphatidylserine
- B.
Phosphatidylethanolamine
- C.
Phosphatidylinositol
- D.
Peripheral membrane protein
- E.
Carbohydrate moiety of glycolipid
Correct Answer
E. Carbohydrate moiety of glycolipidExplanation
The carbohydrate moiety of glycolipid is found on the outer half of the plasma membrane bilayer, facing the extracellular environment. It is involved in cell recognition and cell-cell communication.Rate this question:
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- 7.
Which of the following post-translational protein modifications DOES NOT occur in the rough ER?
- A.
Formation of disulphide bonds
- B.
Formation of GPI anchors
- C.
Addition of N-linked carbohydrate
- D.
Protein folding
- E.
Addition of O-linked carbohydrate
Correct Answer
E. Addition of O-linked carbohydrateExplanation
O-linked carbohydrate is not added in the rough ER. The rough ER is responsible for the initial stages of protein synthesis, including protein folding and the addition of N-linked carbohydrates. O-linked carbohydrates, on the other hand, are added in the Golgi apparatus, which is a separate organelle involved in protein modification and sorting. Therefore, the addition of O-linked carbohydrates does not occur in the rough ER.Rate this question:
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- 8.
Which of the following would probably never pass through nuclear pores in an interphase nucleus?
- A.
MRNA
- B.
Ribosomal protein
- C.
Histones
- D.
TRNA
- E.
SRP (signal recognition particle)
Correct Answer
E. SRP (signal recognition particle)Explanation
The nuclear pores in an interphase nucleus allow for the transport of molecules such as mRNA, ribosomal proteins, histones, and tRNA. However, the signal recognition particle (SRP) is a protein-RNA complex that is involved in targeting proteins to the endoplasmic reticulum (ER) for membrane insertion. It is unlikely to pass through nuclear pores because its function is specific to the ER and not the nucleus. Therefore, SRP would probably never pass through nuclear pores in an interphase nucleus.Rate this question:
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- 9.
Which of the following statements is INCORRECT regarding peripheral membrane proteins of the plasma membrane?
- A.
They can be removed from the membrane with high salt
- B.
They can be found on both the cytoplasmic face and the extracellular face of the plasma membrane
- C.
They can be bound at the membrane to either membrane lipids or other membrane proteins
- D.
They are immobile in the membrane
- E.
They are held at the membrane via ionic interactions with membrane components Properties of peripheral membrane proteins.
Correct Answer
D. They are immobile in the membraneExplanation
Peripheral membrane proteins are not immobile in the membrane. Unlike integral membrane proteins, which are embedded within the lipid bilayer, peripheral membrane proteins are loosely bound to the membrane surface and can move along the membrane. They can associate with the membrane through various interactions, such as binding to membrane lipids or other membrane proteins. Additionally, peripheral membrane proteins can be removed from the membrane with high salt. Therefore, the statement "they are immobile in the membrane" is incorrect.Rate this question:
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- 10.
Mitochondria DO NOT carry out which of the following processes?
- A.
Lipid synthesis
- B.
Protein synthesis
- C.
Carbohydrate synthesis
- D.
RRNA synthesis
- E.
MRNA synthesis
Correct Answer
C. Carbohydrate synthesisExplanation
Mitochondria are known as the powerhouse of the cell and are responsible for producing energy in the form of ATP through a process called cellular respiration. While they are involved in various metabolic processes, including lipid and protein synthesis, they do not participate in carbohydrate synthesis. Carbohydrates are mainly synthesized in the cytoplasm of the cell through processes such as glycolysis and gluconeogenesis.Rate this question:
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- 11.
Which of the following statements describing the morphology of apoptotic cells is INCORRECT?
- A.
The apoptotic cell shrinks in size
- B.
The nucleus of an apoptotic cell is smaller and appears darker by light or electron microscopy than the nucleus of a healthy cell
- C.
The plasma membrane of an apoptotic cell becomes disrupted
- D.
The apoptotic cell fragments into smaller pieces
- E.
The phospholipid phosphatidylserine (PS) is exposed o the extracellular face of the plasma membrane of an apoptotic cell
Correct Answer
C. The plasma membrane of an apoptotic cell becomes disruptedExplanation
The plasma membrane of an apoptotic cell does not become disrupted. Instead, it undergoes changes such as blebbing and budding, but remains intact. This allows the cell to be recognized and engulfed by phagocytes without releasing its contents into the surrounding tissue.Rate this question:
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- 12.
At the end of prophase, how many chromosomes does a mitotic human cell have?
- A.
23
- B.
46
- C.
69
- D.
92
- E.
115
Correct Answer
B. 46Explanation
At the end of prophase, a mitotic human cell has 46 chromosomes. During prophase, the chromosomes condense and become visible. In humans, there are typically 46 chromosomes in each cell, organized into 23 pairs. These pairs consist of one chromosome inherited from each parent. Therefore, at the end of prophase, each cell will have 46 individual chromosomes, with 23 pairs.Rate this question:
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- 13.
Which of the following statements about clathrin is INCORRECT?
- A.
Clathrin cycles between an assembled and unassembled state
- B.
Clathrin assembly on a membrane deforms that membrane
- C.
LDL receptors only cluster in clathrin-coasted pits after binding LDL
- D.
Clathrin clusters LDL receptors via adaptins
- E.
Clathrin is not found on caveolae
Correct Answer
C. LDL receptors only cluster in clathrin-coasted pits after binding LDLExplanation
Clathrin is a protein that plays a crucial role in receptor-mediated endocytosis. It forms a lattice-like structure, known as a clathrin-coated pit, on the cytoplasmic side of the plasma membrane. LDL receptors, which are responsible for the uptake of low-density lipoproteins, cluster in these clathrin-coated pits before binding to LDL. Therefore, the statement "LDL receptors only cluster in clathrin-coated pits after binding LDL" is incorrect. LDL receptors actually cluster in clathrin-coated pits before binding to LDL.Rate this question:
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- 14.
Which of the following statements about mitochondria is CORRECT?
- A.
Mitochondria import proteins co-translationally through contact sites in the membrane
- B.
Mitochondria maintain an acidic pH inside the lumen of the intermembrane space.
- C.
Mitochondria localize mot of the protein components of the respiratory chains in the inner mitochondrial membrane or the matrix.
- D.
Mitochondria pump protons across themitochondrial inner membrane into the matrix
- E.
Mitochondria localize their DNA inside the intermembrane space
Correct Answer
C. Mitochondria localize mot of the protein components of the respiratory chains in the inner mitochondrial membrane or the matrix.Explanation
Mitochondria localize most of the protein components of the respiratory chains in the inner mitochondrial membrane or the matrix. This means that the proteins involved in the respiratory chain, which is responsible for generating energy in the form of ATP, are mainly found in the inner mitochondrial membrane or the matrix. This is important because it allows for efficient energy production within the mitochondria.Rate this question:
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- 15.
Which of the following IS NOT a function of the actin cytoskeleton?
- A.
Forms the mitotic spindle
- B.
Forms the contractile ring that separates daughter cells at mitosis
- C.
Forms microvilli
- D.
Forms lamellopodia
- E.
Forms the terminal web
Correct Answer
A. Forms the mitotic spindleExplanation
The actin cytoskeleton is involved in various cellular processes, such as cell division, cell movement, and maintaining cell shape. It forms the contractile ring that separates daughter cells at mitosis, forms microvilli, forms lamellopodia, and forms the terminal web. However, it does not directly form the mitotic spindle. The mitotic spindle is primarily composed of microtubules, not actin filaments. Therefore, forming the mitotic spindle is not a function of the actin cytoskeleton.Rate this question:
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