Question 1

Protein molecules are most likely to be actively folded and cross-linked in which of the following structures?

Accepted Answer

The granular endoplasmic reticulum, also known as the rough endoplasmic reticulum, is where protein synthesis occurs, and it is involved in the folding and modification of proteins, including the formation of disulfide bonds (cross-linking).

Question 2

The citric acid cycle (Krebs cycle) takes place in which of the following?

Accepted Answer

The citric acid cycle (Krebs cycle) takes place in the mitochondrial matrix, where the enzymes and cofactors necessary for the cycle are located. The inner mitochondrial membrane and inner mitochondrial space are involved in oxidative phosphorylation, which uses the energy generated by the citric acid cycle to produce ATP. The outer mitochondrial membrane is involved in regulating the passage of molecules in and out of the mitochondria.

Question 3

Cholesterol in the cell membrane most likely serves which of the following functions?

Accepted Answer

Cholesterol decreases membrane fluidity by preventing phospholipids from packing too closely and inhibiting movement of phospholipid tails. This allows for a stable membrane structure.

Question 4

Lipid synthesis occurs in which of the following locations?

Accepted Answer

Lipid synthesis primarily occurs in the smooth endoplasmic reticulum, which lacks ribosomes (agranular). The Golgi complex is involved in the modification and sorting of lipids and proteins synthesized in the ER but is not directly involved in lipid synthesis. The nucleus contains genetic material and is primarily involved in transcription and replication, not lipid synthesis. Lysosomes are organelles involved in the breakdown of cellular waste, not lipid synthesis. Rough endoplasmic reticulum is responsible for protein synthesis and does not have a primary role in lipid synthesis.

Question 5

Ubiquinone, an electron acceptor in the electron transport chain (oxidative phosphorylation), is found in which of the following?

Accepted Answer

Ubiquinone (also known as coenzyme Q) is a component of the inner mitochondrial membrane where it plays a role in transferring electrons within the electron transport chain. It is not found in the mitochondrial matrix, outer mitochondrial membrane, or nucleus.

Question 6

The cell membrane is least permeable to which of the following substances?

Accepted Answer

The cell membrane is least permeable to ions such as sodium due to its hydrophobic core, which repels ions and other polar molecules. Oxygen, ethanol, carbon dioxide, and water can all pass through the cell membrane to some degree.

Question 7

All the following processes depend on adenosine triphosphate except which of the following?

Accepted Answer

Movement of oxygen across the lipid bilayer is a passive process that does not require the use of ATP. The other processes listed all require ATP for energy.

Question 8

A pure phospholipid bilayer is most permeable to which of the following?

Accepted Answer

A pure phospholipid bilayer is most permeable to small, nonpolar molecules like oxygen, which can easily diffuse through the hydrophobic core of the bilayer.

Question 9

Which of the following substances in most likely to represent the highest percent of cell mass in a typical cell of the body?

Accepted Answer

Water typically represents the highest percent of cell mass in a typical cell, often making up about 70% or more of the cell's total mass.

Question 10

The observation that abnormal cleavage of mannose residues from glycoproteins causes an autoimmune disease in mice is most consistent with the role of which of the following structures in the normal immune response?

Accepted Answer

The glycocalyx is a sugar-rich layer that surrounds cells and plays a role in cell-cell recognition and communication. It also contains glycoproteins that can trigger an immune response. Abnormal cleavage of mannose residues from glycoproteins suggests that the normal immune response involves recognition and response to specific glycoproteins, making option B the most consistent choice. The other structures listed, such as peroxisomes or microtubules, do not have a direct relationship with the immune response.

Question 11

Proteins are sorted for their delivery to lysosomes, secretory vesicles, and the plasma membrane in which of the following?

Accepted Answer

Proteins are sorted and delivered to their correct destinations in the Golgi apparatus.

Question 12

This cytoskeletal element plays a role in certain forms of cell movement and is an essential component of the mitotic spindle ____________.

Accepted Answer

Microtubules play a role in cell movement by forming structures such as cilia and flagella, and are an essential component of the mitotic spindle, which is responsible for segregating chromosomes during cell division. Phospholipids and glycocalyx are not cytoskeletal elements, while F-actin and clathrin are involved in different cellular processes.

Question 13

Which of the following is true for both pinocytosis and phagocytosis?

Accepted Answer

Both pinocytosis and phagocytosis involve the recruitment of actin filaments to carry out the process of engulfment of extracellular material. The other options are not true for both processes.

Question 14

The abnormal cleavage of mannose residues during the posttranslational processing of glycoproteins has been shown to result in the development of a lupus-like autoimmune disease in mice. The abnormal cleavage is due to a mutation of the enzyme $\alpha$-mannosidase II. Based on your understanding of the processing of membrane proteins, you would predict this enzyme to be localized to which of the following?

Accepted Answer

Mannosidase II is responsible for processing of N-linked glycoproteins in the Golgi apparatus, specifically in the cis-Golgi network and medial Golgi cisternae. Therefore, it is most likely localized in the Golgi apparatus.

Question 15

Which of the following best describes the glycocalyx of a cell?

Accepted Answer

The glycocalyx is a layer of negatively charged carbohydrates that covers the surface of a cell. It serves numerous functions, including participating in cell-cell recognition and communication, and protecting cells from mechanical and chemical damage.

Quiz 2: The Cell and Its Functions