unit 3 ,lesson1, part 2, Membrane Traffic and Lipids

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Questions and Answers

What primarily determines the specific functions of different cellular membranes?

The overall size and shape of the organelles they enclose.
The types of carbohydrates present on the membrane surface.
The ratio of cholesterol to phospholipids.
The specific asymmetry and composition of lipids. (correct)

How does the composition of lipids in the plasma membrane contribute to membrane asymmetry?

By symmetrically arranging cholesterol to stabilize both leaflets equally.
By dynamically changing the lipid composition in response to external stimuli, ensuring symmetry over time.
By ensuring an equal distribution of all lipid types between the inner and outer leaflets.
By localizing specific lipids to either the inner or the outer leaflet, creating distinct domains. (correct)

Which of the following mechanisms is primarily responsible for maintaining the asymmetric distribution of lipids in cellular membranes?

Uniform synthesis and insertion of lipids into both leaflets of the membrane.
The high concentration of cholesterol that stabilizes the lipid bilayer equally on both sides.
Spontaneous diffusion of lipids across the membrane.
The action of flippases and floppases, which selectively move lipids across the bilayer. (correct)

Within a cell, how do organelles maintain their unique lipid compositions?

Lipid-transfer proteins selectively transport lipids between organelles. (D) Signup and view all the answers

What is the primary role of clathrin-coated vesicles in cellular trafficking?

To mediate the selective uptake of specific cargo molecules during endocytosis. (C) Signup and view all the answers

What role do adaptins play in clathrin-mediated endocytosis?

They link cargo receptors to clathrin, ensuring selective cargo capture. (D) Signup and view all the answers

Which protein is directly responsible for constricting and pinching off clathrin-coated vesicles from the plasma membrane?

Dynamin. (C) Signup and view all the answers

What is the primary function of the low pH environment in endosomes and lysosomes?

To promote the dissociation of ligands from their receptors and activate hydrolytic enzymes. (B) Signup and view all the answers

How does the acidification of endosomes contribute to the regulation of receptor-mediated endocytosis?

It induces a conformational change in receptors, leading to ligand release. (C) Signup and view all the answers

What is the role of vacuolar ATPases (V-ATPases) in endosomal and lysosomal function?

To maintain the acidic pH within the organelle lumen. (A) Signup and view all the answers

Which of the following is a typical pH range found within lysosomes?

pH 5.5-4.5 (A) Signup and view all the answers

What type of enzymes are predominantly found within lysosomes?

Hydrolases. (A) Signup and view all the answers

In receptor-mediated endocytosis, what happens to LDL after it is internalized and reaches the lysosome?

It is degraded to release free cholesterol. (B) Signup and view all the answers

What is the primary function of the transferrin receptor?

To facilitate the uptake of iron into the cell. (B) Signup and view all the answers

During the endocytosis of iron via the transferrin receptor, what triggers the release of iron from transferrin in the endosome?

The decrease in pH within the endosome. (D) Signup and view all the answers

What typically happens to the transferrin receptor after it delivers iron to the endosome?

It is recycled back to the plasma membrane. (D) Signup and view all the answers

How does endocytosis of growth factor receptors, such as the epidermal growth factor (EGF) receptor, contribute to the regulation of cell signaling?

It downregulates signaling by removing receptors from the cell surface and targeting them for degradation. (C) Signup and view all the answers

What are the primary destinations for endocytosed receptors after they enter the endosomal system?

Lysosomes for degradation or the plasma membrane for recycling. (D) Signup and view all the answers

What distinguishes phagocytosis from other forms of endocytosis?

Phagocytosis involves the engulfment of large particles or cells, while other forms of endocytosis involve smaller vesicles. (B) Signup and view all the answers

Which cell types are primarily responsible for carrying out phagocytosis in mammals?

Immune cells such as macrophages and neutrophils. (D) Signup and view all the answers

What is the primary purpose of autophagy in cells?

To degrade and recycle damaged organelles and proteins. (D) Signup and view all the answers

Which cellular structure is primarily involved in the process of autophagy?

The autophagosome. (A) Signup and view all the answers

Following the formation of an autophagosome, what is its next destination inside the cell?

The lysosome. (D) Signup and view all the answers

Which of the following best describes the path of proteins from the endoplasmic reticulum (ER) to the extracellular space?

ER → Golgi → Secretory Vesicles → Extracellular Space. (B) Signup and view all the answers

What distinguishes constitutive secretion from regulated secretion?

Constitutive secretion is continuous and does not require a specific signal; regulated secretion requires a signal for protein release. (D) Signup and view all the answers

Which of the following proteins is typically released via regulated secretion?

Insulin. (C) Signup and view all the answers

How is insulin processed from its initial precursor form to its mature form?

Through proteolytic cleavage in the endoplasmic reticulum and Golgi apparatus. (B) Signup and view all the answers

What is the role of the C-peptide in insulin production?

It facilitates the folding and assembly of insulin in the endoplasmic reticulum. (C) Signup and view all the answers

Pepsinogen is secreted by chief cells and converted to its active form, pepsin, in the stomach lumen. What triggers the activation of pepsinogen?

Low pH (B) Signup and view all the answers

What is the relationship between membrane traffic dysregulation and disease?

It can lead to a wide range of diseases, including cystic fibrosis and lysosomal storage disorders. (B) Signup and view all the answers

Which protein is affected in cystic fibrosis, leading to defects in chloride ion transport?

The cystic fibrosis transmembrane conductance regulator (CFTR). (C) Signup and view all the answers

How does the mutation in CFTR typically affect its function and localization?

It prevents the protein from reaching the plasma membrane. (B) Signup and view all the answers

What is the underlying cause of Niemann-Pick Type C (NP-C) disease?

Defects in lipid transport, leading to accumulation of lipids in lysosomes. (A) Signup and view all the answers

To maintain cellular homeostasis, how do cells ensure that cholesterol is transported efficiently?

Specific proteins, such as apolipoproteins, transport it in lipoprotein complexes. (B) Signup and view all the answers

Familial hypercholesterolemia is linked to defects in which of the following processes?

LDL receptor-mediated endocytosis. (C) Signup and view all the answers

What role do apolipoproteins play in lipid transport?

They solubilize lipids for transport in the bloodstream and facilitate their uptake by cells. (D) Signup and view all the answers

How does the asymmetry of lipids in cellular membranes primarily impact cellular function?

By creating distinct environments on either side of the membrane which facilitates specific signaling pathways and protein interactions. (B) Signup and view all the answers

What is the significance of the pH difference between the endosome and the cytosol?

It facilitates the dissociation of ligands from their receptors, allowing receptors to be recycled. (B) Signup and view all the answers

What is the role of glycosidases within the lysosome?

To degrade complex carbohydrates into simpler sugars. (D) Signup and view all the answers

How does the endocytosis of the Epidermal Growth Factor Receptor (EGFR) contribute to the regulation of cell growth and proliferation?

By decreasing the amount of EGFR on the cell surface and targeting the receptor for degradation, reducing cell signaling. (B) Signup and view all the answers

How does the disruption of CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) trafficking lead to cystic fibrosis?

It leads to the accumulation of misfolded CFTR protein in the endoplasmic reticulum, preventing its proper localization to the plasma membrane and disrupting chloride ion transport. (A) Signup and view all the answers

Flashcards

Membrane Traffic

The movement of substances into, within, and out of cells.

Endocytosis

Uptake of extracellular nutrients, iron transport, protein degradation, and signal regulation are examples of this process