Endomembrane System

How many cellular structures the rough endoplasmic reticulum is associated with?

6

When the pH was increased from 5 to 7 in an in vitro experiment, these structures purified from animal cells stopped digesting their contents. What are these structures? A) smooth ER B) lysosomes C) nucleus D) mitochondria E) Golgi vesicles

B) lysosomes

Fresh water protists such as paramecium maintain homeostasis of its salt concentration by pumping water out of the cell. Which of the following structures would serve this purpose? A) Large central vacuole B) Small central vacuole C) Proton pump D) Contractile vacuole E) Food vesicle

D) Contractile vacuole

The major differences in the function of rough ER compared to smooth ER is to __________________ A) make steroid hormones B) synthesize phospholipids C) detox drugs D) make proteins E) make carbohydrates

D) make proteins

What will happen if the segment of DNA coding for target sequence is deleted from a gene encoding a protein located in lysosomes? A) Its mRNA will not be made in nucleus. B) Its mRNA will not be processed properly. C) Protein synthesis will not happen for this mRNA. D) Once the protein is made, it will return to nucleus. E) It will not reach the target site, lysosome.

E) It will not reach the target site, lysosome.

Which of the following pathway is the most probable pathway for secretory proteins that is glycosylated along the way? A) ER → Vesicle → nucleus → lysosomes → plasma membrane B) Nucleus → Smooth ER → Golgi apparatus → plasma membrane C) Golgi Apparatus → vesicles → lysosomes → plasma membrane D) Ribosomes → lysosomes → Golgi apparatus → plasma membrane E) Rough ER → vesicles → Golgi apparatus → plasma membrane

E) Rough ER → vesicles → Golgi apparatus → plasma membrane

CYP3A4 is a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are monooxygenases that catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids, and other lipids components. The CYP3A4 protein localizes to the endoplasmic reticulum, and its expression is induced by glucocorticoids and some pharmacological agents. Cytochrome P450 enzymes metabolize approximately 60% of prescribed drugs, with CYP3A4 responsible for about half of this metabolism; substrates include acetaminophen, codeine, ciclosporin (cyclosporin), diazepam, and erythromycin. The enzyme also metabolizes some steroids and carcinogens. Most drugs undergo deactivation by CYP3A4, either directly or by facilitated excretion from the body. If someone is addicted to Oxycontin, shown below, which of the following enzymes and structures would try to detoxify them?

cytochrome p450, smooth ER

Cells have complex membranous organelles for the compartmentalization and regulation of most intracellular processes. Organelle biogenesis and maintenance requires newly synthesized proteins, each of which needs to go from the ribosome translating its mRNA to the correct membrane for insertion or translocation to an organellar subcompartment. Decades of research have revealed how proteins are targeted to the correct organelle and translocated across one or more organelle membranes to the compartment where they function. The paradigm examples involve interactions between a peptide sequence in the protein, localization factors, and various membrane-embedded translocation machinery. Membrane translocation is either cotranslational or posttranslational depending on the protein and target organelle. Meanwhile, research in embryos, neurons, and yeast revealed an alternative targeting mechanism in which the mRNA is localized and only then translated to synthesize the protein in the correct location. In these cases, the targeting information is encoded by cis-acting sequences in the mRNA ("Zipcodes") that interact with localization factors and, in many cases, are transported by molecular motors on cytoskeletal filaments. Recently, evidence has been found for this "mRNA-based" mechanism in organelle protein targeting to the endoplasmic reticulum, mitochondria, and the photosynthetic membranes within chloroplasts.

mRNA and