Question

According to the Endosymbiotic Theory, infoldings in the cell membrane of an ancestral prokaryotic cell gave rise to endomembrane components, including the nucleus, endoplasmic reticulum and golgi apparatus in what would become eukaryotic cells. The evolution of endomembrane components provided for compartmentalization in eukaryotes, leading to more efficiency in cell processes. The endomembrane system includes the endoplasmic reticulum. Which statement does NOT describe the endoplasmic reticulum (ER)?
A) The ER is an extension of the nuclear envelope.

B) The ER serves as a transport network for the proteins produced in its membrane.

C) The ER provides separate microenvironments for each of the modifications that must take place to proteins.

D) The ER serves a role in protein folding, lipid and steroid synthesis, carbohydrate metabolism and calcium storage

Answer 1

Explanation:

False: C) The ER provides separate microenvironments for each of the modifications that must take place to proteins.

The golgi apparatus comprised of several components called cisternae, these function as different microenvironments, where further modification proteins and lipids into functional biomolecules occurs.

During protein synthesis, transcription occurs in the nucleus, followed by translation within ribosomes, the newly synthesized proteins enter endoplasmic reticulum where they undergo folding and modification. Within the golgi body, the proteins are tagged and parceled into lysosomes for export.

Further Explanation:

The endoplasmic reticulum is a membrane system within the cytoplasm that extends from the outer nuclear membrane. Apart from increasing the surface area within the cell, this continuous system also carries out protein folding, synthesis and transport. In the endoplasmic reticulum or ER, some sections called the smooth ER, do not contain ribosomes, and may contain lipids, enzymes, and other proteins. Other sections bound to ribosomes, are called the rough Er. As a protein destined for the endomembrane system is being synthesized by a ribosome, the first amino acids in the growing polypeptide chain act as a signal sequence. That signal sequence ensures that the ribosome binds to the outer membrane of the ER and that the protein enters the ER lumen. The proteins undergo major modifications and are packed into vesicles.

Golgi bodies are flat, disk-like membranous regions. Proteins traverse the organelle by first having their vesicles bind to the cis face or receiving end. Like a post office, the golgi complex, or golgi body recognizes specific signal sequences, targets and further modifies and packages these compounds into lysosomes for delivery to their final destination.  Proteins here undergo peptide processing and glycosylation

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