Multiple Choice
A protein contains 5 start/stop transfer sequences. How many times will this protein cross the membrane?
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13. Intracellular Protein Transport
ER Processing and Transport
Multiple Choice
In eukaryotic cells, what is the key difference between rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER) in terms of structure and primary function?
A
RER is found only in plant cells and SER is found only in animal cells.
B
RER is the site of DNA replication, whereas SER is the site of transcription and mRNA processing.
C
RER lacks ribosomes and is primarily involved in lipid synthesis, whereas SER is studded with ribosomes and is primarily involved in protein synthesis.
D
RER is studded with ribosomes and is primarily involved in synthesis and initial processing of secreted and membrane proteins, whereas SER lacks ribosomes and is primarily involved in lipid synthesis and detoxification.
Verified step by step guidance1
Step 1: Understand the structural difference between rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). The RER is characterized by the presence of ribosomes attached to its cytoplasmic surface, giving it a 'rough' appearance under a microscope, while the SER lacks these ribosomes and appears 'smooth'.
Step 2: Identify the primary function of the RER. Because of the ribosomes on its surface, the RER is the site where protein synthesis occurs, especially for proteins that are destined to be secreted from the cell, incorporated into the plasma membrane, or sent to lysosomes.
Step 3: Recognize the primary function of the SER. Without ribosomes, the SER is not involved in protein synthesis but instead specializes in lipid synthesis, metabolism of carbohydrates, detoxification of drugs and poisons, and storage of calcium ions.
Step 4: Compare the roles of RER and SER in the context of eukaryotic cells. The RER focuses on producing and processing proteins, while the SER focuses on lipid production and detoxification processes.
Step 5: Conclude that the key difference lies in both structure (presence or absence of ribosomes) and function (protein synthesis vs. lipid synthesis and detoxification), which aligns with the correct answer provided.
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