Question

Cells that line your intestines are known to possess a large number of membrane proteins that transport small molecules and ions across the plasma membrane. Which of the following cell structures would you expect to be required for this function of the cells? a. the endoplasmic reticulum b. peroxisomes c. lysosomes d. the cell wall

Short answer

The correct cell structure required for the function of transporting small molecules and ions across the plasma membrane in intestinal cells is (a) the endoplasmic reticulum, as it plays a direct role in protein synthesis, folding, and transportation, which are essential for the formation and proper functioning of membrane proteins involved in molecule/ion transport.

Step-by-step solution

Understand the role of membrane proteins and transport

Membrane proteins are proteins that are either a part of the cell membrane or are associated with it. They are critical for transporting small molecules and ions across the plasma membrane. In the given context, the focus is on intestinal cells that line the intestines and require a large number of membrane proteins for transport.

Review the cell structures and their functions

Let's briefly go through the function of each cell structure provided in the options: a. The endoplasmic reticulum (ER) is an organelle that is responsible for protein synthesis, folding, and transportation. It also plays a role in lipid synthesis. b. Peroxisomes are small organelles that are involved in the breakdown of fatty acids and detoxification of certain substances. c. Lysosomes are membrane-bound organelles containing enzymes that break down waste materials and cellular debris. d. The cell wall is a rigid structure that surrounds and protects plant cells and provides structural support.

Identify the correct cell structure

To determine which organelle would be required for the transport function of the intestinal cells, we can analyze the functions of each of the provided structures. Only the endoplasmic reticulum (ER) has a direct role in protein synthesis, folding and transportation, which are essential for the formation and proper functioning of membrane proteins involved in molecule/ion transport. Therefore, we can choose option (a) as the correct answer.

Review the answer

Based on the functions of the cell structures and understanding the role of membrane proteins in transporting small molecules and ions in intestinal cells, we can conclude that: - Required cell structure: the endoplasmic reticulum (option a). So, the correct answer is (a) the endoplasmic reticulum.

Key concepts

Membrane Proteins

Membrane proteins are essential components of cellular membranes. They serve a pivotal role in facilitating the movement of ions and small molecules across the cell's plasma membrane. This transfer is crucial for maintaining cellular homeostasis and allowing cells to perform various functions effectively.
Membrane proteins can be categorized into different types:

• Integral proteins, which are permanently embedded within the lipid bilayer.
• Peripheral proteins, which are temporarily attached to the lipid bilayer or other integral proteins.
• Lipid-anchored proteins, which are covalently bonded to lipids within the cell membrane.

These proteins function as:

• Channels that provide pathways for ions and molecules to pass through passive transport.
• Pumps that actively transport substances across the membrane using energy.
• Receptors that receive and transmit signals, aiding in cell communication.

In intestinal cells specifically, a high concentration of such proteins is necessary to efficiently absorb nutrients, electrolytes, and water.

Endoplasmic Reticulum Function

The endoplasmic reticulum (ER) is a network of membranes within the cell that plays a key role in producing and processing proteins indispensable for various cellular functions.
There are two types of ER:

• Rough ER, which is studded with ribosomes and is primarily involved in the synthesis and folding of proteins.
• Smooth ER, which lacks ribosomes and is involved in lipid synthesis, detoxification processes, and calcium ion storage.

Protein synthesis on the rough ER begins when ribosomes synthesize polypeptides and insert them into the ER lumen to undergo folding and modification. Properly folded proteins are then transported to the Golgi apparatus for further processing and eventual delivery to their functional destinations.
The ER is vital for producing the membrane proteins that intestinal cells rely on for transporting nutrients and ions.

Intestinal Cell Structure

Intestinal cells, or enterocytes, line the walls of the intestine and are imperative for absorbing nutrients from digested food. Their structure is specialized to optimize this absorption process.
Key structural adaptations include:

• Microvilli on the cell surface, which significantly increase the surface area for absorption.
• Tight junctions that connect adjacent cells, preventing leakage and maintaining the intestine's barrier function.
• Complex network of membrane proteins that facilitate the selective transport of different ions and molecules.

These structural characteristics enable intestinal cells to efficiently absorb nutrients while protecting the internal environment of the intestine. The interaction of membrane proteins and transport mechanisms ensures a steady supply of essential nutrients to the body.

Protein Synthesis and Transport

Protein synthesis and transport are central to cellular function and involve several organelles working together. This process primarily occurs in the endoplasmic reticulum and is aided by the Golgi apparatus.
The process begins in the nucleus with transcription, where the DNA's genetic instructions are copied into messenger RNA (mRNA). This mRNA travels to ribosomes on the rough ER, where its information is translated into protein chains through a process called translation.
After synthesis, proteins may undergo modifications such as:

• Folding into specific three-dimensional shapes.
• Addition of carbohydrate or lipid groups (glycosylation or lipidation).

Properly modified proteins are then transported to their specific cellular destinations. For example, membrane proteins synthesized in the ER are integrated into the cell membrane to aid in transport functions, critical for activities such as nutrient absorption and signal transmission in intestinal cells.