The internal membrane system where lipid components of the cell are assembled along with proteins and other materials is called the endoplasmic reticulum (ER).

Here's a breakdown:

* Endoplasmic Reticulum (ER): A network of interconnected membranes that extend throughout the cytoplasm of eukaryotic cells. It plays a crucial role in lipid synthesis, protein folding, and transport.

* Lipid Synthesis: The ER is the primary site for the synthesis of lipids, including phospholipids, cholesterol, and steroid hormones. This process involves enzymes embedded within the ER membrane.

* Protein Folding and Modification: The ER provides an environment for newly synthesized proteins to fold into their correct three-dimensional structures. It also modifies proteins by adding sugars (glycosylation) or other chemical groups.

* Transport: The ER serves as a transport pathway within the cell. It helps move newly synthesized lipids and proteins to other organelles or to the cell membrane.

There are two types of ER:

* Rough ER: Studded with ribosomes, which are responsible for protein synthesis.

* Smooth ER: Lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage.

In summary, the endoplasmic reticulum is a crucial organelle responsible for the assembly of lipids, proteins, and other materials essential for cell function.