Study Guide: Cell Structure and Function - Endomembrane System

Introduction

  • Instructor discusses the need for attention and engagement in class, indicating students may be tired or unfocused.

  • Acknowledges that some students are recovering from being sick.

Learning Objectives

  • Goal of the session: Understand the cell structure and function, specifically the endomembrane system.

  • Students are reminded to review previous knowledge as this topic should largely be a recap.

Endomembrane System Overview

  • Definition: The endomembrane system is a continuous network of membranes that begins at the nuclear membrane and extends to the cell membrane.

  • Components of the endomembrane system include:

    • Nuclear membrane

    • Endoplasmic reticulum (ER)

    • Golgi apparatus (also known as Golgi body)

    • Vesicles

Ribosomes and Protein Synthesis

  • Key Question: "What do ribosomes make?"

    • Answer: Ribosomes synthesize proteins.

    • Importance of proteins:

    • Proteins are fundamental for cellular structure and function, making up approximately 80% of the cell.

Ribosome Locations and Functions

  • Ribosome Types:

    • Free ribosomes: Ribosomes not bound to any membrane, synthesizing proteins that remain in the cytoplasm or nucleus.

    • Example proteins include:

      • DNA polymerase

      • RNA polymerase

      • Telomerase

      • Topoisomerase

      • Cytoskeletal proteins (e.g., actin and tubulin)

    • Bound ribosomes: Ribosomes attached to the rough ER, synthesizing proteins that are secreted from the cell or integrated into membranes.

    • Example functions:

      • Insulin secretion from beta pancreatic cells

      • Hormones like cortisol, testosterone, and estrogen production

      • Enzymes associated with digestive processes, particularly in microvilli of intestinal cells

      • Integral membrane proteins and lysosomal enzymes (which are synthesized by bound ribosomes)

Detail on Rough Endoplasmic Reticulum (RER)

  • Rough ER: The portion of the endoplasmic reticulum that has ribosomes attached to its surface, facilitating the synthesis of proteins that are either secreted from the cell or destined for specific cellular locations.

Membrane Dynamics and the Endomembrane System

  • The endomembrane system comprises the following key structures:

    • Nuclear envelope

    • Endoplasmic reticulum (rough and smooth)

    • Golgi apparatus

    • Various vesicles, vacuoles, endosomes, and lysosomes (the latter being formed by the Golgi apparatus)

    • Plasma membrane

  • Contextual Note: The plasma membrane may be discussed in relation to exocytosis and endocytosis, emphasizing its dynamic interactions with the internal cellular environment.

Class Engagement and Activities

  • Instructor offers students time to copy notes and diagrams related to the discussed topics.

  • Encourages students to utilize a blank page for organizing their notes.

Instructional Materials

  • A mention of diagrams and visual aids used in class.

  • Specific diagrams that illustrate the structures and functions of the endomembrane system and the roles of ribosomes are referenced, though students are not required to recreate these illustrations from scratch.

Conclusion and Homework

  • Students are assigned homework to copy the relevant diagrams and notes as outlined during class.

  • Emphasis placed on understanding the endomembrane system and protein synthesis mechanisms as foundational content for future discussions.