Cell Biology: Endomembrane System

Structured Study Session (SSS) Notes

• The SSS session covered the Endomembrane System and Semi-Autonomous Organelles.

• The session was presented by Janelle and Steve on September 24, 2024.

• The material for this study session was developed by a peer mentor, not course professors. Selection of materials was based on the peer mentor's knowledge of the course and input from the SSS peer mentor team.

• Land Acknowledgement: The session began with an acknowledgement that the session was taking place on Treaty 6 Territory and the homeland of the Métis, with respect to the First Nations and Métis ancestors.

• Before the start: Students were encouraged to ask questions for clarification or to address areas of difficulty experienced during lectures. The session would focus on high-yield topics frequently tested. Google Forms (anonymous) were provided to gather feedback on topics covered in the SSS and topics students wanted further clarification. Google Forms were also linked in Canvas.

• What's On Today's Menu?: The discussion would cover the Endomembrane System, semi-autonomous organelles, and cytoskeletal details.

• Part 1: Endomembrane System: The session commenced with an explanation of the endomembrane system's role.

• Endomembrane System (Definition): A network of organelles and structures (membranes) that play a part in protein and lipid synthesis and transport.

• TL;DR: The structures are involved in sending and receiving vesicles.

• Discussion Topics: Students were prompted to consider which organelles might participate in the endomembrane system—given their previous knowledge of proteins, lipids, and the respective organelles.

• Key Structures (LEGVVNP): Lysosomes, Endoplasmic Reticulum (rough and smooth), Golgi body (complex/apparatus), Vacuoles, Vesicles, Nuclear membrane/envelope, Plasma membrane.

• Lysosomes: Membrane-bound vesicles involved in digesting nutrients, eliminating waste, recycling dysfunctional organelles. Lysosomes contain enzymes that work best in acidic environments. They are primarily found in animal cells.

• Endoplasmic Reticulum (ER): Rough ER is responsible for protein folding and modification and has ribosomes on its surface. The smooth ER is involved in lipid synthesis, calcium storage, and detoxification.

• Golgi body (complex/apparatus): Processing and packaging center modifying proteins, sending them to their correct destinations, and creating molecules like glycolipids. Cis face is the receiving site and trans face is the shipping site. Interacts directly with vesicles and rough endoplasmic reticulum.

• Vacuoles: Membrane-bound areas with diverse functions, including water, pigments, ions storage, turgor pressure regulation, waste digestion in plant and fungal cells. Central vacuoles are specifically found in plant cells.

• Vesicles: Small membrane-bound sacs that transport materials within the cell and between the cell and external environment. Endocytosis (taking materials inside) decreases membrane surface and Exocytosis (releasing materials) increases membrane surface area.

• Nuclear Membrane (Envelope): Surrounds the nucleus with a double layer, connected directly to the endoplasmic reticulum.

• Plasma Membrane: Separates the cell from its environment, can be used in endocytosis and exocytosis. Maintains cell shape and is a crucial phospholipid bilayer.

Questions

• Question 1: The Golgi complex sends vesicles from its ___ face and receives vesicles from its ___ face.
• Question 2: Which organelle is responsible for lipid synthesis and drug detoxification?
• Question 3: Endocytosis is movement ____ the cell and will ____ the membrane surface area.
• Part 2: Semi-Autonomous Organelles: These organelles have their own DNA and some self-replication and protein synthesis.
• Semi-Autonomous Organelle Examples: Mitochondria, Chloroplasts, Plastids (chromoplast, leucoplast, amyloplast, elaioplast).
• Not Part of the Endomembrane System: Semi-autonomous organelles.
• Mitochondria: Sites of cellular respiration which are involved in glucose (sugar) breakdown to produce energy in the form of ATP. They have a double membrane composed of outer membrane, inner membrane with intermembrane space between. The inside of the inner membrane is called the matrix, full of cristae. Mitochondria are found in plants and animals.
• Chloroplasts: Site of photosynthesis which involves light, water, and carbon dioxide to create glucose. They have a double membrane, and thylakoids (that form stacks called grana) within. The stroma is the space between the outer membrane and the thylakoid membrane in the liquid portion of the chloroplast.
• Question 4: Which of the following are considered semi-autonomous organelles?
• Question 5: In mitochondria, ___ is broken down to generate ___, while in chloroplasts, ___ is made by using ___ energy.
• Question 6: Which statement is false?
• Question 7: Which cytoskeletal pairing has the correct motor protein?
• Question 8: Which cytoskeletal fiber is correctly matched with the element that it is composed of?
• Peroxisomes: Not part of the endomembrane system or semi-autonomous but perform important functions within the cell.
• Part 3: Cytoskeleton: The cell's framework/skeleton made of proteins (fibers and tubes) that helps maintain cell shape and polarity and assist with cell processes and reproduction.
• 3 Types of Cytoskeleton Structure: Microtubules, Intermediate filaments, Microfilaments.
• Microtubules: A long hollow structure made of tubulin dimers (+ and - ends). Functions include movement, maintaining cell shape, mitotic spindle formation that separates chromosomes, and formation of cilia and flagella (which move cells). Motor proteins kinesin and dynein interact with microtubules.
• Cilia and Flagella: Hair-like structures constructed from microtubules used for movement (ciliary beating and flagellar whipping / spinning).
• Microfilaments: Thin solid fibres made of actin polymers (+ and - ends). Functions include maintaining cell shape, muscle contractions via myosin interaction, cytoplasmic streaming, and cell division.
• Intermediate Filaments: Made of various types of protein filaments; provide cell support and structure. The exact proteins vary between cell types. Functions include maintaining cell shape, stabilizing organelles, and providing structure, particularly throughout the cell's nuclear lamina
• Question 9: Of the following groups, which is composed only of structures found within the endomembrane system?
• Question 10: Photosynthesis takes place on a structure within chloroplasts that form a stack. These structures (not the stack) are called ___.