endomembrane system + bulk transport Flashcards
What is the endomembrane system?
The endomembrane system is a network of organelles and structures within eukaryotic cells that work together to modify, package, and transport lipids and proteins
what does the endomembrane system include
- Nuclear envelope – encloses the nucleus, connected to the ER
- Endoplasmic reticulum (ER) – smooth (sER) and rough (rER)
- Golgi apparatus – modifies and sorts proteins and lipids
- Vesicles – transport materials between organelles
- Lysosomes – break down macromolecules and cellular waste
-Vacuoles – store nutrients, waste, and other substances (mainly in plants) - Plasma membrane – controls what enters and exits the cell
What is the function of the smooth endoplasmic reticulum (sER)?
The smooth ER (sER) plays a role in various metabolic processes, including:
✔ Lipid synthesis – produces phospholipids and steroids for membranes
✔ Carbohydrate metabolism – modifies glycogen stores
✔ Detoxification – breaks down drugs, poisons, and alcohol in liver cells
✔ Calcium ion storage – releases Ca²⁺ for cell signaling (muscle contraction, neurotransmitter release)
✔ Dynamic structure – the amount of sER can increase/decrease based on the cell’s needs
What is the function of the rough endoplasmic reticulum (rER)?
The rough ER (rER) is responsible for protein synthesis and processing:
✔ Protein synthesis – ribosomes on its surface produce proteins
✔ Secreted & membrane proteins – enter the rER lumen for folding/modification
✔ Glycoprotein production – proteins are tagged with sugars for recognition
✔ Part of the endomembrane system – sends proteins to the Golgi apparatus via vesicles
➡ Key difference: The rough ER has ribosomes on its surface, while the smooth ER does not.
What is the Golgi apparatus
The Golgi complex is a stack of membrane-bound sacs that modifies, sorts, and ships proteins and lipids.
function of golgi aparatus
✔ Receives vesicles from the rough ER at the cis face
✔ Modifies proteins through glycosylation (adds carbohydrate chains)
✔ Sorts proteins by adding molecular markers (e.g., mannose-6-phosphate directs proteins to lysosomes)
✔ Ships proteins in vesicles from the trans face to their final destinations (lysosomes, plasma membrane, secretion)
✔ Synthesizes polysaccharides (e.g., pectin and hemicellulose) for cell walls (plants)
What is the purpose of glycosylation in the Golgi complex?
✔ Glycosylation is the process of adding or modifying carbohydrate chains on proteins.
✔ It is crucial for cell communication, protein stability, and cell recognition.
✔ Some proteins require glycosylation to function properly in the extracellular environment.
Example: Glycoproteins in cell membranes help with immune recognition (e.g., blood group antigens).
What are the three types of endocytosis?
1️⃣ Phagocytosis (“cell eating”)
2️⃣ Pinocytosis (“cell drinking”)
3️⃣ Receptor-mediated endocytosis
what is Phagocytosis (“cell eating”)
the cell engulfs large particles (e.g., bacteria) into a phagocytic vacuole, which fuses with a lysosome for digestion.
what is pinocytosis
the cell non-selectively takes in extracellular fluid containing dissolved solutes using a coat protein.
what is receptor mediated endocytosis
allows cells to take up specific molecules in low concentrations using receptor proteins (e.g., cholesterol uptake via LDL receptors).
What are lysosomes
✔ Lysosomes are membrane-bound organelles filled with hydrolytic enzymes that break down macromolecules.
lysosome functions
Digest proteins, lipids, carbohydrates, and nucleic acids.
Recycle cellular materials through autophagy.
Play a role in programmed cell death (apoptosis).
Fuse with phagocytic vacuoles to degrade engulfed materials.
Why is the inside of a lysosome acidic?
The acidic environment (pH ~5) is required to activate digestive enzymes.
Lysosomal storage diseases
occur when enzymes malfunction, leading to accumulation of undigested material
What are the differences between constitutive and regulated exocytosis?
Constitutive exocytosis – occurs continuously to release extracellular matrix proteins and deliver membrane proteins to the cell surface.
✔ Regulated exocytosis – occurs in response to a signal (e.g., hormone or neurotransmitter release from specialized cells).
Example: Insulin is stored in vesicles and released only when blood sugar levels rise.
How does the cell transport proteins out of the cell?
Step 1: Synthesis – Proteins are made in the rER.
✔ Step 2: Tagging & Packaging – The Golgi complex modifies and sorts proteins.
✔ Step 3: Transport & Delivery – Vesicles transport proteins to their final destinations.
What are vesicles and their functions?
✔ Vesicles are small, membrane-bound sacs used for transport.
✔ Types of vesicles:
Transport vesicles – move molecules within the cell
Secretory vesicles – release substances outside the cell
Lysosomes – contain hydrolytic enzymes for breakdown
✔ Artificial vesicles (liposomes) are used in drug delivery.
What is the function of vacuoles?
✔ Vacuoles are large membrane-bound compartments derived from the ER and Golgi.
✔ In plants, vacuoles:
Store nutrients and waste.
Maintain turgor pressure by absorbing water.
Store pigments and defensive compounds.
✔ In animals, vacuoles function similarly to vesicles and lysosomes.
