The Endomembrane System Flashcards
What is the endomembrane system?
A series of interconnected, membrane-bound compartments in eukaryotic cells
What helps determine the properties and maintain distinct identities of the compartments within the cell?
The lipids and proteins present in their membranes
In plants, what allows the endomembrane system to be continuous between cells?
Plasmodesmata
T or F: Extensive internal membranes are not common in prokaryotic cells.
True
How can green fluorescent protein (GFP) be used to track cell components?
By fusing the GFP with cellular proteins and observing them under a microscope
What is a vesicle?
A small membrane-enclosed sac that transports substances within the cell or between the cell interior and exterior
How do vesicles transport material?
By budding off of an organelle and taking a piece of its membrane and contents, then fusing with another organelle or plasma membrane and unloading their contents
What is the main difference between exocytosis and endocytosis?
- Exocytosis: Uses vesicles to transport material out of the cell
- Endocytosis: Uses vesicles to transport material into the cell
How does a vesicle move?
Using the cytoskeleton and motor proteins
What type of proteins are used to bring the membranes of the vesicle and target compartment close enough so they can fuse?
SNARE proteins
During vesicle trafficking, what does the energy from SNARE assembly provide energy for?
Fusion of the vesicle with the target membrane
What are the two types of SNARE proteins?
- v-SNARE proteins
- t-SNARE proteins
Which type of SNARE protein is incorporated into the vesicle membrane during assembly of the vesicle coat?
v-SNARE proteins
Which type of SNARE protein is responsible for the eventual fusion of a vesicle with the target membrane?
v-SNARE proteins
Which type of SNARE protein is incorporated into the target membrane?
t-SNARE proteins
What is the endoplasmic reticulum?
An organelle composed of a network of membranes
T or F: The endoplasmic reticulum is not continuous with the outer membrane of the nuclear envelope.
False
What is the lumen?
The continuous interior of the endoplasmic reticulum
What is the main difference between the smooth ER and the rough ER?
- Smooth ER: Does not contain ribosomes
- Rough ER: Studded with ribosomes
Which endoplasmic reticulum is largely responsible for lipid synthesis?
The smooth ER
Which endoplasmic reticulum is largely responsible for the production of steroid hormones?
The smooth ER
Which endoplasmic reticulum is largely responsible for detoxification?
The smooth ER
Which endoplasmic reticulum is largely responsible for the sequestration/storage of calcium?
The smooth ER
Why is calcium excluded from the cytosol?
Because it binds water together loosely and precipitates phosphates which will make proteins insoluble
Which endoplasmic reticulum is largely responsible for the synthesis of membrane phospholipids?
The rough ER
Which endoplasmic reticulum is largely responsible for the glycosylation of membrane proteins?
The rough ER
Which endoplasmic reticulum is largely responsible for protein folding/quality control?
The rough ER
Which endoplasmic reticulum is largely responsible for protein synthesis, modification, and transport?
The rough ER
Which organelle is the major site of protein synthesis?
Ribosomes
Which organelle modifies proteins and lipids produced by the ER and acts as a sorting station as they move to their final destinations?
The golgi apparatus/complex
Is the golgi apparatus continuous with the ER?
No
What are the three primary roles of the golgi apparatus?
- Further modify proteins and lipids produced by the ER
- Sort proteins and lipids as they move to their final destinations
- Act as the site of synthesis for most of the cell’s carbohydrates
What are cisternae?
The series of flattened membrane sacs that make up the golgi apparatus
T or F: Each cisterna is biochemically unique?
True
Why are modifications by the golgi performed in a sequence of steps, each in a different region of the golgi?
Because each region contains a different set of enzymes that catalyses specific reactions
What are three of the chemically distinct regions of the Golgi complex?
- Cis-golgi network(CGN)
- Medial-gogli
- Trans-golgi network (TGN)
Which region of the golgi complex is the most proximally located?
The cis-golgi network
Which region of the golgi complex acts as a sorting station?
The cis-golgi network
Which region of the golgi complex if the most distally located?
The trans-golgi network
Which region of the golgi complex receives fully processed proteins and sorts them into different types of vesicles?
The trans-golgi network
In which direction does traffic usually travel through the golgi apparatus?
Proximal to distal
In a cell, is the ER proximal or distal?
Proximal
In a cell, is the plasma membrane proximal or distal?
Distal
Why is it important for a small amount of traffic to be able to move from the golgi to the ER (reverse pathway)?
Important to retrieve proteins in the ER or golgi that were accidentally moved forward and to recycle membrane components
The transfer of vesicles from the ER to golgi and between golgi subcomponents is achieved by what type of proteins?
Coat proteins
What are the two functions of coat proteins?
- Helps form the vesicle
- Helps select the “cargo” going in or on the vesicle
Where do COP I and COP II assemble?
On the cytosolic surface of donor compartment membranes where budding takes place
In what direction does COP I direct movement?
Retrograde
In what direction does COP II direct movement?
Anterograde
What pathway do vesicles follow when moving in a retrograde direction?
From golgi to ER
What pathway do vesicles follow when moving in an anterograde direction?
From ER to golgi
Where do AP/clathrin-coated vesicles transport cargo?
From the trans-golgi network to other vesicles
What is glycosylation?
The process in which sugars are covalently linked to lipids or specific amino acids of proteins, forming glycoproteins
Where does glycosylation occur?
The golgi apparatus
What are lysosomes?
Digestive organelles
Where are lysosomes derived from?
The golgi apparatus
Which organelle contains enzymes able to break down macromolecules?
Lysosomes
What is the lysosomal membrane composed of?
Glycosylated proteins
Where are the enzymes inside lysosomes synthesized?
In the rough ER
What mechanism is responsible for maintaining the internal environment of lysosomes at an optimal pH?
Proton pumps embedded in the lysosomal membranes
What are the two primary function of lysosomes?
- Autophagy
- Degradation of internalized material
What is autophagy?
The process involving the decomposition of intracellular components via lysosomes
Which function of lysosomes plays an important role in maintaining and regulating cell homeostasis?
Autophagy
What are the four phases of the autophagic pathway?
- Initiation/autophagosome formation
- Lysosome recruitment
- Autolysosome formation
- Digestion and release
During autophagy, what is formed when an isolation membrane from the ER engulfs target organelles?
An autophagosome
During autophagy, what is formed when a lysosome fuses with the ER-derived autophagic vesicle?
An autolysosome
What is phagocytosis?
The process in which phagocytic cells destroy pathogens like bacteria and viruses
What occurs during phagocytosis?
- The pathogen is internalized by a phagocytic cell and is degraded by the lysosomes that associate with the pathogen containing vesicle
- debris is released outside the cell
What is the plant equivalent to a lysosome?
Vacuoles
What are the three primary functions of plant vacuoles?
- Intracellular digestion
- Mechanical support via turgor pressure
- Storage
In what form do vacuoles store amino acids, sugars, and CO2?
In the form of malate
What is the tonoplast?
The vacuolar membrane
What is embedded in the tonoplast?
Active transport systems
