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RELEVANT LEARNING OUTCOME:
(c) Outline the functions of the membrane systems and organelles.
🕐Estimated Time: 10 minutes
'Endo' means 'within/inner'. Hence, the endomembrane system refers to the system of internal membranes within an eukaryotic cell. While the cell surface membrane is not an endomembrane, it is related by function to the internal membranes, and is hence included in the endomembrane system.
The system is involved in the
Synthesis of proteins and transporting these proteins into membranes and organelles
Transport proteins out of the cell
Metabolism and movement of lipids
Detoxification of poisons
💡Internal membranes
💡Internal membranes
The internal membranes are connected either through physical continuity or by the transfer of membrane segments (i.e., vesicles).
👁️🗨️Watch the video to see how the components of the membranes are connected together (physically or functionally) to process and transport biomolecules within the cell.
Think of the following while watching the video:
what is the relationship between the ER and Golgi apparatus?
what is the fate of digestive enzymes synthesised by the RER that is transported to the Golgi appratus?
proteins bound for export out of the cell are synthesised by the RER and transported to the Golgi apparatus, how does it eventually get exported out of the cell?
Proteins synthesised in RER and lipids synthesised in SER are transported to the Golgi apparatus via vesicles.
Digestive enzymes are packed into a vesicle and buds off the Golgi apparatus to form lysosomes.
Proteins to be exported are packaged into secretory vesicle which buds off the Golgi apparatus, and transported to the cell surface membrane, where it fuses and releases the proteins out of the cell via exocytosis (see video)
👁️🗨️Watch the video to see how the Golgi acts as the 'Post Office' of the cell.
Think of the following while watching the video:
which face of the Golgi apparatus receives vesicles from the RER and SER?
which face of the Golgi apparatus buds off to form vesicles that transports the proteins to its target location?
transport vesicles from RER fuses with the cis face of the Golgi apparatus
secretory vesicles / lysosomes buds off from the trans face of the Golgi appratus
Simple way to remember: alphabetical order! Cis > Trans
📂 Recall
📂 Recall
Why don't bacteria have endomembrane systems?
They (prokaryotes) don't have membrane bound organelles.
🖊️ Check Your Understanding: Lecture Notes Checkpoint
🖊️ Check Your Understanding: Lecture Notes Checkpoint
What is the correct sequence of the events described below?
Proteins are chemically modified in the RER.
Proteins are released out of the cell by exocytosis.
Polypeptides are synthesized by fixed ribosomes.
Proteins are packaged into a vesicle that leaves the GA.
Proteins are packed into a vesicle that fuses with the GA.
Correct sequence: 3, 1, 5, 4, 2
This is a description of the synthesis, modification and transport of a secretory protein.
💡The Cell Surface Membrane
💡The Cell Surface Membrane
The membranes of cells consist of a double layed (bilayar) of phospholipids with various proteins attached to or embedded in it. The membrane is about 7 nm thick and is visible under the electron microscope.
It serves as a surface area for the exchange of substance and is selectively permeable in nature, allowing only certain ions/molecules to pass through. It also provides shape and protection to the cell.
More details about the cell membrane can be found in 'Membrane Structure & Cellular Transport'.
🖊️Check Your Understanding
🖊️Check Your Understanding
Attempt Qn 16-18 of the learning goals.
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