Lecture 8 Flashcards
Endomembrane system
What is the endomembrane system?
The endomembrane system manufactures, sorts and distributes molecules. It is responsible for physical continuity or vesicle transfer between components.
What are the components of the endomembrane system?
- Endoplasmic Reticulum
- Nuclear Envelope
- Golgi apparatus
- Plasma membrane
- Lysosome
Endoplasmic Reticulum
Is an extensive membrane system with nuclear membranes, tubes and sacs. There are two different kinds of ER. Rough ER has a rough sheet like appearance due to the ribosomes. Smooth ER has smooth tubular appearance as it has no ribosomes.
Smooth ER Functions
Ca2+ ion (calcium) storage (muscle contraction). Lipid synthesis, and detoxification (alcohol). Organs such as our livers which have to deal with toxins such as alcohol are enriched with smooth ER.
Rough ER Functions
Protein synthesis (secreted & membrane proteins). Glycosylation. Can make lipids for membrane synthesis. All proteins made at the rough ER are secreted.
What do proteins destined for secretion contain?
They have a hydrophobic signal peptide that will bind to a signal recognition particle (SRP) to stop translation.
Golgi apparatus
The golgi apparatus is a series of flattened sacs. It’s purpose is to distribute cell products (enzymes) to their specific destinations, or secretion from the cell.
Lysosomes
Lysosomes are membrane-enclosed organelles that contain an array of enzymes capable of breaking down all types of biological polymers.
Lysosomes Function
Lysosomes function as the digestive system of the cell, serving both to degrade material taken up from outside the cell and to digest obsolete components of the cell itself.
Why are lysosomes important?
Lysosomes are filled with digestive enzymes fuse with molecules being ingested in food vacuoles and break it down. The products it breaks down are used by the cell to ensure survival. Old broken down cells are put into vacuoles which fuse with lysosomes to be broken down and give fuel to other cells. Lysosomes also break down toxic chemicals.
What is the route taken by secreted proteins?
Secreted proteins begin synthesising in the rough ER. They contain hydrophobic signal peptides which bind with the signal recognition particles and are attached to an ER bound ribosome to continue translation. They are then put into transport vesicles move to the golgi apparatus. The golgi packages them into secretory vesicles, they exit the golgi, and merge with the cell membrane, exporting the protein into the external environment.
What is the route taken by non-secreted proteins?
Non-secreted proteins are synthesised in in the rough ER. Dependant on their function they remain within the cell and are targeted to specific organelles to carry out their biological functions.
What is the role of the signal peptide?
The signal peptide sticks out of secreted proteins to be recognised and bound to the signal recognition particle to slow/stop translation.
What is the role of the signal recognition particle?
The signal recognition particle recognises and binds to the signal peptide on the protein. It stops translation and binds the protein to an ER bound ribosome, to then resume translation.
What is glycosylation?
Glycosylation is a form of protein modification in the secretory pathway. It attaches carbohydrates to the proteins amino acids to ensure the protein structure is biologically correct. It occurs in the golgi, and the endoplasmic reticulum.
