Lecture 4 Flashcards
How did the cell nucleus evolve in ancient prokaryotic cells?
Nucleus initially resulted from invagination and internalization of the plasma membrane. The internalization of the plasma membrane contains another branch which forms the ER membrane which is continuous with the ER.
Where did the golgi come from in eukaryotic cells?
Golgi arose from the endoplasmic reticulum.
What are modern membrane-bound structures of the cell that originally arose from the plasma membrane invagination?
Nuclear Membrane
ER
Golgo
Endosomes
Lysosomes
*These structures are part of what is known as the endomembrane system.
Where did mitochondria and plastids arise from?
Endosymbiosis as a result of consuming ancient bacteria.
What are the features of membrane-bound structures that arose from endosymbiosis?
Have their own DNA
Are enclosed by 2 membranes
They are isolated from extensive protein transport in the endomembrane system.
How is the mitochondria regulated in a cell?
Functionality of mitochondria relies on genes from the nucleus.
What is the function of the ER?
ER is the entry point for proteins destined for other compartments of the endomembrane system. This includes exocytosis from the cell.
How does cargo travel between membrane bound compartments?
Membrane bound compartments of the endomembrane system transport cargo via transport vesicles.
What is the advantage of the endomembrane system used in prokaryotic cells?
Cargo only needs to cross the ER membrane once. After that it is transported between structures of the endomembrane system via vesicles which internalise the cargo. This allows the system to be highly regulated.
Where does sorting of cargo and targeting of cargo occur?
Trans Golgi Network (TGN)
How are vesicles targeted to the correct location?
Each transport vesicle that buds from a compartment must be loaded with appropriate proteins for its destination.
Why is there a great variability in vesicle coats?
Different classes of transport vesicle shuttle between the various organelles
How are membranes deformed to form buds?
Vesicle budding is driven by the assembly of a protein coat on cytosolic surface of the membrane.
What happens after coat proteins are distinct from the original membrane?
Vesicle coats need to be removed for the vesicle to interact with the next compartment.
What is the function of the vesicle beside pinching out the membrane?
Coats are also important for capturing cargo. Only specific cargo can enter the vesicle.
What is the usual function of COP1?
Transport from Golgi to ER
What is the usual function of COP2?
Transport from ER to golgi
What is the usual function of clathrin?
Transport from golgi to plasma membrane
What happens to misfolded proteins during vesicle formation?
Only properly folded proteins are allowed to exit the ER. Misfolded proteins are retained by chaperones
How are cargo transported from the cis to the trans golgi?
2 theories as to how cargo is transported between membranes:
Vesicular transport model: Vesicles are made between layers.
Cisternal maturation model: Cisternae migrates from cis to trans.
What is the function of COP1?
Sometimes resident ER molecules leak out and move to the golgi with transport vesicles. These resident ER proteins contain a KDEL sequence which can bind to a KDEL receptor which returns the resident protein back to the ER. Return is carried out by COP1. The binding (in the golgi) and dissociation (in the ER) of KDEL to its receptor is mediated by the differing pH.
ER membrane can ‘run out’ and so COP1 transport is essential to maintain membrane homeostasis.
What is the amino acid sequence for KDEL?
-Lys-Asp-Glu-Leu- at the C-terminus
Where are KDEL receptors found?
Within all cysternae of the golgi where the pH is slightly acidic..
How are ER resident proteins released into the ER after the vesicles fuse with the ER?
pH in the ER is more than the pH of the golgi and so the pH causes conformational change in the KDEL receptor.
What are the potential pathways of secretion and how are they different from each other?
Direct pathway is constitutive secretion.
Regulated pathway contains many intermediate organelles prior to reaching secretion.
