endomembrane system continued Flashcards
endosomal compartment
endosomal compartments are temporal sorting stations where the fate of endocytosed cargo is determined.
endosomal compartment is the same as
ENDOSOMES
which pathway are endosomal compartment part of
the endocytic cycle
how many types of endosomes are involved in processing endocytosed material and what are their names
3: early endosomes, recycling endosomes, late endosomes
membrane trafficking along the endocytic pathways
1) formation of a vesicle at the plasma membrane
2) fusion of vesicle with early endosome
3) decision: degradation or recycling?
4) recycling via recycling endosome
5) maturation of early endosome to late endosome
6) recycling from late endosome to golgi
7) maturation of lat endosome into lysosome
what is membrane trafficking
Membrane trafficking is the process by which proteins and other macromolecules are distributed throughout the cell, and released to or internalised from the extracellular space. Membrane trafficking uses membrane-bound vesicles as transport intermediaries.
what occurs to pH during maturation in the endosomal compartment
it decreases from 6.5 to 4.5
late and early endosomes can be distinguished because
they look different (early is much rounder)
EE
early endosome
LE
late endosome
recycling can occur in three ways:
1) straight from the early endosome and out of the cell
2) from he early endosome to the golgi and then out the cell
3) from the late endosome to the golgi and out of the cell
lysosomal compartment
also known as vacuole
what do lysosomes serve as
disposal containers
how does the pH in a lysosomes help serve their purpose
it is much lower than the rest of the cell (pH of 5 instead of 7)
what occurs in the the lysosome
acid hydrolases (proteases, lipase)
in order to reach the pH in the lysosome what is used
a H+ ATPase pump to create optimum pH for acid hydrolases
lysosomes ar known as ……. in plant and fungi cells
vacoule
lysosomes are much …. than vacoules
smaller compared to the cell size
hydrolases
chop proteins and lipids up into building blocks to be reused
three pathways that degrade lysosomes
1) phagocytosis
2) pinocytosis
3) autophagy
phagocytosis
in macrophages, cleans the body from invading pathogens and damaged cells. some pathogens stop the process and escape the phagocyte
incomplete phagocytosis
underlies the endosymbiont hypothesis
endosymbiont hypothesis
concerns the origin of mitochondria and chloroplast–> according to this hypothesis, these organelles originated as separate prokaryotic organisms that were taken inside a primordial eukaryotic cell
pinocytosis and receptor mediated endocytosis
endocytosis of solved proteins and molecules and receptor mediated uptake of membranes.
Simple:the ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.
autophagosome
organelles have a limited life span (liver mitochondrion- 10 days) autophagy recycles the organelle.
more detail autophagy
Autophagy is a normal physiological process in the body that deals with destruction of cells in the body. It maintains homeostasis or normal functioning by protein degradation and turnover of the destroyed cell organelles for new cell formation. During cellular stress the process of Autophagy is upscaled and increased
under starvation the cell
recycles cytosol by autophagy
pinocytosis is also known as
endocytosis–> much smaller molecules than pathogens
autophagy example
eating of own organelles. If a cell is starving before it dies it will eat its own mitochondria vesicles fuse around the organelle . Ultra phagosome will fuse with lysosome and it will be degraded. Organelles have a limited life span e.g. mitochondria have a 10 day life span. Under starvation the cell recycles cytosol by autophagy
what fuses with the lysosome in autophagy
ultraphagosome
mitochondrial life span in a liver cell
10 days
under starvation the cell recycles cytosol by
autophagy
transport vesicles
can move molecules between locations inside the cell, e.g., proteins from the rough endoplasmic reticulum to the Golgi apparatus. Membrane-bound and secreted proteins are made on ribosomes found in the rough endoplasmic reticulum.
minimum size of a transport vesicle
25-30nm –> minimum size due tot eh bending of the membrane preventing it from being smaller
example of a transport vesicle
synaptic vesicles
how many types of proteins in transport vesicle
50 types
how many types of phospholipids in a transport vesicle
7000
how many cholesterol molecules in a transport vesicle
5700
most prominent proteins found in vesicles are
vSNARES
SNARES
The primary role of SNARE proteins is to mediate vesicle fusion, that is, the fusion of vesicles with their target membrane bound compartments (such as a lysosome). The best studied SNAREs are those that mediate docking of synaptic vesicles with the presynaptic membrane in neurons.
fusion of vesicle with a target membrane (3)
1) tethering
2) docking–> involves interaction between tSNARES and vSNARES, this process docks it to the membrane and provides force to bend the membrane
3) fusion- tSNARE bound to vSNARE –> liana is now exposed to inner area of the endosome –> pH drops and this releases the ligand from the receptor
what provides membrane specificity
SNARE receptors
vSNAREs ligan will be complementary to
tSNARE receptor
e.g. an endocytic transport vesicle vSNARE will be complementary with early endosome target membrane but not the golgi apparatus target membrane 2
vesicles can be
coated
what role does the coat play
concentrates specific proteins in patches and moulds the forming vesicle
coats are specific
for a particular place in the endocytic and exocytic pathway
which protein coats the ER vesicle
COPII
what protein coats the cis end of the golgi
COPI
what protein coats the tans end of the golgi and all the early endosome
clathrin
formation of a clathrin-coated vesicle in transport vesicles
- specification is provided by the adaptor-receptor interaction
- coat formation curves the membrane and shapes the vesicle
- the coat gets rapidly least and the vesicles interact with the cytoskeleton for intracellular transport
clathrin coat
triskelion (3 arms)- 6 proteins, three are clathrin heavy chains, 3 are clathrin light chains. A coat is formed when many trickskelion assemble together- due to proteins recognising each other- no proteins are needed
no proteins ar needed to form
clathrin coat due to proteins recognising each other
when is the cathrin coat removed
when he vesicle becomes active, the clathrin coat is recycled for the next vesicle
