4.2 Endosomal Membranes: Golgi, Lysosomes, Vacuoles Flashcards
How is the Gogli apparatus divided?
Into three parts: Cis cisternae, medial cisternae, and trans cisternae.
material (newly synthesized proteins) enter the cis side. Then move to the medial, and leave from the trans.
What is the role of golgi apparatus?
further modification (post translational) modification of the protein, including targeting the proteins to appropriate organelles down the system.
Processes in the golgi occur in sequential order cis to medial to trans.
What is the cis golgi network responsible for?
Phosphorylation of oligosaccharides on lysosomal proteins
What is the cis cisternae responsible for?
removal of Man
What is the medial cisternae responsible for?
removal of mann
addition of GlcNac
What is the trans cisterna resposible for?
addition of Gal
addition of NANA
What is trans gogli network responsible for?
sulfate of tyrosines and carboydrantes (sorting)
what are the two models for how the golgi works and moves material/proteins?
Vesicular tranport model
Cisternal maturation model
What is the difference between vesicular transport model and cisternal maturation model?
VTM proposes that cisternae are fully differentiated structures taht maintain a static position w/in the stack. Proteins move through the stacks by entering smaller vesicles that are moving in one direction or another due to targeting signals
CMM proposes that the entire cisternae moves through the golgi from one end of the gogli to the other instead of proteins moving in vesicles them move with the moving cisternae
How are proteins modified in the ER?
Proteins transferred from the ER to the golgi are further modified in the gogli by adding/removing sugars:
Processing the N-linked oligosaccharides (10) left over from the ER is to CORE 5 sugars.
What is the similarity between high mannose oligosaccharides and complex oligosaccharides? Difference?
They both share a common core five saccharide residue.
Complex oligo are trimmed back to a core of 5 saccharide residues and then have a variety of residues added,
high mannose oligo are created by removing all other types of sugar residues, leaving just mannose.
How does the golgi add its own oligosaccharides to proteins? How does it differ from glycosylation in the ER?
GOLGI: O-linked glycosylation, in which the sugar chain is attached to the hydroxyl group (OH) found on serine or threonine. one sugar at a time is added by glycosyl transferase
IN the ER: it’s a N-linked glycosylation and a complete, fourteen unit oligosaccharide was assembled on a membrane-bound
lipid, called dolical, and then was transferred as a complete unit to the target protein.
What is the role of proteoglycans? Where are they formed?
formed in the Golgi by the addition of long chains of disaccharide subunits to a protein using and O linkage. The saccharide monomers are often sulfated, giving the resulting molecules high amounts of negative charges.
Proteoglycans are secreted and become components of extracellular matrix or stay
anchored to the exoplasmic side of the plasma membrane, e.g., as mucus on the surface
of epithelia
In addition to post translational modifications what other role does the gogli have?
sorting proteins and membrane vesicles to an appropriate target
How are secretory vesicles formed?
secretory vesicles are membraned bound containing high concentrations of proteins. They are formed directly by pinching off pouches of the gogli apparatus.
What is on the exterior of a secretory vesicle?
often have attached motor proteins that are used to carry the vesicle to particular places in the cell and they have docking proteins that facilitate the merging of the vesicular membrane with the cell plasma membrane
What is the role of lysosomes?
play important role in neutralizing harmful substances and recycling contents of cells such as aging proteins.
How do lysosomes dispose and recylce?
lysosomes contain about 40 different digestive enzymes. There are specific enzymes present for degrading almost every component of the cell as well as enzymes that remove post-translational modification of proteins such as phosphate and sulfide groups.
What are lysosomal enzymes called? what does this mean?
called acid hydrolases. This means they work very efficiently at a very acidic or low pH
How is low pH generated in lysosomes?
by the activity of protein pumps of the v-pump variety. They pump H+ into the lysosome
How do lysosomes ensure that the digestive enzymes inside don’t end up harming the cell?
1) the membrane boundary itself - restricts activity of the lysosomal enzymes
2) The relatively neutral pH of the cytoplasm effectively inactivates enzymes that are accidentally released from lysosome.
What cellular processes are lysosomes involved in?
1) Endocytosis
2) Phagocytosis
3) Autophagy
4) Autholysis
5) Digestion of extracellular materials.
What is endocytosis?
the engulfment of small things and small fluids. Digest materials brought in from the outside by endosomes
What is phagocytosis?
engulfing of extracellular material that is large like cells or bacteria.
What is autolysis?
programmed cell death aka suicide
What is an example of digestions: lysosomes discharging acid hydrolases to the extracellular space?
relatively uncommon function (releasing contents inside lysosome into extracellular space) but it occurs during some specialized events such as the penetration of the egg cell covering by some types of sperm cells.
Why are two type of lysosomes created? What are they?
Primary and secondary lysosomes.
created b/c various pathways for obtaining material to be degraded meet up with the lysosomes somewhere in the cytoplasm
What are primary lysosomes?
lysosomes that have been prepared for action. They contain acid hydrolases but don’t engage in digestive activity
What are secondary lysosomes?
ones that have already docked w/another vesicle of some type, containing something that needs to be destroyed. Secondary lysosome result from fusion of primary lysosomes and endosomes w/particles to be digested (endolysosomes)
What is the difference between primary and secondary lysosomes?
secondary lysosomes have heterogeneous content and are often larger than primary lysosomes, whereas the contents of primary lysosomes is very smooth and homogeneous.
What is authophagy?
Autophagy can remove large objects—macromolecules, large protein aggregates, and even whole organelles—that other disposal mechanisms such as proteasomal degradation cannot handle.
Alberts, Bruce. Molecular Biology of the Cell (p. 726). W. W. Norton & Company. Kindle Edition.
What are the characteristics of plant cell vacuoles? How are they formed?
- size of vacuole can be anywhere from 30-90% of the volume of a single cell.
- vacuoles are part of the endosomal organelle system and are formed by the fusion of vesicles derived from the gogli apparatus. The membrane that surrounds the vacuole is called tonoplast
What is tonoplast? where is it found?
membrane that surrounds the vacuole. Found in plants and fungi cells
What are the functions of vacuoles?
- functions are heterogeneous.
1) generate high turgor pressure that pushes outward against the cell wall, so the plant cell can maintain its cell shape and increase the cell size
2) site of intracellular digestion
3) storage space before transport, nutrients, waste and digestion products.
4) storage for chemical weapons for defense (released when cells are injured by herbivore or fungi)
How do vacuoles help plants cell maintain its cell shape and increase the cell size?
generate high turgor pressure (pressure created w/in cells as a result of osmosis). They use this pressure to increase their size of cells during growth.
Altering turgor pressure can change their shape.
Why do some plants wilt?
loss of turgor pressure as water levels in plant cells are reduced during dry periods.
When proteins leave the gogli where can they go?
that proteins in membranes leave the Golgi and are targeted to
1) lysosomes,
2) secretory vesicles
3) cell plasma membrane
Proteins that go into the golgi come from where?
Endosomal compartments or the ER
What are the components of authophagy?
1) a double-membrane compartment is
formed around structures that need to be recycled and this forms an autophagosome
2 the autophagosome then docks with a lysosome that has acid hydrolase
3) digestion occurs after fusion of autophagasome and lysosome
