Lecture 11 - Endomembranes Golgi Flashcards
(29 cards)
what do endosomes do
- carry and sort material brought into the cell
what do lysosomes do
- digest ingested material and unneeded cellular components
what do transition, transport, and secretory vesicles do
- move molecules between the compartments and plasma membrane
what are the components of the endomembrane system
- rough and smooth ER
- golgi complex
- endosomes
- lysosomes
- transition, transport, and secretory vesicles
what do peroxisomes do
- house hydrogen peroxide generating reactions
what is the role of the golgi complex
- further processes and sorts glycoproteins and membrane lipids
- plays a central role in membrane and protein trafficking in eukaryotic cells
- proteins released into the ER lumen are routed to the golgi, secretory vesicles, lysosomes, or back to the ER
- further glycosylation and processing of carbohydrate side chains occurs, then the macromolecules are sorted and distributed to other locations
what is the schematic of the golgi
- CGN (cis golgi network) transition vesicle sorting station
- sorting of proteins to be sent back to the ER or on to the golgi
- TGN (trans golgi network) vesicles sorting station
- segregating proteins into vesicles headed to the plasma membrane or other intracellular destinations
what happens in the cisternae of the golgi
- proteins/lipids are glycosylated finishing a port-translational modification process that began in the ER
what is terminal glycosylation
- occurs in the golgi
- refers to modifications of glycoproteins through the removal/addition of sugars side chains on the core oligosaccharides (added in the ER)
where do glycosylation reactions take place
- on the luminal (interior) side of the membrane thus contributing to membrane asymmetry
what occurs in the ER in regards to glycosyl transferase
- biosynthesis of core oligosaccharide for N-linked glycosylation of certain asparagine residues
- initial processing of core oligosaccharides
- identification and removal of misfolded proteins
what is the key point in glycosyl transferases
- each step of glycosylation is strictly dependent on the preceding modification
- the addition of the next sugar often relies on the presence of previous carbohydrates, therefore each set is critical and this becomes a linear process
what is o-linked glycosylation
- happens in the golgi
- addition of carbohydrates to OH group on Ser and Thr
what happens if one glycosyl transferase is missing
- Incomplete or incorrect sugar chains form
- Proteins or cell signals may not work properly
- Can lead to disorders or affect blood type
what are the functions of glycosylation
- participate in protein/lipid sorting in the trans-golgi network (a sorting signal)
- makes glycoproteins/membranes more resistant to digestion by proteases. by creating the glycocalyx (can form a carbohydrate layer)
- serve as a recognition molecules in cell-cell interaction unfortunately viruses also use it for viral entry
- regulatory roles (protein folding/stability), ABO blood type, and immune recognition
- gives a cell the ability to generate many chemically distinct molecules at the cell surface
how is ABO blood type determined by glycosylation
- ABO blood group antigens are carbohydrate structures added to lipids and proteins on the surface of red blood cells
- type A adds N-acetylgalactosamine (GalNAc)
- type B adds galactose
- type O remains unmodified
what are the 2 models that explain the movement of lipids and proteins within the golgi
- the stationary cisternae model (vesicular transport model)
- the cisternal maturation model
what are the similarities between the two models
- each golgi cisternae has a distinct population of resident proteins
- cargo moves from the cis to trans side of the golgi complex
- large numbers of vesicles can be seen budding from the cisternae
- vesicles can move and fuse to “anterograde” and “retrograde” cisternae
what are the differences between the 2 models
- stationary cisternae model = cisternae and the resident enzymes stay in place, while cargo moves from one stack to the next
- cisternal maturation model = cargo remain within a cisternae, while the cisternae move forward (cis to trans) and resident enzymes shuffle backwards in vesicles
where can proteins be found in each model
stationary cisternae model - cargo would be found in the vesicles
cisternal maturation model - resident enzymes would be found in the vesicles
where are golgi residents found on the 2 models using fluorescence microscopy
stationary cisternae model - early and late golgi resident proteins would never co-localize
cisternal maturation model - a cisternae would express early golgi resident proteins then transition to expressing a late golgi resident protein
what is unique about the golgi in s. cerevisiae
- less organized
- individual cisternae are spread in an irregular manner throughout the cell
what supports the cisternal maturation model
- large cargo is too long to be stuck in vesicles so it never leaves the cisternae
- resident proteins are returned in vesicles
what is vesicle trafficking (the big picture)
- vesicles (containing protein and lipids) move to and from the plasma membrane, and between intracellular structures including the ER, golgi, and lysosome
