B2.076 Cellular Organelles Flashcards
what are Rabs?
Rabs are barcode type proteins that mark vesicles for transport, they have different protein characteristics that allow them to be differentiated
what are the 3 major steps in protein trafficking and their mediators?
- tethering (Rab-GTP, v-SNARE)
- docking (Rab effector)
- fusion (t-SNARE)
how many Rabs are there?
11; each have specific functions, though they may overlap
what are lysosomes?
acidic vesicles in the cytoplasm that are full of hydrolytic enzymes
what is the primary function of lysosomes?
hydrolyze all macromolecules to monomeric subunits and recycle subunits via transmembrane transport to the cytoplasm
how does ATPase work in lysosomes?
runs backward compared to ATPase in mitochondria, pumps H+ into the lysosome to decrease pH
describe the endosome/lysosome continuum
endosomes become acidified by the cell, as they do the enzymes within the endosome are activated forming a lysosome
what happens to lysosomal enzymes if they leak into the cytoplasm?
don’t work outside because pH is too high; enzymes inactivate
how are proteins trafficked to the lyso-endosome?
- lysosomal hydrolase precursors are made in the ER and sent to the Golgi
- a mannose is attached and a phosphate is attached on the 6th position of the mannose
- the protein binds to a receptor on the trans Golgi that is specific
- vesicle buds off and is taken by a Rab to an early endosome
- conformational change occurs with the pH change removing the phosphate and activating the enzyme
how many lysosomal storage diseases are there?
over 50
what characterizes lysosomal storage diseases?
lack of a lysosomal enzyme or the lack of enzymes needed to tag them
what is hexosaminidase A?
the only enzyme that can hydrolyze Gm2 gangliosides in vivo
what is Tay Sachs disease?
an autosomal recessive disease characterized by a lack of hexosaminidase A and thus an accumulation of gangliosides in neurons
what is I cell disease (inclusion cell disease)?
autosomal recessive disease caused by a defective GlcNac phosphotransferase
why is I cell disease the most serious lysosomal storage disease?
no enzymes can be tagged, so they never get transported to the lysosomes, nothing ever gets broken down properly
what is axonal transport?
movement of neurotransmitters from the neuron cell body to the synapse using ATP
what is anterograde transport?
movement of a vesicle along a microtubule from the cell body to the synapse, mediated by kinesin
what is retrograde transport?
movement of a vesicle along a microtubule from the synapse to the cell body, mediated by dynein
how is tau normally arranged?
along microtubules, can be phosphorylated or dephosphorylated
what characterizes pathogenic tau kinase?
aberrant phosphorylation which can lead to aggregation, modification, and conformational change
what type of behavior and protein accumulations are associated with frontal lobe damage?
impulsive behavior
tau tangles in brain
what is chronic traumatic encephalopathy?
progressive degenerative disease, diagnosed post mortem in individuals with a history of multiple concussions and other forms of head injury, characteristic degeneration of brain tissue and the accumulation of tau protein
what are some symptoms of CTE?
dementia, such as memory loss, aggression, confusion, and depression
can tau tangles spread?
yes, can transfer between cells during synapse
what is the diameter, structure, and subunit examples of microfilaments?
6 nm
double helix
actin
what is the diameter, structure, and subunit examples of intermediate filaments?
10 nm
two anti-parallel/dimers, forming tetramers
vimentin (mesenchyme), glial fibrillary acidic proein (glia), neurofilament (neurons), keratins (epithelia), nuclear lamins, desmin (muscle)
what is the diameter, structure, and subunit examples of microtubules?
23 nm
13 protofilaments
alpha and beta tubulin
what can result from a defective keratin filament network?
epidermolysis bullosa (skin blistering)
