B2.076 Cellular Organelles

Question 1

what are Rabs?

Answer 1

Rabs are barcode type proteins that mark vesicles for transport, they have different protein characteristics that allow them to be differentiated

Question 2

what are the 3 major steps in protein trafficking and their mediators?

Answer 2

1. tethering (Rab-GTP, v-SNARE)
2. docking (Rab effector)
3. fusion (t-SNARE)

Question 3

how many Rabs are there?

Answer 3

11; each have specific functions, though they may overlap

Question 4

what are lysosomes?

Answer 4

acidic vesicles in the cytoplasm that are full of hydrolytic enzymes

Question 5

what is the primary function of lysosomes?

Answer 5

hydrolyze all macromolecules to monomeric subunits and recycle subunits via transmembrane transport to the cytoplasm

Question 6

how does ATPase work in lysosomes?

Answer 6

runs backward compared to ATPase in mitochondria, pumps H+ into the lysosome to decrease pH

Question 7

describe the endosome/lysosome continuum

Answer 7

endosomes become acidified by the cell, as they do the enzymes within the endosome are activated forming a lysosome

Question 8

what happens to lysosomal enzymes if they leak into the cytoplasm?

Answer 8

don’t work outside because pH is too high; enzymes inactivate

Question 9

how are proteins trafficked to the lyso-endosome?

Answer 9

1. lysosomal hydrolase precursors are made in the ER and sent to the Golgi
2. a mannose is attached and a phosphate is attached on the 6th position of the mannose
3. the protein binds to a receptor on the trans Golgi that is specific
4. vesicle buds off and is taken by a Rab to an early endosome
5. conformational change occurs with the pH change removing the phosphate and activating the enzyme

Question 10

how many lysosomal storage diseases are there?

Answer 10

over 50

Question 11

what characterizes lysosomal storage diseases?

Answer 11

lack of a lysosomal enzyme or the lack of enzymes needed to tag them

Question 12

what is hexosaminidase A?

Answer 12

the only enzyme that can hydrolyze Gm2 gangliosides in vivo

Question 13

what is Tay Sachs disease?

Answer 13

an autosomal recessive disease characterized by a lack of hexosaminidase A and thus an accumulation of gangliosides in neurons

Question 14

what is I cell disease (inclusion cell disease)?

Answer 14

autosomal recessive disease caused by a defective GlcNac phosphotransferase

Question 15

why is I cell disease the most serious lysosomal storage disease?

Answer 15

no enzymes can be tagged, so they never get transported to the lysosomes, nothing ever gets broken down properly

Question 16

what is axonal transport?

Answer 16

movement of neurotransmitters from the neuron cell body to the synapse using ATP

Question 17

what is anterograde transport?

Answer 17

movement of a vesicle along a microtubule from the cell body to the synapse, mediated by kinesin

Question 18

what is retrograde transport?

Answer 18

movement of a vesicle along a microtubule from the synapse to the cell body, mediated by dynein

Question 19

how is tau normally arranged?

Answer 19

along microtubules, can be phosphorylated or dephosphorylated

Question 20

what characterizes pathogenic tau kinase?

Answer 20

aberrant phosphorylation which can lead to aggregation, modification, and conformational change

Question 21

what type of behavior and protein accumulations are associated with frontal lobe damage?

Answer 21

impulsive behavior

tau tangles in brain

Question 22

what is chronic traumatic encephalopathy?

Answer 22

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

Question 23

what are some symptoms of CTE?

Answer 23

dementia, such as memory loss, aggression, confusion, and depression

Question 24

can tau tangles spread?

Answer 24

yes, can transfer between cells during synapse

Question 25

what is the diameter, structure, and subunit examples of microfilaments?

Answer 25

6 nm
double helix
actin

Question 26

what is the diameter, structure, and subunit examples of intermediate filaments?

Answer 26

10 nm
two anti-parallel/dimers, forming tetramers
vimentin (mesenchyme), glial fibrillary acidic proein (glia), neurofilament (neurons), keratins (epithelia), nuclear lamins, desmin (muscle)

Question 27

what is the diameter, structure, and subunit examples of microtubules?

Answer 27

23 nm
13 protofilaments
alpha and beta tubulin

Question 28

what can result from a defective keratin filament network?

Answer 28

epidermolysis bullosa (skin blistering)