Kandpal - Protein Targeting and Vesicular Trafficking

Question 1

what do the ribosomes do that are free in the cytosol

Answer 1

synthesize cytoplasmic, nuclear, and mitochondrial proteins

Question 2

what do the bound/ER ribosomes synthesize

Answer 2

secreted proteins, plasma membrane proteins, ER proteins, golgi proteins and lysosomal proteins

Question 3

what is a nuclear localization sequence (NLS) on a protein

Answer 3

either a signal sequence on the N-terminal or a signal patch in the center of the protein that are hydrophobic

Question 4

what is the signal hypothesis

Answer 4

translation in the presence of ribosomes = larger proteins and in the presence of microsomes = smaller proteins

Question 5

what are 3 types of protein traffic

Answer 5

gated transport, transmembrane transport, and vesicular transport

Question 6

where does gated-transport occur, how does protein enter and does it require ATP

Answer 6

cytosol -> nucleus, through pore complexes (nucleoporins), yes

Question 7

how do import receptors work in gated transport

Answer 7

protein NLS binds to nucleoporin -> cargo is delivered to nucleus -> Ran-GTP binds to receptors -> leaves nucleus -> Ran-GDP dissociates from receptor

Question 8

how do export receptors work in gated transport

Answer 8

Ran-GTP binds to receptors -> protein + nuclear export signal leave nucleus -> Ran-GDP dissociates and cargo is delivered to cytosol

Question 9

what regulates GTP and GDP in gated transport

Answer 9

GTPase activating protein (GAP) in cytosol and guanine exchange factor (GEF) in nucleus

Question 10

in the transmembrane transport from cytosol to mitochondria, what is the signal peptide and where is it located

Answer 10

a helical structure with + charged clusters on one side and - charged regions on the other
at the N-terminus

Question 11

what 2 things are located on the outer membrane for transmembrane transport

Answer 11

TOM (translocation channel/receptor) and SAM complex

Question 12

what 2 things are located on the inner membrane for transmembrane transport

Answer 12

TIM 23 complex (Hsp70 import ATPase) and OXA complex

Question 13

where is the signal located for cytosol-> peroxisome transport

Answer 13

3 amino acid sequence at the C-terminus

Question 14

what happens in peroxisome transport disorder -> Zellweger Syndrome

Answer 14

mutations in transport protein Pex2 - leave empty peroxisomes

Question 15

which type of transmembrane transport has translation and translocation at the same time

Answer 15

cytosol -> endoplasmic reticulum

Question 16

what recognizes the signal sequence in the cytosol for ER transport

Answer 16

signal recognition particle (SRP) - complex 300 nucleotides, 7SL RNA and 6 proteins

Question 17

after SRP recognizes signal sequence in cytosol for ER transport - what does the protein bind to

Answer 17

binds on the nascent protein, large ribosomal unit and SRP receptor (Methionine residues on p54 bind to signal sequence) and hydrolyzes GTP

Question 18

there are 4 topological classes or proteins (cytosol -> ER space/lumen) what are the based on

Answer 18

classified by orientation, transmembrane domains, and signal sequences

Question 19

what is the cleavable signal on Type 1 topological protein

Answer 19

cleavable signal is “COO-“ on cytosol and the hydrophobic residues stop transport and gets embedded into membane

Question 20

what is the cleavable signal on Type 2 topological protein

Answer 20

no cleavable signal - but NH3+ is in cytosol

Question 21

what is the cleavable signal on Type 3 topological protein

Answer 21

no cleavable signal but has hydrophobic regions that stop transport and get embedded into membrane

Question 22

what is the cleavable signal on Type 4 topological protein

Answer 22

multiple

Question 23

secretory proteins have a coat in vesicular transport, what are the 3 types of coats

Answer 23

clathrin, COPI, and COPII

Question 24

what are the steps for vesicle formation and fusion in vesicular transport

Answer 24

coat-recruitment by GTPase control, Rab proteins regulate flow of vesicle to correct membrane and SNARE proteins mediate fusion

Question 25

what are the 2 paths for secretory proteins

Answer 25

constitutive pathway or regulated pathway

Question 26

what happen in the constitutive pathway (unregulated) for secretory proteins

Answer 26

after golgi sorts into vesicles -> has unregulated fusion into extracellular space (occurs all the time)

Question 27

what regulates the regulated pathway in secretory proteins

Answer 27

hormone or neurotransmitter (only occurs when signal occurs)

Question 28

what do lysosomes store

Answer 28

hydrolytic enzymes - glycosidases, proteases, phosphatases, and sulfatases

Question 29

what “tag” do lysosomal hydrolases carry

Answer 29

unique “mannose-6P” tag on N-linked oligosaccharide that is recognized by receptor on lysosome

Question 30

what is I-cell disease

Answer 30

lysosomal storage disease

Question 31

what happens with a deficiency of mannose-6P attaching enzyme

Answer 31

no transport of lysosomal enzymes to lysosomes -> accumulation in circulation

Question 32

what are 3 endocytic pathways

Answer 32

phagocytosis, pinocytosis, and receptor-mediated endocytosis

Question 33

what is autosomal dominant hypercholesterolema caused by

Answer 33

mutations in LDL (low density lipoprotein) receptor - which normally removes LDL from circulation

Question 34

what are 2 protein modifications that occurs after translation

Answer 34

glycosylation at OH groups of serine and theronine residues (O-linked) or amide group of asparagine (N-linked) and disulfide bonds are added for folding

Question 35

what does a1-antitrypsin do (secreted from hepatocytes and macrophages)

Answer 35

inhibits trypsin and blood pretease elastase

Question 36

what does a deficiency in a1-antitrypsin cause

Answer 36

hereditary emphysema - and an absence leads to elastase degrading lung tissue