destinations of the cytoplasmic pathway
* translated on free ribosomes cytosol mitochondria nucleus peroxisomes
destinations of the secretory pathway
- translated on free ribosomes -> sent to ER for processing -> sent to final destination
- Lysine/Arginine on N-ter.
- Hydrophobic on C-term.
1. Signal recognition particle (SRP) recognizes these signals -> binds to ribosome
2. SRP wraps itself around rib-tRNA complex
3. Bring to ER, further processing
ER lumen
lysosomes
membrane proteins
secrete
mitochondrial signaling sequence
- N-terminus hydrophobic a-helix
- recognized by transporter outer/inner membrane (TOMs and TIMs)
- protected by chaperones (need to unfold to fit through transporters) heat shock ptns
nucleus signaling sequence
4 continuous basic residues (lysine, arginine)
imported via nuclear pores
large ptns requires KKKRK signal seq.
peroxisomes signaling sequence
C-terminus SKL (serine, lysine, leucine)
ER lumen signaling sequence
KDEL lysine aspartate glutamate leucine
lysosome signaling sequence
mannose 6 phosphate
I-cell disease if this process is defective (lysosomal ptns don’t make it to the lysosome)
membrane ptns signaling sequence
N-term. apolar region
stop transfer sequence
proteins destined for secretion
tryptophan-rich domains
Steptomycin inhibition
30S -> initiation
prevents fmet-tRNA from binding
50S cannot bind
Tetracycline inhibition
30S –> elongation
block aminoacyl-tRNA entry to complex
Chloramphenicol inhibition
elongation
inhibits peptidyl transferases
Clindamycin + Erythromycin inhibition
50S –> elongation
block translocation of ribosome
*used for Pertussis treatment
Diptheria Toxin
elongation
inactivates EF2-GTP
Cycloheximide inhibition
elongation
inhibits peptidyl transferase
* Streptomyces griseus
Shiga-toxin + Ricin
60S (euks) –> elongation
block aminoacyl-tRNA from ribosome complex
*Shingella dysenteriae, Castor oil plant
Puromycin
premature chain termination (prok/euks)
resembles the 3’ aminoacylated tRNA -> enters A site -> premature release
