BICD 110 Lecture Notes - Lecture 5: Insulin Receptor, George Emil Palade, Amylase
28 Jun 2018
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BICD110 Lecture 5 Notes 4/17/18
- Building the cell requires targeting proteins to specific destinations
- Fundamentals of cell biology
o1) Cells are compartmentalized
o2) Cells have structure
oeach cell has unique set of proteins that provide different
functions
- all mRNAs start translation on identical cytoplasmic or free ribosomes
oall proteins made by the cell are initially made by ribosomes in the cytoplasm, no matter
where the protein’s destination is
ohalf of all proteins have a signal that targets them (sorting signal or signal sequence
(ss)). 1st proposed by Gunter Blobel
Type of Signal
Sequence
Protein Synthesis
Location
Protein Transport
Location
How Protein is
transported
no signal sequence cytoplasm cytoplasm
nuclear ss (NLS) cytoplasm nucleus post-translational
import: import
after translation
mitochondria ss cytoplasm mitochondria
peroxisome ss cytoplasm peroxisome
ER ss ER ss translated in
cytoplasm, rest of
protein translated
into the ER
ER -> Golgi ->
lysosome -> PM or
secreted out of the
cell
co-translational
import: import
during translation
- targeting proteins to the ER: co-translational import into the ER
oonce proteins enter the ER, they don’t go into the cytoplasm again
ofor proteins destined to start their journey to the ER, they contain ER
signal sequence, which is usually 16-30 AAs long. Starts with at least one
positive amino acid, and 6-12 hydrophobic AAs at the N-terminus
ooverview of process
1) Ribosome translates the mRNA that codes for the ER signal
sequence (ER ss) in the cytoplasm.
It is ~30 AA
2) Signal recognition particle (SRP)
binds to the ER ss and blocks
translation (translation arrest)
3) an SRP receptor and protein
translocator (translocon) are found
at the membrane of rough ER
4) The SRP binds to the SRP
receptor on the RER. This binding is
stabilized by 2 GTPs
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Document Summary
Building the cell requires targeting proteins to specific destinations. Sequence no signal sequence nuclear ss (nls) mitochondria ss peroxisome ss. Er ss translated in cytoplasm, rest of protein translated into the er. Er -> golgi -> lysosome -> pm or secreted out of the cell. Starts with at least one positive amino acid, and 6-12 hydrophobic aas at the n-terminus: overview of process, ribosome translates the mrna that codes for the er signal sequence (er ss) in the cytoplasm. This binding is stabilized by 2 gtps: ribosome binds to translocon. Er ss enters translocon: translation begins again and the rest of the protein is translated into the er with the translocon open, translation ends. Er ss of protein moves sideways out of translocon: er ss is cleaved off by signal peptidase. Protein free in er lumen (for secreted or soluble proteins) integral membrane protein translation: type 1 single pass transmembrane proteins examples: ldl receptor, insulin receptor, growth hormone receptor.
