Summary Cell biology -- Chapter 1 part 2

Cell Biology
Intracellular Transport
In eukaryotes proteins have to go to organelles to do things.
In prokaryotes there are no organelles so the proteins are secreted

Cell organelles
In nucleus; RNA/DNA synthesis
In cytoplasm;
 Cytosol (hierin drijft alles); protein syntheses
 Organelles
o Have lumen and membrane
o Specific lipid and protein in lumen and membrane
o Specific position in cell

Organelles involve in evolution
1. DNA was surrounded by membrane, so the nucleus arrived.
2. Ribosomes stacked around that membrane
3. Mitochondria was arrived by endosymbiosis (uptake of bacteria)

Transport mechanisms Tr
 Transport through nuclear pores; large pores. Between cytosol and nucleus
 Transport across membranes; narrow channels. Between cytosol and
ER/mitochondria/chloroplast/perox
 Transport by vesicles; vesicles. Between ER and Golgi between
endosome/lysosome/plasma membrane

Signal sequence
Receptor of organelle recognize the protein to bring it to a specific organelle. Each
organelle has its own signal sequence, consist of amino acids  targeting or sorting
signals
These signals are necessary and sufficient for sorting.

The signals switch, for example the protein has a signal to be in the ER when you
remove this it goes to the cytosol. The protein in the cytosol then go to the ER.

Transport trough nuclear pore
Outside consist of nuclear envelop
 Inner nuclear membrane
 Outer nuclear membrane

Inside consist of nuclear lamina

In the nuclear pores the transport take place.
Function;
 Nuclear export; RNA, ribosomal subunits
 Nuclear import; nuclear proteins with NLS (nuclear
localization signal) signal

, o Nuclear protein is bound to nuclear localization signal. To this nuclear
transport receptor is bound so that is can go through the membrane of
the nucleus
Energy is needed for this transport, so active transport.
The transported proteins are folded.

Transport across membranes
o Transport into mitochondria
o ATP synthesis
o Derived from bacteria, therefore still contain DNA/ribosomes 
endosymbiosis
o Part of proteins are synthesized in this organelle, most are imported
from cytosol
o Consist of different sub compartments
 Outer membrane
 Inner membrane
 Lumen; matrix space
 Intermembrane space
o Import in mitochondria
 Syntheses in cytosol with mitochondria signal sequence
 Binding to cytosolic chaperones/targeting factors
 Protein is completely unfolded to go through the narrow channels
o Transport to chloroplasts (plastids)
o Consist of different sub compartments
 Lumen; called stroma
 Outer membrane
 Inner membrane
 Intermembrane space
 Thylakoid; where photosynthesis take place, it need extra signal
sequence.
 Thylakoid space
 Thylakoid membrane
o Transport to peroxisomes
o Oxidation of fatty acids
o Single membrane
o No DNA/ribosomes, not derived from bacteria  endosymbiosis
o Import peroxisomes
 Synthesis with peroxisomal targeting sequence
 Binding to receptor in cytosol
 Binding to receptor in membrane
 Translocation through the membrane channel
 Cytosolic receptor returns to cytosol
 Transport in folded form, despite of the narrow channel. Nobody
know how this could be.
o Transport to ER
o Continuous network
o Two types
 SER (smooth); specialized functions (e.g. production of steroid
hormones, storage of Ca)