Chapter 15 – Intracellular compartments and protein transport
Membrane-enclosed organelles
In eukaryotes proteins have to go to organelles to do things.
In prokaryotes there are no organelles so the proteins are secreted
The major membrane-enclosed organelles
Cytosol; contain many metabolic pathways, protein synthesis, cytoskeleton
Nucleus; contain main genome, DNA and RNA synthesis
ER; synthesis of most lipids, synthesis of proteins for distribution to many
organelles and to the plasma membrane. And modification of proteins
o Rough; ribosomes on it. Synthesizing proteins
o Smooth; steroid hormone synthesis in some endocrine cells of adrenal
gland and organic molecules (like alcohol) are detoxified (ontgiftigd) in
liver cells
Golgi apparatus; modification, sorting and packaging of proteins and lipids for
secretion or delivery to another organelle
o Membrane-enclosed sacs; cisternae.
Lysosomes; intracellular degradation
Endosomes; sorting of endocytosed material and some recycles back to the
plasma membrane. First go to this before to lysosome.
Mitochondria; ATP synthesis by oxidative phosphorylation
Chloroplast; ATP synthesis and carbon fixation by photosynthesis
Peroxisomes; oxidation of toxic molecules, break down things. Synthesis
phospholipids, including those that are abundant in the myelin sheath.
Nuclear envelope communicates with cytosol via nuclear pores.
Endomembrane system; the interiors of these organelles; ER, golgi apparatus,
peroxisomes, endosomes and lysosomes communicate extensively with each other
and with the outside of the cell with small vesicles that bud off from one of the
organelles and fuse with another
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)
Protein sorting
Proteins are transported into organelles by
Transport through nuclear pores (gated transport); large pores.
proteins have NOT to be unfolded. Actively transport and
free diffusion of smaller molecules.
Between cytosol and nucleus.
Transport across membranes (transmembrane transport)
(protein translocator); narrow channels. proteins have to be
unfolded
Between cytosol and ER/mitochondria/chloroplast/peroxisomes
Transport by vesicles (vesicular transport); vesicles.
Between ER and Golgi between endosome/lysosome/plasma membrane
, Signal sequence
Proteins have an amino acid sequence that contain a sorting signal/targeting signal
(signal sequence) that directs the protein to the organelle in which it is required.
When they lack it they remain permanent in the cytosol.
Receptor of the organelles recognize these signal sequence and bring the protein to
a specific organelle.
Proteins enter the nucleus
Nuclear envelop
Inner nuclear membrane contains proteins that
o Acts as binding for the chromones
o Provide anchorage (verankering) for the nuclear lamina, a meshwork of
protein filaments
Outer nuclear membrane; closely resembles the membrane of ER
Transport via nuclear pores, they have not to be unfolded.
Many of the proteins that line the nuclear pore are largely disordered.
Nuclear export;
These disordered segments from soft, tangled meshwork that fills the center of the
channel preventing the passage of large molecules, but allow small molecules
Nuclear import;
Large molecules must display a sorting signal. This signal sequence
directs a protein from the cytosol into the nucleus; nuclear localization
signal
Nuclear protein is bound to nuclear localization signal, this signal is
recognized by nuclear import receptors. These receptors help direct
protein to nuclear pore by interacting with fibrils.
Energy is needed for this transport, so active transport
Proteins unfold to enter mitochondria and chloroplast
Mitochondria and chloroplast both synthesis ATP.
They have inner and outer membrane, chloroplast has
third membrane; thylakoid membrane.
Both make their own protein, but most are encoded in
nucleus and are imported from the cytosol.
These proteins have signal sequence at N-terminus.
Transport via transmembrane transport, proteins need to be unfolded
Protein chaperone; is inside the organelle. Help to pull proteins across the membrane
and fold it once is inside.
The growth and maintain of mitochondria an chloroplast require not only import of
proteins but also new lipids. They are imported form the ER, main site of lipid
Membrane-enclosed organelles
In eukaryotes proteins have to go to organelles to do things.
In prokaryotes there are no organelles so the proteins are secreted
The major membrane-enclosed organelles
Cytosol; contain many metabolic pathways, protein synthesis, cytoskeleton
Nucleus; contain main genome, DNA and RNA synthesis
ER; synthesis of most lipids, synthesis of proteins for distribution to many
organelles and to the plasma membrane. And modification of proteins
o Rough; ribosomes on it. Synthesizing proteins
o Smooth; steroid hormone synthesis in some endocrine cells of adrenal
gland and organic molecules (like alcohol) are detoxified (ontgiftigd) in
liver cells
Golgi apparatus; modification, sorting and packaging of proteins and lipids for
secretion or delivery to another organelle
o Membrane-enclosed sacs; cisternae.
Lysosomes; intracellular degradation
Endosomes; sorting of endocytosed material and some recycles back to the
plasma membrane. First go to this before to lysosome.
Mitochondria; ATP synthesis by oxidative phosphorylation
Chloroplast; ATP synthesis and carbon fixation by photosynthesis
Peroxisomes; oxidation of toxic molecules, break down things. Synthesis
phospholipids, including those that are abundant in the myelin sheath.
Nuclear envelope communicates with cytosol via nuclear pores.
Endomembrane system; the interiors of these organelles; ER, golgi apparatus,
peroxisomes, endosomes and lysosomes communicate extensively with each other
and with the outside of the cell with small vesicles that bud off from one of the
organelles and fuse with another
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)
Protein sorting
Proteins are transported into organelles by
Transport through nuclear pores (gated transport); large pores.
proteins have NOT to be unfolded. Actively transport and
free diffusion of smaller molecules.
Between cytosol and nucleus.
Transport across membranes (transmembrane transport)
(protein translocator); narrow channels. proteins have to be
unfolded
Between cytosol and ER/mitochondria/chloroplast/peroxisomes
Transport by vesicles (vesicular transport); vesicles.
Between ER and Golgi between endosome/lysosome/plasma membrane
, Signal sequence
Proteins have an amino acid sequence that contain a sorting signal/targeting signal
(signal sequence) that directs the protein to the organelle in which it is required.
When they lack it they remain permanent in the cytosol.
Receptor of the organelles recognize these signal sequence and bring the protein to
a specific organelle.
Proteins enter the nucleus
Nuclear envelop
Inner nuclear membrane contains proteins that
o Acts as binding for the chromones
o Provide anchorage (verankering) for the nuclear lamina, a meshwork of
protein filaments
Outer nuclear membrane; closely resembles the membrane of ER
Transport via nuclear pores, they have not to be unfolded.
Many of the proteins that line the nuclear pore are largely disordered.
Nuclear export;
These disordered segments from soft, tangled meshwork that fills the center of the
channel preventing the passage of large molecules, but allow small molecules
Nuclear import;
Large molecules must display a sorting signal. This signal sequence
directs a protein from the cytosol into the nucleus; nuclear localization
signal
Nuclear protein is bound to nuclear localization signal, this signal is
recognized by nuclear import receptors. These receptors help direct
protein to nuclear pore by interacting with fibrils.
Energy is needed for this transport, so active transport
Proteins unfold to enter mitochondria and chloroplast
Mitochondria and chloroplast both synthesis ATP.
They have inner and outer membrane, chloroplast has
third membrane; thylakoid membrane.
Both make their own protein, but most are encoded in
nucleus and are imported from the cytosol.
These proteins have signal sequence at N-terminus.
Transport via transmembrane transport, proteins need to be unfolded
Protein chaperone; is inside the organelle. Help to pull proteins across the membrane
and fold it once is inside.
The growth and maintain of mitochondria an chloroplast require not only import of
proteins but also new lipids. They are imported form the ER, main site of lipid
