chap15
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Eukaryotic cells contain many membrane-enclosed _, including a nucleus, an endoplasmic reticulum (ER), a Golgi apparatus, lysosomes, endosomes, mitochondria, chloroplasts (in plant cells), and _. The ER, Golgi apparatus, peroxisomes, endosomes, and lysosomes are all part of the _
organelles peroxisomes endomembrane system.
Most organelle proteins are made in the _ and transported into the _ where they function. _ in the amino acid sequence guide the proteins to the correct _; proteins that function in the cytosol have _ and _
cytosol organelle Sorting signals organelle no such signals remain where they are made.
Nuclear proteins contain _ that help direct their active transport from the cytosol into the nucleus through _, which penetrate the _ of the nuclear envelope. The proteins are transported in _ conformation.
nuclear localization signals nuclear pores double membrane their fully folded
Most mitochondrial and chloroplast proteins are made in the _ and are then transported into the _ by _ in their membranes. The proteins are _ during the transport process.
cytosol organelles protein translocators unfolded
The ER makes most of the cell’s _ and many of its _. The proteins are made by _ that are directed to the _ by a _ in the cytosol that recognizes an _ on the growing polypeptide chain (protein being synthesized at the same time). The _ complex binds to a _ on the _ membrane, which passes the ribosome to a _ that _ the growing polypeptide across the _
lipids proteins ribosomes ER signal-recognition particle (SRP) ER signal sequence ribosome– SRP receptor ER protein translocator threads ER membrane.
Water-soluble proteins destined for _ or for the _ of the endomembrane system pass _ into the _, while transmembrane proteins destined for either the _ of these organelles or for the _ remain _ in _ by one or more _
secretion lumen of an organelle completely ER lumen membrane plasma membrane anchored the lipid bilayer membrane-spanning α helices.
In the ER lumen, proteins fold up, _ with their protein partners, form _ bonds, and become decorated with _ chains.
assemble disulfide oligosaccharide
The disulfide bonds help to _ of proteins that will encounter _ enzymes and changes in _ outside the cell
stabilize the structure degradative pH
The oligosaccharides on proteins can serve various functions. They can protect a protein from _, hold it in the _ until it is _, or help _ it to the _ by serving as a _ signal for _ the protein into appropriate transport vesicles.
degradation ER properly folded guide appropriate organelle transport packaging
_ is an important quality-control step; proteins that either fail to fold properly or fail to _ are _ by _ proteins, which _; proteins that still fail to fold or assemble are _.
Exit from the ER assemble with their normal partners retained in the ER chaperone prevent their aggregation and help them fold _ transported to the cytosol, where they are degraded _
Excessive accumulation of misfolded proteins triggers an _ that _ the ER, increases its _, and _ protein synthesis.
unfolded protein response (UPR) expands capacity to fold new proteins properly reduces
Protein transport from the ER to the _ and from the _ to other destinations is mediated by _ that _ off from one membrane and _ with another, a process called _
Golgi apparatus Golgi apparatus transport vesicles continually bud fuse vesicular transport.
Budding transport vesicles have distinctive _ proteins on their _ surface; the assembly of the _ helps drive both the _ process and the _, with _, into the forming vesicle.
coat cytosolic coat budding incorporation of cargo receptors their bound cargo molecules
Coated vesicles rapidly lose their _, enabling them to _ and then _ with a particular target _; _ are mediated by _ and target membrane, including _, _, and _ proteins.
protein coat dock fuse membrane docking and fusion proteins on the surface of the vesicle Rab tethering SNARE
The _ receives _ proteins from the ER; it modifies their _, _ the proteins, and _ them from the _ network to the plasma membrane, lysosomes (via endosomes), or secretory vesicles.
Golgi apparatus newly made oligosaccharides sorts dispatches trans-Golgi
In all eukaryotic cells, transport vesicles continually bud from the _ and fuse with the _; this process of constitutive _ delivers proteins to the cell surface for secretion and _ lipids and proteins _.
trans-Golgi network plasma membrane exocytosis incorporates into the plasma membrane
Specialized secretory cells also have a _ pathway, in which molecules _ in secretory vesicles are released from the cell by _ when _.
regulated exocytosis concentrated and stored exocytosis the cell is signaled to secrete
Cells ingest fluid, molecules, and sometimes even particles by _, in which regions of plasma membrane _ and _ to form endocytic vesicles.
endocytosis invaginate (clathrin-coated) pinch off (Dynamin)
Much of the material that is endocytosed is delivered to _, which mature into _, in which the material is _ by _; most of the components of the endocytic vesicle membrane, however, are _ back to the plasma membrane for reuse.
endosomes lysosomes degraded hydrolytic enzymes recycled in transport vesicles
Membrane-enclosed organelles import proteins by one of three mechanisms.
TRANSPORT THROUGH NUCLEAR PORES TRANSPORT ACROSS MEMBRANES TRANSPORT BY VESICLES
_ direct proteins to the correct destination.
Signal sequences
Proteins destined for the ER possess an _ that directs them to that organelle, whereas those destined to remain in the cytosol _
N-terminal signal sequence lack any such signal sequence.
The nuclear pore complex forms a gate through which _ macromolecules and larger complexes enter or exit the nucleus.
selected
Protein _ protrude from both sides of the pore complex; on the nuclear side, they _ to form a _ structure. The spacing between the fibrils is _ that the fibrils _ obstruct access to the pores.
fibrils converge basketlike wide enough do not