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An animal pancreatic cell that exports digestive enzymes would have a lot of_____
ER and Golgi
An animal testis cell that exports lipid-soluble signals (testosterone), would be packed with ________.
smooth ER
Plant leaf cell that manufactures ATP and sugar would be packed with _______.
chloroplasts
Plant root cell that stores starch would be packed with _______.
vacuoles
Nuclear envelope
surrounds the nucleus
double membrane
studded with pore-like openings
continuous with the ER
Nuclear lamina
intermediate filament network on the inside of the nucleus
linked to the nuclear envelope
Nucleolus
rRNA synthesis
Assembly of ribosome subunits
distinct region in the nucleus
Nuclear pores
regulate traffic in and out of the nucleus
highly selective
Outbound nuclear traffic
ex) RNAs exit nucleus into cytoplasm
Inbound traffic into the nucleus
Nucleoside triphosphates
Proteins responsible for copying DNA & synthesizing RNA
Proteins needed for assembling ribosomes
Free Ribosomes
ribosomes located in the cytosol
synthesize proteins mostly for use within the cell
Bound Ribosomes
ribosomes bound to organelles
synthesize proteins for export (secretion) from the cell or for use in lysosomes
Protein sorting
the process by which proteins end up where they need to be to perform their function
Signal sequences
directs a protein’s localization
Do all proteins have signal sequences
NO
Where will a protein with no signal sequence end up?
cytosol
Where will a protein with an animo-terminal signal go?
chloroplast, mitochondria
Where will a protein with an internal signal go?
nucleus
nuclear localization sequence
allows the proteins destined for the nucleus to enter the nucleus
Proteins made on the RER enter the endomembrane system and go to these destinations:
INSIDE an endomembrane organelle
secreted from the cell
as a transmembrane protein
Endomembrane system: Structure
a set of interconnected membranes within a cell
connected physically and by vesicles
Endomembrane system: Function
Produce, modify, package, and deliver proteins to the correct locations
What membranes compose the endomembrane system:
nucleus, ER, Golgi, Lysosome, Peroxisome, and plasma membrane
The Signal Hypothesis
proteins bound for the endomembrane system have a “zip code” that directs the growing polypeptide to enter the ER
“zip code” on proteins
20-amino acid long signal sequence
Signal Hypothesis steps
Signal sequence is synthesized by ribosome
Signal sequence binds to signal recognition particle (SRP)
Signal recognition particle binds to SRP receptor in ER membrane
Protein synthesis continues. Protein enters ER. SRP is released.
Protein synthesis is complete. Signal sequence is removed.
How to proteins enter the endomembrane system?
The signal hypothesis
What happens when the protein reaches the Golgi?
They are sorted into vesicles and delivered
What does each protein that comes out of the Golgi contain?
A molecular tag that places it in a particular type of transport vesicle. The transport vesicle also has a tag that allows it to be transported to the correct destination
What side of the Golgi do proteins enter?
cis face
What side of the Golgi do proteins exit/ bud off?
trans face
How are proteins intended for secretion from the cell made and processed?
Protein enters ER while being synthesized by a ribosome
Protein exits ER, travels to the cis face of Golgi apparatus
Protein enters Golgi and is processed as the cisternum moves toward the trans face
Protein exits Golgi at trans face in a transport vesicle and moves to plasma membrane
Protein is secreted from cell
What types of tags do proteins bound for lysosomes or RER have?
carbohydrate tags
How are proteins targeted to the membrane
Transmembrane protein targeting
Transmembrane Protein targeting
Polypeptide containing a signal-anchor sequence are inserted into the RER membrane
When a signal-anchor sequence is encountered, the RER channel releases the protein into the membrane
The signal anchor sequence is hydrophobic and diffuses laterally in the lipid bilayer
The ribosome disassociates from the channel and translation continues
When translation is complete, the carboxyl end of the protein is in the cytosolic side of the RER and the amino end is in the lumen of the RER
These transmembrane proteins can stay in the membrane of the ER or end up in the plasma membrane. They can serve as channels, pumps, receptors, or enzymes
Note
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