PROs in the ER (12) Flashcards
location of ribosomes
free in cytoplasm
attached to the ER
what are the 3 movements of PROs?
remain in the cytoplasm
move to cellular compartments via the cytoplasm
enter the endomembrane sys
what type of PROs remain in the cytoplasm?
enzymes involved in glycolysis
integral PRO
integrated in the membrane, on both sides of the membrane
steps of transport of PROs through the endomembrane sys
- Enter the ER (stay here or move with vesicles)
PROs reside in the lumen (space b/w ER) or are embedded in the membrane - Move via transport vesicles (budding & fusing “carriers” b/w other compartments)
- To Golgi (may be processed & then go off to diff directions)
- Trans-Golgi network, then to:
Lysosomes, or
Storage vesicles, or
Secretory vesicles & PM
what are the possible locations of PROs after passing through the Golgi?
lysosomes
storage vesicles
secretory vesicles & PM
structure of the ER
Network of membranous tubules in the cytoplasm of a cell; involved in the production of phospholipids
Encapsulates a space where PROs reside
RER
studded with ribosomes, continuous with nuclear envelope
Roughness enables the adherence of ribosomes
SER
no ribosomes; site of synthesis of specialized enzymes, functions
which ER is concentrated in specialized cells?
SER
Which ER is found in most cells?
RER
which ER is found in skeletal muscles?
SER
which ER is found in kidney tubules?
SER
which ER is found in endocrine glands?
SER
which ER is involved in the synthesis of the gonad & adrenal cortex?
SER
which ER is involved in the synthesis of the detoxification enzymes in the liver?
SER
which ER is found in glucose release from the liver?
SER
which ER is found in cells that release Ca2+ ions used in muscle contractions?
SER
which ER is found in cells of lipid biosynthesis?
SER
which ER is found in secretory vesicles?
RER & SER
which ER is found in lysosomes?
RER
which ER is involved in synthesis of integral PROs?
RER
which ER is involved in membrane biosynthesis?
RER
which ER is responsible for glycosylation of PROs?
RER
Every cell has plenty of _____ not every cell has an abundance of ______
RER
SER
PRO Folding
PROs have a correct or “native” state; the tertiary structure of a PRO needs to be correct for it to work properly
Can be misfolded or denatured
Molecular chaperones
PROs that bind to & alter the folding of newly forming PRO
Quality Control
PROs that misfold cannot bind to chaperones properly & are destroyed
what PRO is involved in assisting the bonding of disulfide bonds? & its location?
Disulfide isomerase
in the lumen of the ER
What are the chemical modifications of PROs in the ER & Golgi?
disulfide bond formation & folding
addition of chemical grps
addition of lipids
formation of multimeric PROs
proteolytic cleavage
glycosylation
What do glycoPROs include? & what is their role?
PROs destined for secretion
the extracellular matrix
endomembrane system
PM
enable identification
what level of PRO structure is effected with the addition of extra chemical groups in the ER & Golgi?
tertiary
what level of PRO structure is effected with the formation of multimeric PROs in the ER & Golgi?
quaternary
RER is the site of synthesis of PROs destined for:
secretion
integral PROs & PROs within the lumen of the endomembrane sys
ER, Golgi, lysosomes, vesicles & plant vacuoles
PROs that are made in the cytoplasm, not the RER:
Cytosolic PROs
Peripheral PROS of the inner cell membrane
PROs interacting with cell membrane, adhere to the inner lining of cell help giving the cell its cell structure
PROs sent to the nucleus
PROs destined for chloroplasts, mitochondria & peroxisomes
what occurs after the signal sequence is synthesized?
PRO synthesis temporarily stop until the signal sequence is detected by a PRO complex on the RER
How does a PRO enter the RER?
Translation occurs on the cytoplasmic ribosome/mRNA complex
During translation, a signal sequence is synthesized & will poke outside of the ribosome
The signal sequence is recognized by SRP which binds to the ribosome & signal sequence –> causes translation to stop until the ribosome is brought to the ER membrane
SRP guides the complex to the membrane to reach the RER receptor
Translocon binds to the ribosome causing a shift
Signal peptide is released for SRP & binds to the interior of the translocon
(Peptide release from SRP causes GTP –> GDP)
Translation resumes
Translated PRO is threaded through the RER lumen
Signal sequence removed by signal peptidase enzyme & the signal sequence is recycled
Signal sequence
Directs PROs to the RER
is a sequence of hydrophobic AA usually at the N terminal
when does translation resume when a PRO is entering the RER?
Signal peptide released from SRP along with GTP hydrolysis
Polyribosomes
multi ribosomes on one mRNA –> increases the rate of translation
what do PROs embedded in the RER lipid bilayer have that PROs destined for the lumen don’t have?
single transmembrane domain
single transmembrane domain
a stretch of hydrophobic AAs that are embedded in the lipid bilayer
how do PROs become embedded in the RER lipid bilayer?
with a single transmembrane domain
&
the translocon can open up to allow lateral movement, allows hydrophobic sequences to move into a hydrophobic envr
What side of the membrane does an integral membrane’s positive AAs point? & how?
cytosolic side
positively charged AAs are aligned with negatively charged translocon
What determines orientation of an integral PRO?
timing of which end of the PRO enters the translocon first
how the transmembrane sequences are orientated within the translocon
start transfer & stop transfer sequences
alternating hydrophobic regions on a double pass transmembrane PRO
hydrophobicity plot
scores each AA on how hydrophobic it is
predicts the number of transmembrane domains a multipass transmembrane PRO can have
multipass transmembrane PRO
membrane PROs that pass through the membrane multiple times
contain multiple start & stop signals
how are integral PROs classified?
number of transmembrane domains they have
what are the roles of transmembrane PROs?
communication b/w cells (direct contact or with integral PROs)
communication b/w organelles & cytoplasm
ion transport
nutrient transport
connections for cytoskeleton
25% of cells PRO
