Protein transport in ER Flashcards
Function of Endoplasmic Reticulum
lipid and protein synthesis
makes a major contribution to mitochondrial and peroxisomal membranes by producing most of their lipids
ER membrane
an amino-terminal protein sequence that targets newly synthesized polypeptides to the endoplasmic reticulum (ER) for co-translational transfer and insertion into the ER membrane, or for translocation into the ER lumen.
ER signal sequence
binds to the ER signal sequence, pausing translation and directing the ribosome to the rough ER
signal recognition particle (SRP)
Function of RER
- Surface for ribosomes
- Formation of glycoprotein
*Linking of sugars to protein to
make glycoprotein - Synthesis of precursors
*Produce enzyme precursors for
the formation of lysosomes
a chain-like structure composed of multiple sugar molecules (monosaccharides) linked together, forming carbohydrates or saccharides, and playing various roles in biological systems
glycan
Temporary sugar added for quality control during glycoprotein folding.
Glucose
A core sugar component
Mannose
The base sugar directly linked to Asn
N-acetylglucosamine
A lipid carrier embedded in the ER membrane that holds a pre-assembled oligosaccharide
Dolichol
Enzyme that transfers the glycan onto the asparagine residue of a growing polypeptide
Oligosaccharide transferase
Newly synthesized protein moving into the ER lumen through a translocation channel.
Translocating protein
The glycosylation site where the oligosaccharide is attached
Asparagine (Asn)
________ release ________ when the allergen is encountered
Mast cells; histamines
glands that secrete substances, like sweat, tears, saliva, and digestive juices, onto an epithelial surface or into a duct that leads to the body’s surface or a cavity
Exocrine gland
which organelle can we find vast amounts of protein
Rough ER
- exocrine cells of the pancreas
- antibody-secreting plasma cells
- insulin-secreting β cells
Exocrine cells of the pancreas (____% rough ER)
- secrete digestive enzyme
60%
Type of smooth ER:
- transport vesicles carrying newly synthesized proteins and lipids bud off for transport to the Golgi apparatus
Transitional ER
Organelles that synthesize steroid hormones
Smooth ER
- site of lipoprotein particles production
- functions in detoxification
Hepatocytes
Carry lipids via the bloodstream to other parts of the body
lipoprotein particles
Small ducts that collect bile from hepatocytes
canaliculi
The main functional cells of the liver
Hepatocytes
Specialized macrophages located in the liver sinusoids.
Engulf pathogens, dead cells, and debris, playing a role in immune defense
Kupffer cells
Form the walls of liver sinusoids, allowing the exchange of nutrients and waste between the blood and hepatocytes.
Liver sinusoidal endothelial cells
Most extensively studied of the detoxification reactions
converts water-insoluble drugs or metabolites into water-soluble for excretion
Cytochrome 450
Endoplasmic reticulum vs. Sarcoplasmic reticulum
Which is an excitable cell
Sarcoplasmic reticulum
is a specialized smooth ER found in muscle cells, primarily involved in calcium storage and release for muscle contraction
Sarcoplasmic reticulum
releases Ca²⁺ rapidly upon stimulation
RyR (ryanodine receptor)
actively pumps Ca²⁺ back into the SR to relax the muscle
SERCA pump
The SR has junctional and longitudinal regions:
Junctional SR is near T-tubules and facilitates rapid Ca²⁺ release.
Longitudinal SR helps in Ca²⁺ reuptake.
Synthesizes phospholipids (gonads and skin oil glands), steroid, and CHO
Smooth ER
During transport in ER, a _______________ binds to ER signal
Also state the processes undergone during transport in ER
Signal-Recognition Particle (SRP)
- mRNA is being translated to the polypeptide tide chain with the signal sequence attached.
- SRP binds to the signal sequence.
- SRP binds to the SRP receptor (α - top part) located beside the closed translocon (sec61 complex).
- GTP from SRP and GTP from SRP receptor is released forming GDP + Pi, releasing the SRP, and opening the translocon (sec61 complex).
- Signal peptidase cleaves the signal sequence from the growing polypeptide chain.
- Polypeptide continue to be translated into the ER lumen.
- mRNA is released when ribosomal subunits detach, the translocon (sec61 complex) is closed, and protein is folded inside the ER lumen.
consists of 3 or 4 protein complexes, each composed of 3 transmembrane proteins, that assemble into a donut-like structure.
facilitates the translocation of proteins into the ER lumen or insertion into the ER membrane, acting as a crucial player in protein biogenesis.
Sec61 complex
Import of proteins begins before the polypeptide chain is completely synthesized
Co-translational translocation
Two modes of transport and which domain performs them (Bacteria, Archaea, Eukaryotes)
Co-translational translocation
- Bacteria
- Archaea
- Eukaryotes
Post-translational translocation
- Bacteria
- Eukaryotes
