ER and Secretory Vesicles Flashcards
Describe the pathways of vesicular transport of proteins(4)
- From the Golgi apparatus to lysosomes, the plasma membrane or the exterior.
- Destination is determined in the ER when the protein/cargo bind to a specific receptor.
- Various characteristics of the cargo protein are recognised e.g. aa sequence or added CHO.3.
- From the plasma membrane to lysosomes.
- From endosomes to the plasma membrane
Describe the quality control checks in place to determine whether proteins can enter the vesicles(4)
- proteolysis,
- glycosylation,
- disulfide bond formation,
- folding or assembly into complex.
Describe the structure of Golgi Apparatus(3)
“1. Single-membrane compartment
- 4 to 8 stacked layers of thin, flat, enclosed vesicles (cisternae) lying near one side of the nucleus
- Three networks: cis (first cisternae structure, closer to nucleus), medial and trans compartments (final structure, closer to cell membrane).”
Describe the structure of the ER(4)
1.Single-membrane compartment -continuous network of tubular and flat vesicular structures in the cytoplasm
- Space inside relates to the space between the two membrane surfaces of the nuclear membrane- continuous with the nuclear envelope
- Two parts with different functions: granular/rough ER and agranular/ smooth ER
- Takes up about 10% of the cell
Describe the synthesis of secretory proteins and what is different about proteins that are secreted?(4)
- Are synthesized by ribosomes of the RER,
- segregated within the cisternal space of the RER,
- transferred to the Golgi apparatus
- differ from other proteins because the first part of the protein that emerges at the 5’ terminus has a signal sequence which is rich in hydrophobic amino acids
Explain the process of protein targeting(5)
→translation begins at a ribosome that is free in the nucleus
→when the signal sequence emerges from the ribosome, the SRP interacts with it and guides it to an SRP receptor in the membrane of the ER. Translation stops transiently
→the SRP helps dock the ribosome onto a translocon so the ribosome becomes part of the ER.
The signal sequence is cleaved off by signal peptidase
→once the ribosome is attached translation continues and the mature PP chain passes into the ER because the signal protein opens the lumen while the signal sequence remains bound to the channel.
How are different types of RNA transported?(2)
·tRNA and microRNAs bind directly to export receptors.
. Large RNAs such as ribosomal RNAs and mRNA recruit specific adaptor proteins.”
How is bud formation facillitated?
Bud formation is facilitated by binding of different Coat proteins (e.g. COPs).
Recall the functions of the Golgi (4)
- Protein modification: Glycosidases, glycosyltransferases O-linked glycosylation, Sulfatases, Proteases
- Lipid Synthesis: Sphingomyelin, Glucosylceramide
- Protein and lipid sorting to: Secretory granules, Plasma membrane, Basolateral versus apical membrane, Endosomes, Lysosomes
- Vesicles fuse to the Golgi and deposit their cargo inside the complex.”
Recall the three stages of the budding vesicles
BuddingMovementFusion
What are ERADs?
ERAD(endoplasmic reticulum associated protein degradation) is responsible for destruction.
What are the major functions of the ER?(6)
Majority of proteins in the structure are there transiently and are meant to be transported to other locations in the cell.
. Some proteins are manufactured and stay in the ER these are called resident proteins- those that are misfolded
·Protein synthesis, glycosylation, folding and assembly and multi-protein complexes. -RER
·Lipid synthesis (cholesterol, phospholipids). -SER
. Ca2+ sequestration. -SER- orchestrates the accumulation of Ca2+ in contraction of muscle cells.
. Detoxification by cytochrome P450 enzymes- SER. transform the inactive form of the drug into the active form by these enzymes.
What happens if proteins fail the quality control checks and give example of a disease?
Then the protein cannot be exported and instead is degraded,
e.g cystic fibrosis has a protein that cannot fold properly and is degraded so it never reaches the golgi (chloride transporter proteins).
What happens when transport vesicles are formed and released?(3)
- Coat proteins are removed revealing v-SNARE (integral protein).
- v-SNARE binds to t-SNARE (target) in the target membrane,
- the transport vesicle fuses to the target membrane and the cargo delivered.
What is the difference between free ribosomes and bound ribosomes?(2)
Free ribosomes - are in the cytosol. They translate soluble proteins for release into the cytoplasm.
·Bound ribosomes - attached to the ER and translate proteins which are secreted from the cell or incorporated into membranes or lysosomes.
