Explain how the translocation of a protein that stays in the lumen of the ER is
ID: 85261 • Letter: E
Question
Explain how the translocation of a protein that stays in the lumen of the ER is similar and different from that of a single-pass transmembrane protein that resides in the HR membrane. You may use a diagram to help explain your answer. Explain how growth and shrinkage of actin filaments differs from that of microtubules? Describe the various types of intermediate filaments found in eukaryotic cells, including their specific role in the different cell types in which they are found. Name one human disease that is due to loss of or defects in intermediate filaments. Explain the three processes that must take place for a cell to migrate Be sure to state the key proteins required for each step. Explain 1) the process by which collagen is synthesized and secreted, and 2) how loss of collagen can affect the human body.Explanation / Answer
2. Translocation of a protein: The first step in the biogenesis of various soluble organelle proteins in eukaryotic cells is protein translocation into the endoplasmic reticulum (ER). This process involves cleavable amino terminal signal peptides in precursor trasport mechanism in the cytosol, the ER membrane and the ER lumen.
Describing the similarity and differences with the protein transport ER lumen and the single transmembrane protein is to show the mechanical and functional similarity and differences between them.
Protein translocation into the ER and then folding and assembly of proteins involves few components and their specific mechanism, such as BiP and its co-chaperones and nucleotide exchange factors.
Folding and assembly completion of native proteins are delivered to their functional location by vesicular transport (except the resident ER proteins). If misfolding happens they are transported back to cytosol and delivered to the proteasome for degradation.
Now the similarity between the ER lumen proteins is that they also contains the same of the above-mentioned components.
Co or posttranslationally protein transport into the ER, for the cytosolic transport components, those are dedicated either to cotranslational (signal recognition particle) or posttranslational (heat shock proteins) transport.
Meanwhile, many protein synthesis from polypeptides is initiated on ribosomes that are continuously attached to the ER-membrane. Here the heat shock proteins and signal recognition particle are not required.
3. Growth and shrinkage of Actin filaments: The cytoskeleton of a cell is highly dynamic and these filaments constantly grow and shrink through subunit additions or deletions from it. For example, as seen in Macrophages which relies on directed growth of actin filaments at the cell front, the directed crawling mechanism is seen.
The microtubulin complex consists of /-tubulin dimers, they could be nucleated from various sites. The tubulins acts as a template for its growth and elongation. For growth GTP /-tubulin works. The cells containing centrosome helps growing this substance through the use of certain factors. In case of shrinkage of it, this happens when depolimerisation of KInesin 8 and Kinesin 13 takes place by catastrophes, GDP /-tubulin works here.
4. Nearly all eukaryotic cells possess the Intermediate filaments, but their presence in single cellular organism and fungi is controversial. In epidermal cells and the axons of neurons, here the presence of Intermediate filaments are almost 10 times of microfilaments or microtubules. They have a functional character as making structuresto reinforce cells and to organize cells into tissues. It gives strength to plasma membranes.
6 types of them are explicitly understood- all are from -helical proteins family:
Type I (Acidic Keratins) - found in Epithelia,
Type II ( Basic Keratins)- found in Epithelia,
Type III (Vimentin, Desmin) - found in Mesenchyme and Muscles,
Type IV (NF-L, NF-M, NF-H) - found in Mature neurons,
Type V (Lamin A, Lamin B) - found in Nucelus of all cells,
Type VI is similar to others,
A disease associated with this is Desminopathy, mutations in closely interacting proteins, desmin and alphaB-crystallin.
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