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Week 1 lec intracell
Intracellular Processes Lecture
| Question | Answer |
|---|---|
| How do proteins know where to go within the cell or how is protein trafficking acheived? | Acheived by two default pathways: The default cystolic pathway and the default secretory pathway |
| The Default secretory pathway? | Ribosome-->ER->Golgi where the pathway can go either to Plasma membrane or for secretion or to a lyzosome |
| The Default cystolic pathway? | Ribosome to either: Mitochondria, cytosol, nucleus or perioxisomes |
| Signal Peptide | A specific sequence of N-terminal amino acids |
| In the "Post Office Analogy" what is the letter? | New protein |
| In the "Post Office Analogy" what is the address label? | Signal Peptide |
| In the "Post Office Analogy" what is the postman? | Signal Recognition Particle |
| In the "Post Office Analogy" what is the name-plate on door? | SRP receptor in ER membrane |
| In the "Post Office Analogy" what is the letterbox? | Translocon (pore in er) |
| Default pathway: Translocation into lumen of ER | The growing peptide chain(protein) is threaded through the pore in the ER. Signal Peptidase( an ER enzyme) cleaves of the signal peptide. The finished protein ends up in the ER lumen. Next, transport vesicles containing protein bud from the ER. |
| What is the next stop for proteins once transport vesicles containing the proteins in their lumen bud from the ER? | The Golgi Apparatus. |
| Golgi Apparatus function? | Is the sorting organelle of the cell, also known as the post office of the cell |
| Describe the process of protein movement from ER to golgi. | Proteins are carried in vesicles which fuse to become the cis cisterna. According to the cis maturation model, the proteins move through teh golgi stack. As they do, they undergo enzymatic modification which labels them for specific cell destinations. |
| How does the protein move through the golgi? Cis maturation model? | Movement occurs in waves. First the cis cisterna becomes part of the medial cisternae, behind it a new cis cisterna is formed by the fusion of vesicles from the ER. Meanwhile one of the medial cisternae migrates and becomes the new trans cisternae. |
| Phosphorylation, acetlyation, farnesylation and ubiquitination are all types of? | Post-Translational modifications |
| Phosphorylation | A phosphate group is added which alters the activity of a protein |
| Acetylation | An acetly group is added. In histones, this regulates gene expression |
| Farnesylation | a farnesyl group is added whoch targets proteins to cytoplasmic face of plasma membrane. |
| Ubiquitination | A ubiquitin chain is added which targets proteins for degradation |
| What are proteins that have been glycosylated called? | Proteoglycans |
| What are proteins that have a small sugar component called? | Glycoproteins |
| Describe the pathway proteins, that are targeted to the lysosome take using hyrdrolase as an example. | Hydrolase is delivered from ER to the golgi apparatus via a vesicle. While it is being transferred through the ER and cis cisterna of the golgi apparatus, the modification of the core oligosaccharide begins. The term for this process is glycosylation. |
| Describe the pathway proteins that are targeted to the lysosome take using hydrolase as an example. | Defects in glycosylation can lead to specific diseases. Once the hydrolase reaches the trans golgi cisternae. The mannonse-6-phosphate signal has been completed. Only proteins destined for the endosome have the MP6 signal. Once modified the hydrolase |
| Describe the pathway proteins that are targeted to the lysosome take using hydrolase as an example. cont...(3) | is bound to the mannose-6-phosphate receptor protein through the M6P molecule. The receptor has a domain that extend through the trans golgi membrane. Through the interaction with this receptor the hydrolase is associated with the trans golgi membrane. |
| Describe the pathway proteins that are targeted to the lysosome take using hydrolase as an example. cont.. (4) | Next a vesicle containing the hydrolase buds off from the the trans golgi and moves to the endsome. Endosome eventually mature into lysosomes. Other proteins have different sugar side chains and they are delivered to other cellular locations |
| Describe the pathway proteins that are targeted to the lysosome take using hydrolase as an example. cont.. (5) | or to the cell membrane where it is embedded or secreted. The vesicle docks and fuses with the endosome. At this point, the hydrolyase is released. Soon after the "mannose" portion of the M6P signal is removed. Before it can go on to degrade other |
| Describe the pathway proteins that are targeted to the lysosome take using hydrolase as an example. cont.. (6) | molecules the hydrolase will undergo a final modification to become and active enzyme. The MP6 receptors are then recycled back to the golgi. The sugar side chain signals are then recycled back to the golgi. The sugar side chain added by glycosylation |
| Describe the pathway proteins that are targeted to the lysosome take using hydrolase as an example. cont.. (7) | in the golgi apparatus is a key element in the signal of the process, that directs proteins to their proper cellular locations |
| What is the mechanism for proteins in the default cystolic pathway targeted to the cytosol? | Default- newly synthesized protein lacks signal peptide |
| What is the mechanism for proteins in the default cystolic pathway targeted to the nucleus? | comparable to ER for secretory proteins. Nuclear localisation signal (NLS) in protein sequence. Importin is analogous to SRP. Importin receptor +nucleur pore = SRP receptor + ER pore. |
| What is the mechanism for proteins in the default cystolic pathway targeted to the mitochondria? | 99% mitochondrial proteins encoded by nuclear DNA. Mitochondrial importin sequence in N-terminus of protein. Kept unfolded by binding to ATP-dependant chaperone proteins. Imported via translocases(TOM+TIM) |
| What is the mechanism for proteins in the default cystolic pathway targeted to the perioxisomes? | address label is a C-terminal tripeptide |
| what happens to proteins that are past their sell-by date? | 2 mechanisms exist: Lysosomal degradation + proteosomal degradation |
| Proteosomal degradation | Short half life, key metabolic enzymes, defective proteins |
| Lysosomal degradation | Long half life, membrane proteins, extracellular proteins. |
| By what process is protein degradation carried out? | Autophagy |
| Describe the process of autophagy? | Envelopment, sealing, merging with lysosome, resulting residual body |
| By what process are membrane proteins brought into the cell? | Endocytosis |
| By what process are extracellular protiens brougt into the cell via? | Receptor mediated endocytosis |
| By what process are proteins brought into the cell via? | phagocytosis |
Created by:
Taryn Miller
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