Anatomy of the Cell
List 5 different membrane-enclosed organelles in a eukaryotic cell.
- Cytosol
- Nucleus
- ER (smooth and rough)
- Golgi apparatus
- Lysosomes, endosomes, peroxisomes
- Mitochondria, chloroplasts
Nucleus, ER, golgi, endosomes/lysosomes
What sequence is necessary for targeting a protein specifically to the ER and what are its characteristics?
Signal sequence with 15-25AAs that is close to the N-terminus of the protein. 10-15 of those AA are hydrophobic
Define signal transduction and give an example.
Process that converts one type of signal into another.
(ex. electrical to chemical and extracellular to intracellular signal)
What type of signaling pathway utilizes phosphorylation of a dimer transmembrane protein?
Enzyme-linked receptors (receptor tyrosine kinase (RTK))
If the ER was damaged and some of the membrane was lost, what organelle would produce materials to repair it?
Smooth ER
What part of a protein's sequence determines where it will go after it is synthesized?
Sorting siganl
For double the points, what sorting mechanism is used when a large protein that increases transcription reach its final destination, and what type of sequence allows this to happen?
If a protein is fully synthesized outside of the ER and has the correct signaling sequence, can it be inserted into the ER lumen?
No!
During translation, the SRP (signal-recognizing protein) binds to the ribosome and stops transcription. The SRP then binds additionally to its receptor in the ER membrane, and the the ribosome binds to the translocon. Translation resumes after the SRP dissociates. After some growth, the peptide's signal sequence is cleaved.
For double the points, can proteins synthesized this way be inserted into the membrane of the ER?
Give two examples of different signaling types.
Endocrine, paracrine, autocrine, neuronal, contact-dependent
True or false, the methods by which G-protein coupled receptors and RTKs amplify their signals is the same.
False!
What two organelles degrade proteins?
Lysosome, proteosome
What are the two classes of molecular chaperones and what makes them different?
- HSP70s
- Cylindrical chaperonins
Chaperonins do not assist in the original folding of the proteins, only in correcting a misfolded protein. Chaperones (like HSP70) do both.
Predict the membrane orientation of a protein that is synthesied with an uncleaved, internal signal sequence (start-transfer sequence) but did NOT contain a stop-transfer sequence.
A transmembrane protein with the N-terminus on the cytosolic side
What are the levels of regulation of the primary signal
0. Primary transduction
1. relay
2. Transduct and amplify
3. feedback/integrate
4. Distribute
5. Modulate (via feedback pathways)
For double points, give one example of a molecule that is part of step #2 of regulation
In RTK signaling pathways, what protein is very commonly activated
Ras
What membrane are G-protein coupled receptors and RTK part of?
The outer cell membrane
What are the four steps of protein importation into the mitochondria and briefly describe each.
1. Delivery of protein to mitochondria: after translation of protein, mitochondrial membrane proteins bind to HSP70 (presequence free to bind to TOM complex)
2. Translocation across mitochondrial membrane: polypeptide transfered to TOM40, which opens (polypeptide remains unfolded)
3A. Translocation across inner membrane to matrix: Outer TOM complex interacts with inner membrane TIM complex and polypeptide passes through TIM complex into mitochondrial matrix (prevented from moving backward by HSP70 proteins). Signaling sequence is cleaved off.
3B. Translocation into inner membrane bilayer: target sequence interacts with "Tiny Tims" (exist between bilayers) which escort protein to membrane and insert it into the membrane
What type of protein coat lines vesicles moving in the "forward" (anterograde) direction? What about the "reverse" (retrograde) direction?
Forward: COPII
Reverse: COPI
What is the most common mechanism to changes in proteins in these signaling pathways, why is it the most common, and why does it cause change?
1. Phosphorylation
2. It is easily reversible
3. Electrostaic repulsion (via additional negative charges) and steric hinderance (phosphate groups are bulky)
What are two purposes of Akt?
Induce cell growth (activating S/T kinase Tor), prolong cell death (phosphorylation of Bad to release Bcl2)
For double the points, what signaling pathway is this protein a part of?
Where are proteins that are located within the ER lumen produced?
On ribosomes attached to the ER
What are the types of sequences that assist in inserting a protein into a membrane. If the protein has one end on either side of the membrane, is one of those sequences cleaved?
- Start-transfer sequences and stop-transfer sequences.
- Yes, the start-transfer sequence would be cleaved
What are the steps of clathrin-shell formation?
1. Coat assembly and cargo selection: adaptins interact with cargo receptors
2. Vesicle bud formation: adaptins interact
3. Vesicle formation: dynamin helps pinch of lipid membrane of vesicle
4. Uncoating: clathrin coating disassembles and the vessicle vibes around on its own
What type of signaling pathway is olfaction?
G-protein
Cancer