11 - Cell compartmentalisation & Protein sorting Flashcards
What type of transport happens between the nucleus and the cytoplsam?
Gated transport
What type of transport takes proteins and other organelles into the ER?
Transmembrane Transport
What type of transport takes materials into the extracellular portion?
Vesicular transport.
What is the nuclear pore made out of?
Each complex appears to be made of 8 subunits with a central plug.
What do the nuclear pore complexes do?
They are involved in moving substances across the nuclear envelope.
What is the role of histone molecules in DNA synthesis?
They are needed to package the new DNA, that will be transported from the cytoplasm.
What molecule is needed for protein production to occur?
Ribosomes, which are formed in the nucleolus.
What are the 2 processes in which transport can occur?
- By diffusion
- By active transport
How does the molecular weight of a substance affect diffusion?
As the ,olecular weight increases the longer it takes to diffuse through the membrane.
What are signals linked to for active transport of proteins?
A peptide sequence, nuclear transport recognition sites rich in Pro, Lys and Arg
What happens to the T-Antigen SV40 virus in the presence of the protein sequence Pro-Lys-Arg?
The T-Antigen can be localised in the nucleus, when the sequence is disrupted the traslocation stops.
How are new proteins transported into organelles?
Either co or post- translationally.
What is co-traslational translocation?
As the protein is being made its being transported into the lumen of the ER (coupling method).
What is post-translational translocation?
When proteins are completely made in the cytoplasm and after they are completely formed they are post-translationally translocated into the ER.
What is the signal hypothesis?
The idea that translocation into the ER requires a signal.
In the signal hypothesis what needs to happen for there to be a signal?
The mRNA on the ribosome needs to be due to be translated.
How are proteins translocated through the membrane of the ER?
Through the translocator SEC61 of the protein on the membrane which is closed till the signal is recieved, then opens allowing the protein through.
How is the signal stopped?
By the closing of the pore and the removal of the signal by the signal peptidase.
What molecules help the protein to fold?
Chaperones. (Bip)
How are membrane proteins inserted into the ER?
- The protein moves through the translocator apparatus like before but encounters a stop transfer sequence.
- The siganl peptisade then stops the translocation.
What is gycosylation?
the post-translational addition of sugar
What is the role of glycosylation in protein insertion?
It ensures the quality control of the folding of the protein in the membrane.
What happens if folding doesnt occur properly?
The process happens in reverse.
What is an example of a muation casued by defects in protein folding?
CTFRdelta508 - The misfolded protein stimulate the unfolded protein response.
What is the unflolded protein response (UPR)?
A transcriptional programme thats upregulates the sysnthesis of chaperones and also closes down translation to help cells recover.
What happens when there are too many proteins present?
The apoptotic response is stimulated.
How do proteins get into the mitochondrial matrix?
- Proteins are translocated in the cytosol and associated with chaperones.
- The N-Terminal sequence is recognised by the TOM and TIM23 complexes.
- The protein is then translocated through the TOM complex on the outer membrane and the TIM complex on the innner membrane to enter the matrix.
- The signal is then cleared off.
