describe the signals and mechanisms required for import into the peroxisome correct answers peroxisomal matrix proteins have targeting sequences which are recognized by Pex5 receptor and brought to peroxisomal matrix
what is a peroxisome? correct answers organelles that carries out redox reactio...
NROS 310 - EXAM 2 || with 100% Errorless Answers.
describe the signals and mechanisms required for import into the peroxisome correct answers
peroxisomal matrix proteins have targeting sequences which are recognized by Pex5 receptor
and brought to peroxisomal matrix
what is a peroxisome? correct answers organelles that carries out redox reactions to clean out the
cell (neutralizes waste)
Describe the functions of SRP. correct answers brings ribosome to protein translocator and docks
it on ER membrane
How do multiple transmembrane proteins get inserted correctly into the membrane? correct
answers Brought to ER membrane by SRP, then based on its signal sequence, it becomes integral
or goes all the way through based on docking or undocking of the ribosome
How do you get proteins w the NH2 terminus inside the ER or outside of the cell? correct
answers There's a transfer sequence right next to the n-terminus, and is cleaved once the protein
enters the ER
How do you get proteins with the carboxyl terminus inside the ER? correct answers Amino
terminus rejects the positive charge on the inside of the membrane (bc its positively charged too),
so it stays outside when it gets docked
How do proteins end up completely inside the ER membrane? correct answers just one extreme
amino targeting sequence, which gets cleaved
What signals are necessary for a secreted protein to be correctly targeted? What happens to it if
those sequences are missing? correct answers - The sequence must be at the amino terminus (N-
terminus) and C terminus
- If it is missing, the proteins gets degraded or stays in the cytoplasm
What is the difference between a stop transfer and a start transfer (signal anchor) signal
sequence? correct answers Stop transfer -> released the ribosome
Start transfer -> docks the ribosome on the membrane
If the signal sequence does get cleaved off, what part of the protein ends up inside the ER?
correct answers If the signal sequence gets cleaved off, the amino terminus sequence stays inside
the ER (extreme amino terminus signal)
where would a protein w a nuclear localization signal and ER signal end up? correct answers
Goes to ER, SRP binds on and pauses translation of it
where would a protein w peroxisomal targeting sequence and a mitochondrial matrix targeting
sequence go? correct answers Whichever signal is met first
, where would a protein w no discernable signal sequences go? correct answers Stays in the
cytoplasm
where would a protein w a mitochondrial inner membrane stop transfer sequence and a
mitochondrial matrix targeting sequence correct answers Mitochondrial inner membrane
What is the normal path of a soluble protein that enters the ER? correct answers Protein has a
signal sequence made of 5 AA's, which causes the ribosome to dock
What processing events happen in the ER? correct answers - Lipid synthesis
- Packaging/folding of proteins -> chaperones fold proteins
- Protein synthesis
- Quality control
- Glycosylation
what is glycosylation? correct answers sugars added to proteins in ER
How and where are proteins glycosylated? correct answers - signal sequence sticks sugar inside
the ER and outside the plasma membrane
Why are the glycosylated parts of proteins usually found on the outside of the plasma
membrane? correct answers Protect the outside of plasma membrane/cell recognition, attracts
water to outside of the cell
what is the misfolded proteins response? correct answers - Glycosyl transferase -> recognizes a
proteins has misfolded and marks/tags them
- Calnexin -> chaperone that recognizes signal and tries to refold the protein
Why do proteins eventually get degraded if they don't fold properly? correct answers First it gets
sent back to be refolded, but eventually it gets degraded by proteasomes
What role(s) do chaperones play in the proper processing of proteins in the ER? correct answers
Respond to too many unfolded proteins in the ER -> more chaperones are made
What is the unfolded protein response? (Quality control in ER) correct answers - There is a
protein translocator complex that puts an ubiquitin on a misfolded protein, to be sent to the
proteasome to be destroyed
- IRE1 and PERK are triggered by too many unfolded proteins
what is the role or IRE1? correct answers causes more chaperones to be made by splicing and
recruiting transcription factors to make them
what is the role of PERK? correct answers - unfolds proteins, allows them to dimerize,
selectively translates transcription factors, causes more chaperones to be make
- Cause a translation initiation factor to be phosphorylated and stops translation of problematic
proteins to regulate what gets processed in the ER
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