Unit 1 (Chapter 4, Part 6) Protein Sorting to Organelles Flashcards
What is the sorting signal?
A short amino acid sequence in a protein that directs the protein to its correct location in a cell; also known as a traffic signal.
Where does the synthesis of most eukaryotic proteins begin?
Ribosomes in cytosol using messenger RNA (mRNA) that contains the information for polypeptide synthesis.
What provides the amino acids which are used as building blocks to the make the proteins during translation?
The cytosol
Cytosolic proteins and amino acids lack sorting signals so they just remain there.
At what point does proteins destined for organelles within a cell’s cytosol start to move?
When the ribosome has become bound to the ER membrane and translation resumes with the polypeptide synthesizing into the ER.
Where are proteins first directed when they are destined for the ER, Golgi, lysosomes, vacuoles, plasma membrane, or secretion?
They are first directed to the ER. This process is called cotranslational sorting.
The sorting process in which the synthesis of certain eukaryotic proteins begins in the cytosol and then halts temporarily until the ribosome has become bound to the ER membrane.
When does the uptake of most proteins for the nucleus, mitochondria, chloroplasts, and peroxisomes occur?
After the protein is completely made (that is, completely translated) in the cytosol.
This process is called post-translational sorting.
What is a sorting signal in a polypeptide that is usually located near the N-terminus and is recognized by SRP (signal recognition particle), allowing the polypeptide to be directed to the ER membrane?
ER signal sequence.
N-terminus is the first part of the protein that exits the ribosome.
What is a protein-RNA complex that recognizes the ER signal sequence of a polypeptide, pauses translation, and directs the ribosome to the ER to complete translation.
Signal recognition particle (SRP)
What prevents a protein destined for the ER from being completely synthesized in the cytosol?
The signal sequence of such a protein is recognized by SRP, which halts translation. The growing polypeptide and its ribosome are then transferred to the ER membrane, where translation resumes.
What prevents proteins from leaving certain organelles when said protein arrives?
Retention signals that are attached to the signal sequence.
What is an example of post-translational sorting?
A protein is directed to the mitochondrial matrix using a short amin acid sequence called a matrix-targeting sequence.
What protein keeps another protein in an unfolded state during the process of post-translational sorting?
Chaperone
T/F Chaperone proteins exist within the inner membrane of mitochondria to keep the protein in a an unfolded state.
True
