Exam 3: Lect. 18

What factors assist protein folding in the cell (names of the class of proteins)? Do they use energy to work? How do they work?

Proteins called molecular CHAPERONES assist the cell with proper folding of proteins. They DO NOT NEED ENERGY TO WORK (do not hydrolyze ATP or GTP as a source of energy) PROTEIN FOLDING IS DRIVEN BY HYDROPHOBIC FORCES WHICH FORCE THE NONPOLAR AMINO ACIDS

What are the possible fates of a misfolded protein? (3)

Misfolded proteins can either be 1. 1. REFOLDED properly WITH the help of a molecular CHAPERONES(hsp60 proteins) 2. incompletely folded and DEGRADED BY the PROTEASOME; or 3. BECOME A PROTEIN AGGREGATE in the cell(built up garbage)

What is it attached to proteins to mark them for degradation?

Misfolded proteins are recognized by enzymes that attach small copies of the protein UBIQUITIN to lysine residues, thereby marking them for degradation. Ubiquitin then directs the misfolded protein to the proteasome

What enzymes attach ubiquitin to proteins?

The E1, E2, and E3 proteins attach ubiquitin to misfolded proteins

True or false, only misfolded proteins are actively degraded in the cell.

FALSE, Misfolded proteins are not the only proteins actively degraded in the cell; properly folded/functioning proteins can be marked with ubiquitin in order to regulate the levels of that specific protein in the cell

How are proteins targeted for degradation? How are they eliminated from the cell?

First, E1 (the ubiquitin-activating enzyme) binds the ubiquitin molecule. The E1-ubiquitin complex then binds to the ubiquitin-conjugating enzyme (E2). E1 then disbands, leaving E2 primed with ubiquitin. As soon as a degradation signal on the target prote

What are the roles of the core and cap of the proteasome?

the CAP'S UNFOLDASE RING UNFOLDS PROTEINS, IN CORE PROTEINS ARE DEGRADED BY PROTEASES exposing them to the proteases(the enzyme that degrades the protein, it's located inside proteasome) lining the core of the proteasome; The core of the proteasome is whe

During the life of a protein, which factor in the cell interacts with it last?

The PROTEASOME is the factor in the cell that interacts with a protein last during its lifetime, as the proteasome is the site of protein degradation

Where are degradation signals located? Are they always active?

Degradation signals are typically located in the N-TERMINUS of the protein and are NOT ALWAYS ACTIVELY EXPRESSED. Degradation signals can be activated by (3 ways) 1. the phosphorylation of the protein by a protein kinase 2. unmasked by the dissociation of

Describe three ways ATP is used to mediate the destruction of a protein?

1. WHEN MARKING IT WITH UBIQUITIN. ubiquitin requires ATP hydrolysis in order to bind to E1; 2. THE CAP OF PROTEASOME USES ATP IN ORDER TO UNFOLD THE PROTEIN BEFORE IT REACHES THE PROTEASOME CORE 3. THE PROTEASOME CONFORMATIONALLY CHANGES TO PULL THE SUBS