Mitochondria

ID #2265

In one of the homework questions it said "The electrochemical gradient helps proteins move from Tom to Tim, and finally into the matrix." But in the lecture notes, it said "the moving of protein from Tim into Matrix needs help of the Tim's ratchet ability and the hydrolysis of the ATP." So is the statement from the quiz contradictory to the lecture note?


No, the two statements are not contradictory, instead, their combined effects help bring the protein into the matrix of the mitochondria.
As we learned early in the semester, the electrochemical gradient is due to the difference in proton concentration between the intermembrane space and the matrix of the mitochondria, brought about by the proton-pumping action of the electron transport chain. The positive charge of the mitochondrial transit sequence (or presequence) makes it want to leave the intermembrane space and head towards the more favorable location of the matrix. So, the electrochemical gradient helps proteins move from Tom (crossing the intermembrane space) into Tim (crossing the inner membrane) and finally into the matrix. 
A part of TIM located on the matrix side is going to have a ratchet ability, which grabs onto a protein as it is coming through TIM, and pull it the rest of the way in.The ratcheting ability of Tim in concert with the tugging ability of mitochondrial Hsp70 proteins is what fully pulls the protein into the matrix. 

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