The big idea: Cells are always breaking proteins down and building new ones. Proteasomes break proteins into amino acids, which are recycled into new proteins.
The points to remember
- The proteome is all the proteins a cell makes; it changes all the time.
- Damaged, misfolded or unneeded proteins are tagged and taken into a proteasome.
- The proteasome uses ATP to unfold the protein and feed it in.
- Inside, the protein is hydrolysed into short peptides and then amino acids.
- The amino acids are reused by ribosomes to make new proteins.
Remember it as: Break down, release, rebuild: the proteome is never finished.
Real example: cyclins. Proteins called cyclins control the cell cycle. At set points proteasomes destroy them quickly, so the cell can move on to the next stage.
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Why constant turnover?: Breaking proteins down is as important as making them.
Four reasons
- Recycling: amino acids are reused to make new proteins.
- Damage: proteins become denatured or misfolded over time and stop working.
- Safety: misfolded proteins can harm the cell if they build up.
- Change: cells need different proteins at different times, so old ones must go.
What the ATP is for: ATP is used to unfold proteins and feed them into the proteasome. Do not say it powers the hydrolysis itself.
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How it is asked: Short parts about proteasomes: name the structure, the final product, the use of ATP, then a Justify of why proteins are broken down.
IB-style questionJustify[3 marks]
Justify the need for protein breakdown by proteasomes.
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