Ch 6 - Proteolysis

Lysosomal degradation

process by which lysosomes break down and recycle unwanted/damaged cellular components; responsible for longer lived proteins; nonselective

Ubiquitin dependent proteolysis

responsible for degrading 80 to 90% of short lived proteins; 76 amino acid peptide (very conserved)

Conjugation

tagging a no longer useful component with ubiquitin, which is then sent to the proteasome where it is broken down

Degradation

breakdown of a protein into smaller polypeptides or amino acids; broken down in the proteasome (acts like a shredder)

Ubiquitin activating enzyme (E1)

activating enzyme that gets ubiquitin chemically situated to attach to a protein; passes ubiquitin to E2

Ubiquitin conjugating enzymes (E2)

accepts ubiquitin from E1 and works with E3 to transfer ubiquitin to the target protein

Ubiquitin ligases (E3)

recognizes the target protein; transfers ubiquitin from E2 to the target protein; process repeats to build a polyuquibitin chain to signal for proteasomal degradation

Monoubiquitylation

occurs when only 1 ubiquitin molecule is attached to a single lysine residue on a protein; used for regulation, not destruction; important in signaling

Histone regulation

controls gene activity for cell function and differentiation; degrading histones can change chromatin structure and gene expression; allows DNA access via the ubiquitin proteasome system

Multi Ubiquitination

occurs when there is 1 ubiquitin molecule on MULTIPLE lysines on the same protein; affects signaling and is often used for endocytosis

Endocytosis

process when a cell engulfs a substance from their environment by surrounding it with the cell membrane, forming a vesicle

Polyubiquitylation

occurs when a chain of ubiquitin molecules are added onto a single lysine; used for degradation of the marked protein

Protein degradation

process of breaking down proteins into amino acids to regulate protein levels and remove damaged/unneeded proteins

DNA repair

set of processes that cells use to fix damaged DNA and maintain the genome; proteolysis regulates the proteins involved

Phosphorylation

the addition of a phosphate group; catalyzes by kinases and is reversed by phosphatases; regulates protein activity

Allosteric ligand

molecule that binds to a site that is not the active site; can inhibit or activate the protein’s function

Subunit addition

the joining of individual protein units to build a larger functional complex

Subunit removal

process of separating individual protein subunits from a larger complex

Proteolytic cleavage

enzymatic cutting of a protein at specific peptide bonds by proteases

26S proteasome

the degradation machinery

20S core protease

chops proteins into peptides

Multiple protease activities

the different ways proteases break down proteins; vary by specificity, mechanism, and function

19S regulatory cap

recognize, unfold, and feed substrates into 20S core