1. PROTEOLYSIS, PROTEIN
DEGRADATION AND
TURNOVER

2. PROTEIN SYNTHESIS OVERVIEW

3. PROTEOLYSIS

4. LIMITED PROTEOLYSIS
 Peptide bond cleavage by specific enzymes =
proteases.
 Limited cleaving of peptides.
 New protein product  new functions.
 Classified = posttranslational modification.

5. PROTEASES
 Exopeptidases = cleave near the N- or C-
terminus of peptides and proteins.
 endopeptidases (proteinases) = cleave internal
peptide bonds in peptides and proteins.

6. PROTEIN DEGRADATION
 Several sites on peptide are cleaved. Complete
degradation to AA.
 Classified = protein turnover
 Occurs in several compartments. Ex:
 Lysosomes - acidified compartment, individual
proteases degrade proteins
 Cytosol - ubiquitindependent proteasome system
degrades - at neutral pH.

7. LYSOSOMAL PROTEIN BREAKDOWN
 Acidic pH
 Various hydrolyses (proteases, nucleases..)
 Significance –
 degradation of extra/intracellular fragments
 Phagocytosed microorganisms
 Nutrition
 Protein uptake:
 Endocytosis
 Autophagy
 Phagocytosis
 Specific targeting

8. UBIQUITIN-DEPENDENT PROTEIN
BREAKDOWN
 Neutral pH
 ATP-dependent degradation
 Significance –
 Digestion of proteins programmed for quick
destruction
 Digestion of misfolding
 Denaturated
 Abnormal proteins