12 protease families 1 serine cleave peptide bonds in

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Protease families:
1. Serine
- Cleave peptide bonds in proteins where serine serves as nucleophilic amino acid
at the enzyme's active site and plays a major role in proteolysis event.
- Trypsin type, chymotrypsin type, elastase type, carboxypeptidase
2. Aspartate/aspartyl
3. Cysteine
4. Matrix metallo (MMP)
5. Glutamic acid
6. Threonine
7. Asparagine
8. Unknown catalytic type
Protease regulators:
- Activators/binding partners; accelerate protein cleavage
- Inhibitors; prevent cleavage
- Physiological (trypsin and antitrypsin)
- Serpins (serine protease inhibitors)
- Synthetic
Protein-ligase enzymes (protein ligases):
- Join protein and polypeptide chains to generate a single larger protein
Ligases:
Opposite of proteases.
DNA ligases common, involved in DNA repair, DNA replication and recombinant DNA
experiments
DNA-ligation (joining 2 DNA molecules) occurs in presence of the DNA-ligase enzyme
Proteoligase:
Less common, mediates in joining or attaching proteins
Mitochondrion, Aerobic respiration, Cell Membrane Trafficking
Chapter 5,8: Cytoplasmic systems, Cell trafficking, Mitochondrion
Endomembrane System (ES):
ES consist of different membrane bound vesicles that are suspended in the cytoplasm of a
eukaryotic cell. Membrane-bound vesicles containing material of different electron density; long
channels bounded by membranes form cisternae. These cytoplasmic membrane organelles
constitute the ES.
Cytosol: Fluid part of cell’s cytoplasm
Cytoplasm: Cytosol+organelles
- Organelles of ES part of network for shuttling materials

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- Materials shuttled between organelles from Golgi complex to plasma membrane
- Transport vesicles move by motor proteins on tracks formed by microtubules and
microfilaments
Biosynthetic and endocytic pathways:
Materials follow an exocytic (biosynthetic) pathway from the ER, through the Golgi complex, out
to various locations including lysosomes, endosomes, secretory vesicles, secretory granules,
vacuoles, plasma membrane.
Two distinct exocytic pathways: regulated or constitutive
Materials follow the endocytic pathway from cell surface to interior by endosomes and
lysosomes, where they are degraded by lysosomal enzymes.
Protein biosynthesis:
Biosynthetic pathway: proteins are synthesized in ER, modified by golgi complex, transported to
destinations
Constitutive pathway: secretory vesicles from their sites of synthesis are discharged into the
extracellular space continuously
Secreted pathway: proteins are stored in large membrane bound vesicles called secretory
granules and secreted in a regulated manner in response to stimuli
Protein trafficking:
Traffic: defined routes for vesicles with their proteins
Sorting signal: specific destination for vesicle to unload cargo
Autoradiography: a means to visualize biochemical processes by determining location of
radioactively labeled materials in a cell.