Bio Lecture 19 PTM Flashcards
What is post translational modification and why is it needed?
It is modification of proteins after their formation that involves trimming, covalent modifications, folding, binding to other proteins/molecules, and degradation.
It is needed to increase the diversity of proteins and their functions.
What is the main driver for protein folding and how is this related to chaperons?
Hydrophobic AA’s drive folding to put these AA’s in the center of the molecule. Chaperons can see when these AA’s are exposed and they will help the protein to fold properly.
What is HSP 70?
It is a Heat Shock Protein that is a chaperone protein. It binds to the protein chain as translation is happening and stabilizes it until it is ready to be folded. It also transfers proteins to chaperonin which folds proteins.
What is co-translational insertion?
A signal sequence on the end of the protein being made tells it to be inserted into the ER immediately. Signal Recognition Particle (SRP) binds the signal sequence and brings to the ER where it binds to SRP receptor in the ER membrane. Protein Translocator in the membranebinds the ribosome and the new polypeptide. GTP hydrolysis releases the SRP protein from the ribosome.
Explain phosphorylation.
Reversible reaction carried out by kinases and phosphatases.
Addition of a phosphate group to serine, threonine, or tyrosine (OH groups).
Adds a negative charge to the AA
Describe acetylation.
Reversible reaction that adds an acetyl group to Lysine. Acetyl group is a CH3-C=O.
Carried out by Histone Acetyl Transferases and HDAC’s
Describe methylation.
Lysines and arginines get methyl groups added on.
Describe disulfide bond formation.
Disulfide bonds form between cysteines and they are formed by Protein Disulfide Isomerase.
PDI only exists in the ER.
Describe N-linked glycosylation.
Attachment of a sugar molecules to asparagine (N) residue of a protein to form a glycoprotein.
Often involves large and branched glycans.
The modifying enzymes are in the ER and golgi.
Two sugars added at a time.
Describe O-linked glycosylation.
Takes place in lumen of golgi.
Serine or Threonine OH groups.
One sugar added at a time.
Not branched.
Describe gamma-carboxylation.
Adds a second carboxyl group to glutamate with the help of vitamin K. Involved in clotting factors.
How do lysosomal and proteasomal degradation work?
Lysosomal is used to degrade particles that have been endocytosed. The particles fuse with a lysosome and the particles are broken down.
Proteasomal is the routine breakdown of proteins through proteasomes.
Describe Ubiquitination.
Ubiquitin is a polypeptide that binds to lysines in proteins and alters their function. Proteins with several ubiquitin are often degraded faster by the proteasome.
What is the process of adding ubiquitin to a protein?
Ub is activated by E1 protein then transferred to E2 protein which catalyzes attachment to the protein. E3 is a ligase that works with E2 to help with specificity of protein.
Describe proteasomes.
They are barrel shaped with two caps and a core called a shredder. With ATP, it unfolds and breaks down the proteins into small chains.
