Proteins

Step 1: Understanding the -lactam structure
A -lactam ring is a four-membered cyclic structure that contains a nitrogen atom and a carbonyl group. This ring is a key feature of several classes of antibiotics, including penicillins and cephalosporins. The -lactam ring inhibits the bacterial enzyme responsible for synthesizing the cell wall, which is why these antibiotics are effective against bacteria.
Step 2: Review of the given options
Penicillin: Penicillin is an antibiotic that contains a -lactam ring. It is commonly used to treat bacterial infections by inhibiting cell wall synthesis in bacteria.
Sulphanilamide: Sulphanilamide is a type of sulfonamide drug, but it does not contain a -lactam ring. Instead, it works by inhibiting bacterial folic acid synthesis.
Erythromycin: Erythromycin is a macrolide antibiotic. It does not contain a -lactam ring. Instead, it inhibits protein synthesis in bacteria.
Chloramphenicol: Chloramphenicol is another antibiotic that does not contain a -lactam ring. It also works by inhibiting bacterial protein synthesis.
Step 3: Conclusion
The only drug in the list that contains a -lactam ring is Penicillin. Thus, the correct answer is Penicillin.

Step 1: Understand N-terminal modifications.
N-terminal modifications occur at the start (N-terminal) of a protein and are important for stability, localization, and function.
Step 2: Review common natural N-terminal modifications.
Acetylation: A very common natural N-terminal modification.
Myristoylation: Another natural modification where a myristoyl group (fatty acid) is attached to the N-terminal glycine.
Sumoylation: Involves addition of SUMO (Small Ubiquitin-like Modifier) protein and although it can occur at different lysine residues, it is still considered a natural protein modification.
Benzylation: This is not a recognized natural N-terminal protein modification. It is a chemical modification, not commonly found in biological systems. Hence, the correct answer is Benzylation.