Description - Animation illustrating the synthesis of a peptidoglycan layer. New peptidoglycan synthesis occurs at the cell division plane by way of a collection of cell division machinery known as the divisome. Bacterial enzymes called autolysins, located in the divisome, break both the glycosidic bonds at the point of growth along the existing peptidoglycan, as well as the peptide cross-bridges that link the rows of sugars together. Transglycosidase enzymes then insert and link new peptidoglycan monomers into the breaks in the peptidoglycan. Finally, transpeptidase enzymes reform the peptide cross-links between the rows and layers of peptidoglycan to make the wall strong

Description - Animation Illustrating the Role of Penicillins in Blocking Transpeptidase Enzymes from Assembling the Peptide Cross-Links in Peptidoglycan. During normal bacterial growth, bacterial enzymes called autolysins put breaks in the peptidoglycan in order to allow for insertion of peptidoglycan building blocks (monomers of NAG-NAM-peptide). These monomers are then attached to the growing end of the bacterial cell wall with transglycosidase enzymes. Finally, transpeptidase enzymes join the peptide of one monomer with that of another in order to provide strength to the cell wall. Penicillins and cephalosporins bind to the transpeptidase enzyme and block the formation of the peptide cross-links. This results in a weak cell wall and osmotic lysis of the bacterium.

Description - Animation Illustrating the Role of Vancomycin in Blocking Transpeptidase Enzymes from Assembling the Peptide Cross-Links in Peptidoglycan During normal bacterial growth, bacterial enzymes called autolysins put breaks in the peptidoglycan in order to allow for insertion of peptidoglycan building blocks (monomers of NAG-NAM-peptide). These monomers are then attached to the growing end of the bacterial cell wall with transglycosidase enzymes. Finally, transpeptidase enzymes join the peptide of one monomer with that of another in order to provide strength to the cell wall. Vancomycins bind to the peptides of the peptidoglycan monomers and block both the formation of gycosidic bonds between the sugars by the transgycosidase enzymes and the formation of the peptide cross-links by the transpeptidase enzymes. This results in a weak cell wall and osmotic lysis of the bacterium.

Description - Animation showing the mechanism of action of fluoroquinolones. The fluoroquinolones (norfloxacin, lomefloxacin, fleroxacin, ciprofloxacin, enoxacin, trovafloxacin, gatifloxacin, etc.) work by inhibiting one or more of a group of enzymes called topoisomerase, enzymes needed for supercoiling, replication and separation of circular bacterial DNA. For example, DNA gyrase is a topoisomerase that catalyzes the negative supercoiling of the circular DNA found in bacteria. Topoisomerase IV, on the other hand, is involved in the relaxation of the supercoiled circular DNA, enabling the separation of the interlinked daughter chromosomes at the end of bacterial DNA replication. In gram-positive bacteria, the main target for fluoroquinolones is DNA gyrase (topoisomerase II), an enzyme responsible for supercoiling of bacterial DNA during DNA replication; in gram-negative bacteria, the primary target is topoisomerase IV, an enzyme responsible for relaxation of supercoiled circular DNA and separation of the inter-linked daughter chromosomes. When an antibiotic binds to a bacterial enzyme, it may alter the activate site of the enzyme and prevent it from reacting with its substrate

Description - Animation showing the mechanism of action of Sulfonamides. The sulfonamides ( sulfamethoxazole, sulfanilamide) and diaminopyrimidines (trimethoprim) block enzymes in the bacteria pathway required for the synthesis of tetrahydrofolic acid, a cofactor needed for bacteria to make the nucleotide bases thymine, guanine, uracil, and adenine. This is done through a process called competitive antagonism whereby a drug chemically resembles a substrate in a metabolic pathway. Because of their similarity, either the drug or the substrate can bind to the substrate's enzyme. While the enzyme is bound to the drug, it is unable to bind to its natural substrate and that blocks that step in the metabolic pathway. Typically, a sulfonamide and a diaminopyrimidine are combined. Co-trimoxazole, for example, is a combination of sulfamethoxazole and trimethoprim.Sulfonamides such as sulfamethoxazole tie up the first enzyme in the pathway, the conversion of para-aminobenzoic acid to dihydropteroic acid. Trimethoprim binds to the third enzyme in the pathway, an enzyme that is responsible for converting dihydrofolic acid to tetrahydrofolic acid. Without the tetrahydrofolic acid, the bacteria cannot synthesize DNA or RNA.

Description - Animation showing the translation of mRNA by tRNA. It is important to know how the normal bacterial cell works and so this animation is put up here.

Description - Animation showing the Mechanism of Action of Aminoglycosides 1 (Aminoglycosides interfering with the translocation of tRNA from the A-Site to the P-Site).
The aminoglycosides (streptomycin, neomycin, netilmicin, tobramycin, gentamicin, amikacin, etc.) bind irreversibly to the 30S subunit of bacterial ribosomes. There is evidence that some prevent the transfer of the peptidyl tRNA from the A-site to the P-site, thus preventing the elongation of the polypeptide chain.

Description - Animation showing the Mechanism of Action of Aminoglycosides 2 (Aminoglycosides Interfering withTranslation by causing a Misreading of the Codons along the mRNA)
The aminoglycosides (streptomycin, neomycin, netilmicin, tobramycin, gentamicin, amikacin, etc.) bind irreversibly to the 30S subunit of bacterial ribosomes. Aminoglycosides interfere with the proofreading process that helps assure the accuracy of translation. Possibly the antibiotics reduce the rejection rate for tRNAs that are near matches for the codon. This leads to misreading of the codons or premature termination of protein synthesis.

Description - Animation Illustrating the Role of Tetracyclines in Blocking Translation during Bacterial Protein Synthesis
The tetracyclines (tetracycline, doxycycline, demeclocycline, minocycline, etc.) block bacterial translation by binding reversibly to the 30S subunit and distorting it in such a way that the anticodons of the charged tRNAs cannot align properly with the codons of the mRNA.

Description - Animation Illustrating the Mode of Action of Macrolides in Blocking Translation during Bacterial Protein Synthesis: Blocking Peptidyltransferase. The macrolides (erythromycin, azithromycin, clarithromycin, dirithromycin, troleandomycin, etc.) bind reversibly to the 50S subunit.They can inhibit elongation of the protein by the peptidyltransferase, the enzyme that forms peptide bonds between the amino acids.

Description - Animation Illustrating the Mode of Action of Macrolides in Blocking Translation during Bacterial Protein Synthesis: Preventing the Transfer of the Peptidyl tRNA from the A-site to the P-site. The macrolides (erythromycin, azithromycin, clarithromycin, dirithromycin, troleandomycin, etc.) bind reversibly to the 50S subunit. They appear to inhibit elongation of the protein by preventing the enzyme peptidyltransferase from forming peptide bonds between the amino acids. They may also prevent the transfer of the peptidyl tRNA from the A-site to the P-site as shown here.

Description - Animation Illustrating the Mode of Action of Oxazolidinones Blocking the Attachment of the 50S Ribosomal Subunit to the Initiation Complex. The oxazolidinones (linezolid) bind to the 50S ribosomal subunit and interfere with its binding to the initiation complex.