The Great 21st century world
Hello Guest !
Welcome to biology world by students !

The Beta-Lactams

Go down

The Beta-Lactams Empty The Beta-Lactams

Post by admin @ shivam on Sun Jan 18, 2009 9:06 pm

The Beta-Lactams

The Beta-Lactams PenicillinG
The beta-lactams get their name from the characteristic ring structure — shown here in blue
— that they all share. (The green arrow shows the bond that is broken by the beta-lactamases that are synthesized by many penicillin-resistant bacteria.)

They include the

  • penicillins such as

    • penicillin G (a natural product) produced by the fungus Penicillium chrysogenum
    • ampicillin (a semi-synthetic)
    • amoxicillin (semi-synthetic)

  • cephalosporins
    There are over two dozen of them in current use. Most are
    semi-synthetics derived from the secretion of the mold Cephalosporium.
    Some examples:

    • cephalexin (e.g., Keflex®️)
    • cefaclor (e.g., Ceclor®️)
    • cefixime (e.g., Suprax®️)

  • carbapenems such as

    • meropenem (Merrem®️)
    • ertapenem (Invanz®️)

The Chink in the Armor = the bacterial cell wall

The Beta-Lactams MureinThe
beta-lactams all work by interfering with the synthesis of the
bacterial cell wall — a structure that is not found in eukaryotes.
The walls of bacteria are made of a complex polymeric material called peptidoglycan. It contains both amino acids and amino sugars.
The amino sugars are of two kinds

  • N-acetylglucosamine (NAG) and its close relative
  • N-acetylmuramic acid (NAM).

These two form a linear polymer of NAG alternating with NAM. They are linked by a glycosidic bond between the #1 and #4 carbons (this is the linkage attacked by lysozyme) and are oriented in the same way they are in cellulose.
Side chains containing 4 or 5 amino acids are attached to each NAM.
These form covalent bonds with amino acids in adjacent chains. The
bonds may
The Beta-Lactams NAG_NAM

  • be direct to the next chain or
  • include additional peptide cross bridges (e.g., 5 glycine residues) which
  • extend to chains in the same plane (shown here) as well as to chains above and below.

This elaborate, covalently
cross-linked structure provides the great strength of the cell wall. It
also leads to the remarkable conclusion that the bacterial cell wall
meets the definition of a single molecule!

The beta-lactam antibiotics bind to and inhibit enzymes needed for
the synthesis of the peptidoglycan wall. While they have little effect
on resting bacteria, they are lethal to dividing bacteria as defective
walls cannot protect the organism form bursting in hypotonic surroundings.

The Beta-Lactams Ubda7389

The Beta-Lactams Ubd2029fs5
admin @ shivam
admin @ shivam

Male Number of posts : 254
Age : 24
Location : Bareilly , UP
Points : 37950
Reputation : 20
Registration date : 2009-01-09

View user profile

Back to top Go down

Back to top

- Similar topics

Permissions in this forum:
You cannot reply to topics in this forum