Untitled Flashcard Set

Bacterial Cells- Structures and Functions

• Nucleoid- Gel-like region within the cytoplasm containing the single, circular, double- stranded DNA molecule. This chromosomal DNA is supercoiled, meaning tightly packed into a twisted form. The DNA contains all of the genetic information necessary for normal functioning of the cell.

• Plasmids- Circular double-stranded DNA molecules. A single bacterial cell can carry multiple plasmids. Normal functioning of a bacterial cell is not dependent on the genetic information contained in a plasmid, but the DNA often codes for proteins that are advantageous to the cell.

• Ribosomes- Structures involved in protein synthesis. They facilitate the joining of amino acids.

 • Cell Wall- Rigid barrier that surrounds the cell, keeping the contents from bursting out. Peptidoglycan provides the rigidity for the cell wall. Bacterial Cell Structures

• Plasma Membrane- Semipermeable membrane that surrounds the cytoplasm of the cell. This phospholipid bilayer is embedded with proteins that act as a barrier between the cytoplasm and the outside environment.

• Capsule- A distinct and gelatinous layer, called glycocalyx, that envelops the cell. This layer enables the bacterial cell to adhere to specific surfaces and sometimes protects bacterial cells from human immune systems.

• Flagella- Protein appendages that are anchored in the membrane and protrude from the surface. The flagella spin like propellers, moving the bacterial cell forward.

• Pili- Filamentous appendages that are similar in structure to flagella, but function in a different manner. Some pili enable the bacterial cell to attach to a specific surface (these pili are called fimbriae). Other pili are involved in conjugation, a mechanism of DNA transfer from one bacterial cell to another (these pili are called sex pilus). Bacterial Cell Structures

• Endotoxins- Lipopolysaccharide molecules that make up the outer leaflet of the outer membrane of Gram-negative bacteria. Endotoxins are different from exotoxins, proteins that are synthesized by both Gram negative and Gram-positive bacteria and function as potent toxins

What are antibiotics?

·       a substance produced by or derived from a microorganism and able in dilute solution to inhibit or kill another microorganism

What does antibodic effectiveness depend on?

·       Dependent on the mechanism of the drug and the structure of the bacteria.

Classes of Antibiotics

 •β-Lactam Antibiotics • Irreversibly inhibit enzymes involved in the final steps of cell wall synthesis. The enzymes inhibited by these drugs mediate the formation of the peptide bridges between adjacent strands of peptidoglycan. These drugs vary in their spectrum of activity. Some are more active against Gram-positive bacteria; others are more active against Gram- negative bacteria. Classes of Antibiotics

•Tetracyclines • Reversibly bind to the 30S ribosomal subunit, blocking the attachment of tRNA to the ribosome and preventing the continuation of protein synthesis. They are effective against certain Gram-positive and Gram-negative bacteria.

• Fluoroquinolones • Inhibit one or more of a group of enzymes called topoisomerases, which maintain the supercoiling of chromosomal DNA within the bacterial cells. The inhibition of these enzymes prevents essential cell processes. Fluoroquinolones are active against a wide variety of bacteria, including both Gram-positive and Gram-negative bacteria.

• Sulfonamides • Inhibit the growth of many Gram-positive and Gram-negative bacteria. They are structurally like par aminobenzoic acid (PABA), a substrate in the pathway for folic acid biosynthesis. Because of this similarity, the enzyme that normally binds with PABA preferentially binds with the sulfonamide drugs, resulting in its competitive inhibition. Human cells are not affected by these drugs because they lack this enzyme.