Gram (-) vs. Gram (+)

• Gram-negative bacteria

  • Thin layer of peptidoglycan

  • Outer membrane is composed of endotoxins

  • Outer membrane contains porins that allow certain substances to pass

  • Periplasm is the space between the plasma and outer membrane

  • Gram-negative cells show up as pink in Gram stains

• Gram-positive bacteria

  • Thick layer of peptidoglycan

  • No outer membrane

  • No porins

  • Gram-positive bacteria show up as purple in Gram stains

Bacteria Structures

• Nucleoid: region in the cytoplasm that contains the bacteria’s DNA molecule

  • The bacterial chromosomal DNA is supercoiled

• Plasmid: Circular and double-stranded DNA molecules

  • Plasmids can be transferred and typically contain genetic material for antibiotic resistance

• Ribosomes: facilitate bonding of amino acids for protein synthesis

• Cell Wall: Rigid wall that prevents lysis

  • Peptidoglycan contributes to the rigidity of the cell wall

• Capsule (glycocalyx): allows attachment to surfaces and protection

• Flagella: Protein appendages that move the bacteria

• Pili: Filamentous appendages that allow for attachment

  • Involved in conjugation

• Endotoxins: LPS molecules