MICROBIO:3

• Characteristics of a prokaryotic cell:

  • DNA is not enclosed within a membrane and is usually a singular circularly arranged chromosome
  • DNA is not associated with histones
  • Lacks membrane-enclosed organelles
  • Cell walls almost always contain peptidoglycan
  • Usually divides by binary fission

  
• Characteristics of a eukaryotic cell:

  • DNA is found within the nucleus, separated from the cytoplasm by a nuclear membrane
  • DNA is consistently associated with histones
  • Contains membrane-enclosed organelles like mitochondria, endoplasmic reticulum, Golgi complex, and lysosome
  • If present, cell walls are chemically simple
  • Cell division usually involves mitosis

  
• Basic shapes of bacteria:

  • Bacteria come in various sizes and shapes, ranging from 0.2-2.0 μm in diameter & 2-8 μm in length
  • Basic shapes include spherical Coccus (pleural: cocci), rod-shaped Bacillus (pleural: bacilli), and Spirals (including vibrios, spirillas & spirochetes)

  
• Polymorphism in bacteria:

  • Polymorphic bacteria can have many shapes, like Corynebacterium and Rhizobium

  
• Structures external to the cell wall in bacteria:

  • Glycocalyx
  • Flagella
  • Axial filaments
  • Fimbriae
  • Pili

  
• Functions of glycocalyx in bacteria:

  • A "sticky" coating made up of polysaccharide surrounding the cell membranes
  • Serves as a glue that holds cells in place such as those in biofilms

  
• Functions of flagella in bacteria:

  • Long filamentous appendages that propel bacteria
  • Consist of filament, hook, and basal body
  • Enable various patterns of motility

  
• Functions of fimbriae and pili in bacteria:

  • Hair-like appendages used for attachment and transfer of DNA to another bacterium
  • Fimbriae are for adherence to each other & different surfaces
  • Pili are involved in motility (twitching motility) & DNA transfer
• Composition of the bacterial cell wall:

  • Composed of a network of peptidoglycan, consisting of a repeating disaccharide attached by polypeptides to form a lattice
  • Alternating NAM and NAG molecules are linked in rows of 10-65 sugars to form a carbohydrate "backbone"

  
• Gram classification of bacteria:

  • Gram stain is a method for classifying bacteria based on their cell wall
  • Gram-positive bacteria have many layers of peptidoglycan, forming a thick, rigid structure
  • Gram-negative bacteria have only a thin layer of peptidoglycan

  
• Prokaryotic cell structures:

  • Cell membrane
  • Cytoplasm (80% water & 20% compounds like proteins, carbohydrates, lipids, & inorganic ions)
  • Nucleoid (region with bacterial chromosome)
  • Ribosomes
  • Inclusions

  
• Nucleoid contains the bacterial chromosome, a single long continuous thread of double-stranded DNA
• Plasmids are small circular DNA molecules in the cytoplasm not connected to the main bacterial chromosome, associated with proteins of the plasma membrane
• Ribosomes are cytoplasmic structures for protein synthesis, composed of 30S and 50S subunits
• Endospores are specialized "resting" forms of certain bacteria during nutrient depletion, occurring in Gram-positive bacteria like Clostridium & Bacillus
• Eukaryotic flagella & cilia:

  • Used for locomotion
  • Eukaryotic flagella move in a wave-like manner
  • Eukaryotic flagella & cilia consist of 9 pairs of microtubules arranged in a 9+2 array

  
• Eukaryotic cell walls are simpler than prokaryotic cell walls, with plant cell walls made of cellulose, fungal cell walls of chitin, and yeast cell walls of glucan & mannan
• Eukaryotic plasma membrane is similar in function & structure to prokaryotes but contains sterols, allows endocytosis, and has carbohydrates serving as receptors for cell-to-cell interactions
• Eukaryotic ribosomes are sites of protein synthesis, larger than prokaryotic ribosomes (80S), and can be free in the cytoplasm or attached to the rough endoplasmic reticulum
• Eukaryotic organelles include the nucleus, endoplasmic reticulum, Golgi complex, mitochondria, lysosomes, vacuoles, chloroplasts, peroxisomes, and centrosomes