Prokaryotic Cell Structure

Bacterial Internal Structures

• Cytoplasm: a gel-like matrix composed of 80% water, containing nucleic acids, enzymes, amino acids, carbohydrates, lipids, inorganic ions, and low molecular weight compounds, and is the site of most bacterial metabolism that leads to growth and replication.
• Mesosomes: plasma membrane infoldings that aid in:
  • Cell wall formation
  • DNA replication in prokaryotes
  • Increasing plasma membrane surface area and enzymatic content
  • Transferring chromosomes to daughter cells
• Nucleoid:
  • A region with a single circular chromosome of double-stranded, supercoiled DNA
  • No nuclear membrane or nucleoli
  • Chromosome size varies from 580,000 base pairs in Mycoplasma gallinarum to 9,140,000 bp in Myxococcus xanthus

Plasmids

• Small, nonessential, extra-chromosomal DNA molecules that:
  • Can confer protective traits such as drug resistance or toxin production
  • Can be passed on during conjugation
  • Replicate independently
  • Can be gained or lost by bacteria
• Conjugative plasmids allow for the exchange of DNA between bacterial cells
• Plasmids are useful tools in genetic engineering/rDNA Technology

Ribosomes

• The most abundant component in the cytoplasm, with up to 15,000 ribosomes
• Site of protein synthesis in all organisms
• Prokaryotic ribosomes are 70S, composed of a 50S subunit and a 30S subunit
• Function as a workbench for protein synthesis, translating mRNA into proteins

Inclusion Granules

• Nonliving components that do not possess metabolic activity
• Not bounded by membranes
• Examples:
  • Volutin granules (inorganic phosphate)
  • Polysaccharide granules (glycogen or starch)
  • Lipid inclusions (e.g., PHB granules)
  • Sulfur and nitrogen granules
  • Gas vacuoles (in some aquatic bacteria)

Endospores

• Dormant, resistant structures produced intracellularly upon starvation
• Resistant to:
  • High temperatures
  • Irradiation
  • Cold
  • Organic solvents
• Contain calcium dipicolinate
• Not a mechanism of reproduction
• Examples: Bacillus and Clostridium sp.

Endosporulation

• Process of forming an endospore, involving:
  • DNA replication
  • Formation of a spore septum
  • Pinching off of the plasma membrane to form a double membrane around the DNA
  • Incorporation of calcium dipicolinate
  • Formation of a peptidoglycan cortex and spore coat
  • Dehydration and maturation of the endospore

This quiz covers the internal structures of a prokaryotic cell, including the composition and functions of the cytoplasm, nucleic acids, and other components.