Bacterial Structure

Bacterial genome:

• Contains double-stranded DNA
• Prokaryotic DNA differs to eukaryotic DNA:
  • Few repeated sequences
  • Most of the DNA is transcribed
  • No intervening sequences within structural genes

Cytoplasm:

• Does not contain mitochondria, lysosomes or Golgi bodies (found in eukaryotic cells)
• Contains mesosomes- thought to be primitive endoplasmic reticulum

Surface components:

Structure of cell wall Franciscop2 2008, WikiMedia Commons

• Fimbriae- also known as pili, these are hair-like structures that allow bacteria to adhere to each other
• F-type pili- also known as sex pili, these act as conjugation tubes during sexual reproduction
• Capsules/slime- serve to adhere bacteria to cells and provide protection from phagocytosis and dehydration, e.g. hyaluronic acid
• Flagella- help the bacteria move around

One way bacteria can be classified is by the structure of the cell wall:

• Gram-positive bacteria: cell wall consists of peptidoglycan layer, with teichoic polymers attached, e.g. Staphylococcus
• Gram-negative bacteria:peptidoglycan layer is thinner, but surrounded by outer membrane of lipopolysaccharides and lipoproteins, e.g. salmonella

Arrangement of bacilli bacteria

Arrangement of cocci bacteria

Components of bacterial envelope

Component	Gram positive	Gram negative
Peptidoglycan	Yes	Yes
Teichoic acid	Yes	No
Lipoprotein	No	Yes
Lipopolysaccharide	No	Yes
Phospholipid	No	Yes

Another method of classification is the shape and arrangement of the bacteria themselves:

• Cocci- round shape, e.g. Streptococci, Staphylococci, Neisseria
• Rods or bacilli- long shape, e.g. Coliforms, Bacillus, Spirochaetes