Bacteria

What are bacteria

• Prokaryotes

• Cell membrane is surrounded by a cell wall

• Chromosome is a single strand of DNA

• No mitochondria, chloroplasts, nuclear membrane………

Bacterial Structure

• Typical size: 1-10 micromenter (10-100 micrometer for eukaryote cells)

• Single circular chromosome (DNA)

• Cell membrane made of protein and lipids

• Cell wall present

• Sometimes plasmids present

Bacterial Cell Wall

• Composed of complex carbohydrate and peptidoglycan

• Functions to regulate transport (molecules that flow in and out of the cell)

• Bacteria are identified based on their cell walls

Hans Christian Gram and His Stain

• Cell walls with carbohydrate take up the stain that Gram invented– These cells are purple under a light microscope– They are called Gram-positive bacteria

• Cell walls with carbohydrate and lipids do not take up Grams stain– These cells are not purple under a light microscope– These are Gram-negative bacteria

• Infection with Gram-negative bacteria is usually very serious

Structure and Function

• Cell classified by shape – Bacillus (bacilli) are rod shaped– Coccus (cocci) are spherical – Spirillum (spirilli) are spiral shaped

• Nutrition and metabolism– Energy capture (page 582)– Metabolism (page 583)

Two Kingdoms of Bacteria

• Eubacteria

• Archaebacteria

• Classification based on differences in ribosomal RNA

Eubacteria

• Largest group of bacteria

• Found everywhere

• Diverse ecology and biochemistry

• Some are photosynthetic, free living in soil, parasitic

Archaebacteria

• Ancient bacteria

• Live in extreme environments (extremeophiles)

• Many survive in the absence of oxygen

• Cells walls lack peptidoglycan

Growth and Reproduction

• Binary Fission

• Conjugation

• Spore formation

Binary Fission

• Cell doubles in size

• Chromosome replicates

• Cell splits into two identical daughter cells

• No exchange of genetic information– This is asexual reproduction

Conjugation

• Protein bridge forms between two cells

• Some DNA exchanged between the cells

• Cells incorporate the new DNA, chromosome replicates

• Cells divide– This is a form of sexual reproduction

Sporulation

• Form a structure called a spore when environmental conditions are adverse

• Spore encloses some cytoplasm and the DNA• Spore resists heat, drying, desiccation, radiation,

and chemical disinfectants• Spore survives for years• When conditions are better the spore “hatches”

and the bacteria can grow again

Bacteria and disease

• Pasteur found the link between bacteria and disease

• Strep throat, diphtheria, tuberculosis, typhoid, tetanus, syphilis, gonorrhea, cholera, lyme disease, bubonic plague, food poisoning, botulism

Bacteria cause disease in two ways

• Attacking cells and tissues of the body directly, using cells and tissues for nutrients

• Producing toxins which in turn interfere with functions in the body

• Fighting disease– Vaccination– Antibiotics