Prokaryotes

Prokaryotes – aka Bacteria

– Prokaryotes• are found wherever there is life,• have a collective biomass that is at least ten times

that of all eukaryotes,• thrive in habitats too cold, too hot, too salty, too

acidic, or too alkaline for any eukaryote,• cause about half of all human diseases, and• are more commonly benign or beneficial.

The Structure and Function of Prokaryotes

– Prokaryotic cells• lack a membrane-enclosed nucleus,• lack other membrane-enclosed organelles,• typically have cell walls exterior to their plasma

membranes, but• display an enormous range of diversity.

The Structure of Prokaryotes

Plasma membrane

Cell wall

Capsule

Prokaryoticflagellum

Ribosomes

Nucleoid

Pili

Identifying Prokaryotes

• * Prokaryotes are identified by:– Their shapes– The chemical natures of their cell walls– The ways they move

Cell Shape

• Three shapes possible:• Rod shaped – called bacilli

• Sphere-shaped – called cocci

• Spiral-shaped – called spirilla

• Can form chains or clumps/clusters – use these prefixes:

• Diplo = pair• Strepto = chain• Staphlyo = cluster/bunch

– Ex. Diplobacilli = pair of rod-shaped bacteria– Ex. Streptococci = chain of sphere-shaped bacteria– Ex. Staphlyococci = cluster/bunch of sphere-shaped bacteria

Cell Wall

• Gram staining – 2 stains: 1 violet, 1 red – Bacteria stain purple – Gram positive – cell

wall contains mainly peptidoglycan– Bacteria stain red – Gram negative – have

second, outer, layer of lipid and carbohydrate molecules

Bacterial Movement

– Flagella – whip-like structures for movement– Slime-like material like a slug– May not move at all

Growth and Reproduction

• Can divide every 20 minutes!• Growth held in check by food and waste

products (think limiting factors)• Binary fission – just like cell division – two

“daughter” cells – asexual reproduction• Conjugation – transfer genetic material from one

cell to another – increases genetic diversity• Spore formation – form endospores when

conditions are unfavorable for growth

Obtaining Energy

• Autotrophs– Photoautotrophs – found where light is plentiful

(surfaces of lakes, streams, oceans)– Chemoautotrophs – energy from inorganic molecules

– chemical reactions (hydrothermal vents on ocean floor)

• Heterotrophs – Most bacteria are heterotrophs, like humans – may

even compete with humans for food – can lead to food poisoning

– Photoheterotrophs – combine autotrophic and heterotrophic styles

Releasing Energy

• Respiration – requires oxygen (O2) – obligate aerobes

• Fermentation – absence of oxygen (O2) – obligate anaerobes

• Facultative Anaerobes – can live with or without oxygen (O2) – can switch between respiration and fermentation = grow just about anywhere

The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea

• 2 Kingdoms – used to be just be one - Monerans - By comparing diverse prokaryotes at the molecular level, biologists have identified two major branches of prokaryotic evolution:

– Bacteria – larger of two kingdoms; live almost everywhere, E. coli, cell walls contain peptidoglycan

– Archaebacteria – cell walls lack peptidoglycan, may be ancestors of eukaryotes, live in extremely harsh environments (oxygen-free, salty, hot)

Bacteria and Disease

– Bacteria and other organisms that cause disease are called pathogens.

– Most pathogenic bacteria produce poisons.

****Disease – some bacteria damage the tissues of the infected organism directly by breaking them down for food. Others release toxins (poisons) that harm the body.****

• Vaccines can prevent bacterial infections (ex. tetanus shots). Antibiotics block growth and reproduction of bacteria; cure many bacterial diseases; sanitation important

Common Diseases Caused by Bacteria

Tooth decay

Lyme disease

Tetanus

Tuberculosis

Salmonella food poisoning

Pneumonia

Cholera

Streptococcus mutans

Borrelia burgdorferi

Clostridium tetani

Mycobacterium tuberculosis

Salmonella enteritidis

Streptococcus pneumoniae

Vibrio cholerae

Regular dental hygiene

Protection from tick bites

Current tetanus vaccination

Vaccination

Proper food-handling practices

Maintaining good health

Clean water supplies

Disease Pathogen Prevention

Bacteria in Nature

– Pathogenic bacteria are in the minority among prokaryotes.

– Far more common are species that are essential to our well-being, either directly or indirectly.

– * Bacteria are vital to maintaining the living world. Some are producers that capture energy by photosynthesis. Others help to break down the nutrients in dead matter and the atmosphere, allowing other organisms to use the nutrients.

Bacteria in the Environment - Benefits

• Decomposers – nutrient/chemical recycling (dead trees, leaves, etc.)• Nitrogen fixation – convert pure nitrogen (N) to compounds that can be used

by other organisms– Ex. Clover plants and nodules on roots with bacteria inside

• Symbiotic relationships with other organisms– Us – E. coli and our intestines– Cattle – bacteria to help them digest cellulose

Human Uses of Bacteria

• Food – cheese, yogurt, buttermilk, sour cream, pickles, vinegar, some bread

• Industry – Bioremediation - digest oil spills, remove waste products/poisons in the water, sewer treatments, synthesize drugs and chemicals

Controlling Bacteria

• Refrigeration, canning, sterilization, chemical treatments

• Disinfectants used on surfaces outside the body