AP Biology Ch. 27 PROKARYOTES

Bacteria on the head of a pin—they are found everywhere!

Domains of Organisms Prokaryotes are microscopic organisms without a nucleus. Prokaryotes are everywhere, outnumbering other organisms and living in every environment. Two domains of living things are prokaryotes: Bacteria and Archaea The third domain is made up of eukarytoes: Eukarya

Prokaryotic domains By comparing ribosomal RNA, genomes, and other key structural, biochemical, and physiological characteristics, prokaryotes were divided into two domains. Bacteria: live almost everywhere, cell walls contain peptidoglycan (carbohydrate) Archaebacteria: live in extreme environments, cell wall do not contain peptidoglycan, membrane lipids are different, DNA is more like eukaryotes than Bacteria

Epulopiscium fisheloni

Cocci

Bacilli

Spirilli

Cell Wall Cell walls in Bacteria contain peptioglycan; Archaea bacteria have cell walls containing polysaccharides and proteins The function of the cell wall is to maintain the cell shape, and provide physical protection for the cell

Gram staining Gram-positive bacteria have a simple cell wall with large amounts of peptidoglycan. Stain purple. Gram-negative bacteria have less peptidoglycan and are structurally more complex with an outer membrane containing lipopolysaccharides. More threatening, do not respond well to antibiotics. Stain red.

Pili and flagella Pili are hairlike appendages on the bacterium used for attaching to a surface or to each other. Flagella are whiplike structures anchored in the cell wall and plasma membrane of bacteria and other organisms, used for movement

Terms Binary fission- cell division by which prokaryotes reproduce Transformation-assimilation of external DNA by a cell Conjugation- the direct transfer of DNA between cells that are temporarily joined. Transduction- transfer of bacterial DNA (genes) from one host cell to another, usually by means of phages

Endospores Endospores are thick-coated, resistant cells produced within a bacterial cell exposed to harsh conditions. Can only be destroyed using high heat and pressure (steam at C). Autoclaving is the method used by labs and the food industry.

Nutritional modes Photoautotrophs- use light energy to drive the synthesis of organic compounds from CO 2. Chemoautotrophs- oxidize inorganic substances to obtain energy for producing organic compound from CO 2.

Nutritional modes, cont. Photoheterotrophs- use light energy to metabolize organic compounds Chemoheterotrophs- must consume organic compounds for energy and as a carbon source

Saprobes vs. Parasites Saprobes are chemoheterotroph that are decomposers, absorbing nutrients from dead organic matter. Parasites are organisms that obtain nutrition by living in or on a host, causing harm to the host organism.

Nitrogen fixation Nitrogen fixation is the process by bacteria change atmospheric N 2 into ammonia (NH 3 ). This is a form that can be used by cells to produce amino acids and other molecules.

Oxygen: yes or no? Obligate aerobes- use oxygen for cellular respiration and cannot grow without it Facultative anaerobes- use O 2 if present, but can also grow by fermentation if it is absent Obligate anaerobes- poisoned by oxygen, live exclusively by fermentation

Origin of Photosynthesis Early prokaryotes were probably chemoautotrophs, absorbing organic compounds in the primordial sea. Natural selection favored those who developed enzymes to make ATP. Some early prokaryotes may have had light- absorbing pigments, enabling them to use light energy to generate ATP and metabolize inorganic compounds, eventually fixing carbon dioxide.

Cyanobacteria Cyanobacteria developed the structures and pathways needed to produce organic compounds from CO 2 and water. They “changed the world” by producing oxygen by photosynthesis. This addition of oxygen to the atmosphere forced organisms to evolve in order to do cellular respiration. Some organisms maintained their metabolism in an anaerobic environment.

Archaea bacteria: extreme environments Methanogens- use CO 2 to oxidize H 2, producing methane (CH 4 ). Live in swamps and marshes, and intestinal tract of herbivores. Extreme halophiles- live in highly saline environments, such as the Great Salt Lake. Extreme thermophiles- thrive in very hot environments, such as hot springs and hydrothermal vents

Environmental roles Decomposers Nitrogen fixers Symbiotic relationships Pathogens

Symbiosis Mutualism- both organisms benefit. Ex) flashlight fish and bacteria Commensalism- one organism benefits while the other is not helped or harmed. Ex) Algae on aquatic turtle shells Parasitism- one organism benefits at the expense of the host Ex) tapeworms steal nutrition from the host, debilitating them

Pathogenic prokaryotes Prokaryotes that cause disease are pathogenic. Pathogenic bacteria are said to be “opportunistic” because they are normal residents of the host, but become problems when the organism has weakened defenses.

Koch’s postulates Robert Koch was a German physician who developed criteria for linking a pathogen to the disease it causes. He developed “Koch’s Postulates”: 1) Find the pathogen in each infected individual 2)Isolate the pathogen from the patient and culture it 3)Induce the disease in experimental animals by inoculating them with the pathogen 4)Isolate the pathogen in the experimental animals after symptoms develop

Endotoxins vs. Exotoxins Both of these agents are capable of causing disease. Endotoxins are components of the cell membrane of gram-positive bacteria. Exotoxins are secreted by prokaryotes, causing disease even if the bacterium itself is not present.

Salmonella