Chapter 23 Sections 1-6 - Prokaryotes

Ancient Organisms

• Life is estimated to have begun over 3.5 BYA based on evidence from microfossils

  • Microfossils

    • Fossilized forms of microscopic life

• Prokaryotes are the most abundant forms of organisms, estimated only 1-10% of species are known, found in every environment

• Archaea

  • Discovered in mid 1970’s, prokaryotes were divided into 2 groups

Characteristics of Prokaryotes

• Unicellular

• Small cell size

  • Compared to Eukaryotes

• No membrane bound organelles

• Internal compartmentalization

• Flagella

  • In some

• Circular chromosome of DNA, many also have plasmids

• Reproduce asexually through binary fission, can transfer genetic material between cells (horizontal gene transfer)

• Metabolic Diversity

  • Photosynthetic can be oxygenic (produce oxygen) or anoxygenic (produce sulfur and sulfate)

• Chemolithotrophic

  • Produce carbohydrates using energy stored in chemical bonds.

Domain Archaea

• Difference from bacteria

  • Cell Wall

    • Archaeal cells do not contain peptidoglycan, protein-carb found in bacterial cell walls that make their cells walls rigid

  • Have a different lipid structure in membrane

  • Flagella have a different structure

• Archaeal groups

  • (based on environment they live in) include methanogens

    • Anaerobes that produce methane, halophiles - high salt levels, acidophiles-high acid environments and themophiles - higher temps

• Replication is different

  • Single origin like bacteria but initiation and expression are more like eukaryotes

  Domain Bacteria

• Come in many shapes and sizes

• 3 shapes

  • Rod shaped, sphere-shaped, spiral-shaped

    • rod-shaped, bacilli. ex: Escherichia coli

    • sphere-shape, cocci. ex: Micrococcus luteus

    • spiral-shaped, spirilla ex: Spirillum volutans

  • Strepto

    • Chains

  • Staphylococcus

    • Clusters

• Gram Stain

  • Classified into 2 categories based on structure of cell wall, determined by technique called Gram Stain

  • Gram-positive

    • Thick layer of peptidoglycan in cell wall; appear purple under microscope after the gram-staining

  • Gram-negative

    • Thin layer of peptidoglycan in cell wall; appear reddish-pink under a microscope after gram-staining

  Characterizing Bacteria

• Early methods

  • Mobility, photosynthetic or not, unicellular or colonies, spore formation, pathogenic

    • Pathogenic means disease causing

• Molecular approaches

  • Base sequences in DNA and RNA, amino acid sequencing, whole- genome sequencing

• Domains

  • Rely on molecular approaches and rRna sequences (high level of evolutionary conservation)

• Bergey’s manual systematic bacteriology

  • Widely accepted method of classifying prokaryotes

    • There’s a major clades chart oni pg. 502 - 503

• Most recent system uses four divisions

  • Thermophiles

    • Grow in elevated temperatures, ex. Aquificae

  • Gram-positive

    • Bacilli and cocci species

      • Cause many diseases/infections in humans (anthrax, pneumonia, food poisoning)

      • Actinobacteria

        • Aerobic, decomposers, release antimicrobials that have been used to make antibiotics

  • Photosynthetic

    • Cyanobacteria

      • Base of many aquatic food chains, produce oxygen as a by product

  • Proteobacteria

    • Largest and most diverse group, include Beta, Delta, and Gamma

      • Many are pathogenic

Structure and Function of Prokaryotes

• Major Structures:

  • Cell wall, cell membrane, cytoplasm, ribosomes, DNA; sometimes capsule, pili, endospores, and flagella

• Cell wall

  • Bacterial cell walls contain peptidoglycan

  • Archaeal cell walls lack peptidoglycan

• Cell membrane and Cytoplasm

  • Lipid bilayers w/ proteins

  • Lipids and proteins of archaeal membranes differ from thosr of bacterial ones

  • Cytoplasm is a semifluid solution w/ ribosomes, DNA, small organic and inorganic molecules

• DNA

  • Prokaryotic DNA is a single closed loop of double-stranded DNA

  • Some have plasmids

    • Small, circular, self-replicating loops of double-stranded DNA

• Capsules and Pili

  • Many have outer covering of polysaccharides called a capsule that protects the cell against drying, pathogens, or harsh chemicals

  • Pili

    • Short, hair-like structures on the surface of some bacteria that help bacteria connect to each other and to surfaces, such as those of a host cell

• Endospores

  • Some of the Gram + bacteria can form a thick-coated, resistant structure called an endospore when environmental conditions become harsh

• Prokaryotic Movement

  • Many have flagella

  • Taxis [tax - iss]

    • Moving toward or away from a stimulus

    • Some have other modes

      • Slime, twisting

Structural Characteristics of Bacteria

• Capsule

  • Protects cells & aids in attachment

• Cell Wall

  • Protects cell & gives it shape

• Cell Membrane

  • Regulates movement of substances in/out

• Cytoplasm

  • Contains DNA, ribosomes, & organic compounds, transports w/in

• Nucleoid Region

  • Genetic info

• Plasmid

  • Small circular loop of DNA

• Pilus

  • Aids in attachment of cells to surfaces & other cells

• Flagellum

  • Motility

Nutrition and Metabolism

• Prokaryotes obtain nutrients either from the nonliving environment or by utilizing the products or bodies of living organisms

• Heterotrophs obtain carbon from other organisms

• Autotrophs obtain carbon from CO2

• Phototrophs get energy from light

• Chemotrophs get energy from chemicals in the environment

Reproduction and Recombination

• Usually reproduce by binary fission

• Genetic recombination in prokaryotes can occur by the following three ways

  • Transformation

    • Taking in DNA from the outside environment

  • Conjugation

    • Exchanging DNA with other bacteria with Pili

  • Transduction

    • Transmission of bacterial DNA with viruses

      Why Not Kill All Bacteria

• Decomposers

  • Break downi dead organisms and wastes

• Producers

  • Photosynthetic varieties help form the base of many food chains

• Nitrogen fixers

  • 90% of nitrogen used by other organisms comes from bacteria converting N2 in the air to a usable form

Studying Diseases

• Pathology

  • Study of diseases

• Pathogens

  • An organism that causes disease (bacteria)

• Vector

  • An intermediate host that transfers a pathogen or parasite

• Includes

  • Humans, mosquitos and other animals

Chapter 23 Sections 6-8 - Viruses

Viruses are not living organisms

• Viruses do not:

  • Grow, show homeostasis, metabolize

• Viruses do:

  • Infect cells and use the cell to make more viruses

  • Cause disease in many organisms

Parts of a Virion (a virus particle)

• Nucleic acid

  • RNA (retrovirus) or DNA

• Capsid

  • Protein coat the surrounds the DNA or RNA in a virus

• Simple shapes

  • Helical or icosahedral

• Lipid Membrane

  • A membrane around the capsid in many animal viruses

Retroviruses

• Special class of RNA viruses

  • When retroviruses infect cells, they make a DNA copy of their RNA by injecting the enzyme, reverse transcriptase into the cell

  • This DNA is inserted into the DNA of the host cell

  • Examples

    • HIV

      • Causes AIDS

    • HTLV I and II

      • Can cause leukemia and lymphoma

Bacterial Viruses

• Known as Bacteriophages

• Invade cells and use the host cell’s machinery to synthesize more of their own macromolecules

• Once inside the host, the phage or virus will either go into a:

  • Lytic cycle

    • Destroying the host cell during reproduction

  • Lysogenic Cycle

    • A parasitic type of partnership

Lytic Cycle

• The virus takes over the host cell’s machinery and produces more of itself