Archaea Facts and Characteristics

Chapter 28: Microbiology

• About 2 pounds of bacteria live in or on your body. This is true.
• Microbiology is the study of microbes, including bacteria, archaea, protists, fungi, viruses, and prions.
• Microbes are abundant in air, soil, water, and on objects.
• Some bacteria and fungi are decomposers.
• Photosynthetic protists and bacteria are primary producers.
• Microbiota are on our bodies.
• Pasteur's experiment disproved spontaneous generation.

Pasteur and Spontaneous Generation

• In his first experiment, Pasteur boiled broth in flasks to sterilize it. The flasks were opened briefly to the outside air, and 89% showed growth.
• In Pasteur's second experiment, the flask was open to the air, allowing air to enter, and only 32% showed growth.
• Pasteur's experiments concluded that all organisms come from preexisting organisms.

Origin of Microbial Life

• All life traces back to a single common ancestor called the last universal common ancestor (LUCA).
• Stage 1: Organic monomers (evolution of monomers) - Primordial Soup
• Oparin-Haldane hypothesis
• Miller-Urey Experiment
• Stage 2: Organic polymers (evolution of polymers)
• Stage 3: Protobionts (evolution of protobionts)
• Development of the cell membrane
• Stage 4: Living cells (evolution of living cells)

The Evolution of Monomers

• Miller-Urey experiment (1953)
• Early Earth had a reducing atmosphere.
• After a week, water turned brown.
• Amino acids and other organic acids were produced.
• Tested over the decades.
• Even greater numbers of organic molecules were produced.
• Other sources of organic monomers include hydrothermal vents and meteors/comets. - Other sources are also possible based on scientific studies.

The Evolution of Polymers

• Protein First Hypothesis
• Solar energy causes amino acids at the shoreline to form simple polypeptides with catalytic properties.
• RNA-first hypothesis
• RNA evolved first and acted as hereditary material and enzyme.

The Evolution of Protobionts

• Protobionts have outer membranes made of fatty acids, proteins, and other polymers inside.
• Larger "Vesicles" able to divide.

The Evolution of Living Cells

• Cells with membranes and DNA, RNA, and proteins.
• RNA first hypothesis supports this theory.
• Codon Chart seems optimized to deal with mutations.
• May have been natural selection on codons.

Prokaryotic Diversity: Archaea

• Domain Bacteria and domain Archaea are both prokaryotes.

Archaeal Size and Structure

• Archaea are small.
• Their genome is a single, closed, circular DNA molecule.
• Their plasma membrane is a single lipid layer with branched side chains.
• Three main types based on unique habitats and metabolism.

Organic Monomers

• Organic monomers (like amino acids and sugars) could form without the presence of life. - This is supported by evidence.

Types of Archaea

• Halophiles: love salt. Live in highly saline environments (Great Salt Lake, Dead Sea, etc.).
• Thermoacidophiles: thrive in extremely hot and acidic environments (hot springs, geysers).
• Methanogens: produce methane. Live in anaerobic environments (swamps, intestines). (cows and other animals, including humans)

Domain Bacteria

• Bacteria are the most common type of prokaryote on Earth.
• Over 11,000 different species; millions are likely present.
• Most bacteria are between 0.2-10µm.
• Three basic shapes: rod (bacillus), spherical (coccus), and spiral (spirillum)

Bacterial Size and Structure

• Motile bacteria have flagella for locomotion (structurally different from eukaryotic flagella).
• Some bacteria have fimbriae used to bind to surfaces.
• Certain bacteria that infect the urinary tract use fimbriae to attach to cell surfaces.
• Most bacteria have a single circular chromosome located in the nucleoid region. - Many bacteria also possess plasmids. (accessory DNA rings that carry certain genes).

Bacterial Reproduction and Gene Transfer

• Bacteria reproduce asexually, by binary fission.
• One bacterial cell splits into two daughter cells.
• Some bacteria form resistant endospores for survival in harsh environments.
• Mechanisms of genetic recombination include conjugation (transfer by a sex pilus), transformation (DNA uptake from environment), and transduction (viral transfer).

Bacterial Metabolism

• Most bacteria are heterotrophic (require organic carbon for food).
• Some bacteria are chemoautotrophs (use inorganic chemicals to fix carbon dioxide into organic form).
• Cyanobacteria are photoautotrophs (have chlorophyll and perform photosynthesis).

Bacterial Diseases in Humans

• Most bacteria do not cause disease.
• Pathogenic bacteria often have genes for virulence factors (toxins or factors for tissue attachment).
• Streptococcus infections (strep throat, impetigo, rheumatic fever, scarlet fever)
• Staphylococcus aureus and MRSA (skin infections, often antibiotic-resistant).
• Food poisoning (some produce toxins while others cause infections).

Viruses and Prions

• Viruses are acellular structures that are parasites.
• Viruses use the host cell's replication machinery (like ribosomes) and certain enzymes.
• Viruses are smaller than bacteria (0.03-0.2µm).
• Two main components are the capsid (outer protein layer) and nucleic acid core (DNA or RNA).
• Some viruses have an envelope.

Viral Reproduction

• Viruses are specific to a particular host.
• Spikes on a virus configure exactly to receptor molecules on the host cell membrane.
• The reproductive cycle of an enveloped animal RNA virus typically has six steps (attachment, entry, uncoating, replication, assembly, and budding).

The Common Cold and Influenza

• Colds are mainly caused by rhinoviruses (over 100 species).
• Flu is caused by influenza viruses.
• Antigens on viruses can change, resulting in antigenic drift (mutation) or antigenic shift (new combinations of surface spikes).

Prions

• Prions are protein infectious particles.
• Normal proteins change shape, causing other proteins to change shape.
• This causes degenerative diseases in the nervous system.
• Prions can be passed through ingestion of infected tissue (e.g., mad cow disease, chronic wasting disease).