Chapter #1 - The Evolutions Of Microorganisms and Microbiology Flashcards Preview

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1

Archaea

The domain of life containing anucleate cells that have unique lipids in their membranes, distinctive rRNA sequences, and cell walls that lack peptidoglycan.

Many are found in extreme environments, including those with high temperatures (thermophiles) and high concentrations of salt (extreme halophies).

Although some archae are members of a community of microbes involved in gum disease in humans, their role in causing disease hasn't been clearly established.

2

Eukarya

The Domain of life that features organisms made of cells having a membrane-delimited nucleus and differing in many other ways from Archaea and Bacteria; includes protists, fungi, plants, and animals.

3

Fungi

A diverse group of eukaryotic microorganisms that range from unicellular to multicellular forms.

Molds and mushrooms are multicellular fungi that form thin, threadlike structures called hyphae.

They absorb nutrients from their environment, including the organic material molecules that they use as sources of carbon and energy.

Because of their metabolic capabilities, many fungi play beneficial roles, including making bread rise, producing antibiotics, and decomposing dead organisms. Other fungi cause plant and animal diseases.

4

Genome

The entire genetic makeup of an organism.

5

Genomic Analysis

An approach to studying organisms that involves sequencing the genome, identifying genes, and assigning functions to the genes.

6

Koch's Postulates

A set of rules for proving that a specific microorganism causes a particular disease.

Still widely used, but their application at times is not feasible. When that is so, microbiologists sometime use molecular and genetic evidence.

7

Microbiology

The study of organisms that are usually too small to be seen with the naked eye; special techniques are required to isolate and grow them.

8

Microorganism

An organism that is too small to be seen clearly with the naked eye and lacks highly differentiated cells and distinct tissues.

9

Prions

Infectious agents, composed only of protein, that cause spongiform encephalopathies such as scrapie in sheep and "mad cow disease".

10

Prokaryotic Cells

Cells having a type of structure characterized by the lack of a true, membrane-enclosed nucleus. All known members of Archaea and most members of Bacteria exhibit this type of cell structure.

11

Protists

Mostly unicellular eukaryotic organisms that lack cellular differentiation into tissues. Cell differentiation is limited to cells involved in sexual reproduction, alternate vegetative morphology, or resting states such as cysts.

12

Spontaneous Generation

An early belief, now discredited, that living organisms could develop from nonliving matter.

13

Viroids

Infectious agents of plants composed only of single-stranded RNA.

14

Viruses

Infectious agents having a simple acellular organization with a protein coat and a cucleic acid genome, lacking independent metabolism, and reproducing only within living host cells.

Simplest viruses composed of only proteins and a nucleic acid, and can be 10,000 times smaller than a bacterium.

15

Virusoids

Infectious agents composed only of single-stranded RNA. They are unable to replicate without the aid of specific viruses that coinfect the host cell. Cause some important human diseases.

16

Domains

The accepted sorting of organisms. Bacteria (sometimes referred to as true bacteria or eubacteria), Archaea (sometimes called archaeobacteria or archaebacteria), and Eukarya (all eukaryotic organisms).

17

Bacteria

The domain of life that contains anucleate cells having distinctive rRNA sequences and cell walls that contain the structural molecule peptidoglycan.

Usually single-celled. Most have cell walls that contain the structural molecule peptidoglycan.

Although most bacteria exhibit typical prokaryotic structure, a few members off the phylum Planctomycetes have their genetic material surrounded by a membrane.

Abundant in soil, water, and air, and are major inhabitants of our skin, mouth, and intestines. Some bacteria live in environments that have extreme temperatures, pH, or salinity.

Some bacteria cause disease, but many more play beneficial roles such as cycling elements in the biosphere, breaking down dead plant and animal material, and producing vitamins.

18

Enzymes

Catalytic proteins. They speed up the myriad of chemical reactions that occur in cells. They are the workhorses of the cell.

19

Tetrahymena

A protist that contained an RNA molecule that could cut out an internal section of itself and splice the remaining sections back together. Discovered by Thomas Cech in 1981.

Important discovery because at one point in evolution, there must have been a single molecule that could do both cellular work and replicate itself, the jobs of enzymes and DNA respectively.

20

Ribozymes

Catalytic RNA molecules. Can do both cellular work and replicate oneself.

21

RNA World

Coined by Walter Gilbert in 1986. Describes a stage in evolution when RNA was capable of storing, copying, and expressing genetic information, as well as catalyzing other chemical reactions.

However, for this precellular stage to proceed to the evolution of cellular life forms, a lipid membrane must have formed around the RNA. Easy to believe because lipids spontaneously from liposomes.

22

Liposomes

Lipids are major structural components of the membranes of modern organisms. They spontaneously form liposomes, vesicles bounded by a lipid bilayer.

23

RNA's Function

Much of RNA exists in the ribosome, a structure that consists largely of rRNA and uses messenger RNA (mRNA) and transfer RNA (tRNA) to construct proteins. Also recall that rRNA itself catalyzes peptide bond formation during protein synthesis. RNA seems to be well poised for its importance in development of proteins.

ATP is a ribonucleotide and RNA can also regulate gene expression.

24

RNA Created DNA?

Because RNA and DNA are structurally similar, RNA could have given rise to double-standed DNA. It's suggested once DNA evolved, it became the storage facility for genetic info because it provided a more chemically stable structure.

25

Evolution of Metabolism

Early Earth was a hot environment that lacked oxygen. The cells that arose there must have been able to use the available energy sources under these harsh conditions. Today there are heat-loving archael species capable of using inorganic molecules such as FeS as a source of energy. Some suggest this interesting metabolic capability is a remnant of the first form of energy metabolism.

26

Universal Phylogenetic Tree

Developed by Norman Pace. It's based on comparisons of small subunit rRNA molecules, the rRNA found in the small subunit of the ribosome.

The sequences of the nucleotides in the genes that encode SSU rRNAs from diverse organisms are aligned and pair-wise comparisons are made. For each pair of SSU rRNA gene sequences, the number of differences in the nucleotide sequences is counted. This value serves as a measure of the evolutionary distance between organisms. This is a measure of relatedness, not time. We do not know when they diverged from each other.

At the center of the tree is a line labeled "Root". This is where the data indicates the last universal common ancestor (LUCA) to all three domains. The root is on the bacterial branch, so it appears Archaea and Eukarya evolved independently, separate from Bacteria.

Following the lines of descent away from the root, toward Archaea and Eukarya, it is clear that they shared common ancestry but diverged and became separate domains.

Unfortunately, the nature of LUCA is not known at this time.

27

Endosymbiotic Hypothesis

The origin hypothesis of three eukaryotic organelles: mitochondria, chloroplasts, and hydrogenosomes.

Endosymbiosis is an interaction between two organisms in which one organism lives inside the other. This hypothesis proposes that over time a bacterial endosymbiotic of an ancestral eukaryote lost its ability to live independently, becoming either a mitochondrion, if the bacteria used aerobic respiration, or a chloroplast, if the bacteria was photosynthetic.

28

Hydrogen Hypothesis

Modifies the endosymbiotic hypothesis for mitochondria. This asserts that the endosymbiont was an anaerobic bacterium that produced H2 and CO2 as end products of its metabolism. Over time, the host became dependent on the H2 produced by the endosymbiont. Ultimately, the endosymbiont evolved into one of two organelles. If the endosymbiont could perform aerobic respiration, it evolved into mitochondrion. But if it did not develop this ability, it evolved into a hydrogenosome: an organelle found in some extant protists that produces ATP by a process called fermentation.

29

Horizontal Gene Transfer

SInce the bacteria and archaea do nor reproduce sexually, they must vary their genomes through HGT.

During HGT, genetic info from a donor organism is transferred to a recipient, creating a new genotype. Thus genetic info does not need to be passed to the next generation because it can be passed between the current generation. Maybe even different microbial species.

HGT still shapes their genomes today.

30

Taxonomist's Definition of Species

Group of interbreeding or potentially interbreeding natural populations that is reproductively isolated from other groups. Definition is appropriate for plants, animals, and many eukaryotic microbes that reproduce sexually.

This definition does not apply for bacteria and archaea since they do not reproduce sexually.