22.2 Structure of Prokaryotes: Bacteria and Archaea
There are differences between the two types of cells.
The term "prokaryote" suggests that they are not the same as "eukaryotes", which are organisms whose cells contain a nucleus.
The four structures of the cell are: the cytoplasm, a complex solution of organic molecules and salts inside the cell, the double-stranded DNA genome, and the plasma Membrane, which functions as a barrier for the cell and separates it from its environment.
There are three types of prokaryotes: cocci (spherical), bacilli (rod-shaped) and spirilli (spiral-shaped).
The three basic categories of prokaryotes are cocci, spherical, and bacilli, rod-shaped.
Prokaryotes are unicellular organisms that lack internal structures.
Most prokaryotes have a cell wall.
There is a capsule outside the cell wall.
The capsule allows the organisms to attach to surfaces, protects them from dehydration, and makes them more resistant to our immune responses.
Some species use flagella and pili for attachment to the surfaces of other cells.
Extrachromosomal DNA is present in many species ofbacteria and archaea.
All prokaryotes have flagella, capsule, and pili.
The three domains of life are comprised of the two different domains ofbacteria and Archaea.
Both the Archaea and the Bacteria are prokaryotes.
Eukarya, the third domain of life, is believed to have been given rise to by an ancestors of modern Archaea.
The major groups of Archaea are shown.
The Proteobacteria, the Chlamydias, the Spirochaetes, the photosynthetic Cyanobacteria, and the Gram-positivebacteria are some of the majorbacteria.
The Alpha- to the Epsilon proteobacteria are the different classes of the Proteobacteria.
The descendants of alphaproteobacteria are thought to be the Eukary chloroplastotic mitochondria.
One of the 52bacteria is the phylum Proteobacteria.
Alpha through Epsilon is one of the five classes of proteobacteria.
This table describes the different types ofbacteria.
The shape of the bacterium is not dependent on the shape of the phylum.
The Korarchaeota, Euryarchaeota, Crenarchaeota, and Nanoarchaeota are all part of the Archaea.
The inside of a cell can be separated from the outside with the help of a thin bilayer.
The cell's permeable nature keeps it from moving into the extracellular environment, while other molecules may move through it.
The general structure of a cell is composed of two layers oflipids.
There are isoprene chains in the archaeal cell membranes.
Bilayers are found in some archaeal membranes.
There are two ways in which Archaeal phospholipids differ from those found in Eukarya.
They have branched sidechains.
An ether bond connects the lipid to the glycerol.
The prokaryotic cells have a high concentration of dissolved solutes.
The osmotic pressure within the cell is high.
The cell wall surrounds some cells and gives them rigidity.
It is located outside the cell's outer shell and prevents osmotic lysis.
There are many different forms of peptidoglycan.
The outside of cell walls of both Archaea and Bacteria contain surface layer proteins.
All Gram-positive and Gram-negativebacteria are in the same phylum.
Hans Christian Gram was the inventor of the Gram staining method.
The cell wall structure is to blame for the different responses to the staining procedure.
Gram-positive organisms have the outer membrane found in Gram-negative organisms.
Most of the rest of the cell wall is composed of acidic substances called teichoic acids.
Teichoic acids can be linked to the lipids in the plasma membrane to form lipoteichoic acids.
The cell wall is anchored by Lipoteichoic acids.
Gram-negativebacteria have a thin cell wall composed of a few layers of peptidoglycan, surrounded by an outer envelope containing lipoproteins.
The second lipid bilayer is sometimes referred to as the outer envelope.
The chemistry of the outer envelope is very different from that of the typical bilayer.
Gram positive and Gram negative are the major groups ofbacteria.
Both groups have a cell wall made of peptidoglycan, which is thicker in Gram-positivebacteria.
In Gram-negativebacteria, the cell wall is surrounded by an outer membrane.
Substances can pass through the outer membrane of Gram-negativebacteria with the help of porins.
The Archaean cell walls do not have peptidoglycan.
There are different types of archaean cell walls.
There are three types of cell walls.
Table 22.2 shows the differences between the two.
The features related to DNA replication, transcription and translation in Archaea are similar to those seen in the eukaryotes.
It is asexual in prokaryotes.
The growth of the cell leads to the creation of two separate copies of the same chromosomes.
The prokaryote is pinched inward at its equator and the two resulting cells are clones.
There is no opportunity for genetic recombination or genetic diversity, but prokaryotes can share genes by three other mechanisms.
If a nonpathogenic bacterium takes up DNA for a toxin from a pathogen and puts it into its own chromosomes, it may become pathogenic.
Genetic material may be transferred from one person to another.
There are two ways in which the DNA can be transferred, in the form of a plasmid or a composite molecule.
It can take a few minutes for a species to reproduce.
The rapid evolution of prokaryotes is possible because of the short generation time and high rates of genetic recombination.
There are three ways in which prokaryotes can exchange genes.
The cell takes up prokaryotic DNA from the environment.
The host genome may be incorporated with the DNA.
A small fragment of DNA from a different prokaryote is injected into a cell.
After the sex pilus draws the twobacteria close enough to form the bridge, DNA is transferred from one cell to another.
The artifacts in the fossil record of prokaryotes offer very little information.
The fossils look like bubbles in the rock.
The principle of the molecular clock holds that the more recent two species have diverged, the more similar their genes will be.
More genes that are different will be found in species that have diverged long ago.
The model they derived from their data indicates that three important groups ofbacteria--Actinobacteria, Deinococcus.
Actinobacteria are a group of Gram-positivebacteria that produce branched structures like mycelia and are important in the decomposition of organic waste.
Deinococcus is a group of bacterium that is resistant to ionizing radiation.
It has features of both Gram-positive and Gram-negativebacteria because it has a thick peptidoglycan layer.
The production of oxygen on the ancient earth is thought to have been done by the crucibacteria.
The timelines of divergence show that the Archaea and the bacteria differed between 3.1 and 4.1 billion years ago.
The archaean line was later diverged by Eukarya.
The work suggests that stromatolites that formed prior to the advent of cyanobacteria photosynthesized in an anoxic environment because of the modifications of the Terrabacteria for land.
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