Recent Changes

Escherichia Coli (bacteria)
Aynslie D'Avanzo November-December 2013
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Classification/Diagnostic Characteristics

The only predators of E. coli are bacteriophages, or viruses that target bacteria, and their human hosts. Viruses use cells to produce viral copies of itself, starting by inserting its own genetic material into that of the target. E. coli have a restriction enzyme known as EcoRI, which recognizes particular DNA sequences injected by bacteriophages sequences and cuts it out to protect the cell from being overtaken. When pathogenic strains of E. coli target their larger predator, they release endotoxins, which are lipopolysacchrides that form part of the outer bacterial membrane, when they lyse. These chemicals vary by strain, commonly causing fever, vomiting, diarrhea, or any combination of the three, but rarely cause death. E.coli have become resistant to antibiotics due to overuse, which kills off the vulnerable strains and gives rise to those that are not effected by such medications. Mutations in the genetic information of the organism allow it to possibly and unintentionally change in a way that gives it antibiotic resistance, and may then undergo conjugation, in which genes in a plasmid are transferred from one cell to another. Antibacterial resistance and other defensive genes are often passed this way in order to maintain the species.
Nutrient Acquisition
Passive transport via diffusion across plasma membrane
Limited to few molecules due to selective nature of cytoplasmic membrane
small, uncharged polar molecules and gases can easily diffuse through the hydrophobic membrane
Solute concentration drives diffusion across the membrane, concentration inside the cell can never be more than outside the cell for diffusion to occur
Facilitated diffusion via protein channels
Carrier proteins (uniporters) and Porin proteins assist molecules to enter
A carrier protein, called GlpF permease (GlpF gylcerol MIP channel), transports glycerol across the plasma membrane in E. coli
Transports molecules across the membrane at a faster rate than diffusion, however, does not require energy
Porin Proteins facilitate transport of molecules from outside the cell to inside the periplasmic space (surrounded by two selectively permeable barriers) and have two types
Nonspecific Porins allow a wide range of small, hydrophobic and hydrophilic molecules to pass through the membrane. Large molecules cannot pass through the membrane by nonspecific porins due to the size of the pores in the proteins
Substrate-Specific Porins recognize specific types of molecules and allow them to pass through. Most of these molecules are too large to enter E. coli via nonspecific porins. Some of the substrate-specific porins will recognize a similar family of molecules.
Active Transport via proteins and expenditure of cellular energy
ABC transporters (ATP Binding Cassette transporters): use hydrolysis of ATP as the driving force of uptake. A solute binding protein, a transmembrane spanning protein, and a ATP hydrolyzing protein make up the ABC transporter system
P-Type ATPases: transport cations such as K+ and Mg+2 (using ATP as the source of energy)
Secondary transport systems: uptake many amino acids, inorganic molecules, and sugars
Group translocation systems: more complex than other systems, chemically modifies molecules as the enter the cell, and uses PEP (phosphoeonolpyruvate) or ATP as energy source (2)
AsAs a single ABC transporters, are one way that molecules are actively transported into the cell, and are made of molecules. Another type is P-Type ATPases, which are proteins that transport cations like K+ and Mg+2, also using ATP as the source of energy. Secondary transport systems uptake many amino acids, inorganic molecules, and sugars. Group translocation systems are more complex than other systems, as they chemically modify molecules upon entry, using either ATP or PEP (phosphoeonolpyruvate, another energy carrying molecule) as energy sources (2).
Reproduction and Life Cycle
Matured individual E. coli reproduce asexually via binary fission. Each individual has a single circular chromosome that must be replicated, so two replication forks depart from the ori (origin of replication) sequence. Even though it takes 40 minutes to replicate an entire chromosome, E. coli daughter chromosomes begin replication again prior to completion, and therefore are able to divide approximately every 20 minutes. All offspring are genetically identical to the parent, and thusly are clones, so any changes in the genetic coding between generations are due to mutations during chromosome replication. Only prokaryotes may undergo binary fission, and it begins with DNA replication at the ori sequence in the centre of the cell. Secondly, the cell replicates its DNA as it grows, followed by the daughter chromosomes separating, led by the regions including the ori. Finally the cells divide by pinching in at the middle and cytokinesis--the division of cells--is complete.

Secondary transport systems: uptake many amino acids, inorganic molecules, and sugars
Group translocation systems: more complex than other systems, chemically modifies molecules as the enter the cell, and uses PEP (phosphoeonolpyruvate) or ATP as energy source (2)
also doesn't consume energy from the cell. Carrier proteins, sometimes called uniporters, and porin proteins assist molecules that cannot diffuse through the plasma membrane to enter; for example, the carrier protein GlpF permease, called the GlpF glycerol MIP channel, transports glycerol across the plasma membrane in E. coli. Molecules are able to cross the membrane at a faster rate than diffusion without requiring energy with facilitated diffusion. Surrounded by two selectively permeable barriers, two types of porin proteins facilitate the transport of molecules from the outside of the cell to inside the periplasmic space. Nonspecific porins allow a wide range of small, hydrophobic and hydrophilic molecules to pass through the membrane, but large molecules cannot pass through these porins because of their small size. On the other hand, substrate specific porins recognize specific types of molecules and allow them to pass through. Most of these molecules are too large to enter E. coli cells through the nonspecific porins. Some of the substrate specific porins will recognize a similar family of molecules. The third method of nutrient acquisition is active transport with proteins and the use of cellular energy. ATP (the energy transporting molecules of cells) Binding Cassette transporters, known also as ABC transporters, are made up of a solute binding protein, a transmembrane spanning protein, and an ATP hydrolyzing protein. The hydrolysis--or the splitting of a molecule via a reaction with water--of ATP is the driving force of the uptake of molecules.
Reproduction and Life Cycle
Matured individual E. coli reproduce asexually via binary fission. Each individual has a single circular chromosome that must be replicated, so two replication forks depart from the ori (origin of replication) sequence. Even though it takes 40 minutes to replicate an entire chromosome, E. coli daughter chromosomes begin replication again prior to completion, and therefore are able to divide approximately every 20 minutes. All offspring are genetically identical to the parent, and thusly are clones, so any changes in the genetic coding between generations are due to mutations during chromosome replication. Only prokaryotes may undergo binary fission, and it begins with DNA replication at the ori sequence in the centre of the cell. Secondly, the cell replicates its DNA as it grows, followed by the daughter chromosomes separating, led by the regions including the ori. Finally the cells divide by pinching in at the middle and cytokinesis--the division of cells--is complete.

Secondary transport systems: uptake many amino acids, inorganic molecules, and sugars
Group translocation systems: more complex than other systems, chemically modifies molecules as the enter the cell, and uses PEP (phosphoeonolpyruvate) or ATP as energy source (2)
cellular energy. Diffusion limits the cell's intake to a few molecules due to the selective nature of the cytoplasmic membrane, which allows only small, uncharged polar molecules and gases through. In order for nutrients to be taken in, the concentration outside of the cell must be greater than that inside, so that the molecules flow into the cell where concentration is lower. Just like diffusion, facilitated diffusion also doesn't
Reproduction and Life Cycle
Matured individual E. coli reproduce asexually via binary fission. Each individual has a single circular chromosome that must be replicated, so two replication forks depart from the ori (origin of replication) sequence. Even though it takes 40 minutes to replicate an entire chromosome, E. coli daughter chromosomes begin replication again prior to completion, and therefore are able to divide approximately every 20 minutes. All offspring are genetically identical to the parent, and thusly are clones, so any changes in the genetic coding between generations are due to mutations during chromosome replication. Only prokaryotes may undergo binary fission, and it begins with DNA replication at the ori sequence in the centre of the cell. Secondly, the cell replicates its DNA as it grows, followed by the daughter chromosomes separating, led by the regions including the ori. Finally the cells divide by pinching in at the middle and cytokinesis--the division of cells--is complete.

Secondary transport systems: uptake many amino acids, inorganic molecules, and sugars
Group translocation systems: more complex than other systems, chemically modifies molecules as the enter the cell, and uses PEP (phosphoeonolpyruvate) or ATP as energy source (2)
As a single celled organism, E. coli have three methods of acquiring nutrition: passive transport via diffusion across the plasma membrane, facilitated diffusion via protein channels, and active transport via proteins and expenditure of cellular energy.
Reproduction and Life Cycle
Matured individual E. coli reproduce asexually via binary fission. Each individual has a single circular chromosome that must be replicated, so two replication forks depart from the ori (origin of replication) sequence. Even though it takes 40 minutes to replicate an entire chromosome, E. coli daughter chromosomes begin replication again prior to completion, and therefore are able to divide approximately every 20 minutes. All offspring are genetically identical to the parent, and thusly are clones, so any changes in the genetic coding between generations are due to mutations during chromosome replication. Only prokaryotes may undergo binary fission, and it begins with DNA replication at the ori sequence in the centre of the cell. Secondly, the cell replicates its DNA as it grows, followed by the daughter chromosomes separating, led by the regions including the ori. Finally the cells divide by pinching in at the middle and cytokinesis--the division of cells--is complete.

Movement
Motile E. coli propels itself forward by rotating its flagella counterclockwise. Periodically, it will stop, tumble, and continue moving in a new, random direction, as seen in part "A" of the diagram. Chemotaxi is the movement toward or away from chemicals. As seen in part "B," E. coli will travel toward substances such as amino acids and sugars (1).
{http://www.ccbi.cam.ac.uk/iGEM2005/images/f/f9/Chemotaxis.gif} (11)Model of the Movement and Chemotaxi of E. coli(11)
Sensing the Environment
E. coli respond to changes in the environment by changing the expression of their genes. Individuals can sense either the presence of absence of gasses and chemicals in its environment, and swims towards or away from what it senses as the sources. An individual can stop swimming and grow fimbriae that specifically attach to a cell or a receptor on the surface of the cell. When mainly lactose is present, the cell produces three lactose-specific enzymes that transport the sugar into the cell and breaks it down; when the environment primarily contains glucose, very few of those enzymes are present. The coding for the lactose metabolizing enzymes are adjacent to each other on the E. coli chromosome, and therefore are all created at once. Repressor proteins known as lac operons prevent transcription until the lac-encoded proteins are needed--when lactose is the predominant sugar available in the environment. Either all or none of these enzymes are made at any particular time.

{http://www.ccbi.cam.ac.uk/iGEM2005/images/f/f9/Chemotaxis.gif} (11)
Sensing the Environment
Must be ableE. coli respond to changes in chemical environment as the foods consumedenvironment by its host changesItchanging the expression of their genes. Individuals can sense the presence orof absence of in its environmentenvironment, and swimswims towards or away from them. E.Coliwhat it senses as the sources. An individual can stop cell or a receptor on the cell.
E. coli responds to changes by changing expression of genes
When When mainly lactose is present, the cell produces enzymes are present
Codingpresent. The coding for the at once. Either all or none of these enzymes are made at any particular time.
Has aRepressor proteins known as lac operon: repressor protein preventsoperons prevent transcription until proteins are needed (not transcribed unlessneeded--when lactose is the prodominantpredominant sugar available in the cell's environment)environment. Either all or none of these enzymes are made at any particular time.
Gas Exchange
Anaerobic respiration is used by E. coli to perform gas exchange and is done through the membrane of the cell.
Waste Removal
semipermeable plasma membrane. (14)membrane (14).
Environmental Physiology
E.coli thrives in an environment with a neutral pH level and a stable temperature around 37º Celsius; however it does possess the adaptive qualities necessary to survive in an environment with changing temperatures. Utilizing its peritrichous flagella, or flagella that cover the body surface in a uniform distribution, E.coli move away from specific areas where it senses chemical imbalances and changes in osmolarity. E.coli also physically change the diameter of porins found on the cell membrane in response to changes in temperature and concentration, allowing larger molecules to pass through if necessary by expanding, and contracting to prevent permeation by undesired molecules. (10)