5. Sensing and Responding to the Environment Flashcards
What are signal transduction systems?
Something that has a role in sensing and responding to the environment. It is protein-based and there are two kinds: one component and two component systems. The proteins have domains.
What are one component systems?
A single protein serves two functions: one to make the text signal in another domain initiates the cellular response. The signal is received directly by the binding a small chemical from the environment to the input domain.
What are two component systems?
One protein is called the sensor. It detects the signal and interacts with the second protein called the response regulator. This band affects the output domain of the response regulator which mediate the cellular response. The signal is the direct binding of a small chemical from the environment to be input domain of the sensor proteins. However, in other two component systems, the signal is received indirectly by the sensor protein through an interaction with another protein called a chemoreceptor that binds an environmental chemical.
What are chemotaxis?
A change in motile behaviour as a result of sensing a chemical concentration difference in the environment.
Describe spatial sensing.
A concentration difference is sense by comparing the concentration of a chemical at two points in space at the same time.
Describe temporal sensing.
A concentration difference is sensible comparing the concentration of a chemical at two points in time. The prokaryote has to swim to tell the difference.
Describe changing direction of monotrichous organisms.
Some change direction by reversing flagellar rotation. This pose the cell backward in an erratic way and causes a random change in direction.
Describe changing direction in lopotrichous and peritrichous organisms.
These organisms possess many flagella. The rotation of all flagella and One Direction causes them to come together in a bundle and a change in direction is mediated by a tumble. A tumble results from a switch in the direction of rotation by at least one flagellum. The bundle flies apart and then pursues a random direction. Archaea have not been observed to tumble.
How does E. coli control and switch the direction of flagellar rotation?
The mechanism involve a transmembrane chemoreceptor protein and the two component signal transduction system composed of proteins CheA and CheY. Transmembrane chemo receptors have sites present on the periplasmic side and the cytoplasmic side. CheA is associated with the cytoplasmic portion of the chemo receptor and in the absence of an attractant bound to the chemo receptor, it rapidly phosphorylates to yield phosphorylated CheA. CheA-P phosphorylates CheY. CheY-P binds to the flagellar C ring also called the switch complex. When it is bound, the flagellum rotates in a clockwise direction and the organism tumbles. CheZ dephosphorylates CheY so tumbling is brief. With attractant present, phosphorylation of CheA is slowed.
What is constitutive, developmentally regulated, cell specific, and environmentally regulated gene expression?
Constitutive: genes expressed all the time. Developmentally regulated: genes must be expressed at different times so that different proteins are made at different times. Cell specific: all cells that make up prokaryotic organisms contain the same genetic information. Some jeans are expressed only in certain cell types. Environmentally regulated: genes that are expressed only under certain environmental conditions.
Defined regulatory proteins.
Proteins of one component systems that bind to DNA. Usually exhibit nucleotide sequence specificity.
Define effectors.
A small signal chemical derived from the environment.
Define inducers and corepressors.
Inducers: find to a repressor, causing it to dissociate from the operator. Corepressor: helps the repressor protein to bind well to operator DNA.
Describe iron acquisition proteins.
Enzymes for the synthesis of siderophores: a siderophore is a small organic molecule that has a higher affinity for ferric iron.
Membrane and periplasmic proteins for binding and transporting siderophore-ferric iron complexes: siderophores are made in the cytoplasm and moved into the environment once it has bound to ferric iron, the complex is transported into the cytoplasm.
Describe the fepCDG operon.
It’s genes are only transcribed at high levels when iron is limiting in the environment. The operator is called the fur box. Regulatory gene is called Fur. If iron is sufficient, iron binds to the for protein and changes its shape. This modifies the binding equilibrium between Fur and the operator such that Fur spends most of its time bound to the operator as a repressor.
