The false statement is: (a) Transcriptional regulators usually interact with the sugar–phosphate backbone on the outside of the double helix to determine which DNA sequence to bind.
Transcriptional regulator or factor is protein with the ability to control and regulate gene expression at the transcription level by binding to DNA. Transcriptional factors have domain-DNA-binding domain which contains structural motif that recognizes DNA and it is responsible for the attachment to specific DNA sequence. It usually binds to the DNA major groove (hydrogen bonding) because it is less degenerate than that of the DNA minor groove.
Transcriptional factors also contain trans-activating domain for the binding of other proteins and signal-sensing domain for the detection of external signals.
Answer:
Blood clothing is an example of positive feedback.
This type of feedback mechanism is useful to the body because it multiplies the factor that intervenes in clotting accelerating the process.
If a toxin affects the molecules that signal for platelets the feedback will not be effective enough to produce clotting and the body will keep bleeding.
Explanation:
Blood clotting is an example of positive feedback due to the fact that when the vascular endothelium is damaged platelets will go to this area and activate themselves once they are in contact with the collagen fibers of the damaged structure. When the platelets are activated they will release the contents that is stored in their granules. One of the contents is a Gq-linked protein receptor cascade, that will increase the concentration of calcium in the platelets. Calcium activates protein kinase C, which, in turn, activates phospholipase A2 (PLA2). PLA2 will modifies an integrin membrane increasing its affinity to bind fibrinogen. The activated platelets change their shape , and the fibrinogen cross-links with the integrin membrane aiding in the aggregation of adjacent platelets. After this the coagulation cascade takes place. there are two pathways the extrinsic and the extrinsic one.
The extrinsic pathway will be activated due to tissular factor released by the platelets and the intrinsic pathway will be activated due to endothelial collagen. The final product of both pathways is factor x.
Factor x will transform prothrombin into thrombin will activate the conversion of fibrinogen into fibrin. Thrombin will form a net of fibrin that will the clot.
A cascade reaction is useful because every component of the cascade are related making a quick reaction once that one of then is activated and can activate other or more factors.
If a toxin affects the molecules that signals for platelets, platelets will not go to the damaged area and in consequence there will not be thrombin and fibrin to form the clot together with platelets.
The sky is blue because blue<span> light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. </span>Blue<span> is scattered more than other colors because it travels in shorter and smaller waves. This is why we see a </span>blue sky most<span> of the time. Hope this helps!</span>
