Class A (type D) CpG ODNs (CpG-A ODNs) contain a central palindromic phosphodiester (PO) CpG sequence and a PS-modified 3â poly-G tail. The poly G tails form intermolecular tetrads that result in high molecular weight ordered structures.
Why does a tornado form when cold and hot air meet? The collision of warm and cold air is not the direct cause of a tornado, nor is it absolutely necessary. When a cold air mass pushes into a warm air mass (this is called a câ¦old front) the warmer, less dense air is forced upwards.
Tornado alley. Click on the image to view the large version. The middle part of the United States is an area that has many tornadoes, particularly in the spring. This area is known as tornado alley. The reason is because it is an area where large cold air masses and large warm air masses collide. When these air masses crash into each other, it can cause thunderstorms and they can create tornadoes.