Types of gravel include: 1  Bank gravel: naturally deposited gravel intermixed with sand or clay found in and next to rivers and streams. 2  Bench gravel: a bed of gravel located on the side of a valley above the present stream bottom, indicating the former location of the stream bed when it was at a higher level.
1 is the sixth part of 6. 2 is two sixths, and also the third part, of 6. 3 is three sixths, and also half of 6. 4 is four sixths, and also two thirds, of 6. is the sixth part of 6. 2 is two sixths, and also the third part, of 6. 3 is three sixths, and also half of 6. 4 is four sixths, and also two thirds, of 6.
So the 3' OH is always a requirement for addition of new bases to a DNA strand. The 5' refers to the dangling 5' end of the first Phosphate, while the 3' refers to the 3' OH of the Ribose sugar at the last base of the DNA. The entire reaction is catalysed by DNA Polymerase. P.S. They are not really free, there are many modifications which make them inert. So that is why DNA is anti-parallel.