I do not understand the 3' and 5' ends in DNA replication. In my textbook, it says that DNA polymerase can only grow in the 5' to 3' direction, and that DNA grows in short pieces?? This just does...

I do not understand the 3' and 5' ends in DNA replication. In my textbook, it says that DNA polymerase can only grow in the 5' to 3' direction, and that DNA grows in short pieces?? This just does not make sense! I've tried rereading a million times and even watching videos, but I just cannot get this through to understand. Can someone explain this to me in a way I can understand? Thanks!

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gsenviro | College Teacher | (Level 1) Educator Emeritus

Posted on

The DNA molecule has two strands that are interconnected in such a fashion as to give it a double-helical shape. Each strand contains four different types of nucleotides, corresponding to four different nucleobases Adenine (A), Guanine (G0, Cytosine (C) and Thymine (T). Each nucleotide contains deoxyribose sugar, a phosphate and one of these nucleobases. 

The 3' and 5' ends in DNA refer to the location of carbon atom in deoxyribose sugar to which the next phosphate in the chain attaches. Now the two DNA strands are anti-parallel to each other in the sense that while one may have 5' to 3' directionality, the other will have 3' to 5' directionality. 

The DNA replication is carried out by enzymes known as DNA polymerase. These enzymes extend the DNA strand by progressively adding complementary nucleotides to the DNA strand through phosphodiester bonds. The DNA replication always takes place in 5' to 3' direction, without exception. The nucleotide addition by DNA polymerase is highly accurate with an error of less than 0.1 in every  million nucleotides added. The 5' to 3' replication directionality is sometimes confused with 3' to 5' directionality of DNA reading. The replication process is initiated by addition of a initiator protein at 3' end, which is what is meant by DNA reading. However, the replication or addition of nucleotides always takes 5' to 3' directionality.

Hope this helps.

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Nolan McShea | Student, Grade 11 | (Level 2) Honors

Posted on

Thanks. I understand how on one strand, the DNA Polymerase continually makes a daughter strand, but I just don't really understand the opposite side, where on my textbook, it says that the polymerase molecules need need to work outward from the forking point, and  that the new daughter strand is created in short pieces.. why so? What does the outward of the fork mean?

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