24 Nov DNA REPLICATION
Science tuition classes in Miracle Learning Centre are easy to understand and help you to improve in your grades. If you do not understand science, you must definitely attend the science tuition class at Miracle Learning Centre. Let us learn about the DNA replication in this science tuition lesson.
A student at Miracle Learning Centre has already learnt in primary school science that the sperm and egg cells from your mother and father fuse to become a zygote, a single cell organism. He was interested to know how does the sperm and egg cells from your parents, after fertilisation, become the many cells in your body today, and asked his teacher, Ms Ong, at Miracle Learning Centre. This was his reply: Cells are constantly dividing, and that requires a complete copy of all of that DNA information in the sperm cell and egg cells. How does DNA replication work? The process starts when DNA is wrapped around special protein molecules called histones. The combined loop of DNA and the protein formed is called a nucleosome. Next, the nucleosomes are packaged into a thread. The end result is a fibre known as chromatin. The fibre is then looped and coiled yet again leading finally to the familiar shapes known as chromosome, which can be seen in the nucleus of dividing cells. Chromosomes are not always present. They form around the time two cells divide when the two copies of the cell’s DNA need to be separated.
When DNA replicates, its two strands are separated by the enzyme helicase and single stranded DNA proteins keep the strands from re-annealing. The double stranded DNA is separated into 2 strands – the leading strand (5′ to 3′ direction) and the lagging strand (3′ to 5′ direction). The DNA strand that encodes the leading strand forms from its 5′ to its 3′ end using DNA polymerase III. However, in the lagging strand, this presents a problem. DNA can only be copied in the 5′ to 3′ direction, and the lagging strand is 3′ to 5′. It has to form from 5′ to 3′ too. Thus, it forms in pieces called Okazaki fragments. First, a RNA primase lays down an RNA primer. Then, DNA Polymerase III lays down new DNA. the process repeats again and again. DNA Polymerase I replaces the RNA primers with DNA. Finally DNA ligase links the Okazaki fragment, and the cycle repeats if they need to replicate more DNA.
Miracle Learning Centre would like to bring you more articles on science tuition concepts. We hope you have understood how DNA replicates. Do come to Miracle Learning Centre for more science tuition lessons to learn more about DNA replication.
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