Kamis, 07 November 2013

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Hypotheses on DNA Replication Animation Model

DNA Replication Most cells in living organism undergo DNA replication within their nucleus which  occurs before cell division.  Just like any other chemical reactions within cell, replication  is also a chemical  reaction  involving some enzymes  as follows.

  • DNA polymerase functions in new DNA elongation process in replication.
  • Helices functions is to unwind double helix DNA in replication.
  • DNA primase functions to assembly RNA nucleotides to form primary RNA. Primary RNA is the first strand in elongation process.
  • DNA ligase functions to assembly DNA fragments into growing strands.
  • DNA nuclease functions to cut DNA strand, such as when damage occurs in certain part of DNA strand.

There are three hypotheses on DNA replication that explain how double helix DNA makes the copy of itself as follows.
  • Conservative explains that the two strands of DNA generate a completely new strands.
  • Semi-conservative explains that both of DNA strands unwind and each strand produces a new DNA strand that is the complementary sequence to the parental DNA.
  • Dispersive explains that the two DNA molecules with section of both old and new DNA interspersed along each strand. Therefore, the new strands are a mix of old and new strands.

DNA  replication Animation model.  (a) Hypotheses  conservative,  (b) hypotheses semi-conservative,  dan (c) hypotheses dispersive.

In 1950s, Franklin Stahl and Matthew Meselson tested the three hypotheses  of DNA replication by using bacteria E.coli. Their Experiment result showed that only semi-conservative hypothesis was considered  to be the right one  to explain  DNA  replication,  while conservative and dispersive  hypothesis  were not proved  yet.

DNA  Animation replication. Base  added  in new  nucleotide  strands.

DNA replication begins with the unwinding of two polynucleotide chains, each of which functions  as template.  To synthesize a new complementary chain,  helicase  enzyme forms  replication  bubbles. A single strand  bond protein will make  the both. strands  in each bubble stays separated.  Replic

ation  bubbles  in eukaryote  can reach  hundreds to thousands  along the DNA molecule.
At the end of each bubble  there  is the  replication  fork, which  is a Y form area. Fragment, which is in the form of DNA nucleotides, one by one,  is formed  and added  to new nucleotide  until  it makes  a long nucleotide  chain. The fragment addition is catalyzed by DNA polymerase, whereas the attachment of each  fragment along DNA strand  is done by DNA  ligase. After  the formation of new DNA strands  is done, each of the two old strands will wind again.

source:life:the science biology, 2003

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