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DNA Replication

DNA Replication. Biology Ms. Halbohm. Replication: . Because each side of a strand of DNA double helix has all the information, due to base pairing, it is able to match the other half, which makes them complementary.

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DNA Replication

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  1. DNA Replication Biology Ms. Halbohm

  2. Replication: • Because each side of a strand of DNA double helix has all the information, due to base pairing, it is able to match the other half, which makes them complementary. • Before a cell divides, it must duplicate its DNA so that each new cell will have a complete set of DNA. • The copying process of DNA is known as replication and is carried out by a series of enzymes. (Hint: remember Avery’s experiment).

  3. Replication: • The enzyme that unwinds or “unzips” the DNA is helicase. • Its job is to come in and brake the hydrogen bonds between the nitrogenous bases and split the two strands apart. • This breaking of the bonds creates a replication bubble.

  4. Replication: • A replication bubble occurs when the hydrogen bonds are broken and the strands are unwound into a replication fork. • You would find helicase inside a replication bubble. • There may be hundreds of replication bubbles within a single cell. • Therefore, we would need a large amount of helicase to unwind the DNA.

  5. Replication: • Eukaryotic DNA (us) has over 6 millions bases in one strand of DNA. • If helicase started at one end and worked its way to the other instead of making replication bubbles, it would take years to unwind our DNA! • Replication bubbles speed things up by breaking the work up into little snip-its instead of trying to unwind it all at once.

  6. Replication: • Once the two strands of DNA are unwound, you will have two separate helices, a 5’ strand, and a 3’ strand. • These two helices are complementary. • What does complementary mean?

  7. Replication: • DNA Polymerase is the enzyme that does the majority of the work in DNA replication. • DNA polymerase’s main job is to take nucleotides and put them in the right place. • DNA polymerase needs to be told where to start by RNA primer, another enzyme.

  8. Replication: • RNA primer tells DNA polymerase where to start, and then DNA polymerase adds the correct nucleotides in the right place. • The DNA polymerase then goes and gets another nitrogenous base, and places it in the right place. • DNA polymerase can only move 5’ to 3’. • The 5’ strand is called the leading strand, and the 3’ strand is called the lagging strand.

  9. Replication: • DNA polymerase then moves 5’ to 3’ adding in nitrogenous bases where the RNA Primase tells it to until it creates a whole new strand of DNA. • Ligase is another enzyme that comes in and snips out the RNA primer, gets rid of it. • DNA polymerase’s second job is to come through afterwords and make sure all the bases are paired the right way.

  10. DNA polymerase will then take out the wrong bases and replace them with the right ones. • It “proofreads” the new strands of DNA.

  11. Replication: • Because DNA polymerase cannot move 3’ to 5’ on the lagging strand, it must create what is called an Okazaki fragment. • An okazaki fragment is a loop that is created by the DNA polymerase. • What happens is it is connected at the 3’ end, but must loop around and start at the 5’ end to add in the new nitrogenous bases.

  12. http://www.youtube.com/watch?v=OnuspQG0Jd0

  13. Next: • On a separate sheet of paper, create a step by step process of DNA replication using drawings. • Make a diagram that will be easy for you to study and memorize for the test.

  14. DNA Lab: • http://misterguch.brinkster.net/MLX031.pdf

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