DNA Replication

DNA FUN FACTS Humans share 50% of their DNA with bananas. Cells can contain 6-9 feet of DNA. If all the DNA in your body was put end to end, it would reach to the sun and back over 600 times. DNA in all humans is 99.9 percent identical. It is about one tenth of one percent that makes us all unique, or about 3 million nucleotides difference. DNA can store 25 gigabytes of information per inch and is the most efficient storage system known to human. So, humans are better than computers!! In an average meal, you eat approximately 55,000,000 cells or between 63,000 to 93,000 miles of DNA. It would take a person typing 60 words per minute, eight hours a day, around 50 years to type the human genome.

Remember the “CELL CYCLE”?

Which model does DNA follow? THE 3 IDEAS: Semi-conservative: One NEW strand with the PARENT strand Conservative: 2 NEW strands Dispersive: NEW and PARENT are intersperced.

Meselson and Stahl

Remember those #’s? 3’ 5’ 3’ 5’

THE PROCESS

What were those enzymes called? Helicase DNA Polymerase DNA Ligase

DNA Replication There are 4 main stages: Initiation: When a portion of the double helix is unwound. Elongation: When two new strands of DNA are assembled. Termination: When the new DNA molecules re-form into helixes. Proofreading and Correction: Occurs throughout the process to minimize the errors that may occur.

Initiation: The enzyme Helicase unwinds the DNA model by breaking H-bonds. Elongation: The enzyme DNA Polymerase adds complimentary nucleotides to the leading strand in the direction of 5’-3’ Since the lagging strand is facing the opposite direction it must be built in the 3’ to 5’ direction. Thus it is copied BACKWARDS in little fragments called “Okazaki” fragments Since DNA can only be put together in the 5’ to 3’ direction due to the structure of the enzyme. These fragments are glued together by the enzyme DNA ligase. Termination: Once the DNA has been copied, it separates into 2 strands and winds back together. Proofing: DNA Polymerase runs over the new strands to double check for mismatches. This improves accuracy up to one error per million base pairs.