Bell Work DNA replication is the process of making a copy of DNA. DNA replication occurs before a cell divides so each cell has a copy of DNA. Grab science book and find out: How do you think DNA makes a copy of itself?

DNA Replication…. Why? Allows to exact copies of DNA to be made New cells have DNA identical to original cell’s DNA

Replication steps 1. Unwinding and Separating DNA strands 2. Adding Complementary Bases 3. Formation of two identical DNA molecules

Step 1… Unwinding Double helix unwinds Two strands separate and form a Y-shape Y-shape is called Replication Fork

Step 2… Adding complementary bases New nucleotides are added at the fork to each side Base pairs formed according to base-pair rule Example: Original strand has Thymine, then adenine will be paired with Thymine as new strand forms Two original strands serve as templates for two new strands

Step 3….. Formation of Two Identical DNA molecules Once whole sequence of DNA is copied two identical strands of DNA is formed Each double-stranded helix has one original one new strand All nucleotide sequences are identical to original DNA molecule

Replication Proteins DNA helicase – enzyme that unwinds DNA Breaks Hydrogen bonds; unwinds; replication fork DNA Polymerase - enzyme that catalyzes formation of DNA molecule Adds nucleotides to each base pair Can also backtrack and proofread if wrong nucleotide is added Reduces errors - 1 in a billion

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Grab science book turn to page 303 Answer questions 1-3 “Quick Lab” on your notes at bottom of page.