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
• https://www.youtube.com/watch?v=TNKWgcF
PHqw
Grab science book turn to page 303
• Answer questions 1-3 “Quick Lab” on your
notes at bottom of page.