Download Chapter 21

Chapter 21
DNA Replication
Objectives
• Explain the importance of DNA replication in cell reproduction
DNA replication
• During interphase S: DNA is duplicated prior to mitosis.
• Each parent strand serves as a template for making a copy of a new
strand of DNA.
• It is semiconservative because each parent strand is conserved in one
of two DNA strands.
Replication
• DNA helicase enzyme breaks the hydrogen bonds between AT and CG
• DNA polymerase enzyme adds new DNA nucleotides, which are always present in the
nucleus to the complementary strand.
• Adenine bonds to Thymine, and Cytosine bonds to Guanine.
•
•
•
•
•
•
•
Ligase enzyme binds or seals breaks in the sugar-phosphate backbone.
RNA primase lays a starting sequence.
3’ to 5’ direction lagging strand.
5’ to 3’ direction is the leading strand.
Okazaki fragments are made on the lagging strand.
DNA returns to a coiled structure.
Two identical DNA strands are made.
• Takes about 8 hours to complete 3 billion base pairs.
• https://www.youtube.com/watch?v=dKubyIRiN84
Mutations
• Sometimes an errors occurs where one base mistakenly pairs with a
wrong base.
• Cell enzymes repair most mistakes.
• Mutations can be good or bad for the organism.
• Variation makes you different than your neighbor.