DNA Replication

Heredity B-4.3 Explain how DNA functions as the code of life and the blueprint for proteins. (Focus on DNA replication) B-4.4: Summarize the basic process involved in protein synthesis (including transcription and translation).

DNA Replication The double helix structure explains how DNA replication can occur. The two strands of DNA are complementary. They each can be used to make a copy of the other.

DNA Replication Before a cell divides, its DNA has to be duplicated, called DNA replication. DNA molecule separates into two strands Two new complementary strands are produced via base pairing. Happens during Interphase (S) of the Cell Cycle.

DNA Replication: Prokaryotes In prokaryotes, DNA replication starts at one point on the chromosome and proceeds in two directions until the entire chromosome is copied.

DNA Replication: Eukaryotes In eukaryotes, DNA replication starts at hundreds of places and proceeds in two directions until the entire chromosome is copied.

DNA Replication Enzymes “unzip” the DNA. Involves a host of enzymes and regulatory proteins. Principle enzyme involved is called DNA polymerase.

DNA Replication Summary (the very basics!): Step 1: The two strands (called parents) are separated Step 2: new strands (called daughters) are formed using complimentary base pairing Step3: DNA of the daughter strand zips up with a parent strand = 2 identical double helix

DNA Replication Step #1: uses the enzyme DNA Helicase It unzips the 2 parent strands separates base pairs How does it do this? By breaking hydrogen bonds between base pairs DNA helix unwinds

DNA Replication Step #2: uses the enzyme DNA polymerase Each parent strand serves as a template to make a new daughter strand The enzyme ‘reads’ the bases on the parent strand and adds the complimentary base to the daughter strand It also “proofreads” each new DNA strand to make sure that each copy is EXACT

DNA Replication Step #3: Each parent strand stays attached to it’s daughter strand Forming 2 identical double helices Referred to as semi-conservative because each new cell gets 1 old/parent strand and 1 new/daughter strand

Websites DNA Replication Animation from your textbook DNA Replication: Howard Hughes Medical Institute

Practice What would be the complimentary DNA strand to the following nucleotide sequcence? A T C C G A T T A G G C C C A T A C G

Answer A T C C G A T T A G G C C C A T A C G T A G G C T A A T C C G G G T A T G C

DNA Replication Problems What is the first step in DNA replication? What enzyme matches the bases of free nucleotides to the bass on the parent strand? If the DNA double helix were a twisted ladder, what would the sides be composed of? If the DNA double helix were a twisted ladder, what would the rungs be composed of?

Complete the following Nucleotide Base Abbreviation Complementary Base T C A G