Warm Up: November 1, 2013  Homework: None  Due today: Enzyme lab if it was not turned in yesterday  Warm-Up: Fear Factor

DNA Replication How DNA makes a copy of itself

Eukaryotic Cell Cycle: Mitosis

Prokaryotic Cell Cycle: Binary Fission

So what is happening basically?

Who discovered the double helix?

These Guys! Watson and Crick

Semiconserative vs. Conservative Model  Watson and Crick’s model predicts that when a double helix replicates, each of the two daughter molecules will have one old strand, derived from the parent molecule and one newly made strand  This can be distinguished from a conservative model of replication, in which the two parent strands somehow come back together after the process, which means that the parent molecule is conserved

DNA Replication Models

Meselson-Stahl Experiment  3 Theories  Experiment with E. Coli

DNA Replication: A Closer Look  The bacterium E. Coli has a single chromosome of about 4.6 million nucleotide pairs  In a favorable environment, it can copy all of its DNA and divide to form two genetically identical daughter cells in less than an hour  Each of your cells has 46 DNA molecules in its nucleus, one long double-helical molecules per chromosome  That represents 6 billion base pairs, or over a thousand times more DNA than is found in a bacterial cell

Let’s take an even closer look: Nucleotides The sugar phosphate backbone is comprised of a nitrogenous base, a sugar, and a phosphate group. This makes up a nucleotide.

DNA strands run antiparallel to each other The strands run in different directions than one another Both run in a 5’ to 3’ direction Base pairs match up accordingly (A with T, and G with C)

Enzymes involved with DNA Replication  Helicase: Unwinds DNA at replication forks  Primase: Synthesizes an RNA primer at 5’ end of leading strand and each Okazaki fragment of lagging strand  DNA polymerase III: Adds nucleotides to the 3’ end of a pre-existing DNA strand or RNA primer  DNA polymerase I: Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides  DNA ligase: Joins 3’ end of DNA that replaces primer to rest of leading strand and joins Okazaki fragments of lagging strand

Other important components of replication  Single-Strand Binding Proteins: Bind to unpaired DNA strands  Okazaki Fragments: Short, newly synthesized DNA fragments that are formed on the lagging strand during DNA replication