I. DNA: “deoxyribonucleic acid” We know traits are inherited but how are they inherited?

A. X-ray Evidence 1952 Rosalind Franklin took an x-ray diffraction to take picture of DNA shape Picture gave clues to structure of DNA

Watson & Crick Using Rosalind Franklin’s work, Watson & Crick made a model of DNAUsing Rosalind Franklin’s work, Watson & Crick made a model of DNA Created with cut-out pieces held together with wireCreated with cut-out pieces held together with wire Won Nobel PrizeWon Nobel Prize

Enzo di Fabrizio (University of Genoa, Italy) Developed a technique that pulls strands of DNA between two miniscule silicone pillars, then photographs them via an electron microscope.

1. Watson and Crick's model of DNA was a double helix - two strands were wound around each other.

B. Why is DNA important? Contains instructions for genes, which determine traits of an organism Contains instructions for genes, which determine traits of an organism C. Location of DNA? Nucleus Nucleus

The Components & Structure of DNA Nucleotide 1.5-carbon sugar DEOXYRIBOSE DEOXYRIBOSE 2. Phosphate group group 3. Nitrogenous base (4) base (4)Nucleotide 1.5-carbon sugar DEOXYRIBOSE DEOXYRIBOSE 2. Phosphate group group 3. Nitrogenous base (4) base (4) i. Adenine i. Adenine ii. Thymine ii. Thymine iii. Guanine iii. Guanine iv. Cytosine iv. Cytosine i. Adenine i. Adenine ii. Thymine ii. Thymine iii. Guanine iii. Guanine iv. Cytosine iv. Cytosine

Chargaff ’ s Rule Something interesting about nucleotidesSomething interesting about nucleotides % A = % T% A = % T % C = % G% C = % G Erwin Chargaff Photo credit:

- SUGAR & PHOSPHATE form backbone/sides - The BASES form the “ steps ” of ladder, held together by Hydrogen bonds

II. DNA Replication Think about DNA ’ s structure To know one side, you know the opposite! Perfect for use of replication! Each side of DNA provides a template to reproduce the other ½

II. DNA Replication A.When in cell cycle? S phase of Interphase! B.Purpose?: To provide identical copy of DNA to the 2 new cells that form from mitosis

C.How? 1. DNA unzips (uses DNA helicase) 1. DNA unzips (uses DNA helicase) 2. Complementary sides are built (uses 2. Complementary sides are built (uses DNA polymerase) DNA polymerase) D.Practice (next slide) E.Results? 2 new, identical strands of DNA!! 2 new, identical strands of DNA!!

New Strand Original strand Nitrogen Bases Replication Fork DNA Polymerase Replication Fork

PRACTICE!! DNA strand is TACGTT What is the complementary strand? ATGCAA CAGTAC is the DNA strand What is the complementary strand? GTCATG AGCTAGATC is the DNA strand What is the complementary strand? TCGATCTAG

Chromosomes Bacteria have single, circular strand of DNA How is DNA packed in a eukaryotic cell?

DNA Replication Each side of DNA is called a “ template”Each side of DNA is called a “ template” Parent strand: original copy of DNA, used as templateParent strand: original copy of DNA, used as template Daughter strand: newly synthesized complementDaughter strand: newly synthesized complement

How do you replicate something so long? 1. Replication occurs at hundreds of places (“ORIGINS”) (“ORIGINS”) 2. Moves in BOTH directions until each chromosome is completely copied chromosome is completely copied 3. Uses ENZYMES to speed up process

What phase in the cell cycle does replication take place? S Phase! Why does DNA replication occur? makes sure each cell will have a complete set of DNA Where does this happen? Nucleus!

Steps of DNA Replication 1. DNA unwinds 2. DNA HELICASE enzyme unzips the weak hydrogen bonds between base pairs hydrogen bonds between base pairs Steps of DNA Replication 1. DNA unwinds 2. DNA HELICASE enzyme unzips the weak hydrogen bonds between base pairs hydrogen bonds between base pairs 3. Complementary RNA PRIMERS are added to the DNA to begin copying.

4. DNA POLYMERASE enzyme matches up DNA nucleotides to 3’ end continuously (5’ to 3’ directionality) and is called the “leading strand”. Later the RNA primers are replaced with DNA nucleotides DNA nucleotides to 3’ end continuously (5’ to 3’ directionality) and is called the “leading strand”. Later the RNA primers are replaced with DNA nucleotides 5. These fragments are “glued” together using DNA LIGASE using DNA LIGASE

DNA REPLICATION can you spot all the enzymes?

New Strand Original strand “ Semi-conservative ” - why?

PRACTICE!! DNA strand is TACGTT What is the complementary strand? ATGCAA CAGTAC is the DNA strand What is the complementary strand? GTCATG AGCTAGATC is the DNA strand What is the complementary strand? TCGATCTAG