DNA – The Scientists and Their Discoveries. Frederick Griffith (1928) Experiment – worked with bacteria and injected into mice Conclusion – transforming.

Alfred Hershey and Martha Chase (1952)

Experiment – used radioactive proteins and radioactive DNA in bacteriophages Bacteriophage – a virus that infects bacteria

Conclusion – confirmed that DNA was genetic material

http://www.youtube.com/watch?v=3QJ4CjFsflA

Hershey and Chase

Rosalind Franklin (1952)

Experiment – used x-ray diffraction to see structure of DNA X-ray diffraction—powerful x-

rays shown through a concentrated DNA sample

Worked with Maurice Wilkins

Conclusion – DNA is a helix

What is X-ray Diffraction?

James Watson &Francis Crick (1953)

Experiment – Built many 3-D models of DNA; Used Franklin, Wilkins, Pauling’s work

Conclusion – DNA is a double helix, a twisted ladder. Each nucleotide made of sugar, phosphate, and base.

“Sides”: sugar and phosphates “Rungs”: bases Bases are held together by hydrogen

attraction http://www.youtube.com/watch?v=TZUun93_V18

Watson and Crick

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Erwin Chargaff (1947)

Experiment – Analyzed the amounts of the four bases in different organism’s DNA

Conclusion –base-pairing rules adenine = thymine (A-T) cytosine = guanine (G-C)

Erwin Chargaff

Percentage of Bases in Four Organisms

Source of DNA A T G CSource of DNA A T G C

Streptococcus 29.8 31.6 20.5 18.0

Yeast 31.3 32.9 18.7 17.1

Herring 27.8 27.5 22.2 22.6

Human 30.9 29.4 19.9 19.8

Streptococcus 29.8 31.6 20.5 18.0

Yeast 31.3 32.9 18.7 17.1

Herring 27.8 27.5 22.2 22.6

Human 30.9 29.4 19.9 19.8

Nucleotides: Page 291

Adenine Guanine

Cytosine Thymine

Phosphate group Deoxyribose

DNA Structureand

DNA Replication

DNA Structure

DNA stands for Deoxyribonucleic Acid

Shape: Double helix

Monomers: Nucleotides Nucleotide has 3 parts: Sugar (deoxyribose),

phosphate, and a nitrogenous base Bases are held together by hydrogen attractions.

Why are hydrogen attractions important in DNA’s structure?

Four Nitrogenous Bases

Adenine (A), Guanine (G), Cytosine (C), Thymine (T)

Purines (double ring) – Adenine and Guanine

Pyrimidines (single ring) – Cytosine and Thymine

Chargaff’s rule: Adenine pairs with thymine. A –T T – A Guanine pairs with cytosine. G – C C – G

Nucleotides: Page 291

Purines Pyrimidines

Adenine Guanine

Cytosine Thymine

Phosphate group Sugar:

Deoxyribose

So if every living thing has the same 4 bases, how are we so different?

It’s the SEQUENCE!! The order of those 4 nitrogen bases determines whether you are a human or a dog!

It also determines traits of that organism (why you look different than your shoulder partner or sibling.)

A Closer Look at DNA: Page 294

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

A closer look at DNA:How DNA condenses

Chromosome

Supercoils

ChromatinHistones

DNA

double

helix

Centromere

What is DNA Replication?

The process of making copies of DNA during S phase of interphase in the nucleusMakes sure that a daughter cell will have a

complete set of chromosomes

Original strand of DNA serves as a template for 2 new strands Template: a pattern; an original model

Each new strand will be identical to the original strand because of Chargaff’s rule.

How does DNA replication work?

1) Helicase unwinds the double helix, forming a “replication fork,” where replication takes place

2) DNA polymerase bonds the necessary nucleotides to complement the parent/original DNA strand to complete 2 new DNA molecules

3) DNA polymerase also “proofreads” the new DNA strand to make sure it is an exact copy of the original DNA

http://www.youtube.com/watch?v=zdDkiRw1PdU

1. Helicase unwinds/unzi

ps DNA strand

2. DNA Polymerase complements the

original DNA strand using

Chargaff’s Rules A-T C-G

3.. DNA Polymerase

proofreads the exact copy

Parent

New

ParentNew

DNA http://www.youtube.com/watch?v=z685FFqmrpo

Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous basesReplication fork

Original strand

New strand