ap biology 2006-2007 the discovery and structure of the genetic material called “dna”

AP Biology 2006-2007

The Discovery and Structure of The Genetic Material

called “DNA”

AP Biology

Frederick Griffith finds a “Transforming Factor”

“Transformation” something in heat-killed bacteria could still transmit disease-causing properties

live pathogenicstrain of bacteria

live non-pathogenicstrain of bacteria

mice die mice live

heat-killed pathogenic bacteria

mix heat-killed pathogenic & non-pathogenicbacteria

mice live mice die

A. B. C. D.

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So what is this “transforming factor” Deoxyribonucleic Acid

or what we have been calling DNA every single organism on our planet has

its own DNA molecule “blueprint of life” why is it called this?

Franklin Wilkins Pauling

AP Biology

Watson and Crick

CrickWatson

Watson & Crick developed

double helix model of DNA

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DNA is a Nucleic Acid • Nucleic Acids are made from Nucleotides• A Nucleotide has three parts:

1. phosphate group 2. sugar molecule (Deoxyribose)3. nitrogen-containing base (A,T,C,G)

phosphate group

nitrogen-containingbasesugar

You will have torecognize nucleotideshape on EOC!!!!!!

AP Biology

A closer look at the different nitrogen bases!

4 different nucleotides A – adenine T – thymine C – cytosine G - guanine

nucleotide – nucleotide – nucleotide – nucleotide

phosphate

sugar N base

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Making the DNA Molecule

Base pairing rules: adenine (A) = thymine (T) “AT” guanine (G) = cytosine (C)

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Don’t forget about the other nucleic acid RNA is different from DNA molecules

single strand of nucleotides sugar is ribose Thymine (T) is replaced with Uracil (U)

AP Biology Copying DNA

“DNA Replication”How do cells make

new DNA molecules?

AP Biology

Remember why DNA must be duplicated…

nucleus

cell

DNA in chromosomes

nucleus

cell

duplicated chromosomes

Cells divide so each cellneeds own copy of DNA

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But how is DNA copied? Its called replication of

DNA DNA unzips and each

side serves as a template for a new strand

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DNA Replication Step 1: DNA Strands “unzip” at the

weak bonds between bases Enzyme used - helicase

helicase

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DNA Replication

DNA polymerase

Enzyme DNA polymerase adds new bases

DNA basesin nucleus

Step 2: Complementary strand is made

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DNA Replication Result is 2 exact copies of DNA to split

between new cells

DNA polymerase

DNA polymerase

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• DNA replication starts at many points in eukaryotic chromosomes.

• Called “replication bubbles”

Replication is fast and accurate.

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DNAPolymerase

Copying DNA

Build daughter DNA strand direction opposite direction

anti-parallel- think divided highway

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So lets sum it up