DNA: The Genetic MaterialDNA: The Genetic Material

Chapter 9Chapter 9

Mendel’s work was published 1865 and he Mendel’s work was published 1865 and he died in 1884died in 1884

His work was rediscovered in 1900His work was rediscovered in 1900 Mendel’s experiments made people ask Mendel’s experiments made people ask

“What are genes made of?”“What are genes made of?” Through various experiments done by Through various experiments done by

different scientists it was found that DNA different scientists it was found that DNA was the genetic materialwas the genetic material

Now scientists needed to know the Now scientists needed to know the structure of DNA (Deoxyribonucleic Acid)structure of DNA (Deoxyribonucleic Acid)

9.1 Identify the Genetic 9.1 Identify the Genetic MaterialMaterial

(In a nutshell)(In a nutshell)

How did we find structure?How did we find structure? Was found that DNA Was found that DNA

contained 4 basescontained 4 bases Adenine, Thymine, Adenine, Thymine,

Guanine, CytosineGuanine, Cytosine Then found that the Then found that the

number of adenines number of adenines equals the number of equals the number of thymines and the number thymines and the number of guanines equals the of guanines equals the number of cytosinesnumber of cytosines

X-rays got photo of DNAX-rays got photo of DNA

9.2 Structure of DNA9.2 Structure of DNA James Watson and James Watson and

Francis Crick found that Francis Crick found that DNA is a double HelixDNA is a double Helix

Each strand is made up Each strand is made up of nucleotides – subunits of nucleotides – subunits that make DNAthat make DNA

Each nucleotide has Each nucleotide has 3 parts3 parts Phosphate Group Phosphate Group

(same for each (same for each nucleotide)nucleotide)

5-Carbon Sugar (In 5-Carbon Sugar (In DNA = deoxyribose)DNA = deoxyribose)

Nitrogen Containing Nitrogen Containing Base (different for Base (different for each nucleotide)each nucleotide)

4 different bases4 different bases AdenineAdenine GuanineGuanine ThymineThymine CytosineCytosine

Complementary Base PairsComplementary Base Pairs

Adenine always pairs with ThymineAdenine always pairs with Thymine Guanine pairs with CytosineGuanine pairs with Cytosine So if 1 strand was So if 1 strand was

AATGCGTTAAATGCGTTA Then match would beThen match would be

TTACGCAATTTACGCAAT

9.3 Replication of DNA9.3 Replication of DNA

Complementary bases allows for Complementary bases allows for copiescopies

1 strand serves as Template 1 strand serves as Template (pattern)(pattern)

DNA replication making a copyDNA replication making a copy Occurs during synthesis (S) phaseOccurs during synthesis (S) phase

Step 1Step 1

Double helix Double helix unwindsunwinds

DNA helicases open DNA helicases open strand by breaking H strand by breaking H bonds between bonds between basesbases

Once separate kept Once separate kept apart by other apart by other proteinsproteins

Replication forks – Replication forks – areas where double areas where double helix separateshelix separates

Step 2Step 2 At replication At replication

fork DNA fork DNA polymerases polymerases move along move along strands adding strands adding nucleotides to nucleotides to exposed nitrogen exposed nitrogen basesbases

2 new double 2 new double helixes are helixes are formedformed

Step 3Step 3 This continues until all DNA is copied and This continues until all DNA is copied and

polymerases are told to detach the 2 DNA polymerases are told to detach the 2 DNA moleculesmolecules

Checking For ErrorsChecking For Errors

DNA polymerases act as DNA polymerases act as proofreaders proofreaders

Can backtrack if the wrong base is Can backtrack if the wrong base is put onput on

This keeps the errors to 1 for every This keeps the errors to 1 for every billion nucleotidesbillion nucleotides

Rate of ReplicationRate of Replication

Replication does Replication does not begin at 1 end not begin at 1 end and end at the and end at the otherother

Circular DNA of Circular DNA of prokaryotes usually prokaryotes usually has 2 DNA has 2 DNA replication forksreplication forks

EukaryotesEukaryotes

Chromosomes contain a single, long Chromosomes contain a single, long strand of DNAstrand of DNA

If there was only 1 point of If there was only 1 point of replication it would take 33 days to replication it would take 33 days to copycopy

Instead there are about 100 sections Instead there are about 100 sections being copied in about 8 hoursbeing copied in about 8 hours