dna: the genetic material chapter 9. mendel’s work was published 1865 and he died in 1884...
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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
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