DNA: The Genetic Material Chapter 9

Mendel’s work was published 1865 and he died in 1884 Mendel’s work was published 1865 and he died in 1884 His work was rediscovered in 1900 His work was rediscovered in 1900 Mendel’s experiments made people ask “What are genes made of?” Mendel’s experiments made people ask “What are genes made of?” Through various experiments done by different scientists it was found that DNA was the genetic material Through various experiments done by different scientists it was found that DNA was the genetic material Now scientists needed to know the structure of DNA (Deoxyribonucleic Acid) Now scientists needed to know the structure of DNA (Deoxyribonucleic Acid) 9.1 Identify the Genetic Material (In a nutshell)

How did we find structure? Was found that DNA contained 4 bases Was found that DNA contained 4 bases Adenine, Thymine, Guanine, Cytosine Adenine, Thymine, Guanine, Cytosine Then found that the number of adenines equals the number of thymines and the number of guanines equals the number of cytosines Then found that the number of adenines equals the number of thymines and the number of guanines equals the number of cytosines X-rays got photo of DNA X-rays got photo of DNA

9.2 Structure of DNA James Watson and Francis Crick found that DNA is a double Helix James Watson and Francis Crick found that DNA is a double Helix Each strand is made up of nucleotides – subunits that make DNA Each strand is made up of nucleotides – subunits that make DNA

Each nucleotide has 3 parts Each nucleotide has 3 parts Phosphate Group (same for each nucleotide) Phosphate Group (same for each nucleotide) 5-Carbon Sugar (In DNA = deoxyribose) 5-Carbon Sugar (In DNA = deoxyribose) Nitrogen Containing Base (different for each nucleotide) Nitrogen Containing Base (different for each nucleotide) 4 different bases 4 different bases Adenine Adenine Guanine Guanine Thymine Thymine Cytosine Cytosine

Complementary Base Pairs Adenine always pairs with Thymine Adenine always pairs with Thymine Guanine pairs with Cytosine Guanine pairs with Cytosine So if 1 strand was AATGCGTTA So if 1 strand was AATGCGTTA Then match would beTTACGCAAT Then match would beTTACGCAAT

9.3 Replication of DNA Complementary bases allows for copies Complementary bases allows for copies 1 strand serves as Template (pattern) 1 strand serves as Template (pattern) DNA replication making a copy DNA replication making a copy Occurs during synthesis (S) phase Occurs during synthesis (S) phase

Step 1 Double helix unwinds Double helix unwinds DNA helicases open strand by breaking H bonds between bases DNA helicases open strand by breaking H bonds between bases Once separate kept apart by other proteins Once separate kept apart by other proteins Replication forks – areas where double helix separates Replication forks – areas where double helix separates

Step 2 At replication fork DNA polymerases move along strands adding nucleotides to exposed nitrogen bases At replication fork DNA polymerases move along strands adding nucleotides to exposed nitrogen bases 2 new double helixes are formed 2 new double helixes are formed

Step 3 This continues until all DNA is copied and polymerases are told to detach the 2 DNA molecules This continues until all DNA is copied and polymerases are told to detach the 2 DNA molecules

Checking For Errors DNA polymerases act as proofreaders DNA polymerases act as proofreaders Can backtrack if the wrong base is put on Can backtrack if the wrong base is put on This keeps the errors to 1 for every billion nucleotides This keeps the errors to 1 for every billion nucleotides

Rate of Replication Replication does not begin at 1 end and end at the other Replication does not begin at 1 end and end at the other Circular DNA of prokaryotes usually has 2 DNA replication forks Circular DNA of prokaryotes usually has 2 DNA replication forks

Eukaryotes Chromosomes contain a single, long strand of DNA Chromosomes contain a single, long strand of DNA If there was only 1 point of replication it would take 33 days to copy If there was only 1 point of replication it would take 33 days to copy Instead there are about 100 sections being copied in about 8 hours Instead there are about 100 sections being copied in about 8 hours