DNADNA

Objective: SWBAT remember the basic components and structure of DNA

Warm-up: What comes to mind when you see DNA?

What is the purpose of What is the purpose of DNA?DNA?

1.1.To store information and give it To store information and give it to the cell.to the cell.– The information specifies what The information specifies what proteins to make, which determines proteins to make, which determines what the cell does.what the cell does.

– DNA is the “code of life.”DNA is the “code of life.”

2.2.Pass a copy of the information to Pass a copy of the information to newly made cells. newly made cells. – ReplicationReplication

DNADNA

•DDeoxyriboeoxyribonnucleic ucleic AAcidcid•Composed of nucleotides:Composed of nucleotides:

– sugar (Deoxyribose)sugar (Deoxyribose)– phosphate groupphosphate group– nitrogen base (adenine, guanine, nitrogen base (adenine, guanine, cytosine, or thymine)cytosine, or thymine)

•Purines = adenine (A) and guanine Purines = adenine (A) and guanine (G)(G)

•Pyrimidines = thymine (T) and Pyrimidines = thymine (T) and cytosine (C) cytosine (C)

DNADNAChargaff’s Data:

OrganismOrganism AA TT GG CC

HumanHuman 30.4%30.4% 30.1%30.1% 19.6%19.6% 19.9%19.9%

sheepsheep 29.3%29.3% 28.3%28.3% 21.4%21.4% 21.0%21.0%

Sea urchinSea urchin 32.8%32.8% 32.1%32.1% 17.7%17.7% 17.3%17.3%

SalmonSalmon 29.7%29.7% 29.1%29.1% 20.8%20.8% 20.4%20.4%

wheatwheat 27.3%27.3% 27.1%27.1% 22.7%22.7% 22.8%22.8%

E ColiE Coli 24.7%24.7% 23.6%23.6% 26.0%26.0% 25.7%25.7%

Lamda Lamda VirusVirus

21.3%21.3% 22.9%22.9% 28.6%28.6% 27.2%27.2%

ChargaffChargaff’’s Conclusionss Conclusions

• A:T = 1A:T = 1• C:G = 1C:G = 1• A+G = C+TA+G = C+T• A+T:C+G does not = 1A+T:C+G does not = 1• Inferences?Inferences?

– A and T will pair together A and T will pair together and G and C will pair and G and C will pair togethertogether

Structure of DNAStructure of DNA

• Discovered by Discovered by Watson and Crick in Watson and Crick in 19531953

• Discovered that DNA Discovered that DNA is a Double Helix is a Double Helix with the help of with the help of Rosalind FranklinRosalind Franklin

Structure of DNAStructure of DNA• Double helix = 2 Double helix = 2 nucleotide chains nucleotide chains wrapped around each wrapped around each other like a twisted other like a twisted ladderladder

• Alternating Alternating deoxyribose sugar and deoxyribose sugar and phosphate molecules phosphate molecules form the backbone = form the backbone = the rails of the the rails of the ladderladder

• Backbone is held Backbone is held together by strong together by strong covalent bonds so the covalent bonds so the bases stay in the bases stay in the right order right order

Structure of DNAStructure of DNA• Complementary Base pairsComplementary Base pairs– Adenine and Thymine Adenine and Thymine – Guanine and CytosineGuanine and Cytosine

• Base pairs connect the Base pairs connect the strands by hydrogen bonds strands by hydrogen bonds that are easy to breakthat are easy to break

– This forms the steps of This forms the steps of the ladderthe ladder

• This allows the DNA to This allows the DNA to unzip when it needs to be unzip when it needs to be read to make a protein or read to make a protein or copy itselfcopy itself

DNA is the code of lifeDNA is the code of life• There are 4 different types of bases.There are 4 different types of bases.

• The bases are like letters of a word.The bases are like letters of a word.

• Every 3 bases spells out the code for one Every 3 bases spells out the code for one amino acid.amino acid.

• Put enough amino acids together and you get Put enough amino acids together and you get words and eventually you get a sentence words and eventually you get a sentence – In this case, one protein.In this case, one protein.

• A segment of DNA that codes for one protein A segment of DNA that codes for one protein is called a “gene.”is called a “gene.”

• Genes determine what your structure is like Genes determine what your structure is like and what shape your enzymes are.and what shape your enzymes are.

Let’s Review!Let’s Review!• What are the 2 functions of DNA?What are the 2 functions of DNA?

– Store and give information to cells to make Store and give information to cells to make proteins, and to pass that information to proteins, and to pass that information to new cellsnew cells

• What makes up the backbone (the rails) of the What makes up the backbone (the rails) of the ladder?ladder?– Alternating sugars and phosphatesAlternating sugars and phosphates

• What type of bond holds them together?What type of bond holds them together?– Covalent bonds because they are strong and Covalent bonds because they are strong and you want the DNA to stay in the right order.you want the DNA to stay in the right order.

Let’s Review!Let’s Review!

• NucleotidesNucleotides

• What 3 things are a nucleotide made of?What 3 things are a nucleotide made of?– Sugar, phosphate, baseSugar, phosphate, base

• What are the 4 types of nitrogen bases?What are the 4 types of nitrogen bases?– Adenine (A), Thymine (T), Guanine (G), Adenine (A), Thymine (T), Guanine (G), Cytosine (C) Cytosine (C)

• What pairs with what?What pairs with what?– A and T, G and CA and T, G and C

• What type of bond helps make the steps of the What type of bond helps make the steps of the ladder?ladder?– HydrogenHydrogen

Objective: Students will be able to apply the base pairing rules to DNA model making and replication.

Student will be able to discuss why DNA is the carrier for genetic material and not protein.

Warm Up: What is the backbone of DNA made out of? What kind of bond holds it together?

Why DNA and not Why DNA and not Protein?Protein?

•When scientists were first When scientists were first looking for what carried looking for what carried genetic information they genetic information they thought it might be protein.thought it might be protein.– Protein has 20 amino acids for a Protein has 20 amino acids for a more complex codemore complex code

– DNA only has 4 different nitrogen DNA only has 4 different nitrogen basesbases

GriffithGriffith

•Inferences?Inferences?

•Griffith Griffith discovered discovered transformationtransformation the the ability of ability of bacteria to pick bacteria to pick up genetic up genetic information from information from their environment.their environment.

AveryAvery

• Experiment 1: S cells exposed to Experiment 1: S cells exposed to Protease (destroys protein) added to Protease (destroys protein) added to R cells R cells Mouse dies Mouse dies

• Experiment 2: S cells exposed to Experiment 2: S cells exposed to RNase (destroys RNA) added to R RNase (destroys RNA) added to R cells cells Mouse dies Mouse dies

• Experiment 3: S cells exposed to Experiment 3: S cells exposed to DNase (Destroys DNA) added to R DNase (Destroys DNA) added to R cells cells mouse LIVES!! mouse LIVES!!

Hershey- Chase Hershey- Chase ExperimentExperiment

• Martha Chase Martha Chase and Alfred and Alfred Hershey knew Hershey knew that that Bacteriophages Bacteriophages (a type of (a type of Virus) injected Virus) injected their genetic their genetic information in information in to to E. coli E. coli for for replication.replication.

DNA ReplicationDNA Replication

G C T T G G G C T T G G G C TG C T

I only have one strand of DNA.

How do I figure out what the other strand of DNA is?

DNA ReplicationDNA Replication• Double helix unwinds to Double helix unwinds to make 2 single strands.make 2 single strands.

• Enzymes add new Enzymes add new nucleotides (red blocks) nucleotides (red blocks) to make a complimentary to make a complimentary strand.strand.

• The DNA has now copied The DNA has now copied itself. itself.

• Replication is Semi-Replication is Semi-conservative: Each new conservative: Each new set of DNA has one set of DNA has one original strand (black) original strand (black) and one newly made and one newly made strand (red).strand (red).

Steps of DNA Steps of DNA ReplicationReplication

• Nucleotide chain unwindsNucleotide chain unwinds

• Separated by enzymes called Separated by enzymes called Helicases (break apart Helicases (break apart hydrogen bonds)hydrogen bonds)

• DNA Polymerases (enzymes) DNA Polymerases (enzymes) attach the matching attach the matching nucleotides, and two new exact nucleotides, and two new exact copies of DNA are formedcopies of DNA are formed

DNA ReplicationDNA Replication

• DNA only replicates when DNA only replicates when the cell is going to the cell is going to divide.divide.

– In every cell, there are 2.3 In every cell, there are 2.3 meters of DNA (3 billion base meters of DNA (3 billion base pairs).pairs).

• The entire process is The entire process is extremely accurate.extremely accurate.