Chapter 12Chapter 12DNA: The Genetic MaterialDNA: The Genetic Material

http://www.accelrys.com/reference/gallery/life/dna_cpk_lg.jpg http://www.biologycorner.com/bio1/DNA.html

1. Vaccine

2. Transformation

3. Double Helix-twisted ladder shape of DNA.

4. Nucleotide

5. Deoxyribose- five carbon sugar found in DNA

6. Base-Pairing

7. Telomere

8. Replication

9. DNA Helicase- enzyme that “unzips” DNA molecule in preparation for replication

10. DNA Polymerase

Chapter 9 VocabularyChapter 9 Vocabulary

12.1 Identifying the Substance of 12.1 Identifying the Substance of Genes. Genes.

Griffin’s experiment.Griffin’s experiment.• Wanted to find out how bacteria make Wanted to find out how bacteria make

people sickpeople sick• Used different strains of the same Used different strains of the same

bacteriabacteria R strain- harmless form of bacteriaR strain- harmless form of bacteria S strain- disease causing strain of bacteriaS strain- disease causing strain of bacteria

Let’s play with mice!!Let’s play with mice!!

Heated R strain to remove any possible Heated R strain to remove any possible toxinstoxins

Did not expect that? What Did not expect that? What happened?happened?

TransformationTransformation: : the process bythe process by which which one strain of bacteria is changed by a gene or one strain of bacteria is changed by a gene or genes from another strain of bacteriagenes from another strain of bacteria

Later experiments proved that DNA was Later experiments proved that DNA was responsible for transformation of bacteria.responsible for transformation of bacteria.

The Role of DNAThe Role of DNA

The Role of DNAThe Role of DNA

1. 1. storing informationstoring information• Blue-print of the cellBlue-print of the cell• Carries code for making Carries code for making

proteinprotein 2. 2. Copying Information-Copying Information-

before a cell divides, it before a cell divides, it must make a complete must make a complete copy of everyone of its copy of everyone of its genes.genes.

3.Transmitting 3.Transmitting information-information- moves moves information from one information from one generation to the next.generation to the next.

12. 2 The Structure of DNA12. 2 The Structure of DNA

A. Solving the A. Solving the Structure of DNA.Structure of DNA.• 1. Chargaff’s Rule1. Chargaff’s Rule

The amount of The amount of ThymineThymine is always is always equal to the amount equal to the amount of of AdenineAdenine

The amount of The amount of CytosineCytosine is always is always equal to the amount equal to the amount of of Guanine.Guanine.

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Nucleotide Math!Nucleotide Math!

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DNA – A Double HelixDNA – A Double HelixA. Watson and Crick – 1953

1. The first model of DNA2. The key discovery was that DNA

has the shape of a double helixa. 2 strands twisted around

each otherb. A spiral or winding staircase

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B. Rosalind Franklin actually did the experiments1. Watson and Crick used her data, she received no credit2. Did they steal the data ? Ethics ?

2. http://sweetsprings.k12.mo.us/TeachersWeb/mstaples2/rosalind_franklin.jpg

1. http://bioephemera.com/wp-content/uploads/2007/08/288_sextet.jpg

1.

2.

• Between 1951 & 1953 Rosalind Franklin used X-Ray Diffraction to piece together the structure of DNA at Kings College in Cambridge, England.

•At the same time Watson & Crick were working on constructing a model of DNA but were unable to piece the puzzle together

•Maurice Wilkins, working on a similar project at Kings College, Wilkins shared some of Franklins work with Watson & Crick without her knowledge

•Using some of Franklin’s information, Watson & Crick completed their model of DNA.

•Franklin died in 1958 of ovarian cancer.

•1962 Watson & Crick were awarded the Noble Prize. Franklin never received formal credit because the Noble Prize isn’t awarded postmortem

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NucleotidesNucleotides

1. Phosphate group

2. Deoxyribose – a 5-carbon sugar

3. Nitrogen bases – 4 kinds

a. Adenine - A

b. Thymine - T

c. Guanine - G

d. Cytosine - C

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A. The subunits that make up DNA

DNA – A Double HelixDNA – A Double HelixC. DNA is never alone

1. It is always surrounded and covered by many kinds of proteins

2. Histonesa. DNA packagingb. The “reels” that

the “cable” is wrapped around

http://www.accessexcellence.org/RC/VL/GG/nucleosome.html

Pairing Between BasesPairing Between BasesA. Base-paring rules

1. Bases always pair only with their complementary nucleotide

2. Hydrogen bonds connect the two nitrogen bases

a. Adenine – Thymine

A – T

b. Guanine – Cytosine

G – C

What is the complement of:

c. A A T T A G C A T T T A A T C G T A

B. Nucleotides are Joined Together B. Nucleotides are Joined Together along the DNA Backbonealong the DNA Backbone

http://en.wikipedia.org/wiki/Phosphodiester_bond

1. Deoxyribose sugars are connected by Phosphates

2. The alternating sugars and Phosphates are called the Backbone1. One side of the spiral staircase2. Antiparallel strands-two strands

run opposite of each other.

3. The DNA Double Helix is made up of two backbones (strands) connected by paired nucleotides

DNA: How Long is It ?DNA: How Long is It ?• 1 base pair of DNA 0.3 nanometers long (3 x 10-10 meters)

• There are 6 billion (6 x 109) base pairs in a human cell

• In terms of people-size:• If 1 base pair were 2 feet long (about 1 step)

• DNA would be 2.3 million (2.3 x 106) miles long

• The distance from the Earth to the Moon is 239,000 miles

• If you had to drive the distance of a human’s DNA (that was people-size) at 65 MPH, it would take 4 years

• In a cell, DNA replication happens in a few hours

• How ?

Review QuestionsReview Questions1. What are the proteins called that DNA is

wrapped around?

2. What are the 3 parts of Nucleotides?

3. What parts of nucleotides link to form the DNA backbone?

4. Which nucleotide pairs with:a. Adenine (A)b. Thymine (T)c. Guanine (G)d. Cytosine (C)

12.3 DNA Replication12.3 DNA Replication 1. Before a 1. Before a

cell divides, cell divides, it must copy it must copy its DNAits DNA

2. replication (mitosis and meiosis)

1. Making a copy of DNA

DNA is Copied by Many EnzymesDNA is Copied by Many Enzymes

B. Step I: Unwinding

1. DNA Helicase – an enzyme

a. Unwinds the double helix

B. Creates a Replication Fork

C. Y-shaped areas form

i. Where the double helix is separated

ii. Where replication takes place

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DNA is Copied by Many EnzymesDNA is Copied by Many Enzymes

C. Step II: Polymerization

1. DNA Polymerase – an enzyme

a. Moves along the DNA strand

b. Adds nucleotides to exposed bases

i. Base-pairing rules are strictly followed

c. Two new double strands are formed

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D. Step III: Completion

1. DNA Polymerase continues until all exposed bases have been paired

2. Two new strands are created

3. Each new double helix has:

a. One strand – old DNA

i. The Parent strand

b. One strand – new DNA

i. The Daughter strand

DNA is Copied by Many EnzymesDNA is Copied by Many Enzymes

Checking for ErrorsChecking for ErrorsA. DNA Polymerase

1. Proofreads (edits) for errors

2. Backtracks and fixes mistakes

3. Mistakes will create mutations

B. Acceptable error rate

1. One error per 1 billion nucleotides

a. Six errors per complete set of DNA

Why aremutations

bad?

Why arethey good?

Checking for ErrorsChecking for ErrorsC. Errors in Replication can produce mutations

1. The errors are random2. Some may be good, some may be bad

a. “Luck of the draw”

3. Mutations are a mechanism for evolutiona. A good error may provide a survival advantage

i. Good errors will be passed on when the organism reproduces

b. A bad error may cause the organism to diei. Bad errors will not be reproduced or passed on

where replication begins1. This makes replication rapid

a. With 1 replication forki. Replication of 1 human chromosome – 33 days

b. With 100 replication forksi. Replication is complete in a few hours

DNA Replication Starts at Specific DNA Replication Starts at Specific LocationsLocations

A. Origins of Replication

B. Every chromosome has many sites

From: Freifelder, D. Molecular Biology. Jones and Bartlett Publishers, Inc., Boston. (1983) p 310.

A small piece of fruit fly DNA.Areas where replication are occurring are circled in yellow.

TelomeresTelomeres Telomeres:Telomeres:

Repeating DNA Repeating DNA sequeneces at the tips sequeneces at the tips of all chromosomesof all chromosomes

Every time the cell Every time the cell divides, is shortens.divides, is shortens.

They are usually shut They are usually shut off in adultsoff in adults

The shorter the The shorter the telomere, the older telomere, the older the cellthe cell

Research ongoing with Research ongoing with telomeres.telomeres.

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A Closer Look at ReplicationA Closer Look at Replication

DNA – A Concept MapDNA – A Concept MapDNA

deoxyribonucleicacid

nucleotides

double helix

replication

genes

HelicaseDNA

Polymerase5-carbon

sugar

nitrogenbase

phosphategroup

chromosomes

is madeup of

makesup

whichmake up

Which arecomposed of

is shaped like a

is reproduced during mitosis by the process of

requires2 enzymes

adenine thymine

guanine cytosine

thereare 4kinds

whichpairswith

Review QuestionsReview Questions

5. When does DNA replication occur?

6. What are the three steps of DNA Replication?

7. What are 2 key enzymes involved in DNA Replication?

8. What does DNA Helicase do?

9. What are 2 key processes performed by DNA Polymerase?