DO NOW

What is DNA?

What does DNA look like?

How do we use DNA in everyday life?

Objectives

Explain what DNA is and understand it’s significance

Summarize the experiments of Griffith and Avery leading to discovery of DNA as genetic material

Label a diagram of a virus.

Molecular Genetics

Chapter 12

DNA

DNA stands for:– Deoxyribonucleic acid

DNA is located:– In the nucleus of cells

The function of DNA is to:– Tells the cells how to produce things that make

you up (Blueprint)

When was DNA discovered?

We are going to study the scientists who discovered DNA.

1928 Fred Griffith -

Studied two strains of bacteria, Streptococcus pneumoniae

Worked with two strains of bacteria: Rough Strain and Smooth Strain

S strain causes pneumonia and the R strain does not

1928 Fred Griffith-

Discovered that something from the heat killed wild type (smooth) bacteria was turning the mutant (rough) type bacteria into smooth.

Called it the transforming factor Didn’t really know what it was

1944- Avery, McCarty and MacLeod

Purified both protein, RNA, and DNA separately from Streptococcus pneumonia bacteria to determine which would transform the harmless bacteria- How?

Injected protein into bacteria no effect Injected RNA into bacteria no effect Injected DNA into bacteria mice died

Conclusion: DNA is the genetic material!!

Nobody believed Avery

People thought that Avery had inaccurate results and contamination and still thought the transforming factor could be.

Back to square 1! We know there is a “transforming factor” Is it protein or DNA? Lets ask Hershey and Chase!

Hershey and Chase

Worked with viruses to determine what the “transforming factor” was.

*Before we discuss their experiment we must understand what a virus is and how it works!*

Viruses- 6 Characteristics of Viruses

1. Have their own genome (genetic make up) made of either DNA or RNA

2. Does not have enzymes, ribosomes, or ATP

3. Have external protein shells (capsids)

Viruses- 6 Characteristics of Viruses

4. Infect only specific cells 5. 2 life cycles (lytic and lysogenic)

– Lytic – breaks out and spreads– Lysogenic- hangs around

6. Smaller than bacteria

Bacteriophage= virus attacking bacteria…

2 Life Cycles

5 Stages of Attack!!

1) Attachment: virus attaches to it’s host

2) Injection: virus injects it’s DNA into the host cell.

3) Replication: virus copies it’s genetic material many times.

4) Assembly: virus assembles more viruses

5) Release: Viruses are release from the cell ready to attach to new cells!

Identify the Stages

Homework!

Read pgs. 326-328, Summarize the experiments of Griffith and Avery

2/23 DO NOW

Take out your homework!!! Which strain of bacteria killed the mice in

Griffith’s experiment? What is the process that caused rough

bacteria to become smooth? What did Avery discover? What are the 5 stages of attack for a virus?

Objectives

Summarize the experiments of Hershey and Chase.

Identify the stages of replication of a virus. Understand the use of viruses in discovering

DNA.

Lets Review…

Who are the scientists we’ve talked about so far?

What are the 6 characteristics of a virus?

Viruses!

5 Stages of Attack animation

1952 Hershey and Chase

Radioactive Labeling:– Used radioactive phosphorus (32P) to identify DNA in the

bacteriophages – Used radioactive sulfer (35S) to identify proteins in the

bacteriophagesTracking DNA

Radioactive bacteriophages infected bacteria cells After review results found radioactive sulfur outside

of bacteria cells and radioactive phosphorus inside bacteria cells

1952 Hershey and Chase

Used Bacteriophages Two radioactively labeled viruses.

– 1. Sulfur Protein coat– 2. Phosphorous DNA

After infecting cells, only the DNA was still radioactively labeled

DNA is genetic material

Hershey and Chase…

Ok… so we KNOW DNA carries Genetic Material, now what?

Levene discovered that DNA is made of nucleotides

What are nucleotides?

DNA STRUCTURE

Nucleotides:– 5 carbon sugar (Deoxyribose)– Phosphate Group – Nitrogen base

Nitrogenous Bases

Purines– Double ring structure– *Adenine and Guanine

Pyrimidines– Single ring structure– * Thymine, Cytosine, Uracil

Nitrogenous Bases

DNA Structure

Erwin Chargaff

Chargaff’s rule– C= G – T = A

Draw in the complimentary sequence

ATGCTAATTCGCATCG

Rosiland Franklin

X-ray Diffraction use of photo 51

X-ray diffraction data helped solve the structure of DNA

Indicated that DNA was a double helix

X-Ray Crystallography

Watson and Crick

Built a model of the double helix that conformed to the others’ research– two outside strands consist of alternating sugar

and phosphate molecules– cytosine and guanine bases pair to each other by

three hydrogen bonds – thymine and adenine bases pair to each other

by two hydrogen bonds

DNA Structure

DNA often is compared to a twisted ladder.

Rails of the ladder are represented by the alternating deoxyribose and phosphate.

The pairs of bases (cytosine–guanine or thymine–adenine) form the steps.

Label the parts of the DNA molecule

Base Pairs- Rungs of the ladder

-2 Strands of DNA form a helix

Orientation of DNA- Anti Parallel

On the top rail, the strand is said to be oriented 5′ to 3′.

The strand on the bottom runs in the opposite direction and is oriented 3′ to 5′.

Chromosome Structure

DNA coils around histones (proteins) to form nucleosomes,

This coils to form chromatin fibers. The chromatin fibers supercoil to form

chromosomes that are visible in the metaphase stage of mitosis.