DNA: “The Blueprint of Life”

Spring 2014

DNA: Scientists in History

Frederick Griffith

• Trying to figure out how people got sick with pnuemonia—he focused on bacteria

• Tested two types of bacteria: rough and smooth

1939

1939

He noticed:

Frederick Griffith

• Discovered TRANSFORMATION: bacteria (circular DNA) can change by absorbing genetic material

• SO…scientists can engineer bacteria to make things like human insulin by putting that gene in with bacteria for them to absorb.

Oswald Avery

• Question: Which macromolecule is responsible for transformation?

• Repeated Griffith’s experiment, but used enzymes to kill one of the 4 macromolecules for each experiment

• Discovered - nucleic acids store and transmit genetic information. 1937

Alfred Hershey and Martha Chase Question: How is transformation

connected to bacteriophages (viruses that attack bacteria)? Is it the protein coat or the DNA/RNA that carries genetic material?

Radioactively labeled protein and nucleic acids in bacteriophages

Radioactive DNA was found in the bacterial cell while radioactive protein was not

Concluded: DNA is the hereditary material

Looking for the Structure of DNA

• Chargoff’s Rules :• #Adenine = #Thymine• #Cytosine = #Guanine

WRITE THIS DOWN!

Nitrogen Bases

• 2 types of Nitrogen Bases• Purines

• Double ring• G & A

• Pyrimidines• Single ring

• C & U & T

PGA

CUT PY

Looking for Structure of DNA

• Rosalind Franklin: • Pictures of DNA - x-ray diffraction

Looking for Structure of DNA

• James Watson and Francis Crick: • Used Franklin’s pictures, discovered structure of DNA,

double helix (Nobel Prize) • DNA stores information (genetic blueprint) for making

proteins, these proteins determine the phenotype (physical characteristics) of an organism

1953

What is DNA?Deoxyribonucleic acid contains all the

genetic information for living organisms. It is a very long molecule of repeating units called nucleotides, which contain bases of either

adenine (A),

guanine (G),

cytosine (C),

and thymine (T)

DNA or RNA Structure• 3 ways to find DNA or RNA

• Linear - forms in a line• Chromatin inside nucleus of eukaryotes• Circular in prokaryotes

• Eukaryotes - DNA wrapped around histones (a protein)

DNA and RNA

• DNA = deoxyribonucleic acid• RNA = ribonucleic acid• Deoxyribose and ribose are sugars…remember –ose?

DNA Structure• Remember DNA is a type of

nucleic acid, one of the 4 macromolecules

• DNA (polymer) = two long strands of NUCLEOTIDES (monomers).

• Each strand is constructed in opposite directions (5’-3’ or 3’-5’)

DNA consists of two strands of nucleotides. The two strands are complimentary to each other. This means that nucleotides on one strand pair with nucleotides on the other strand in this way:

Adenine (A) pairs with Thymine (T)

Guanine (G) pairs with Cytosine (C)

Therefore:# of adenine nucleotides = # of thymine nucleotides

# of guanine nucleotides = # of cytosine nucleotides

A Nucleotide

• Made of 3 parts• Deoxyribose Sugar (5 Carbons) • Phosphate group • Nitrogen Base (2 types)

• Purines: (2 rings) Adenine and Guanine• Pyrimidines: (1 ring) Cytosine and Thymine

• Hydrogen bonds hold the bases together• 2 between A and T• 3 between G and C

DNA: made of nucleotidesDNA: made of nucleotides

OO=P-O O

PhosphatePhosphate GroupGroup

N

Nitrogenous baseNitrogenous base (A, T(A, T,, G, C)G, C)CH2

O

C1C4

C3 C2

5

SugarSugar(deoxyribose)(deoxyribose)

DRAW THIS!!!

DNA - double helixDNA - double helix

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

T A

The two strands of DNA are attached and twisted, forming what we call a double helix.

The shape and structure of DNA were determined by James Watson and Francis Crick in 1953.

Base Pair Rule

One side:     A   T   A      T   C   A      T   G   C      G   G   G

Other side:

Let's Review What We Know About DNA1.  DNA stands for:   De _____ ribo ______  acid2.  What is the shape of DNA? _______________3.  Who established the structure of DNA?  ____________4.  Adenine always pairs with _______________5.  The sides of the DNA ladder are deoxyribose and _____6.  Guanine always pairs with _____________7.  What is the complimentary sequence:   A A T  G  C A8.  The two sides of DNA are held together by _______ bonds.9.  DNA is composed of repeating subunits called ______________________10.  What are the 4 bases that make up the rungs of the DNA ladder? _______________________________________

Let's Review What We Know About DNA1.  DNA stands for:   De _____ ribo ______  acid2.  What is the shape of DNA? _______________3.  Who established the structure of DNA?  ____________4.  Adenine always pairs with _______________5.  The sides of the DNA ladder are deoxyribose and _____6.  Guanine always pairs with _____________7.  What is the complimentary sequence:   A A T  G  C A

8.  The two sides of DNA are held together by _______ bonds.9.  DNA is composed of repeating subunits called ______________________10.  What are the 4 bases that make up the rungs of the DNA ladder? _______________________________________

oxyDouble-helixse nucleic

Watson & Crick

phophatesThymine

nucleotides

cytosine

hydrogenT T A C G T

Adenine, guanine= purines (double-ring) guanine, cytosine= pyrimidines (single-ring)

DNA ReplicationDNA must replicate in order for all genetic material to be

passed from one generation to the next. DNA replication results in two molecules of DNA, each containing one original strand and one new strand.

Special enzymes are used to “unzip” the two original strands, allowing free nucleotides to pair with those on the original strand, A with T and G with C. The original strand serves as a pattern for the new strand. The original strands then bond with the new strands and two molecules are formed.

DNA REPLICATION

the process by which DNA makes a copy of itself (happens in the S phase of the cell cycle)

SEMI-CONSERVATIVE - half of the old strand is saved

DNA Replication• DNA unzips by breaking the Hydrogen bonds between

the nitrogen bases • DNA Polymerase: enzyme that makes the new strand of

DNA • Each strand gets a new complimentary strand,

synthesized from free-floating nucleotides.

http://www.veoh.com/browse/videos/category/educational/watch/v1011706jGF8tJBF#

• Each strand synthesized 5’ to 3’ direction; one strand made in one direction and other strand in opposite direction

• Two identical strands of DNA are made

Mini-AssessmentSection 12-1: Pre-Watson and Crick

Read about the beginnings of Genetic Research.

1. Describe the experiments of Frederick Griffith. Date? Nationality?

• Define TRANSFORMATION.

• What was Griffith’s primary discovery?

2. Describe the experiments of Oswald Avery. Date? Nationality?

• What was Avery’s primary discovery?

3. Describe the experiments of Alfred Hershey and Martha Chase. Date? Nationality?

• Define BACTERIOPHAGE.

• What was Hershey and Chase’s primary discovery?

4. Define NUCLEOTIDES. What are the 4 nucleotides that make up DNA? How do these nucleotides pair in DNA?

Textbook AssignmentRead Section 12-2.

1. Define HISTONE.

2. Define REPLICATION. What is a replication fork?

3. Define DNA POLYMERASE. What role does this chemical play in DNA replication?

4. Draw a diagram of a piece of DNA undergoing replication. Label the replication fork, and show the complimentary new strand of DNA that would be produced, using the letters A, C, G, T and what you know about how they pair with each other.