DNADNAThe History and Structure of DNA

What does the DNA of all these organisms have in common?

They all share a universal genetic code.

History of Heredity

Why am I so gorgeous?

Gregor Mendel

Gregor Mendel determined that traits were passed from generation to generation.

But, I haven’tfigured out

how thishappens

Frederick Griffith

Griffith was working on a vaccine for Streptococcus pneumoniaeHe worked with 2 strains of the bacteria:A disease causing a strain

which grew in smooth colonies

A harmless grain that grew in rough colonies

Frederick Griffith

He added these bacteria strains, some dead and some living, to lab rats.

These are his results:

Frederick Griffith

Live R+ dead S

Bacteria

Live Smooth Bacteria

Live Rough Bacteria

Dead Smooth Bacteria

Griffith Proved:That somehow the dead bacteria have passed their disease-causing substanct to the harmless, living bacteria. We now know this as “transformation”.

Griffith discovered that transformation could transform harmless bacteria into disease-causing bacteria

DNA

This substance was later determined to be DNA!

Erwin Chargaff

Chargoff discovered that DNA has the same amount of adenosine as thymine and the same amount of cytosine as guanine. A = T and G = C

A AA AA A

AT

T

T

T TT

T

CCC G G

G

Rosalind Franklin &Maurice Wilkins

Franklin and Wilkins used x-ray to discover that DNA was a double helix.

Rosalind Franklin

Diffraction X ray DNA

Watson and CrickWatson & Crick won a Nobel Prize for discovering the structural model of DNA.

They credited Wilkins and Franklin. Wilkins also got a Nobel Prize but Franklin did not. Franklin had passed away and the Nobels are not awarded posthumously.

Watson and Crick

TRY THIS!

For each scientist write one word or phrase that describes their contribution to discovering DNA.

Griffith-

Chargaff-

Franklin-

Watson and Crick-

lipids

lipids

carbohydratescarbohydrates

Nucleic acids

Nucleic acids

ProteinsProteins

DNA is a Nucleic AcidWhat is a nucleic acid?

Nucleic acids are one of the major organic compounds.

DNA

DNA StructureWhat is the monomer for nucleic acids?

What is the structure of this monomer?

phosphatenucleotide

N base

PO4

SugarSugar

PO4

N base

sugarnitrogen base

A NUCLEOTIDE

H

H2

H H

H3

HH H

H

H

O

O

O

C C

C

N

N

PO

O

O

C

C

C C

C

O

OO

C

C

1.

2.

3.

1.

2.

3.

1. Phosphate Group2. 5-Carbon Sugar

(Dexoyribose or Ribose)3. Nitrogen Base

1. Phosphate Group

2. 5-Carbon Sugar(Dexoyribose or Ribose)

3. Nitrogen Base

Nucleotides, too

NucleotidesThere are four nitrogen bases making up four different nucleotides.

Adenine

Guanine

Thymine

CytosinePyrimidines

PurinesA

C

G

T

N base

Chargaff’s Base Pair RulesAdenine always bonds with thymine.

Adenine (A) to Thymine (T)

Guanine always bonds with Cytosine.

Guanine (G) to Cytosine (C)

The lines between the bases represent hydrogen bonds

A

CG

T

C

G

A

A

T

G

Nucleotide

PS

N-b

Pairing DNA NucleotidesWhat is a nucleotide?

Rule

A to

C to

T

G

What is the base pairing rule?What would be the complementary nucleotide pairing?

3’End

3’End 5’End

5’End

DN

A D

OU

BL

E H

EL

IX

ladder shaped molecule

Purpose of DNA

Why do we have DNA?

DNA contains our genetic information

Where is it stored?

In the nucleus of a eukaryotic cell.

In the nucleoid region of a prokaryotic cell.

TRY THIS!

Using the base pairing rules, match up the corresponding bases to this segment of DNA.

DNA left strand: ACTTAGGCGTCA

DNA right strand: ?

TRY THIS!

Answer:

DNA left strand: ACTTAGGCGTCA

DNA right strand: TGAACCGCAGT