DNA TIMELINEDNA TIMELINE

What is DNA?What is DNA?DNADNA stands for stands for Deoxyribo Nucleic AcidDeoxyribo Nucleic Acid..DNA carries all of the genetic information for DNA carries all of the genetic information for

an organism.an organism.

1910: 1910: Thomas MorganThomas Morgan, , through experiments through experiments with fruit flies, with fruit flies, confirms that confirms that chromosomes are the chromosomes are the molecules of molecules of inheritance.inheritance.

1928: 1928: Frederick GriffithFrederick Griffith conducts the first conducts the first genetic experiments on mammals.genetic experiments on mammals.

His experiments dealt with mice and the His experiments dealt with mice and the pneumonia virus.pneumonia virus.

He used two forms: the S form (deadly) and He used two forms: the S form (deadly) and the R form (not deadly).the R form (not deadly).

A transforming material passed from dead S A transforming material passed from dead S bacteria to live R bacteria, making them bacteria to live R bacteria, making them deadly.deadly.

1944: 1944: Oswald AveryOswald Avery becomes the first becomes the first scientist to suggest scientist to suggest that DNA was the that DNA was the molecule of molecule of inheritance.inheritance.

Before Avery, Before Avery, biologists believed biologists believed inheritance was inheritance was controlled by proteins.controlled by proteins.

1950: 1950: Edwin Chargaff Edwin Chargaff determines that certain determines that certain purines and purines and pyrimidines occur in pyrimidines occur in equal amounts in a equal amounts in a DNA strand.DNA strand.

This leads to This leads to Chargaff’s Chargaff’s RulesRules: the amount of : the amount of AA = the amount of = the amount of TT, and , and the amount ofthe amount of G G = the = the amount of amount of CC..

“For every A there is a T, for every G there is a C”

1952: 1952: Rosalind Rosalind FranklinFranklin photographs photographs a DNA molecule using a DNA molecule using an X-ray camera.an X-ray camera.

Her photograph Her photograph provides evidence that provides evidence that DNA is made of more DNA is made of more than a single strand of than a single strand of nucleotides.nucleotides.

Franklin’s co-worker, Franklin’s co-worker, Maurice WilkinsMaurice Wilkins, gives , gives the photograph to a the photograph to a pair of scientists, pair of scientists, James WatsonJames Watson & & Francis CrickFrancis Crick, who , who are trying to determine are trying to determine the structure of DNA.the structure of DNA.

1953: Using Franklin’s 1953: Using Franklin’s photo and Chargaff’s photo and Chargaff’s Rules, Rules, Watson & CrickWatson & Crick develop a model of DNA.develop a model of DNA.

The model consists of The model consists of two strands of two strands of nucleotides bonded nucleotides bonded together in the shape of together in the shape of a twisted ladder.a twisted ladder.

This shape is known as This shape is known as thethe double helixdouble helix..

DNA Structure is the same in all organisms.DNA is a Nucleic Acid (one of the macromolecules [polymers] we

learned about during our Biochemistry unit) made up of long chains of nucleotides.

Each nucleotide has three parts.

phosphate group

deoxyribose (sugar)

nitrogen-containingbase

DNA StructureDNA StructureDNA consists of two DNA consists of two

strands of nucleotides.strands of nucleotides.DNA looks like a DNA looks like a

twisted laddertwisted ladderThe “The “backbonebackbone” of the ” of the

ladder is formed by ladder is formed by bonds between the...bonds between the...Sugars (Deoxyribose)Sugars (Deoxyribose)Phosphates.Phosphates.

The “The “rungsrungs” of the ” of the ladder are formed by ladder are formed by hydrogen bondshydrogen bonds between nitrogenous between nitrogenous bases.bases.

Nucleotide

Sugar-phosphate backbone

Hydrogen bonds

1.1. PurinesPurines: larger : larger bases. There are bases. There are two purines.two purines.

A. A. AdenineAdenine (A) (A)

B. B. GuanineGuanine (G) (G)

2.2. PyrimidinesPyrimidines: : smaller bases. smaller bases. There are two There are two pyrimidines.pyrimidines.

A. A. CytosineCytosine (C) (C)

B. B. ThymineThymine (T) (T) DeoxyribosePhosphate

A G

C T

DNA StructureDNA StructureEach Each base pairbase pair

consists of one purine consists of one purine and one pyrimidine.and one pyrimidine.

Pairs are bonded by Pairs are bonded by HYDROGEN HYDROGEN BONDSBONDS

Following Following Chargaff’s Chargaff’s RulesRules, for every , for every Adenine (A) there will Adenine (A) there will be a Thymine (T), and be a Thymine (T), and for every Guanine (G) for every Guanine (G) there will be a there will be a Cytosine (C).Cytosine (C).

Nucleotide

Sugar-phosphate backbone

Hydrogen bonds

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