lec 2 review nucleic acids [compatibility mo

7/30/2019 Lec 2 Review Nucleic Acids [Compatibility Mo

1/18

The structure of DNA


2/18

Over view of DNA structure and function


3/18

Over view of DNA structure and function

DNA is the molecule that is the basis for heredity.

It contains the patterns for constructing proteins in the body,including the various enzymes.

A new understanding of heredity and hereditary disease was possibleonce it was determined that DNA consists of two chains twistedaround each other.

The two chains are composed, of alternating phosphate and sugargroups, which are held together in a double helix structure byhydrogen bonds between pairs of organic bases.

The bases areAdenine (A)Thymine (T)

Guanine (G)Cytosine (C).


4/18


5/18

The DNA story

In 1962 James Watson (1928present) Francis Crick (19162004), and Maurice Wilkins (19162004) jointly received the NobelPrize in medicine or physiology (in1962) for their determination in1953 of the structure of

deoxyribonucleic acid (DNA).

Because the Nobel Prize can beawarded only to the living,Wilkins's colleague RosalindFranklin (19201958), who died of

cancer at the age of 37, could notreceive the award.


6/18

The DNA story

The background for the work of the four scientists wasformed by several scientific breakthroughs

progress made by X-ray crystallographers in studyingorganic macromolecules;

the growing evidence supplied by geneticists that itwas DNA, not protein, in chromosomes that wasresponsible for heredity

http://www.chemheritage.org/classroom/chemach/pharmaceuticals/watson-crick.html


7/18

The DNA story

Of the four DNA researchers only RosalindFranklin had any degrees in chemistry - herundergraduate and graduate degrees fromCambridge University.

During World War II she gave up her researchscholarship to contribute to the war effort atthe British Coal Utilization ResearchAssociation

After the war she joined the LaboratoireCentrale des Services Chimiques de l'Etat inParis, where she was introduced to thetechnique of X-ray crystallography and rapidlybecame a respected authority in this field.

In 1951 she returned to England to King's

College, London, where her charge was toupgrade the X-ray crystallographic laboratorythere for work with DNA.


8/18

The DNA story

Already at work at King's College was MauriceWilkins, a New Zealandborn but Cambridge-educated physicist.

During World War II he was shipped out to theUnited States to work on the Manhattan Project.Like many other nuclear physicists he became

disillusioned with his subject when it was appliedto the creation of the atomic bomb

It was Wilkins's idea to study DNA by X-raycrystallographic techniques, which he hadalready begun to implement when Franklin wasappointed.

The relationship between Wilkins and Franklinwas unfortunately a poor one and probablyslowed their progress.


9/18

In 1951 James Watson, an American, arrived at the Cavendish Laboratory inCambridge.

Watson had two degrees in zoology: abachelor's degree from the University ofChicago and a doctorate from the Universityof Indiana, where he became interested ingenetics.

At a conference Watson heard Wilkins talkon the molecular structure of DNA and sawX-ray crystallographic photographs of DNA.

The DNA story


10/18

Watson and Crick rapidly put together several models of DNA

and attempted to incorporate all the evidence they could gather.

Franklin's X-ray photographs, to which they had gained access

without her permission, were critical to the correct solution.

The four scientists announced the structure of DNA in articles

that appeared together in the same issue ofNature.

The DNA story


11/18


12/18

Then they moved off in differentdirections.

Franklin - X-ray crystallographic analysisof the structure of the tobacco mosaic

virusa landmark in the field.

Wilkins applied X-ray techniques to thestructural determination of ribonucleic

acid (RNA)

Watson's subsequent - Cold SpringHarbor - director from 1968. From 1988

The DNA story


13/18

DNA Structure

DNA is a very stable molecule

This stability is provided by the

robust repetitive phosphate-sugarbackbone in each DNA strand

Phosphate links the 5 position of

one sugar with the 3 position of

the next sugar.

DNA backbone


14/18

DNA Structure

In addition to the sugar 2 deoxyribose and the phosphate, DNAmolecules contain four nitrogen containing bases.

Two Pyrimidines, Thymine (T) and Cytosine, (C) and two purines,Guanine (G) and Adenine (A).


15/18

DNA DoubleHelix

Complimentarypairing

Gene

Purines are larger than pyrimidinestherefore a regular double helix requires apurine in one strand to be matched by apyrimidine in the other strand

Specific hydrogen bonding required between the bases to fit

opposite one another.

This is called complimentary pairing

DNA strands run in opposite directions therefore DNA isoften represented as one strand in the 5 to 3 direction.


16/18

Complimentary pairing


17/18


18/18

http://www.umass.edu/molvis/tutorials/dna/dnapairs.htm

lec 2 review nucleic acids [compatibility mo

Documents