BY John Roderick

STORES AND PASSES ON GENETIC INFORMATION FROM ONE GENERATION TO ANOTHER. DNA DEOXYRIBONUCLEIC ACID

SOME GENERAL REVIEW

DNA STRUCTURE THE DNA STRUCTURE IS SHAPED LIKED A SPIRAL STAIRCASE, OR TWISTED LADDER.

IMAGES OF DNA STRUCTURE

DNA STRUCTURE THE OUTER PARTS OF THE OF THE LADDER ARE MADE OF SUGARS. DEOXYRIBOSE + PHOSPHATE THESE ARE JOINED TOGETHER BY ESTER BONDS

DNA STRUCTURE RIBOSE IS A SUGAR LIKE GLUCOSE, BUT WITH ONLY 5 CARBON ATOMS IN ITS MOLECULE.RIBOSE IS A SUGAR LIKE GLUCOSE, BUT WITH ONLY 5 CARBON ATOMS IN ITS MOLECULE. DEOXYRIBOSE IS ALMOST THE SAME BUT LACKS 1 OXYGEN ATOM.DEOXYRIBOSE IS ALMOST THE SAME BUT LACKS 1 OXYGEN ATOM. BOTH MOLECULES MAY BE REPRESENTED BY THE SYMBOL:BOTH MOLECULES MAY BE REPRESENTED BY THE SYMBOL:

N Nitrogenous base (A, G, C, or T) (A, G, C, or T) DNA STRUCTURE CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar(deoxyribose) O O=P-O OPhosphate Group Group

DNA STRUCTURE THE STEPS OF THE LADDER ARE MADE OF PAIRS OF NITROGEN BASES. ERWIN CHARGAFF (1947) WROTE THAT IN THE DNA THE AMOUNTS OF THE NITROGEN BASES ARE NOT ALL EQUAL BUT ARE PRESENT IN CHARACTERISTIC RATIO. A=30.9% -T= 29.4%, G=19.9% - C=19.8%

DNA STRUCTURE 1.ADENINE = A 2.GUANINE = G 3.CYTOSINE = C 4.THYMINE = T THEY ARE REPRESENTED BY THEIR CAPITAL LETTER.

DNA STRUCTURE THERE IS ONLY ONE WAY THE NITROGEN BASES CAN FORM ADENINE PAIRS WITH THYMINE GUANINE PAIRS WITH CYTOSINE A==T G==C

DNA STRUCTURE JOINED NUCLEOTIDES A MOLECULE OF DNA IS FORMED BY MILLIONS OF NUCLEOTIDES JOINED TOGETHER IN A LONG CHAIN HOW MANY DO WE SEE IN THIS SLIDE? PO 4 sugar-phosphate backbone + bases

2 STRAN DNA PO 4

DNA STRUCTURE QUESTION ? CAN C JOIN WITH A AND G JOIN WITH T YES NO

CORRECT MOVE ON

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DNA STRUCTURE ACTCATGGTCATG TGAGTACCAGTAC THIS IS AN EXAMPLE OF A GENETIC CODE THAT MAY BE FOUND IN YOUR BODY.

DNA STRUCTURE THE COMBINATIONS OF THE NITROGEN BASES IS THE CODE THAT PRODUCES THE GENES FOR A PARTICULAR TRAIT.

DNA STRUCTURE BECAUSE THERE CAN BE SO MANY DIFFERENT COMBINATIONIS OF THE BASES THE CODE CAN BE LIMITLESS

DNA STRUCTURE EXAMPLE: ATCGTCAGG MAY BE FOR HAIR COLOR. BUT ATCGTCAGC MAY BE FOR EYE COLOR

DNA REPLICATION REPLICATION: IS THE PROCESS WHERE DNA MOLECULES FORM EXACT DUPLICATS.

DNA REPLICATION 1.THE LADDER SPLITS 2. FREE FLOATING NITROGEN BASES BEGIN TO PAIR WITH EACH STRAND 3. TWO NEW DNA CHAINS ARE FORMED

JAMES WATSON AND FRANCIS CRICK THE YEAR 1953 COULD BE SAID TO MARK, IN BIOLOGY AT LEAST, THE END OF HISTORY.THE YEAR 1953 COULD BE SAID TO MARK, IN BIOLOGY AT LEAST, THE END OF HISTORY. JAMES WATSON AND FRANCIS CRICK PUBLISHED A PAPER ON THE STRUCTURE OF DNA WHICH BEGAN A NEW ERA IN ITS UNDERSTANDING.JAMES WATSON AND FRANCIS CRICK PUBLISHED A PAPER ON THE STRUCTURE OF DNA WHICH BEGAN A NEW ERA IN ITS UNDERSTANDING.

RACE TO DETERMINE 3D STRUCTURE IN THE EARLY 1950’S THE RACE FOCUSED ON DISCOVERING THE 3 D STRUCTURE. AMONG THE SCIENTISTS WORKING ON THE PROBLEM WERE LINUS PAULING, MAURICE WILKINS AND ROSALIND FRANKLIN

THE WINNERS OF THE RACE THE FIRST TO THE FINISH LINE, HOWEVER WERE TWO SCIENTISTS WHO WERE RELATIVELY UNKOWN AT THE TIME: JAMES WATSON AND FRANCIS CRICK

FRIENDSHIP BETWEEN THEM THEIR FRIENDSHIP BEGAN WHEN WATSON WENT TO CAMBRIDGE UNIVERSITY, WHERE CRICK WAS STUDYING PROTEIN STRUCTURE WITH A TECHNIQUE CALLED X- RAY CRYSTALLOGRAPHY.

INTERPRETING THE DATA WATSON AND CRICK BASED THEIR MODEL OF DNA ON THE DATA THEY WERE ABLE TO EXTRACT. FROM FRANKLIN’S X-RAY DIFFRACTION PHOTO. THEY INTERPRETED THE X-RAY TO MEAN THAT DNA WAS HELICAL IN SHAPE.

A CRITIQUE OF PAULING AND COREY THE WIDTH DEDUCED FROM THE IMAGE LED THEM TO SUGGEST THAT IT WAS MADE UP OF TWO STRANDS, CONTRARY TO THE THREE STRAND MODEL THAT LINUS PAULING HAD PROPOSED.

CREATION OF A MODEL USING MODELS MADE OF WIRE, THEY BEGAN BUILDING MODELS OF DOUBLE HELIX THAT WOULD CONFORM TO THE DATA FROM X-RAY, AND WHAT WAS KNOWN ABOUT THE CHEMISTRY OF DNA.

CREATION OF A MODEL AFTER FAILING TO MAKE A SATISFACTORY MODEL THAT PLACED THE SUGAR PHOSPHATE ON THE INSIDE OF THE CHAINS, WATSON TRIED PUTTING THEM ON THE OUTSIDE AND FORCING THE NITROGENOUS BASES TO MOVE TO THE INTERIOR.

CREATION OF A MODEL FRANKLIN’S X-RAY DATA INDICATED THAT THE HELIX MAKES ONE FULL TURN EVERY 3.4nm. BECAUSE BASES ARE STACKED 0.34nm APART THERE ARE TEN LAYERS OF BASE PAIRS IN EACH TURN OF THE HELIX.

CREATION OF A MODEL THIS ARRANGEMENT WAS PPEALING BECAUSE IT PUT THE HYDROPHOBIC NITROGEN BASES IN THE MOLECULE’S INTERIOR AND THUS AWAY FROM THE SURROUNDING AQUEOUS MEDIUM.

CREATION OF A MODEL THE NITROGENOUS BASES OF THE DOUBLE HELIX ARE PAIRED IN SPECIFIC COMBINATIONS. IT WAS BY TRIAL AND ERROR THAT WATSON AND CRICK ARRIVED AT THIS KEY FEATURE OF DNA. AT FIRST WATSON IMAGINED THE BASES WERE PAIRED LIKE WITH LIKE: A-A, C-C.THE NITROGENOUS BASES OF THE DOUBLE HELIX ARE PAIRED IN SPECIFIC COMBINATIONS. IT WAS BY TRIAL AND ERROR THAT WATSON AND CRICK ARRIVED AT THIS KEY FEATURE OF DNA. AT FIRST WATSON IMAGINED THE BASES WERE PAIRED LIKE WITH LIKE: A-A, C-C. THIS WAS INCONSISTENT BECAUSE ADENINE AND GUANINE ARE PURINES, NITROGEN BASES WITH TWO RINGS. WHEREAS CYTOSINE AND THYMINE ARE PYRIMIDINES WHICH HAVE A SINGLE RING. THUS PURINES ARE TWICE AS BIG.THIS WAS INCONSISTENT BECAUSE ADENINE AND GUANINE ARE PURINES, NITROGEN BASES WITH TWO RINGS. WHEREAS CYTOSINE AND THYMINE ARE PYRIMIDINES WHICH HAVE A SINGLE RING. THUS PURINES ARE TWICE AS BIG.

CREATION OF A MODEL WATSON AND CRICK REASONED THAT THERE MUST BE ADDITIONAL SPECIFICITY OF PAIRING DICTATED BY THE STRUCTURE OF BASES.WATSON AND CRICK REASONED THAT THERE MUST BE ADDITIONAL SPECIFICITY OF PAIRING DICTATED BY THE STRUCTURE OF BASES. EACH BASE HAS CHEMICAL SIDE GROUPS THAT CAN FORM HYDROGEN BONDS WITH ITS APPROPRIATE PARTNER: ADENINE CAN FORM TWO HYDROGEN BONDS WITH THYMINE AND ONLY THYMINE; GUANINE FORMS THREE HYDROGEN BONDS WITH CYTOSINE AND ONLY CYTOSINE.EACH BASE HAS CHEMICAL SIDE GROUPS THAT CAN FORM HYDROGEN BONDS WITH ITS APPROPRIATE PARTNER: ADENINE CAN FORM TWO HYDROGEN BONDS WITH THYMINE AND ONLY THYMINE; GUANINE FORMS THREE HYDROGEN BONDS WITH CYTOSINE AND ONLY CYTOSINE.

CHEMICAL BONDING BETWEEN BASES CG H-bonds T A

FURTHER DEVELOPMENT THE WATSON-CRICK MODEL EXPLAINED CHARGAFF’S RULES. WHEREVER ONE STRAND OF A DNA MOLECULE HAS AN A, THE PARTNER STRAND HAS A T. AND A G IN ONE STRAND IS ALWAYS PARTNERED WITH A C IN THE COMPLEMENTARY STRAND.THE WATSON-CRICK MODEL EXPLAINED CHARGAFF’S RULES. WHEREVER ONE STRAND OF A DNA MOLECULE HAS AN A, THE PARTNER STRAND HAS A T. AND A G IN ONE STRAND IS ALWAYS PARTNERED WITH A C IN THE COMPLEMENTARY STRAND.