Dna Structure And Replication (1)

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properties of hereditary molecule (4)

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Diversity of structure-contains stable form of information translated into phenotype
Ability to replicate-accurately transmit information from cell to cell and gen to gen
Mutability-changes to produce variation nec for adaptation and evolution
Expression-ability to turn genetic info into biochemical or physical characters

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griffith experiment (1982)

transformation principle

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Observed mice die of pneumonia when injected with smooth virulent strain but not rough virulent bacteria

IIIR had been transformed into IIIS; concluded agent was a protein

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Avery-MacLeod-McCarty Experiment (1944)

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Identify transforming agent
Lysed IIIS cells and plated with living IIR bacteria and they transformed into IIIS
Enzymes degraded macromolecules- transformation when proteins were degraded. no transformation when nucleic acids degraded

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Avery-MacLeod-McCarty Experiment
RNA vs DNA

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RNA nuclease degraded the RNA and transformation occurred

DNA nuclease degraded DNA and no transformation occurred *TRANSFORMING AGENT*

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Hersey-Chase Experiment (1952)

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Verified DNA as transforming agent
Difference in atomic composition of DNA- phosphorus atoms in DNA, sulfur atoms in protein
DNA radioactively tagged with 32P (pink)
Protein radioactively tagged with 35S (yellow)

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Hersey-Chase Experiment steps (3)

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1) tag. T2 bacteriophage infects E.Coli and 32P incorporated into viral DNA 35S incorporated into viral coat
2) Isolate labeled bacteriophage from lysed radioactive E.Coli and reinfect different E.Coli in non-radioactive medium
3) Examine newly infected for radioactive labels
35S label recovered from phage ghosts but not bacterium -not transmitted
32P label recovered from bacterium and phage progeny *DNA INFORMATION MOLECULE* -transmitted

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Experimental Evidence summary

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molecules from infectious bacteria can transform non infectious bacteria (griffith)

enzymes that degrade DNA prevent bacterial transformation (avery macleod mccarty)

labeled DNA transmitted by bacteriophages (hershey chase)

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Primary structure

secondary structure

tertiary structure

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nucleotide sequence (DNA and RNA)

double-helix brings together two polynucleotide strands

condensation of chromosomes to fit inside cell

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nucleotide

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composed of pentose sugar, phosphate groups, and nitrogenous bases

DeoxyNucleotide MonoPhosphate (dNMP)

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Pentose Sugar

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circular in aqueous solution
RNA=ribose 2' and 3' OH group
DNA=deoxyribose 3' OH group only

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Phosphate Group

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single phosphate group group attached to 5' carbon=monophosphate
negatively charged

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nitrogenous base

purine
pyrimidines

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attached to 1' carbon of pentose sugar

two rings- adenine and guanine (wider)
one ring- cytosine and thymine(DNA)/uracil(RNA) (narrower)

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nucleotide linkage

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phosphodiester bonds
5'-3' polarity = phosphate sugar backbone

5' phosphate group of incoming dNTP (deoxynucleotide triphosphate) and 3' OH group of preceding nucleotide

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Chargaff's rules

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determined the proportions of nitrogenous bases in DNA molecules
% Adenine = % Thymine
% Guanine = % Cytosine
% Purines (A,G) = % Pyrimidines (T,C)
(A+G)/(C+T)=1

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X-ray diffraction crystallography

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visualize molecular structure through patterns of x-ray diffraction

Rosalind Franklin concluded DNA had a helical structure

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Watson and Crick's Model

anti-parrallel

sugar-phosphate backbone

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DNA as a double Helix
DNA composed of two strands in right-handed double helix

one strand runs from 5'-3' and the other runs 3'-5'

face out, bases oriented toward central axis

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1 degree

2 degree

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single polynucleotide strands with 5'-3' polarity

two polynucleotide strands line up in antiparallel orientation

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complementary strands

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purine always binds with pyrimidine and contributes to constant width of double helix = 2nm wide
strands are held together by hydrogen bonds

T comp A with 2 H bonds (less energy to denature)
C comp G with 3 H bonds (more energy to denature)

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Spacing in DNA

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2nm wide

.34nm between nucleotides

one turn of a helix 3.4nm

twisting caused by hydrogen bonds (major groove, minor groove)

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special secondary tructure

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somplementary regions of DNA and RNA form hairpin loops