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Structure of DNA
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Read and React
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Homework
Define (Page 362-365)
RNA
Messenger RNA
Ribosomal RNA
Transfer RNA
Transcription
RNA polymerase
Promoter
Intron
Exon
Review Homework
List the conclusions that Griffith and Avery drew
from their experiments?
Griffith concluded that heritable substance transforms
harmless bacteria into harmful bacteria. Avery found
this is DNA
Review Homework
What was the experimental variable that Avery used
when he repeated Griffith’s work?
Molecule-destroying enzyme he used
Review Homework
What conclusions did Hershey and Chase draw from
their experiments?
DNA is the genetic material found in genes
Components of DNA
What does DNA stand for?
Deoxyribonucleic acid
Made up of nucleotides joined into long strands and
chains
Made up of 5 carbon sugar called deoxyribose and
phosphate
Has 4 nitrogen bases: adenine, guanine, cytosine and
thymine
Commonly referred to as A, G, C, T
Components of DNA
Nitrogen bases are bases that contain nitrogen
These bases stick out sideways from each other
Can be joined in any order
Structure of DNA
Erwin Chargaff
Showed percentages of adenine and thymine are
almost always identical in DNA
Percentages of Guanine and Cytosine are also almost
identical
What conclusion would you draw from this?
A=T
G=C
Structure of DNA
Rosalind Franklin
Took x-ray diffraction pictures that revealed the
double-helix structure of DNA
Only showed a 2-D model of DNA, but presents in Xshape
James Watson and Francis Crick
Built a model of the DNA molecule that explained both
structures and properties of DNA
Used Franklin’s x-shape to discover Double-Helix
The Double Helix
The double helix explains Chargaff’s rule of base
pairing
Model shows:
2 strands in double helix run in opposite directions with
bases in the center
Each strand carries a sequence of nucleotides, arranged
like letters of alphabet for recording genetic info
Hydrogen holds strands together
Chemically speaking, H bonds strong or weak?
H bonds form only between pairs (AT – CG)
Base Pairing
The Double Helix
Like a twisted ladder or a spiral staircase
Each strand is “antiparallel”
Antiparallel?
Run in opposite directions
Base Pairing
The perfect fit of Adenine with Thymine
Guanine and Cytocine
Why are the weak Hydrogen bonds important?
Think of the functions of DNA
Final Questions
Why did scientists have to resort to methods other
than a microscope?
Explain the idea of base pairing?
Homework
Define (Page 362-365)
RNA
Messenger RNA
Ribosomal RNA
Transfer RNA
Transcription
RNA polymerase
Promoter
Intron
Exon