2.6 & 7.1 dna & rna structure notes ib biology hl 1 mrs. peters spring 2015
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2.6 & 7.1 DNA & RNA Structure Notes
IB Biology HL 1
Mrs. Peters
Spring 2015
DNA
DNA: deoxyribonucleic acid Molecular basis of
inheritance, genetic material
DNA
Structure discovered by James Watson and Francis Crick in April 1953
their model was based on Rosalind Franklin’s x-ray data and Edwin Chargaff’s nucleotide data
RNA
RNA: ribonucleic acid DNA “photocopy” leaves nucleus to make proteins
U1. Nucleic Acids Nucleic Acids: type of
macromolecule made up of nucleotides (monomers)
Two types: DNA:
Deoxyribonucleic Acid RNA: Ribonucleic Acid
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U1. Nucleotide Structure Nucleotide Structure
Phosphate group Pentose Sugar
DNA: deoxyribose RNA: ribose
Nitrogen base DNA (A,C,G,T) RNA (A,C,G,U)
Held together by covalent bonds
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S1. Nucleotide Structure Diagrams Nucleotide Structure
Draw and label a nucleotide (in class)
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U2. DNA vs. RNA (In Class)
Feature DNA RNA
Strand Double helix Single strand
Pentose Sugar Deoxyribose Ribose
Nitrogen Bases A, C, G, T A, C, G, U
Location Nucleus onlyNucleus and cytoplasm
U3. DNA Structure
Nitrogen Bases Purines: adenine (A),
guanine (G) Two rings
Pyrmidines: cytosine (C), thymine(T)
One ring
U3. DNA Structure
Complementary Base Pairing: A and T bonded by two
H bonds C and G bonded by
three H bonds
U3. DNA Structure
Two nucleotides are bonded together in the center by hydrogen bonds forming a double helix
Sugar and phosphate are covalently bonded, forming the “backbone” of each strand
U3. DNA Structure
Double helix is made of two separate strands which are antiparallel 5’- 3’ 3’-5’ (upside down) 5’ end: phosphate
group (PO43-)
3’ end hydroxide group (–OH) attached to sugar
U3. DNA Structure
Draw and label a diagram of the molecular structure of DNA
DNA Structure
Describe what is meant by the statement: “The structure of DNA is described as a twisted ladder.”
7.1 U2. Nucleosomes
Nucleosomes help to supercoil DNA
8 histone proteins (octomer) with DNA wrapped around twiceH1(specific histone protein) attaches the DNA to the octomerLinker DNA- short segment of DNA connects one nucleosome to another
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7.1 S1. Hershey and Chase
1950’s Alfred Hershey and Martha Chase studied viruses to determine if genetic material was protein or DNA
DNA contains phosphorous, proteins contain sulfur
Used radioactive isotopes of phosphorous-32 and sulfur-35 in T2 bacteriophages (virus) which were injected into E. coli (bacteria)
7.1 S1. Hershey and Chase
Trial 1:Injected bacteria with T2 viruses that contained sulfur-35 in protein coats (on the outside) and normal DNAUsed blender the gently shake the virus off the bacteriaBacteria produced no radioactivity, virus had the radioactive isotopes still attached
7.1 S1. Hershey and Chase
Trial 2:Injected bacteria with T2 viruses that contained phosphorous-32 in DNA, normal protein coatsUsed blender to gently shake virus off bacteriaBacteria produced radioactive DNA
7.1 S1. Hershey and Chase
Conclusion: DNA is the genetic material because the virus DNA had radioactive phosphorous which became present in the bacteria’s DNA
7.1 S1. Hershey and Chase
7.1 A1: Franklin and Wilkins
Rosalind Franklin was a research associate in biophysics unit at King’s College in London.Became skilled in techniques of crystallography and X-ray diffraction while researching other carbon compounds.Created the sharpest X-ray diffraction images of DNA in existenceThrough rigorous analysis of the patterns, she calculated the dimensions of the DNA helix
7.1 A1: Franklin and Wilkins
Maurice Wilkins worked in the biophysics unit at King’s College also.He also used X-ray diffraction to look at DNAShared Franklin’s diffraction pattern and calculations to Watson, without Franklin’s knowledge or permission, before she could publish her findings.
7.1 A1. Franklin and WilkinsDeductions made by Franklin:•Cross in the center indicated a helix shape•Angle of the cross shape showed the pitch of the helix•Distance between horizontal bars shows the turn (3.4 nm apart)
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7.1 A1. Franklin and WilkinsDeductions made by Franklin:•Distance between middle of pattern and top shows repeating structure•Distance is 0.34 nm between repeats
DNA Structure Review
What are the components of DNA?
How is 6 ft of DNA stored in every cell?