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

Ibbiologyhelp.com

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

Ibbiologyhelp.com

S1. Nucleotide Structure Diagrams Nucleotide Structure

Draw and label a nucleotide (in class)

Ibbiologyhelp.com

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

Beyondthedish.wordpress.com

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)

Undsci.berkeley.edu

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?