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8.1 & 8 8.2: Structure of DNA

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Melissa Panzer

on 19 April 2016

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Transcript of 8.1 & 8 8.2: Structure of DNA

8.2-The Structure of DNA
Key Concept:
DNA Structure is the same in all organisms
Main Idea #1: DNA is composed of four types of nucleotides
DNA is polymer made up of a long chain of nucleotides (the monomers).
Viruses Contain ONLY DNA & a Protein Coat
They inject their genetic material into cells and direct the cells to make more viruses
MAIN IDEA 2: Watson & Crick Developed an Accurate Model of DNA’s Three Dimensional Structure Using Chargaff’s Rule and Rosalind Franklin’s data (PHEW!)
Main Idea #3: Nucleotides always pair in the same way.
Chapter 8: From DNA to Proteins
Learning Objectives
1. Define
nucleotide, double helix, base-pairing rules
2. Describe the interaction of the four
that make up DNA (
3. Know the difference between purines & pyrimidines
4. Describe the overall structure of DNA
5. Identify the work of Chargaff, Rosalind Franklin, & Watson & Crick
Review of DNA
DNA stands for Deoxyriobonucleic Acid
Found in the nucleus of cells
Genetic blueprint-It provides the instructions of how to build living organisms
Genes are segments of DNA that code for a specific protein.
8.1 Key Concept: DNA was identified as the genetic material
1. Define bacteriophage
2. Explain how bacteriophages were used to show that DNA was the genetic material
Main Idea #1: Bacteriophages helped to identify DNA as the genetic materials
a virus that infects bacteria
Sections 8.1 & 8.2: DNA as the genetic material & The structure of DNA
Learning Objectives
By discovering which part of a phage entered the bacteria, we'd know what the genetic material is
They tagged viral DNA with radioactive phosphorus.
They tagged viral proteins with radioactive sulfur.
Phosphorus from the tagged DNA was found inside the bacteria; Sulfur from the tagged proteins were not.
DNA is what enters & takes over cells = DNA is the genetic material
Each protein carries out a specific function
Each nucleotide has three parts:
a phosphate group
a nitrogen-containing base
The sugar is why DNA is called
nucleic acid
The nitrogen containing bases are the only difference in the four nucleotides.
The Double Helix
Watson & Crick realized that:
DNA is a
double helix
Sugar-phosphate backbone on the outside
Nitrogen bases on the inside
Double Helix
Three dimensional shape in which two strands wind around one another.
Think: Twisted Ladder
Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff.
Erwin Chargaff's Rule
%A = %T
%G = %C
Rosalind Franklin
Used a technique called X-ray crystallography
Franklin’s x-ray images suggested that DNA was a double helix of even width
base-pairing rules
show how nucleotides always pair up in DNA.
A & T form a base pair
C & G form a base pair
Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width.
Because of complementary base pairing...
The order of the bases in one strand determines the order of the bases in the other strand.

A G G - C T C - A A G - T C C - T A G
C G T – T A G – C A T
Let's Try! (YAY!)
G C A – A T C – G T A
T G A – A G T – G G C - C A A
A C T – T C A – C C G - G T T
T C C - G A G - T T C - A G G - A T C
The sugar-phosphate backbone is connected by strong covalent bonds.
The bases are connected by hydrogen bonds.
provide just enough force to hold the strands together, yet can be easily broken if needed.
DNA strands run antiparallel (they run in the opposite direction)
Full transcript