1. Unit 2 The Molecule of Life Genes and Heredity
DNA
Structure
Unit 2
The Molecule of Life
Genes and Heredity

2. DNA – A Preview
The Book of You –Joe Hanson (TED Ed)

3. What is DNA? The Basics

4. Objectives
Describe the DNA molecule (i.e. what it is made of, importance/purpose, etc)
Explain how DNA contributes to the diversity of life forms
Describe the chemical nature of chromosomes (proteins and nucleic acids)
Summarize the work of Watson and Crick in discovering the DNA molecule
Explain the structure of DNA (include a diagram)

5. Criteria for a material to be hereditary:
separate particle that can function independently
found in the nuclear material of all cells
every cell has the same kind and amount of material
located in a safe place protected from damage
able to be passed on to the next generation
able to copy itself accurately
carries instructions in chemical code
able to translate messages from chemical codes into agents that cause things to happen within the cell/body

6. The DNA Molecule Found in all cells of each living organism
It is the only molecule that can replicate itself which permits cell division
Provides directions that guide the repair of damaged cells or production of new ones
Chemical messages carry information from the nucleus to the cytoplasm where the directions are carried out
What is DNA and how does it work (video)

7. DNA and Diversity
Offspring are genetically different from their parents due to exchange of genes during crossing over and mutations
In both cases, the original DNA code is changed to produce a genetically different offspring
What is a gene?

8. Chemical Nature of Chromosomes
Chromosomes are made up of proteins and nucleic acids
Protein
Basic Unit = amino acid
Nucleic Acid
Basic Unit = nucleotide

9. Genetic code lies in the sequence of nucleotides, not the proteins
Made of:
Phosphates
Sugar (deoxyribose)
One of four different nitrogen bases
Adenine
Thymine
Guanine
Cytosine
Genetic code lies in the sequence of nucleotides, not the proteins

10. Watson and Crick Scientists who discovered the structure of DNA:
Knowing structure leads to knowledge of how it functions
Used X-Ray Crystallography technology (by Rosalind Franklin) to discover that the structure was a double helix
Studied DNA of different organisms.
They presented a 3-D model to scientific community in 1953

11. What they found out….. DNA is Double stranded Twisted into helix
Has a beginning and an end
Nucleotides are found in all organisms but the proportion of nitrogen bases (A, G, T, C) varied from species to species
A=T, C=G suggested they are arranged in pairs

12. DNA has 4 levels of arrangement (structures) dependent on the stage of cell cycle
Example:
as chromatin it is in its primary structure
as a chromosome in prophase it is in its quaternary structure

14. DNA Structure
DNA consists of two molecules that are arranged into a twisted ladder-like structure called a Double Helix.
A molecule of DNA is made up of millions of tiny subunits called Nucleotides = Basic unit of DNA
Each nucleotide consists of:
Phosphate group
Pentose sugar
Nitrogenous base

15. Genetic code lies in the sequence of nucleotides
Phosphate
Nitrogenous
Base
Pentose
Sugar
Genetic code lies in the sequence of nucleotides

16. Nucleotides
The phosphate and sugar alternate to form the backbone of the DNA molecule
The bases are joined by hydrogen bonds form the “rungs”.
There are four types of nitrogenous bases.

17. Nucleotides A
Adenine T
Thymine C
Cytosine G
Guanine

18. Nucleotides Each base will only bond with one other specific base.
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Form a base pair.
Form a base pair.

20. DNA Structure Because of this complementary base pairing,
the order of the bases in one strand determines the order of
the bases in the other strand.

22. A C T G G A T C

24. Break it Down….

25. What holds them together?

26. DNA Structure
To crack the genetic code found in DNA we need to look at the sequence of bases.
The bases are arranged in triplets called codons.
A G G - C T C - A A G - T C C - T A G
T C C - G A G - T T C - A G G - A T C

28. DNA Structure A gene is a section of DNA that codes for a protein.
Each unique gene has a unique sequence of bases.
This unique sequence of bases will code for the production of a unique protein.
It is these proteins and combination of proteins that give us a unique phenotype.

29. Supplementary Resources
Molecular Genetics
The Structure of the DNA Molecule
Build a DNA Molecule
The Discovery of the Molecular Structure of DNA

30. Summary of the Chemical Nature of Chromosomes
Made up of proteins and nucleic acids
Protein
Basic Unit = amino acid
Nucleic Acid
Basic Unit = nucleotide
Nucleotide made of:
Phosphates
Sugar (deoxyribose)
One of four different nitrogen bases
adenine
thymine
guanine
cytosine
*Genetic code lies in the sequence of nucleotides, not the proteins

31. DNA
Gene
Protein
Trait

32. Your Task
Draw a flow chart to show how to get from:

33. The DNA of eukaryotic cell is tightly bound to small basic proteins (histones) that package the DNA in an orderly way in the cell nucleus.
suggest that the binding of proteins to DNA in chromatin protects the regions of DNA from nuclease digestion, so that enzyme can
attack DNA only at sites separated by
approximately 200 base pairs.