1. Journal Entry: What is DNA? What are the subunits of DNA? Objectives:
List 3 important events that led to understanding the structure of DNA.
Describe the basic structure of a DNA molecule.
Explain how DNA molecules can be copied.

2. The Pieces of the Puzzle
DNA stands for deoxyribonucleic acid.
DNA is the genetic material that determines inherited characteristics.
Nucleotides: The Subunits of DNA
DNA is made of subunits called nucleotides.
A nucleotide consists of a sugar, a phosphate, and a base.

3. The Pieces of the Puzzle, continued
Chargaff’s Rule
Erwin Chargaff found that the amount of adenine in DNA always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine. (A = T, C= G)
Franklin’s Discovery
Chemist Rosalind Franklin was able to make images of DNA molecules by using X-ray diffraction.
X-ray diffraction: X rays of a DNA molecule projected on film.
Showed that DNA has a spiral shape.

4. The Pieces of the Puzzle, continued
Watson and Crick’s Model
James Watson and Francis Crick used Chargaff’s and Franklin’s research to build a model of DNA.
The model, which looked like a long, twisted ladder, eventually helped explain how DNA is copied and how it functions in the cell.

5. DNA’s Double Structure
The Double Helix
The shape of DNA is known as a double helix.
The two sides of the ladder are made of alternating sugar parts and phosphate parts.
The rungs of the ladder are made of a pair of bases.

6. Making Copies of DNA How Copies Are Made When Copies Are Made
During replication, a DNA molecule is split down the middle, where the bases meet.
The bases on each side of the molecule are used as a pattern for a new strand.
When Copies Are Made
DNA is copied every time a cell divides.
Each new cell gets a complete copy of all the DNA.

7. Making Copies of DNA, continued
1. Unwinding: Old strands that make up the parental DNA molecule are unwound and “unzipped”. A special enzyme called helicase unwinds the molecule.
2. Complementary base pairing: New complementary nucleotides are paired together.
3. Joining: The complementary nucleotides join to form new strands.

8. Unraveling DNA
In a cell that has a nucleus, the strands of DNA (chromatin) and proteins are bundled into chromosomes.
A gene consists of a string of nucleotides that give the cell information about how to make a specific trait.

9. Genes and Proteins Groups of 3 bases form the code for an amino acid.
Many amino acids strung together form a protein.
Proteins and Traits
Proteins act as chemical triggers for many of the processes within cells.
Proteins help determine traits.
A gene is a segment of DNA that specifies the amino acid sequence of a protein.

10. RNA
Help from RNA
Another type of molecule that helps make proteins is called RNA, or ribonucleic acid.
RNA is so similar to DNA that RNA can serve as a temporary copy of a DNA sequence.
Genes pass genetic information onto RNA molecules which are more directly involved in protein synthesis.
The nucleotides in RNA, however, contain the sugar ribose and the bases adenine, cytosine, guanine, and uracil (which replace thymine).

11. RNA, continued There are 3 major classes of RNA.
Messenger RNA (mRNA): Takes a message from DNA in the nucleus to the ribosomes in the cytoplasm.
Transfer RNA (tRNA): Transfers amino acids to the ribosomes.
Ribosomal RNA (rRNA): Makes up the ribosomes, where amino acids are collected to form proteins (many amino acids form a protein).

12. Journal Entry: Unscramble the following words: tpsoneir neesg
Now think of 3 words you associate with each of the above words and use them all in a paragraph that highlights what you know about DNA.
Objectives:
Explain the relationship between DNA, genes, and proteins.
Outline the basic steps in making a protein.
Describe three types of mutations, and provide an example of a gene mutation.
Describe two examples of uses of genetic knowledge.

13. From DNA to RNA to Protein
The Making of a Protein
The first step in making a protein is to copy one side of the segment of DNA containing a gene.
This copy is called messenger RNA (mRNA).
A ribosome is a cell organelle composed of RNA and protein.
A ribosome uses mRNA, transfer RNA (tRNA), and amino acids to make proteins.

14. Protein Synthesis (Transcription and Translation)

17. Changes in Genes Mutations
Changes in the number, type, or order of bases on a piece of DNA are known as mutations.

18. Changes in Genes, continued
Do Mutations Matter?
There are three possible consequences to changes in DNA: an improved trait, no change, or a harmful trait.
How Do Mutations Happen?
Mutations happen regularly because of random errors when DNA is copied.
Any physical or chemical agent that can cause a mutation in DNA is called a mutagen.

19. An Example of Substitution
A mutation, such as a substitution, can be harmful because it may cause a gene to produce the wrong protein.
A simple change in an amino acid can cause a disease such as sickle cell anemia.

21. Uses of Genetic Knowledge
Genetic Engineering
Scientists can manipulate individual genes within organisms.
This kind of manipulation is called genetic engineering.
Genetic Identification
Your DNA is unique, so it can be used like a fingerprint to identify you.
DNA fingerprinting identifies the unique patterns in an individual’s DNA.