1. Chapter 4 Genes and DNA
Section 1+2
Pages

2. What does DNA look like? Pieces of the Puzzle:
DNA must be able to give instructions for building and maintaining cells.
DNA must be able to be copied each time a cell divides, so each cell contains identical genes.

3. Nucleotides: Subunits of DNA
A nucleotide consists of a sugar, a phosphate, and a base. Nucleotides are identical except for their base.
There are 4 bases: Adenine, Thymine, Guanine, and Cytosine
All four bases have a different shape.

4. Chargaff’s Rules
Guanine and Cytosine always occur in equal amounts in DNA, as do Adenine and Thymine

5. Franklin’s Discovery
Used X Ray diffraction to make images of DNA molecules
Suggested the spiral shape of DNA

6. Watson and Crick’s Model
After seeing Franklin’s image, Watson and Crick concluded that DNA must look like a long, twisted ladder.
This helped explain how DNA is copied and how it functions in the cell.

7. DNA’s Double Structure
Double Helix, 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:
Adenine-Thymine
Guanine-Cytosine

8. Animated DNA

9. Making Copies of DNA
Pairing the bases allows the cell to replicate or make copies of DNA
The pairs are complementary since they always pair A-T and G-C

10. How are copies made?
During replication, a DNA molecule is split down the middle, where bases meet.
The bases on each side of the molecule are used as a pattern for the new strand.
As the bases on the original molecule are exposed, complementary nucleotides are added to each side of the ladder.
Two DNA molecules are formed.
Half of each of the molecules is old DNA, half is the new DNA

11. Unraveling DNA
DNA is often wound around proteins, coiled into strands, and bundled up even more.
Cell’s without a nucleus the DNA forms loose loops within the cell.
Cell’s with a nucleus the DNA and proteins are bundled into chromosomes.

12. When are copies made? DNA is copied every time a cell divides.
The job of unwinding, copying and re-winding the DNA is done by proteins within the cell.

13. Unraveling DNA The structure of DNA allows it to hold information.
The order of the bases is the code that carries the information.
A gene consists of a string of nucleotides that give the cell information about how to make a specific trait.
Humans have over 30,000 genes.
2003 Human Genome Project

14. Unraveling DNA- Quiz Where is the DNA in your cells?
How does so much DNA fit into the nucleus?
What is the name for strands of DNA wound around proteins?
When do chromosomes become visible in cells?
What are chromatids?
In the nucleus
It is coiled up tightly around proteins
Chromatin
When the cell is about to divide
Two identical copies of a chromosome that is about to divide

15. Genes and Proteins
DNA code is read like a book, from one end to the other and in one direction.
Bases form the alphabet of the code.
Groups of 3 bases are code for the amino acid profile. (example: AGC)
A long string of amino acids forms a protein.
Each gene is usually a set of instructions for making a protein.

16. Proteins and Traits
Proteins are found throughout cells and cause most of the differences that you see among organisms.
Proteins act as chemical triggers and messengers for many processes within the cell.
A single organism may have thousands of genes that code for thousands of proteins.

17. Help from RNA
RNA (ribonucleic acid) a molecule that is present in all living cells and that plays a role in protein production
Helps in the process of changing the DNA code into proteins

18. Making of a Protein
Step 1: A copy is made of one side of the DNA segment where a particular gene is located. This copy is transferred to the cytoplasm.

19. Making of a Protein
Step 2: This mirror like copy of a DNA segment is called messenger RNA (mRNA).
Messenger RNA copies the coded message from DNA in the nucleus , and carries the message to the ribosome in the cytoplasm.

20. Making of a Protein
Step 3: Each group of three bases on the mRNA segment codes for one amino acid.

21. Making of a Protein
Step 4: The mRNA segment is fed through the ribosome. A ribosome is a cell organelle composed of RNA and protein.

22. Making of a Protein Step 5: Molecules of
transfer RNA (tRNA) deliver amino acids from the cytoplasm to the ribosome.
Transfer RNA (tRNA) transfers amino acids to the ribosome and adds them to the growing protein.

23. Making of a Protein Step 6: The amino acids are dropped off
at the ribosome.

24. Making of a Protein
Step 7: The amino acids are joined to make a protein. Usually, one protein is produced for each gene.

25. Animated mRNA

26. How is RNA different from DNA?
RNA: one strand
contains uracil instead of thymine
A, G, C, U
DNA: two strands
A, G, C, T

27. Changes in Genes
Mutation: a change in the nucleotide-base sequence of a gene or DNA molecule
Either deletion, insertion or substitution
Causes an improved trait, no change or harmful trait
If the mutation occurs on the sex cells, the mutation can be passed to the next generation
Mutations happen often
Mutagens are any physical or chemical agent that can cause the mutation (examples: UV radiation, X rays, cigarette smoke)
Examples are Cystic Fibrosis, Sickle Cell Anemia, Hemophilia, Down Syndrome

28. Example of Substitution
Sickle Cell Anemia- affects red blood cells. When Valine is substituted for glutamic acid in a blood protein. The change in shape isn’t good for the cell to carry oxygen and clot in vessel (very painful).

29. Genetics
Genetic Engineering: Manipulate individual genes to create new products, such as foods, drug or fabrics
Genetic Identification: DNA is your unique fingerprint, only identical twins share DNA
Clone: a new organism that has an exact copy of another organism’s genes.
Selective breeding: A technique to produce offspring with desirable traits.
Inbreeding: cross two genetically similar (male/female plump turkey)
Hybridization: cross two genetically different (mcintosh and red delicious apple to get an empire)

30. Web sites….. DNA and Genetics:
Genetics: