How DNA Works

1. How DNA Works Pgs 88-93

2. Breaking the DNA code The bases in DNA read like a book from one end to the other and in only one direction. A,T,C,G are the only letters in the code Each ‘word’ of the code consists of 3 bases. Each group of three bases is a code for an amino acid. Proteins are made of amino acids. The order of the bases determine the order of the amino acids in a protein.

4. Why Proteins? Proteins are found throughout cells and act as chemical messengers. They send messages like how tall you will be, and what colors you see, etc. Each one of your cells contains about 100,000 genes (each with a code for an amino acid sequence) Your genes will code for over 50,000 different types of proteins in your body.

5. Making a Protein • Step 1 – • Copy the section of the DNA strand containing a gene • Step 2 – • Messenger molecules carry the copied DNA out of the cell nucleus into the cytoplasm • Step 3 – • In the cytoplasm, the DNA copy is fed into a protein assembly line at a ribosome • The ribosome is like a protein building factory

6. Making a Protein (cont.) • Step 4 – • The DNA copy is fed through the ribosome 3 bases at a time to read the code. • Step 5 – • Transfer molecules act as a translator for the code. • Each molecule, with the complimentary code required, picks up an amino acid specific to the code. • Each amino acid is determined by and specific to the 3 bases. • Step 6 – • The transfer molecules drop off the amino acids. • The amino acids are strung together in a chain to make a protein.

8. Substitutions in genes • A change in the order of the bases in an organisms DNA is a mutation. • Deletion – sometimes a base is left out • Insertion – an extra base is added • Substitution – an incorrect base replaces a correct base • This is the most common

9. Consequences of Mutations • Errors are made, but typically corrected by repair enzymes. Sometimes errors are not caught or not repaired correctly. • Changes in DNA can result in: • 1. Improvement • 2. No change or harm • 3. Harmful change

11. What causes damage to DNA? • Damage can be caused by physical and chemical agents known as mutagens • Examples include: high-energy radiation from X rays and ultraviolet radiation, asbestos and chemicals in cigarette smoke

12. Substitution Example A DNA base sequence is GAA, but a mistake is made in the copying process that makes it GTA. This example is how the disease sickle-cell anemia occurs. This disease affects red blood cells by distorting their shape and function. This disease is fatal and those with it will eventually die.

14. Genetic Disorders Most hereditary disorders are recessive disorders which means both parents pass down a recessive trait. Some parents have the recessive form of a gene and never know it because they are just a carrier. Sometimes a pedigree is used to help trace a disorder through a family’s history.

16. Selective Breeding In this type of breeding, organisms with desirable traits are mated to produce a new breed. Ex) Chickens that produce a large number of eggs, cows that produce more milk, or you family dog.

17. Genetic Engineering Scientist have taken selective breeding to another level with genetic engineering. Genetic engineering allows scientists to transfer desired genes from one organism to another. This is used in manufactured proteins, to repair damaged genes, and identify carriers of diseases.