1. The Genetic Code

2.  It took almost 100 years after the discovery of DNA for scientists to figure out that it looks like a twisted ladder.  When James Watson and Francis Crick published the structure of DNA in 1953, they added another clue to how traits are passes from parent to offspring.  DNA contains the genetic information for cells to make proteins.  Proteins determine a variety of traits.

3.  Parents pass traits to offspring through chromosomes.  Chromosomes are made of DNA and proteins and are located in a cell’s nucleus.  The twisted ladder structure of DNA is also known as a “double helix.”

4.  The sides of the double helix are made up of sugar molecules called deoxyribose, alternating with phosphate molecules.  The name DNA, or deoxyribonucleic acid, comes from this structure.

5.  The rungs of DNA are made of nitrogen bases.  Nitrogen bases are molecules that contain nitrogen and other elements.  DNA has four kinds of nitrogen bases: adenine (A), thymine (T), guanine (G), and cytosine (C).

6.  A gene is a section of a DNA molecule that contains the information to code for one specific protein.  A gene is made up of a series of bases in a row.  The bases in a gene are arranged in a specific order.

7.  A single gene on a chromosome may contain anywhere from several hundred to a million or more of these bases.  Each gene is located at a specific place on a chromosome.

8.  Because there are so many possible combinations of bases and genes, each individual organism has a unique set of DNA.  DNA can be found in all of the cells of your body except for red blood cells.  DNA can be found in blood samples because white blood cells do contain DNA.

9.  A gene contains the code that determines the structure of a protein.  The order of the nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced.  Remember that proteins are long-chain molecules made of individual amino acids.

10.  In the genetic code, a group of three DNA bases codes for one specific amino acid.  For example, the three-base sequence CGT (cytosine- guanine-thymine) always code for the amino acid alanine.  The order of the three base code units determines the order in which amino acids are put together to form a protein.

11.  Guilty or Innocent? Lab  Homework is Guilty or Innocent? Lab questions and pages 112 & 113

12.  Two new cells, or daughter cells, result when a cell divides.  To ensure that each daughter cell has the genetic information it needs to carry out its activities.  DNA copies itself.

13.  DNA replication is the process in which an identical copy of a DNA strand is formed for a new cell.  Replication is very important, since daughter cells need a complete set of DNA to survive.

14.  DNA replication begins when the two sides of a DNA molecule unwind and separate, like a zipper unzipping, between the nitrogen bases.  Next, nitrogen bases in the nucleus pair up with the bases on each half of the DNA.  Because of the way the nitrogen bases pair up, the order of the bases in each new DNA strand exactly matches the order in the original DNA strand.

15.  The pattern is key to understanding how DNA replication occurs.  Adenine always pairs with thymine, while guanine always pairs with cytosine.  At the end of replication, two identical DNA molecules are formed.

16.  Modeling the Genetic Code Lab  Homework is pages 114 & 115