The components and structure of DNA.

DNA Deoxyribonucleic acid (DNA) is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins within the cell. Why is DNA called the blueprint of life?

Why do we study DNA? We study DNA for many reasons: It’s central importance to all life on Earth medical benefits such as cures for diseases We will look at it’s role in evolution. About better food crops, this area is controversial. There is a Dr. Charles Arntzen who is working on bioengineering foods with vaccines in them. People in poor countries could be immunized against diseases just by eating a banana, for instance.

The Shape of the Molecule DNA is a very long molecule. The basic shape is like a twisted ladder or zipper. This is called a double helix. The DNA double helix has two strands twisted together. {Show students a model of the double helix. Explain what a spiral is and a helix is.}

DNA Structure Nucleotides The DNA molecule is made up of nucleotides. A nucleotide contains three parts. O -P O O Nitrogenous base C O Phosphate group {Ask students where they have seen a similar molecule before in this class. Answer: ATP . Emphasize that nucleotides are the basic building blocks or units of a DNA molecule and that a single molecule has many millions of nucleotides.} C C C Deoxyribose O

DNA Structure The backbone of the molecule is alternating phosphate and deoxyribose (sugar)parts. The teeth are nitrogenous bases. {Point to the 3-D mode, if you have one, to show the parts as you discuss them.}

DNA Structure: Adenine (A) Thymine (T) Guanine (G) Cytosine (C) There are four nitrogen bases: Adenine (A) Thymine (T) Guanine (G) Cytosine (C)

Adenine always pairs with Thymine (A – T) Cytosine always pairs with Guanine (C – G) These are called base pairs.

Central Dogma DNA RNA Proteins DNA ultimately controls how the body is made and how it functions.

Genes Genes are short segments of DNA. A gene has instructions to make a protein. Chromosomes are made up of genes, which are made up of DNA.

Genes and Variation Genes are responsible for all the characteristics that make up a species. It just depends on which ones are inherited from the parents. Variation is very important to evolution as we will see later on.

Genetics and Heredity Genetics is the study of genes. Inheritance or heredity is how genes, are passed on from generation to generation. {Ask students where the chromosomes are in this picture. Or ask them where the DNA is. Remind them that the mitochondria also have DNA.}

Alleles A gene controls the expression of a particular trait or characteristic. Alleles are alternate forms (versions) of a gene. So essentially alleles are alternate forms of a trait or characteristic.

Alleles Dominant alleles- alleles or traits that are expressed Recessive alleles- alleles or traits that are covered up or not expressed.

Alleles Homozygous- two of the same alleles. Heterozygous- two different alleles.

Genotype vs. Phenotype Genotype- the types of genes (alleles) present. Phenotype- what the organism looks like (what is expressed).

Mutations Sometimes mistakes in copying the DNA lead to mutations. Mutations = change in the genetic structure (genotype of an individual) Sometimes, these mutations may be expressed (phenotype) and may lead to a different chance of success = natural selection  evolution.