The Structure DNA and Mutations that can occur to it

Recall: DNA controls the activities of the cell (blueprints) found in the nucleus Transcribed into mRNA

Discovery of DNA Structure Rosalind Franklin – used a technique that used X-rays crystallography to photograph molecules and discovered that the pattern in a DNA molecule was a coil (helical) and that the diameter of a DNA was 2nm Watson and Crick – used Franklin’s photographs and scale models to determine the structure of DNA (sugar-phosphate backbone and base pair centers); they also determined the base pair pattern – A with T and C with G

DNA Structure The building blocks of DNA are nucleotides, which are composed of nitrogenous base, phosphate group, and a sugar. The phosphate and sugar will form the backbone of the DNA molecule Inside backbone two nucleotides are paired together, each nucleotide is linked to a backbone The sequence of nitrogenous bases is important for protein synthesis

DNA: Double Helix DNA is made of TWO strands They run ANTI-PARALLEL—in opposite directions

The nitrogen bases can either be purines, which has a double ring structure or pyrimidine, which has a single ring structure Adenine & Guanine are purines (double ring structure) Thymine and Cytosine are Pyrimidines (single ring structure)

Adenine pairs with thymine (A-T) Cytosine pairs with guanine (C-G) This is known as complementary base pairing http://www.youtube.com/watch?v=qy8dk5iS1f0

Mutations Mutations are errors in DNA They can have a positive, negative or no effect on an organism They can be caused by: Exposure to chemicals Errors in cell division (mitosis) Viruses/ Bacteria Negative mutations in cells which continue to replicate can lead to cancer

Types of Mutations 1) Point Mutation – Is a change in your nitrogenous base sequence by either base-pair substitutions, insertion and deletion that occurs when your DNA is being replicated See Figure 2 on p. 234

2) Chromosomal Mutation – errors that involve either whole chromosomes or a large part of the chromosomes which can result in the production of offspring with too few or too many chromosomes non-disjunction disorders are an example of this

3) Inheriting Mutations – occur in the gametes and thus are passed to the offspring the mutation will then become part of the offspring's genetic code If the mutation is dominant then the phenotype will be seen; if it is recessive it will likely not be expressed for many generations Sickle-Cell Anemia is an example of this, which is when there is not enough oxygen red blood cells no longer have a round shape but a C-shaped preventing them from moving through the blood vessel properly

Spontaneous or Induced Mutations Mutations can either occur by accident in nature or the by physical or chemical agents Spontaneous mutations are a caused by incorrect copying of DNA during the replication of the chromosomes in either mitosis or meiosis