DNA & RNA Structure

Regular Biology

Waggy

Discovery of DNA

• James Watson & Francis Crick, 1950’s– Discovered with the help of Rosalind Franklin that the structure of

DNA is a double helix

– Were awarded the Nobel Peace Prize for their discovery

• A double helix is much like a spiral staircase• The handrails are made up of alternating sugars & phosphate

groups

The steps are made up of nitrogenous base pairs

The Double helix• There are two kinds of nitrogenous bases:• Purines & Pyrimidines• Adenine (A) Thymine (T)• Guanine (G) Cytosine (C )

**NO URACIL!!!

• One Purine ALWAYS pairs with one Pyrimidine– Adenine pairs with Thymine– Guanine pairs with Cytosine– These are called complimentary pairs– The order that the pairs are found is called the base

sequence

DNA Structure

• The sides (handrails) are made up of phosphates and sugars

• The steps are made up of complimentary base pairs

• A DNA strand is made up of lots of nucleotides strung together

• One nucleotidenucleotide consists of one one complimentary base complimentary base pair, sugar and pair, sugar and phosphate group on phosphate group on each sideeach side

DNA Replication

• This is the process by which DNA is copied in a cell before cell division

• There are three steps in this process:

• 1. Enzymes called helicases separate the two strands of DNA like a zipper– The fork shaped area

between the two strands is called the replication fork

• 2. Enzymes called DNA polymerases collect the needed complimentary pairs to complete each individual DNA strand

• 3. You now have TWO complete & separate DNA molecules where you only had one before

• Each of the DNA molecules is made up of one original strand and one new strand

• http://www.lpscience.fatcow.com/jwanamaker/animations/DNA Replication - long .html

Replication Errors (mutations)

• Usually replication with great accuracy, but sometimes errors do occur

• An error will occur about once for every billion nucleotides replicated

• When a mistake happens it is known as a mutation

• Most mutations go unnoticed & do not cause any problems but some can cause illness or diseases like cancer

• Mutations will happen more frequently if you are exposed to some types of chemicals or UV radiation

• Chemicals that put you at risk for developing cancer are called carcinogens

• One area of cancer research focuses on DNA replication