Chapter 10DNA, RNA, & Protein Synthesis

Watson & CrickDuring the 1950’sJames Watson – American BiologistFrancis Crick – British Graduate Student• tried to determine the structure of DNA

1953: they came up with the structure- DNA is made up of 2 strands- double helix shape- they relied on other scientists to develop their

DNA model

Wilkins & FranklinMaurice Wilkins – English physicist and molecular biologistRosalind Franklin - British biophysicist, physicist, chemist, biologist and X-ray crystallographer

- took X-ray diffraction photographers of DNA crystals

ChargaffIn 1949

Erwin Chargaff – American Chemist-discovered the key that lead to the understanding of DNA structure

- same amount of A as T- same amount of G as C

- was key because it means that there is base pairingPyrimidine = contains single ring (T & C)Purine = contains double ring (A & G)

Nobel Prize WinnersIN 19621. James Watson2. Francis Crick3. Maurice Wilkins

Why not Rosalind Franklin?

Franklin died in 1958 and could not receive the award, only the living can get a Nobel Prize

ReplicationComplimentary base pairs allow for:

1. hydrogen bonds that help hold the 2 strands of DNA molecule together

2. helps explain how DNA replicates before a cell divides (one strand can serve as a template for making a new complimentary strand)

What is DNA replication?DNA replication = process by which DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission

What basically occurs?1. The two nucleotide strands of the original

double helix separate along the strands.

2. Each strand serves as a template to make new complimentary strands.

3. After replication-2 identical double stranded DNA molecules separate and move to new cells formed during cell division.

Steps of Replication1. helicases = enzymes that separate the DNA strands - Helicases move along DNA molecule, breaking

hydrogen bonds, allowing the 2 strands of DNA helix to split

Steps of Replication2. DNA polymerase = enzymes that add complimentary nucleotides to each of the original strands

- they are free floating in nucleus- hydrogen bonds are formed

Steps of Replication3. DNA polymerases finish replicating the DNA and fall off, resulting in 2 separate and identical DNA molecules that are ready to move to new cells during cell division

• Semi-Conseravtive Replication- 1 strand is new and 1 strand is the original- each (combination) kept (conserved) one of

the 2 original strands

• Replication occurs in many locations otherwise it would take 53 days to replicate

• DNA ligase = enzyme that joins the gaps