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Chapter 10 DNA, RNA, & Protein Synthesis. Watson & Crick. During the 1950’s James Watson – American Biologist Francis 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
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Watson & Crick • During the 1950’s • James Watson – American Biologist • Francis 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 & Franklin Maurice Wilkins – English physicist and molecular biologist Rosalind Franklin - British biophysicist, physicist, chemist, biologist and X-ray crystallographer - took X-ray diffraction photographers of DNA crystals
Chargaff In 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 pairing Pyrimidine = contains single ring (T & C) Purine = contains double ring (A & G)
Nobel Prize Winners IN 1962 James Watson Francis Crick Maurice Wilkins Why not Rosalind Franklin? Franklin died in 1958 and could not receive the award, only the living can get a Nobel Prize
Replication • Complimentary base pairs allow for: • hydrogen bonds that help hold the 2 strands of DNA molecule together • 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? • The two nucleotide strands of the original double helix separate along the strands. • Each strand serves as a template to make new complimentary strands. • After replication • -2 identical double stranded DNA molecules separate and move to new cells formed during cell division.
Steps of Replication 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 Replication 2. 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 Replication 3. 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-Conserative 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
What about errors? • only about 1 error occurs for every billion of paired nucleotides added • DNA polymerases have repair enzymes that “proof read” DNA • example: a friend might check your term paper for spelling errors • DNA example: if A pairs with a C instead of T, the repair enzymes would fix error by removing C
What happens if error is not corrected? Mutation = a change in the nucleotide sequence of a DNA molecule = can have serious effects on the function of an important gene and disrupt an important cell function • some DNA can be damaged from chemicals and UV radiation from the sun • some mutations can lead to cancer • explains how mutations can arise and lead to altered cells and organisms • changes allow individuals to survive and reproduce better, so these variations increase in the population over many generations