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DNA Structure

4.2. DNA Structure. It was determined that DNA comprises of three main components: deoxyribose sugar, phosphate group (-), nitrigenous base.

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DNA Structure

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  1. 4.2 DNA Structure

  2. It was determined that DNA comprises of three main components: deoxyribose sugar, phosphate group (-), nitrigenous base. These three components make up a ________________. These are held together by _______________ bonds (between the ____________ and ___________ groups. 1920S

  3. Erwin Chargaff (1949) Proportion of adenine = proportion of _______________ Proportion of guanine= proportion of _______________ Proportion of pyrimidines = proportion of __________ Structure of Nucleotides Nitrogenous base attached to 1’ carbon of the sugar by a glycosyl bond. Phosphate group attached to the 5’ carbon by an ester bond.

  4. Carries hereditary information Controls cellular processes Accommodates for individual variation Replicates itself DNA... That complicated molecule

  5. What was known: • Chemical composition of DNA (not structure!) • Relative proportions of nitrogenous bases to each other. • What was the structure? • Linus Pauling: California • Rosalind Franklin & Maurice Wilkins: London • Using X-ray diffraction analysis/ X-ray crystallography • Molecule bombarded with X-rays  X-rays deflected by atoms  pattern of lighter and darker lines on photographic film. • Math used to decipher the 3-D shape. • James Watson & Francis Crick: Cambridge U. • Wilkins presented them with informal look at Franklin’s diffraction pattern before it was published (boo!) • Revealed that DNA has the shape of a helix about 2 nm in diameter, with a complete helical turn every 3.4 nm. • Used Franklin’s info + Chargoff’s results to build the famous model of the double-helix structure of DNA in 1953. • Wilkins, Watson, and Crick awarded the Nobel Prize in 1962. 1953: the year of dna

  6. Born to liberal-minded parents  she was raised in the same manner as her brothers. At 15, she decided to pursue a career in science, despite the lack of female role models in the scientific community in the 1930s. Did extensive research with X-ray chrystallography. Died of cancer at the age of 37 in 1958, working until the very end in her wheelchair. She may have been awarded the Nobel Prize had she been alive. Rosalind franklin

  7. Consists of two antiparallel strands of _______. • Bases of one strand paired with bases in the other strand facing inward towards each other. • Purine is always paired with a pyrimidine: complimentary base-pairing. • Which scientist led to this idea? • If sequence of one strand is known, the sequence of the complimentary strand is known. DNA STRUCTURE: the double helix

  8. Yeah, so? • This is consistent with the base-pairing rules • If two purines bond together: wider at some points. • If two pyrimidines bond together, less than 2nm. • Complimentary base pairs held together by hydrogen bonds • Individual H-bond weak • ‘strength in numbers’: DNA is stable. The helix has a consistent diameter of 2nm.

  9. One strand runs in the 5’ to 3’ direction. • One strand runs in the 3’ to 5’ direction. • 3’ end: • Terminates with the hydroxyl group of the deoxyribose sugar • 5’ end: • Terminates with a phosphate group. • By convention, only the 5’ – 3’ strand written when indicating the sequence of nucleotides. Why? _______________________ Antiparallel...

  10. Page 216, #1-3, 5-10. Seatwork/homework

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