Genetics Lecture 20, 10/15 - DNA and its History

-By early 1940's it had been established that DNA was the genetic material. From about 1940 to 1953 there was a race to find out what the structure of DNA was. In 1953 - Watson and Crick proposed their model of the DNA double helix.

• (6:00) They worked with two pieces of evidence that allowed them to come up with this structure (Done by other scientists)
  

• 1st piece of evidence: Chargaff - Base composition studies. Take DNA from an organism and analyzed the % of each of the 4 nitrogenous bases. Findings were that percentage of A and T was always equal.

• 2nd piece of evidence: Maurice Wilins and Rosiland Franklin: exposing DNA to x-rays to attempt to get an x-ray picture of DNA.

• it appeared that the DNA had a consistent width (3.4 angstroms) and it looked like a series of coins stacked on eath other.
• This suggested that DNA had a helical shape
  

- Watson and Crick proposed that DNA exists as a double helix with two strands of DNA wrapped around each other to form a helical shape.

• DNA has a 5' end and a 3' end. Our strands run anti-parallel
• (19:10) The outside of the double helix is the sugar - phosphate backbone.
• nitrogenous bases lie on the inside of the double helix like steps on a ladder. The distance between the steps is consistent (3.4 angstroms).
• It takes 10 Base pairs to go one turn around the double helix. Therefore one turn equals 34 angstroms
• Within the double helix A pairs with T and G pairs with C (complimentary - comes from work done by Chargaff). This also means that you always have a purine pairing wiht a pyrimidine. This leads to a double helix with a consistent diameter (20 angstroms). The base pairs are held together by hydrogen bonds. A-T=2H bonds . . . G-C = 3 H bonds
• overall hydrogen bonds are the weakest of the bonds.
• (28:50) Sugar Phosphate backbone is hydrophilic. The nitrogenous bases are hydrophobic
• Grooves in the structure - places where there are openings - each groove represents 5 Base pairs (major groove is larger opening and minor groove is smaller opening)
• The DNA double helix is a right handed helix

Genetics Lecture 19, 10/13 - Eukaryotes, Nucleic acid chemistry

Genetic material of eukaryotes (10:00)

• We would expect the genetic material to be in the nucleus (it is).
• Which wavelength of UV light is mutagenic?
• DNA and RNA absorb 260nm
• Protein absorbs the 280nm
• The wavelength that is mutagenic would indicate which molecule is the genetic material.
  
• This would indicate that the 260nm wavelength is mutagenic.
• Recombinant DNA work. If you put a piece of Eukaryotic DNA into a bacterial cell you can make protein from that DNA.

Nucleic Acid Chemistry (14:25)

• DNA and RNA are made of long chains of nucleotides.
• Nucleotide is composed of 3 subunits: phosphate group, nitrogenous base and sugar.
• Nitrogenous base:
  
• Purines: adenine and guanine
  
• Pyrimidines: cytosine, thymine and uracil
• In DNA: AGCT are present
• In RNA: AGCU are present
• Sugars: RNA - ribose and DNA - deoxyribose
• Phosphate group. The number of phosphates in the phosphate group determine what nucleotide you're dealing with.
  
• One phosphate - adenine monophosphate (AMP)
• two phosphate - adenosine diphosphate (ADP)
• 3 phosphate - Adneosine triphosphate (ATP)
  

• Know the structrue of the five bases as well as Deoxyribose and ribose.
• When nucleotides are linked together we covalently bond the phosphate of one nucleotide to the sugar of the second nucleotide --> phosphodiester bond.
• Dinucleotide - two nuclotides linked together and Tri would be three, oligo is 4- 50 nucleotides linked together, poly is 51+ nucleotides linked together.