Lecture 4 Flashcards
how did Miescher discover nucleic acid
- pus from used bandages
- white blood cells
- purified nuclei
- extracted nuclei and found a percipitate rich in phosphorus and nitrogen - “nuclein”
The nitrogen rich was the protein and acidic P-rich was nucleic acid
what are nucleic acid repeating units of
five carbon sugar
nitrogenous bases
phosphate
what are the two types of nucleic acid
RNA (in nucleoplasm but not in chromosomes)
DNA (in chromosomes)
chemical properties of the transforming principle (avery)
resistant to proteases - so NOT protein
resistant to lipases - so NOT lipid
resitant to ribonucleases - so NOT RNA
ethanol-insoluble - so NOT carb
high moleculear weight
postive reaction to the dische test for the deoxyribose of DNA
THEREFORE TRANSFORMING PRINCIPLE IS DNA
what did Hershey-Chase use to test what genetic material is
a bacteriophage
what was used to test the structure of DNA
X-ray diffraction
conclusions of x-ray diffraction in terms of DNA
is helix
is 2nm wide (width of two nucleotide chains)
length of each turn is 3.4nm
distance between repeating units is 0.34nm
therefore 10 nucleotide pairs per turn
why is base pairing specfic
purine and purine would be too wide and pyrimidine and pyrimidine too narrow. whereas puring and pyrimidine has a consistance width to X-ray data
what ensures specfic base pairing
hydrogen bonding
semiconservative replication experimental proof (meselson-stahl)
- bacteria cultured in medium with 15N (heavy isotope)
- bacteria transferred to medium with 14N (lighter isotope)
- DNA sample centrifuged after first replication
what does DNA polymerase require
Requires:
-single-stranded template DNA
-all four nucleotide triphosphates
-free 3’ hydroxyl
What does DNA polyermase do
synthesises DNA in 5’ to 3’ direction
inserts complimentary nucleotides
uses energy from breaking phosphate bonds
“proof reading” ability can remove incorrectly inserted nucleotides
proteins involved in DNA replication
Helicase - unwinde the helix to open it up
Single-stranded binding proteins - hold the helix open
primase - synthesises the RNA primers needed for initiation of DNA synthesis
DNA polymerase III - extends the DNA strand from the 3’ end copying the template
DNA polymerase I - removest he RNA primer and fills in gaps between Okazaki fragments
DNA ligase - seals thee gaps between Okazaki fragments
