6.2: DNA Structure and Function

Question 1

Fredrick Meischer

Answer 1

• thought proteins were hereditary material
• collected pus and found substance that was acidic and had a lot of phosphorus, called nuclein later known as DNA

Question 2

Fredrick Griffith

Answer 2

• found function of DNA by collecting 2 strains of pneumonia
• S-strain: capsule causing colonies to look smooth
• R-strain: no capsule so colonies were rough and irregular
• s-strain was pathogenic, r-strain was not
• s-strain has to be alive to virulent
• heated s-strain mixed w r-strain was pathogenic b/c live r-strain was converted to virulent s-strain

Question 3

Transformation

Answer 3

change in genotype or phenotype caused by direct uptake of genetic material by cell

Question 4

Avery, McLoed, McCarthy

Answer 4

• grew strains of streptococcus to see which part of s-strain made r-strain virulent
• mixed each extract w/ 1 of 3 substances (DNA, RNA, and protein
  DNA was tranforming substance

Question 5

Hershey and Chase

Answer 5

bacteriophage: virus that infects bacteria
- used radioisotopes of P^32 for DNA and S^35 for protein
- radioactivity detected in cells infected w DNA and protein coats remained outside

Question 6

What are the 3 major components of DNA?

Answer 6

deoxyribose sugars
phosphate groups
nitrogenous bases

Question 7

4 nitrogenous bases

Answer 7

• adenine and guanine (purines)
• cytosine and thymine (pyrimidines)

Question 8

purines

Answer 8

double ring structures

Question 9

pyrimidines

Answer 9

single ring structure

Question 10

Human DNA contains?

Answer 10

30.9% A, 29.4% T, 19.9% G, 19.8% C

Question 11

Wilkins and Franklin

Answer 11

Rosalind Franklin and Maurice Wilkins used X-ray crystallography to study shape of DNA
- DNA is a double helix and rotated clockwise

Question 12

Watson and Crick

Answer 12

DNA is antiparallel - runs in opposite directions
- one strand has hydroxyl of 3’ carbon attached to deoxyribose sugar at one end and phosphate attached to 5’ carbon of last sugar
- other strand winds around first w/ 5’ end opposite 3’ end of first strand

Question 13

complementary base pairing

Answer 13

chemical tendency of adenine to form hydrogen bonds w thymine and cytosine to form hydrogen bonds w guanine

Question 14

Steps for DNA replication?

Answer 14

1. Helicase enzymes unwind DNA strand and topoisomerase relieves tension caused by helicase
2. Single stranded binding protein prevent annealing of separated strand by attaching to DNA strands to stabilize unwound DNA, replication bubbles are formed to speed up the process and create daughter strands
3. DNA polymerase uses nucleoside triphosphate to make energy to make new strands. Leading strand is continuously synthesized by DNA polymerase III
4. The Lagging strand is discontinuously synthesized. RNA primase makes RNA primers extended by DNA polymerase III to from Okazaki fragments
5. RNA primers replaced by DNA polymerase I and DNA ligase catalyzes reaction and joins Okazaki fragments to growing strand, DNA polymerase II repairs any damage to DNA