DNA structure and discovery

Question 1

Chargaffs’ first rule

Answer 1

concentration of A equals the concentration of T

concentration of C equals the concentration of G

Question 2

Chargaffs’ second rule

Answer 2

the composition of DNA varies between species

Question 3

Chargaffs’ conclusion

Answer 3

as there is significant DNA variation between species, DNA is feasible to be the genetic material

Question 4

Griffiths’ experiment

Answer 4

identified 2 strains of streptococcus pneumonia
S strain (smooth) - protective capsule
R strain (rough) - doesn’t have protective capsule
he tested these on mice

Question 5

Griffiths’ experiment results

Answer 5

the information that determines a bacteria strain and virulence must be encoded in a non-living chemical as this information can be transferred from dead to living bacteria. Because the heat killed s-strain was transferred to the non-virulent r strain in the mice and killed the mice.

Question 6

Griffiths’ conclusion

Answer 6

a chemical substance (transforming principle) is the bearer of genetic information.

Question 7

Averys’ Experiment

Answer 7

he heat killed the s strain and then removed the RNA, DNA and the proteins in seperate experiments and added the r strain and then saw which of the r strains became infected with the s strain, this showed which of the chemical substances was the carrier of the genetic information

Question 8

Averys conclusion

Answer 8

DNA is the chemical substance that causes transformation i.e. the chemical substance that carries genetic information.

Question 9

Key figures in the discovery of the structure of DNA

Answer 9

maurice wilkins
rosalind franklin
james watson
francis crick

Question 10

photo 51

Answer 10

showed the helical structure
double stranded
bases perpendicular to the length of the dna molecule

Question 11

nucleic acid structure

Answer 11

made up of nucleotide monomers that are joined together with phosphodiester bonds to form a polynucleotide = nucleic acid

Question 12

Pyrimides group

Answer 12

C and T

Single hexagon shape

Question 13

Purines group

Answer 13

G and A

hexagon joined to a pentagon shape

Question 14

formation of the phosphodiester bond

Answer 14

the hydroxyl group (OH) on the 3rd carbon of one nucleotide reacts with the phosphate group attached to the 5th carbon on another nucleotide and the bond is formed

Question 15

direction of synthesis

Answer 15

5 prime end to the 3 prime end ALWAYS

2 strands are antiparallel

Question 16

Watson- crick model of DNA structure

Answer 16

DNA has a double stranded helical structure
the sugar and the phosphate are the backbone on the outside
the bases are on the inside
stabilised by hydrogen bonds
the 2 polynucleotide strands are orientated in opposite directions.