DNA Composition And Structure

Question 1

Describe the structure of DNA

Answer 1

• consists of 2 molecules that are arranged into a ladder like structure called a double helix
• made up of million of tiny subunits called nucleotides
• each nucleotide consists if a phosphate group, pentode sugar, nitrogenous base
• the phosphate and sugar form the backbone of the DNA molecule whereas as the bases form the “rungs” (step on ladder)
  A-T
  C-G

Question 2

Base pairing

Answer 2

AT base pairs are held together by 2 hydrogen bonds.

GC base pairing are more strongly bonded with 3 hydrogen bonds

Question 3

Chargaffs Rule

Answer 3

A and G are purines

T and C are pyrimidines

Question 4

Describe how DNA replicates

Answer 4

• 2 strands must be separated & copied
• one protein separates the two strands of DNA
• Another protein brings the correct (a copy of) new base to pair with the existing base, thus using it as template

Question 5

Describe how DNA fits into chromosomes

Answer 5

DNA condenses

• the DNA tightly wraps around a spool just like a kite string. This is a chromosome
• condensing a strand of DNA is like taking a very long string, sewing it into a shirts and balling up the shirt into a very tight wad. The string is DNA