2.6 structure of dna and rna

Question 1

what do dna and rna molecules store?

Answer 1

• main storage molecules for genetic information in cells

Question 2

what are dna and rna molecules made of?

Answer 2

• polymers that use nucleotides as monomers
• each nucleotide has 3 parts
  • 5 carbon sugar, with ribose used in RNA and deoxyribose used in DNA
  • phosphate group
  • nitrogenous base

Question 3

what are the 4 types of nitrogenous bases found in nucleotides for dna and rna?

Answer 3

• adenine
• thymine (uracil for rna)
• guanine
• cytosine

Question 4

how are dna and rna polymers formed?

Answer 4

• polymer for nucleic acids (DNA and RNA) is formed and linked together via the “sugar-phosphate backbone”
• phosphate of 1 nucleotide bonds with the 3rd carbon of the sugar of the adjacent nucleotide
• condensation (dehydration) reaction
• repeated and hence the sugar-phosphate backbone forms in the nucleic acid polymers

Question 5

how does dna and rna differ?

Answer 5

bases:

dna: adenine, thymine, guanine, cytosine
rna: adenine, uracil, guanine, cytosine

sugar:

rna: ribose; 2nd carbon atom has OH group
dna: deoxyribose; 2nd carbon atom has no OH group, just H

number of strands:

rna: single stranded; often but not always linear in shape
dna: 2 anti-parallel, complementary strands form double helix

Question 6

elaborate on structure of dna

Answer 6

• 2 polynucleotide strands wrap around each other to form a DNA double helix
• held together by hydrogen bonds formed between complementary bases on both strands
• complementary base pairing is as such that adenine will bind to thymine on the complementary strand of DNA,
  while guanine will bind to cytosine on the complementary strand of DNA
• anti-parallel in nature, meaning that the two strands run in opposite directions (with respect to their 5’ to 3’ directions)
• rna usually found as single strands in nature

Question 7

how is double helix structure maintained?

Answer 7

• hydrogen bonds hold complementary base pairs together

- hydrogen bonds hold adjacent sections together

Question 8

how did crick and watson discover the structure of dna?

Answer 8

• in 1953, James Watson and Francis Crick managed to deduce the structure of DNA
• mainly used data from X-ray crystallography including data from Rosalind Franklin and Maurice Wilkins
• took into consideration Chargaff’s observation that in DNA, the total amount of adenine was equal to the total amount of thymine, while the total amount of cytosine is equal to the total amount of guanine
• central to their work was the construction of a model of DNA using stick and ball models to see how well the atoms fit with one another
• building of models helped them to visualise the structure of DNA and also test whether the atoms fit well in various proposed models of DNA