2.6 Structure of DNA and RNA

Question 1

Nucleic acids

Answer 1

Genetic material of cells, constructed by linking monomeric units called nucleotides together to form a polymer.

Question 2

Nucleotides

Answer 2

nitrogenous base linked to pentose sugar C1 and phosphate to C5

Question 3

how are nucleotides linked together? [2]

Answer 3

covalent bonds form between phosphate group of one nucleotide and pentose sugar of the next.

this phosphodiester bond links the 3’ C of one nucleotide to 5’ C of the next one, creating a strong sugar-phosphate backbone

Question 4

types of nucleic acids. [2]

Answer 4

DNA
RNA

Question 5

DNA structure [3]

Answer 5

DNA is a double helix structure made up of 2 antiparallel strands of nucleotides (1 oriented in 3’ to 5’ direction, 1 oriented in 5’ to 3’ direction) linked together by H-bonding between complementary bases.

A bonds to T via 2 H-bonds while G bonds to C via 3 H-bonds.

Sugar and phosphate groups are on the outside of the double helix while nitrogenous bases are inside.

Question 6

classify the nitrogenous bases into purine and pyrimidine molecules.

Answer 6

Adenine - purine
Thymine (DNA) - pyrimidine
Uracil (RNA) - pyrimidine
Guanine - purine
Cytosine - pyrimidine

purines - double ringed
pyrimidines - single ringed

Question 7

differences between DNA and RNA. [3]

Answer 7

DNA
pentose sugar: deoxyribose
nitrogenous bases: A, T, C ,G
number of strands: 2

RNA
pentose sugar: ribose
nitrogenous bases: A, U, C, G
number of strands: 1

Question 8

types of RNA. [3]

Answer 8

1. mRNA: transcript copy of gene (encode for specific polypeptide)
2. tRNA: carry polypeptide subunits (AA) to ribosome for synthesis
3. rRNA: primary component of ribosome - responsible for catalytic activity

Question 9

NOS: Watson and Crick’s proposition of the structure of DNA using models. [4]

Answer 9

• use of models allowed them to quickly visualize and assess the viability of each proposed structure
• models built based on past experimental evidence such as Rosalind Franklin’s x-ray diffraction patterns which showed the helical structure of DNA and spacing between both strands
• previous models had faults such a the presence of a triple helix and nitrogenous bases being located on the outside of the structure
• breakthrough happened because of their realization of complementary base pairing which allowed them to arrive at the correct double helix structure