Structure of DNA and RNA

Question 1

What are the two types of nucleic acids and what are its monomers?

Answer 1

• There are two types of nucleic acids: DNA and RNA
• DNA: deoxyribonucleic acid and RNA: ribonucleic acid
• Both are a polymers composed of nucleotides (monomers)

Question 2

How many strands does DNA and RNA have? What do the nucleic acids strands consist of?

Answer 2

• DNA is a double-stranded nucleic acid
• RNA is a single strand
• Nucleic acids are composed of: a pentose sugar, phosphate group and a nitrogenous base

Question 3

How do DNA and RNA differ?

Answer 3

DNA
- Contains the sugar deoxyribose, contains four nitrogenous bases Guanine, Adenine, Thymine, Cytosine and is a double-stranded molecule.
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RNA
- Contains the sugar ribose, has the same bases except for Thymine it is replaced by Uracil and is a single-stranded molecule

Question 4

What is the structure of the nucleic acid strands in DNA?

Answer 4

• The nucleotides are linked together through phosphodiester bond (type of covalent bond) to form a single strand (polynucleotides)
• The bond is present between the phosphate group attached to the 5’ (five prime) C of one sugar and the hydroxyl (OH) group of the 3’ C of another sugar
• The prime number is the carbon position on the ring of the sugar
• The strands in DNA are held together by hydrogen bonds to form a double helix
• The double helix is anti parallel which means the pentose sugars are ‘flipped’ around
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Question 5

What is the complementary base pairing rule?

Answer 5

• G always pairs with C
• A always pairs with T
• The strands are held together by hydrogen bonds GC (3 bonds) and AT (2 bonds)
• The two strands must be antiparallel (run in opposite directions), one runs from 5’ to 3’ the other from 3’ to 5’

Question 6

How did Crick and Watson create a model to elucidate the DNA structure?

Answer 6

• They used the information from the DNA X-ray diffraction patters to deduce that the DNA molecule must have a regular double helix
• They also integrated Chargaff’s base ratio which showed A was equal to T and C was equal to G
• This was done to work out the complementary base pairing
• Using the information they built a 1.8m model out of metal to be able to visualize the molecule and to quickly see how well it fits the evidence.

Question 7

What are two types of RNA?

Answer 7

• mRNA: messenger RNA which is a transcript copy of a gene which encodes a specific polypeptide (protein)
• tRNA: transfer RNA which carries amino acids to the organelles responsible for synthesis (ribosome)