2.6 : Structure of DNA and RNA

Question 1

what are nucleotides? and what are the three main parts?

Answer 1

• monometric subunits of nucleic acids
• nitrogenous base (A,T,C,G or A,U,G,C)
• pentose sugar (deoxyribose & ribose)
• phosphoric head

Question 2

what are polynucleotides? how are nucleotides added to growing polynucleotides?

Answer 2

• successive condensation reaction between nucleotides (form polynucleotide strand)
• nucleotides added to growing polynucleotide chain by condensation reactions –> phosphate combines to pentose sugar (covalent bond) –> link between 5’ end of phosphate group (head) and 3’ end of hydroxyl group (sugar) of two nucleotides.

Question 3

DNA double helix is a double stranded molecule, how are the two polynucleotide chains held?

Answer 3

held together by hydrogen bonds between the complementary base pairs –> the bases are able to react as the strands are anti-parallel (most stable energy confirmation for two strands is when it takes a DNA double helix shape)

Question 4

what is RNA? and what are the bases in RNA?

Answer 4

• single strand of polynucleotide in which the sugar is ribose
• adenine, uracil, cytosine, guanine (A,U,C,G)

Question 5

how are nucleotides combined?

Answer 5

Combined in condensation reaction –> forming nucleotide & two molecules of water (by product)
–> joined together between the phosphate group of one molecule and the deoxyribose sugar –> sugar-phosphate bond via a phosphodiester bond –> polynucleotide formation.

Question 6

who discovered the DNA double helix?

Answer 6

Watson and Crick