2.6 DNA/RNA Structure

Question 1

what are nucleic acids?

Answer 1

the genetic material of the cell and are composed of recurring monomeric units called nucleotides

Question 2

what are the 3 principle components that each nucleotide is comprised of?

Answer 2

• 5 carbon pentose sugar
• phosphate group
• nitrogenous base

Question 3

what are the 2 types od nucleic acids present in cells?

Answer 3

DNA (deoxyribonucleic acid) - more stable double-stranded from that stores the genetic blueprint for cells
RNA - (ribonucleic acid) is a more versatile single-stranded form that transfers the genetic information for seconding

Question 4

how do DNA and RNA nucleotides differ in structure? (3 differences)

Answer 4

DNA
- Has H on the pentose sugar (deoxyribose)
- nitrogenous bases are ACGT
- double-stranded (forms double helix)
RNA
- has OH on the pentose sugar (ribose)
- nitrogenous bases are ACGU
- single-stranded

Question 5

what is the composition of nucleic acids? (4)

Answer 5

nucleotide monomers which are linked into a single strand via condensation reactions
- phosphate groups of one nucleotide attached to the sugar of another nucleotide (at the 3’- hydroxyl (oH) group)
- results in a phosphodiester bond forming between the 2 nucleotides and water being produced as a by-product
- successive condensation reactions result in the formation of long polynucleotide strands

Question 6

how are the 2 polynucleotide chains of DNA held together?

Answer 6

via hydrogen bonding between complementary nitrogenous bases
- adenine and thymine via 2 hydrogen bonds
- guanine and cytosine via 3 hydrogen bonds

Question 7

what must bases be in order to be able to pair?

Answer 7

facing each other and strands must be running in opposite directions / they must be ANTIPARALLEL

Question 8

what happens as the antiparallel chain lengthens?

Answer 8

• the atoms will organise themselves into the most stable energy configuration
• the atomic arrangement resulting in the double-stranded DNA forming double helix

Question 9

who proposed the structural organisation of DNA molecules?

Answer 9

Watson and Crick

Question 10

what did Watson and Crish demonstrate with a model? (3)

Answer 10

• DNA strands are antiparallel and from a double helix
• DNA strands pair via complementary base pairings (A=T, C=G)
• outer edge of bases remains exposed (allows access to replicate and transcriptional proteins)

Question 11

what were some of Watson and Crick’s earlier models’ faults? (3)

Answer 11

• first model was triple helix
• early models have bases on the outside and sugar-phosphate residue in centre
• nitrogenous bases were not initially configured correctly and did not demonstrate complementarity

Question 12

what were Watson and Crick’s efforts guided by? (previous info) (3)

Answer 12

• DNA is composed of nucleotides made up of sugar, phosphate and base
• DNA is composed of an equal number of purines (A+G) and pyrimidines (C+T)
• DNA is organised into helical structure