2.6 DNA / RNA Structure

Question 1

Nucleic acids

Answer 1

The genetic material of the cell
Composed of recurring monomeric units (‘nucleotides’)

Question 2

3 principal components a Nucleotide is comprised of

Answer 2

1. 5-carbon pentose sugar (pentagon)
2. Phosphate group (circle)
3. Nitrogenous base (rectangle)

Question 3

Structure of Nucleotide

Answer 3

1. Phosphate group & nitrogenous base attached to central pentose sugar
2. nitrogenous base attached to 1’ - carbon atom (right point)
3. Phosphate base attached to 5’ carbon atom (left point)

Question 4

Draw Diagram of single nucleotide

Answer 4

(Draw)

Question 5

2 types of nucleic acids in cells

Answer 5

1. DNA (DeoxyriboNucleic Acid)
2. RNA (RiboNucleic Acid)

Question 6

DNA

Answer 6

(DeoxyriboNucleic Acid)
- More stable
- Double-stranded form
- Stores genetic blueprint for cells

Question 7

RNA

Answer 7

(RiboNucleic Acid)
- More versatile
- Single-stranded form
- Transfers genetic information for decoding

Question 8

Differences of composition of DNA & RNA nucleotides

Answer 8

1. Base composition: DNA (T base), RNA (U base)
2. Pentose sugar: Deoxyribose, Ribose
3. Number of strands

Question 9

Compare RNA vs DNA

Answer 9

• More versatile / More stable
• Single-stranded form / Double-stranded form
• Transfers genetic information for decoding / Stores genetic blueprint for cells

Question 10

Composition of nucleic acid

Answer 10

Nucleotide monomers, linked into a single strand via condensation reactions

Question 11

Explain composition of nucleotides in nucleic acid

Answer 11

1. phosphate group of one nucleotide attaches to the sugar of another nucleotide (at the 3’– hydroxyl (-OH) group)
2. > phosphodiester bond forms between the two nucleotides (water produced as by-product)
3. Successive condensation reactions result in the formation of long polynucleotide strands

Question 12

How 2 polynucleotide chains of DNA are held together

Answer 12

Hydrogen bonding between complementary nitrogenous bases

Question 13

Complementary nitrogenous bases

Answer 13

1. Adenine (A) + Thymine (T) via 2 hydrogen bonds
2. Guanine (G) + Cytosine (C) via three hydrogen bonds

Question 14

How bases face each other and pair

Answer 14

Strands must run in opposite directions (‘Antiparallel’)

Question 15

How double helix forms

Answer 15

Antiparallel chain lengthens, atoms organize in the most stable energy configuration
=> double helix (~10 - 15)

Question 16

Draw DNA double helix structure

Answer 16

(‘Draw’)

Question 17

Who/When the structural organisation of DNA molecule was correctly proposed

Answer 17

in 1953
by James Watson & Francis Crick

Question 18

How Watson & Crick made DNA models / what it demonstrated

Answer 18

Using trial and error, their model demonstrated
- DNA strands antiparallel & form double-helix
- Complementary base pairs
- Outer edges of the base remain exposed

Question 19

Faults of early attempts of Watson and Crick’s model

Answer 19

• Triple helix
• Bases on the outside and sugar-phosphate in center
• Nitrogenous bases were not initially configured correctly > not complementarity