Nucleic Acids

Question 1

Pyrimidine tautomers

Answer 1

Predominant: amino
Rare: imino

Question 2

Purine tautomers

Answer 2

Predominant: lactam (keto)
Rare: lactim (enol)

Question 3

Purine numbering

Answer 3

Numbering starts at N on big ring farthest away from little ring and goes to top of big ring (1-6)
Numbering continues at top N of little ring and ends at last N (7-9)

Question 4

Pyrimidine numbering

Answer 4

Numbering begins at bottommost N
#2 position is C double bonded to O
Numbering continues from there

Question 5

Directionality of DNA sequences

Answer 5

5’ -> 3’

Question 6

of H-bonds between A and T

Answer 6

2 H-bonds

Question 7

of H-bonds between G and C

Answer 7

3 H-bonds

Question 8

4 ways that structure of DNA’s double helix is stabilized

Answer 8

1. Pi-stacking interactions between successive base pairs on each rung of ladder
2. H-bonding between bases in a base pair
3. Hydrophobic bases in the middle of the helix and hydrophilic sugar-phosphate backbone on the outside of the helix
4. Electrostatic repulsion between proximal anionic phosphates is stabilized by cations and assorted proteins

Question 9

Melting temperature (Tm)

Answer 9

Temperature at which 50% of DNA has denatured

Question 10

4 types of cellular RNA

Answer 10

1. Ribosomal RNA (rRNA)
2. Transfer RNA (tRNA)
3. Messenger RNA (mRNA)
4. Small RNA (s_RNA)

Question 11

Ribosomal RNA

Answer 11

Integral part of ribosomes and protein synthesis

Question 12

Transfer RNA

Answer 12

Activator and carrier of amino acid residues during protein synthesis

Question 13

Messenger RNA

Answer 13

Product of transcription

Carries information in the genetic code from the nucleus to the cytosol for translation

Question 14

Small RNA

Answer 14

Several types exist and have functions ranging from catalytic activity (ribozymes) and RNA modification

Question 15

Histone octamer

Answer 15

Made up of 2 of each histone subunit: H2A, H2B, H3, H4

Question 16

Histone H1

Answer 16

Helps hold chromatin onto histone octamer

Question 17

Both exonucleases and endonucleases can cleave what end(s) of the phosphodiester bond?

Answer 17

5’ and 3’ ends can be cleaved

Question 18

RNases

Answer 18

Catalyze 5’ phosphodiester cleavage of RNA after 5’->3’ pyrimidine nucleotide residues

Question 19

3 ionic residues of RNAse active site

Answer 19

His-12
His-119
Lys-41

Question 20

Restriction endonuclease selectivity

Answer 20

Specific sequences of DNA, which are typically palindromic sequences (symmetrical)