Nucleic Acids

Question 1

What class of nucleobases has two heterocyclic rings?

Answer 1

Purines

Question 2

Cytosine, with one heterocyclic ring, is what class of nitrogenous base?

Answer 2

Pyrimidine

Question 3

What three bases come under the pyrimidine class?

Answer 3

Thymine, cytosine, and uracil.

Question 4

Adenine and guanine are what type of nucleobase?

Answer 4

Purines

Question 5

The base and sugar of a nucleic acid monomer can be referred to as…?

Answer 5

The nucleoside

Question 6

In PURINES, the glycosidic linkage occurs between the ribose (1’) and which nitrogen?

Answer 6

The 9’ nitrogen.

Question 7

If the glycosidic linkage was between the 1’ carbon of the ribose and the 1’ nitrogen of the nucleobase, would it be a purine or pyrimidine?

Answer 7

Pyrimidine.

Question 8

If a nucleobase has 1 heterocyclic ring, which nitrogen attaches to the ribose in nucleic acids?

Answer 8

The 1’ nitrogen.

Question 9

Alcohol + acid = ester. Where do we find the ‘alcohol’ in nucleic acids?

Answer 9

The hydroxyl groups on the sugars.

Question 10

To which end of nucleic acids can nucleotides be added?

Answer 10

The 3’ end.

Question 11

What is the structural unit of chromatin?

Answer 11

Nucleosomes

Question 12

How many H bonds form between guanine and cytosine?

Answer 12

3

Question 13

How many H bonds form between adenine and thymine?

Answer 13

2

Question 14

What is the distance between complementary nucleobases in dsDNA?

Answer 14

1.08nm

Question 15

What is the distance between stacked nucleobases?

Answer 15

0.34nm

Question 16

How many base pairs are there for every rotation of the DNA helix?

Answer 16

10.5

Question 17

50% of DNA stability is from H bonding between bases. What is the other 50%?

Answer 17

Hydrophobic interactions from tight base stacking.

Question 18

What alternative DNA structure is left-handed?

Answer 18

Z-DNA

Question 19

What alternative DNA structure forms a triple helix?

Answer 19

H-DNA

Question 20

What ‘groove’ do most proteins interact with on DNA?

Answer 20

The major groove

Question 21

What is the purpose of the abundance of positively-charged amino acids (arginine and lysine) in histones?

Answer 21

Neutralises the negative charge of the sugar-phosphate backbone.

Question 22

What is the role of linker histone 1?

Answer 22

It binds to the core histone octamer and links it to the next nucleosome.

Question 23

How many histones are in the core of nucleosomes?

Answer 23

8 (an octamer)

Question 24

What is the structural stage between chromatin fibre and supercoiled structures?

Answer 24

Solenoid or 30nm fibre.

Question 25

Supercoiled structures are also called what fibre?

Answer 25

200nm fibre

Question 26

What RNA makes up 80% of cellular RNA?

Answer 26

Ribosomal (rRNA)

Question 27

Single-stranded RNA often forms what secondary structure?

Answer 27

Stem-loop structure

Question 28

In what pH would nucleic acids be completely hydrolysed?

Answer 28

A pH below 1

Question 29

Between pH 2-4, what occurs to nucleic acids?

Answer 29

Depurination - A and G are removed.

Question 30

Why is DNA stable at pH 10-13 but RNA is not?

Answer 30

The 2' hydroxyl in RNA (absent in DNA) attacks the phosphodiester bond.

Question 31

At what pH would RNA's backbone break but DNA would only become single-stranded?

Answer 31

pH 10-13

Question 32

What wavelength do nucleic acids absorb UV at?

Answer 32

260 nm

Question 33

Does ssDNA or dsDNA absorb more UV light? How much?

Answer 33

ssDNA absorbs 40% more.

Question 34

What defines the melting temperature (Tm)?

Answer 34

Where DNA is 50:50 dsDNA:ssDNA.

Question 35

Would more G-C bonds produce a higher or lower Tm?

Answer 35

Higher, as G-C bonds are more stable.

Question 36

What makes DNA susceptible to shearing?

Answer 36

It is generally a much longer molecule than RNA.