Nucleic acids

Question 1

What percentage of DNA is coding?

Answer 1

• ~99% of DNA is non-coding sequences
• ~1% of DNA is coding sequences

Question 2

What are the three components of nucleic acids?

Answer 2

1. Nitrogenous bases
2. Pentose sugar (ribose in RNA and deoxyribose in DNA- lacking an O on the 2’ C)
3. Phosphate group

Question 3

What are the bonds found in DNA?

Answer 3

• Glycodisic bond between 1’ C on the pentose sugar and the nitrogenous base
• Ester bond between the phosphate group to the 5’ C on the pentose sugar
• Hydrogen bonds between the nitrogenous bases between two DNA strands
• The next nucleotide monomer is attached to the 3’ C

Question 4

How can you divide the bases?

Answer 4

Purines - A and G
Pyrimidines - U/T and C

Question 5

How does the name of a nucleoside change?

Answer 5

Bases ——–> nucleoside
Adenine —–> adenosine
Guanine —–> guanosine
Cytosine —–> cytidine
Uracil ———-> Uridine
Thymine ——-> Thymidine
Note that the end of the nucleoside name varies based on the type of base (purine or pyrimidine)

The abbreviation (e.g., A) is used for both referring to bases and nucleosides.

Question 6

What is Chargaff’s Rule of Base Pairing?

Answer 6

Total amount of purines = total amount of pyrimidines

(A + G) = (C + T/U)

Question 7

What can you call the DNA double helix (think of the direction of the strands) and why?

Answer 7

• Antiparallel
• This is because the 5’ end of one strand is paired with the 3’ end of the complementary strands

Question 8

How is DNA compacted in eukaryotes?

Answer 8

• In chromatin (tightly wound to form this complex)

Question 9

Which is the stronger base pairing hydrogen bond?

Answer 9

A -> T = double hydrogen bond
C -> G = three hydrogen bonds

So the bond between C and G is greater (requires more energy)

Question 10

What are oligonucleotides?

Answer 10

Very short fragments of nucleotides