DNA

Question 1

Nucleotide

Answer 1

Nucleoside (penthose sugar + nitrogenous base on C1) + phosphate group on C5

Question 2

Nitrogenous bases

Answer 2

Purines (2 rings): A, G
Pyrimidines (1 ring): T, C, U

Question 3

Phosphodiester bond

Answer 3

Between C3 of one sugar and C5 of the next sugar. 5’ end-strand with phosphate end and 3’ end-strand with hydroxil group end.

Question 4

Chargaff’s rule

Answer 4

[A] = [T] and [G] = [C]
[A]+[G]=0.5 and [T]+[C]=0.5

Question 5

Double helix structure

Answer 5

Antiparallel right-handed double helix negatively charged, 2 bonds between A and T, 3 bonds between G and C.

Question 6

DNA replication

Answer 6

Semiconservative.
- DNA helicase opens the double strand
- SSB proteins stabilize the single strand
- DNA primase synthesizes RNA primers
- 3’->5’ leading strand since DNApol works 5’->3’
- 5’->3’ lagging strand and DNApol synthesizes DNA in Okazaki’s fragments
- DNApol I with 3’->5’ exonucleasic activity does proofreading and removes primers
- DNA ligase links adjacent DNA fragments

Question 7

DNA compaction levels

Answer 7

• Double helix
  + histones (2 H2A, 2 H2B, 2 H3, 2 H4 positively charges)
  + non-histone proteins
• Nucleosomes
  + linker histone H1
• Solenoids / 30-nm fiber
  + nuclear matrix/scaffold non-histone proteins
• Looped domains that make chromatin:
  – Euchromatin (less condensed, gene trascription)
  – Heterochromatin (highly condensed, facultative if it can interconvert or constitutive if permanently inactive for stability)
• Chromatid
• Chromosome