Case 2

Case 2

Learning goals:
1. Structure of DNA
2. DNA replication
3. RNA vs. DNA
4. Transcription
5. Modifications of mRNA in eukaryotes




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, 1. Structure of DNA
Two types DNA structures:
1. High density heterochromatin: DNA is more densely packed
2. Low density euchromatin: more open structure. So accessible
for transcription.
 in the middle of the nucleus
Structure DNA
- Double helix, double strand.
- Whole structure is built up of: carbon (C), hydrogen (H), oxygen (O),
nitrogen (N) and phosphate (P)
- Two strands are linked to each other with OH-bonds
- 2 OH-bonds between A and T
- 3 OH-bonds between G and C


 A sequence with a A-T base pairs, they are less strongly attached to
each other as compared to G-C.
 DNA-replication always starts at A-T base pairs, because it’s easier to
open that strand.


Two types of bases:
1. Pyrimidine: one ring  U, C, T
2. Purine: two rings  G, A
 Purine is always binding with a pyrimidine. A larger molecule
binds to a smaller one so in each case the distance is similar.


Bases are attached to sugars (sugar = pentose C5-molecule)
- Ribose for RNA: R=OH
- Deoxyribose for DNA: R=H




 These are all phosphodiester linked: sugar + base + phosphate
group




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