1 DNA: localization, structure, double helix. chargaff, conformations

Question 1

DNA and RNA structure:

- nucleid acid bases

Answer 1

nucleid acid bases
DNA:
- adenine
- guanine
- cytosine
- thymine

RNA:
- uracil instead of thymine

Question 2

DNA and RNA structure:

- Nucleosides

Answer 2

base+sugar=nucleoside

A nucleoside consists of a base covalently bonded to the 1’-position of a pentose sugar:

• DNA sugar: deoxyribose
• RNA sugar: ribose

Question 3

DNA and RNA structure:

- Nucleotides

Answer 3

Base+sugar+phosphate=nucleotide

Nucleotides are nucleosides with one or more phosphate groups covalently bound to the 3’ or 5’ position

Question 4

DNA and RNA structure:

nucleic acids polymers

Answer 4

nucleic acids (DNA/RNA) polymers:
- several nucleotides are bound to a chain by 3’,5’ - phosphodiester bonds:
5’position of one sugar is linked to 3’ position of the next by a phosphate

Chromosomes: two DNA polymers bound via non-covalent hydrogen bonds

Question 5

DNA localization

Answer 5

DNA in cells
eukaryotes:
- in the nucleus
- mitochondria 
-  chloroplasts of plants

prokaryotes
DNA is not enclosed in a membranous envelope, although it’s located in a specialized cell region called the nucleoid.

Question 6

Double Helix modell

Answer 6

• two antiparallel, complementary chains of DNA are wound around each other in a coiled/helical path
• with sugar -phosphate backbones on outside and bases on the inside, which are bound by hydrogen bonding
• adenine pairs with thymine, guanine with cytosin
• between the backbone strands run the minor and major grooves

Question 7

DNA conformations

Answer 7

DNA exists in many possible conformations that include A-DNA, B-DNA, and Z-DNA forms. The conformation that DNA adopts depends on the hydration level, DNA sequence, the amount and direction of supercoiling, chemical modifications of the bases, the type and concentration of metal ions, and the presence of polyamines in solution.

Watson - Crick model/ "normal Double Helix" = B-DNA
A-DNA: 
- forms under low humidity
- has wider, more compressed structures
- formed by RNA and DNA-RNA hybrids

Z-DNA

• synthetic,
• nucleotids are in anti-conformation