DNA

Question 1

Structure of DNA

Answer 1

-Deoxyribonucleic Acid
-Helical Double stranded
molecule
-Sequence of nucleotide subunits that twist together into a spiral
-Anti-parallel - run in opposite directions to each other
-4 Nitrogenous bases - adenine, guanine, cytosine, thymine
- Linked together by weak hydrogen bonds (3 G-C, 2 A-T)

Question 2

Nucleotides Structure

Answer 2

Made up of:
-5-carbon pentose sugars - deoxyribose sugar
-Phosphate groups - attached to 2 sugar molecules and by phosphodiester bonds
-A nitrogenous base (adenine, guanine, cytosine, thymine)

Question 3

Chargaff Complementary Pairing rule

Answer 3

-Chargaff - worked out the ratios for the 4 bases (A,T,G,C)
-Found G-C and T-A have equal amounts of each - making them complementary
base pairs
-Guanine always hydrogen bonds with cytosine (shares 3 hydrogen bonds)
Adenine always hydrogen bonds with Thymine (shares 2 hydrogen bonds)

Question 4

Eukaryotes - DNA organisation

Answer 4

• Nucleus - enclosed in the cellular membrane
  -Packed together with histone proteins allowing DNA to fit
  -Beaded string wrapped around a histone protein **? to form a Chromatin fibre which form looped domains which coil and fold to create a metaphase Chromosome

-Circular DNA in mitochondria and chloroplasts

Question 5

Prokaryotes - DNA organisation

Answer 5

• Attached to the plasma
  membrane
• Is a circular single double stranded DNA
• 1 Chromosome
  -Plasmids - small circular double stranded molecule

Question 6

Histone Proteins

Answer 6

• Assist in packaging of DNA to fit in the nucleus
• to form a chromatin
  -DNA molecule:
  1) wraps arounds cone - to form nucleosome beads
  2) coils and folds - chromatin fibre
  3) loop - looped domains
  4) coil and fold - chromatin chromosome/ metaphase chromosome