DNA 1

Question 1

Describe two features of DNA which make it a stable molecule.

Answer 1

Two strands with specific base pairing;
large number of hydrogen bonds (between strands);
helix/coiling reduces chance of molecular damage / protects H bonds;
strong sugar-phosphate backbone;

Question 2

Describe the molecular structure of DNA

Answer 2

Long polymer of nucleotides;
composition of a nucleotide (pentose sugar, phosphate and N containing base)
4 bases named (A, T, C and G) (Uracil (U) is a base in RNA that replaces T), A, G are purine bases (2 ring structure) T, C and U are pyrimidine bases (single ring structures)
sugar-phosphate ‘backbone’;
two (polynucleotide) strands;
specific base-pairing;
example e.g. A–T / C–G; there are 2 H bonds between A/t and three H bonds between C/G
hydrogen bonding between bases

Question 3

Explain how the structure of DNA is related to its function.(6)

Answer 3

sugar - phosphate backbone gives strength (phosphodiester bonds)
(coiling gives) compact shape;
sequence of bases allows information to be stored;
long molecule stores large amount of information;
information can be replicated / complementary base pairing;
(double helix protects) weak hydrogen bonds / double helix makes molecule stable prevents code being corrupted;
chains held together by weak hydrogen bonds;
chains can split for replication / transcription
Complementary base pairing enables information to be replicated / transcribed;
Many hydrogen bonds together give molecule stability;
Hydrogen bonding allows chains to split for replication / transcription OR molecule unzips easily for replication / transcription.

Question 4

Explain how DNA replicates.(5)

Answer 4

hydrogen bonds broken;
semi-conservative replication / both strands used (as templates);
nucleotides line up;
complementary / specific base pairing / A and T / C and G;
DNA polymerase;