Biology 1001A Lecture Notes - Lecture 6: Okazaki Fragments, Helicase, Phosphodiester Bond
Document Summary
Lecture 6 - is: purine and pyrimidine base-pairing in dna/rna. Dna has four nucleotides each with a five-carbon sugar deoxyribose, a phosphate group (phosphodiester bond) and four nitrogenous bases. Nucleo- tides join to form a polynucleotide chain with a sugar-phosphate backbone. Purines: adenine and guanine (built from a pair of fused rings of car- bon and nitrogen); three hydrogen bonds. Pyrimidines: thymine and cytosine (built from a single carbon ring); two hydrogen bonds. Purine always pairs with pyrimidine: adenine with thymine, guanine with cytosine. Dna is in a double helix model and has complementary base pairing. The polynucleotide chain twists around each other in a right handed way. The two strands of a double helix fit together stably only if they are antipar- allel (run in opposite directions) Nucleotides in groups of 3 (codon) make enough to make a protein. Outcome of the classic meselson and stahl experiment. They demonstrated that dna replication is indeed semiconservative.