LIFE 102 Lecture Notes - Dna Replication, Okazaki Fragments, Gene Expression
Document Summary
Enzymes called dna polymerases catalyze the elongation of new dna at a replication fork. Most dna polymerases require a primer and a dna template strand. The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells. Each nucleotide that is added to a growing dna strand is a nucleotide triphosphate datp supplies adenine to dna and is similar to the atp of energy metabolism. The difference is in their sugars: datp has deoxyribose while atp has ribose. As each monomer of datp joins the dna strand, it loses two phosphate groups as a molecule of pyrophosphate. The antiparallel structure of the double helix (two strands oriented in opposite directions) affects replication. Dna polymerases add nucleotides only to the free 3" end of a growing strand; therefore, a new dna strand can elongate only in the 5" to 3" direction.
