DNA 2.7 Replication, transcription and translation 7.1 DNA structure and replication

2.7 Semi-conservative replication of DNA Meselson-Stahl evidence

7.1 DNA replication is carried out by a complex system of enzymes Helicase = unwinds helix DNA polymerase = Different varieties have different functions such as: adding nucleotides, “proof-reading”, polymerization, and removal of the RNAprimers. DNA primase = makes RNA primers needed to initiate the activity of DNA polymerase DNA ligase = connects the gaps between fragments

2.7 Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds

2.7 DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template

2.7 Taq DNA polymerase is used to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR)

7.1 DNA polymerase can only add nucleotides to the 3’ end of a primer DNA replication is continuous on the leading strand and discontinuous on the lagging strand

7.1 DNA replication is continuous on the leading strand and discontinuous on the lagging strand

Sense strand: Anti-sense strand: 2.7 Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase Sense strand: DNA strand with same base sequence as the RNA Anti-sense strand: DNA strand that acts as the template and has complementary base sequence to the RNA and the sense strand.

2.7 Translation is the synthesis of polypeptides on the ribosomes The amino acid sequence of the polypeptide is determined by mRNA according to the genetic code

2.7 Codons of three bases on mRNA correspond to one amino acid in a polypeptide Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA

2.7 Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species Human insulin produced by genetically modified E.coli, yeast cells, and safflower plants (since 1982) The gene is transcribed to mRNA and then translated to produce harvestable quantities of insulin. The insulin produced has the exact same amino acid sequence as if it was produced in human cells.