Molecular Basis for Relationship between Genotype and Phenotype

Molecular Basis for Relationship between Genotype and Phenotype genotype DNA transcription DNA sequence replication RNA translation protein function phenotype organism amino acid sequence

Overview of DNA Synthesis DNA polymerases synthesize new strands in 5’ to 3’ direction. Primase makes RNA primer. Lagging strand DNA consists of Okazaki fragments. In E. coli, pol I fills in gaps in the lagging strand removes RNA primer. Fragments are joined by DNA ligase.

DNA Replication at Growing Fork DNA polymerases add nucleotides in 5’ to 3’ direction. Because of antiparallel nature, synthesis of DNA is continuous for one strand discontinuous for the other strand.

DNA Replication: Synthesis of Lagging Strand Several components and steps are involved in the discontinuous synthesis of the lagging strand. Note that DNA polymerases move in 3’ to 5’ direction on the template DNA sequence.

DNA Replication: Synthesis of Lagging Strand DNA extended from primers are called Okazaki fragments. In E. coli, pol I removes RNA primers and fills in the gaps left in lagging strands. DNA ligase joins these pieces.

Replisome and Accessory Proteins pol III holoenzyme is a complex of many different proteins. Refer to Figure 7 -20 from Introduction to Genetic Analysis, Griffiths et al. , 2012. Looping of template DNA for the lagging strand allows the two new strands to be synthesized by one dimer.

Priming DNA Synthesis Primase enzyme makes short RNA primer sequence complementary to template DNA polymerases can extend (but cannot start) a chain. Primosome is a set of proteins that are involved in the synthesis of RNA primers. Refer to Figure 7 -20 from Introduction to Genetic Analysis, Griffiths et al. , 2012. DNA polymerase extends RNA primer with DNA.

Supercoiling results from separation of template strands during DNA replication.

Helicases and Topoisomerases Helicase enzymes disrupt hydrogen bonding between complementary bases. Single-stranded binding protein stabilizes unwound DNA. Unwound condition increases twisting and coiling, which can be relaxed by topoisomerases (such as DNA gyrase). Topoisomerases can either create or relax supercoiling. They can also induce or remove knots.

Chromatin assembly factor I (CAF-I) and histones are delivered to the replication fork. CAF-I and histones bind to proliferating cell nuclear antigen (PCNA), the eukaryotic version of clamp protein. Nucleosome assembly follows thereafter. Refer to Figure 7 -23 from Introduction to Genetic Analysis, Griffiths et al. , 2012.

Overview of DNA Synthesis DNA polymerases synthesize new strands in 5’ to 3’ direction. Primase makes RNA primer. Lagging strand DNA consists of Okazaki fragments. In E. coli, pol I fills in gaps in the lagging strand removes RNA primer. Fragments are joined by DNA ligase.

Initiation at Origin of Replication Prokaryotes: Fixed origin Dna. A proteins Dna. B (helicase) Eukaryotes: Multiple origins ORC protein complex Cdc 6 and Cdt 1 MCM complex (helicase)