Introduction to Molecular Genetics Studiju materiāli / MolekularasBiologijas / Ievads MolGen / EN
Molecular Biology of the Gene, 5th Edition DNA replication
The replication of DNA is a complex, multi-step process, involving many enzymes
Nucleotide sequence of a DNA strand (the template strand) is copied through complementary base pairing into complementary sequence DNA synthesis is TEMPLATED
DNA polymerase (enzyme that does the work) needs a single-stranded template, primer and dNTPs Molecular Biology of the Gene, 5th Edition
DNA is always synthesized in the 5’-to-3’ direction Molecular Biology of the Gene, 5th Edition
DNA polymerase resembles a hand that grips primer-template junction
DNA polymerase ‘monitors’ ability of the incoming nucleotide to base-pair with the template nucleotide Molecular Biology of the Gene, 5th Edition
Yet, a wrong base is occasionally added (when it is in an unusual tautomeric form) Molecular Biology of the Gene, 5th Edition
EXONUCLEOLYTIC PROOFREADING by DNA polymerase corrects most of these errors primer template Please, be so kind and find an error in this figure!
EXONUCLEOLYTIC PROOFREADING by DNA polymerase corrects most of these errors
DNA replication is SEMICONSERVATIVE Each strand of parental DNA serves as a template for a new, complementary strand The 2 new double helixes each have 1 parental strand and 1 newly synthesized strand
Should it necessarily be so? Life The Science of Biology, 7th Edition
Meselson and Stahl (1958) proved that replication is semiconservative
Both strands are synthesized together at the REPLICATION FORK Lewin, Genes
There is a problem with the simplest model direction of replication direction of strand growth direction of strand growth
The replication fork is ASYMETRIC: one strand (leading) grows continuously, while the other (lagging) is synthesized as fragments
Two DNA polymerases operate at the replication fork Molecular Biology of the Gene, 5th Edition
DNA polymerase needs a primer: primer (RNA!) is provided by DNA primase
Lagging strand is synthesized stepwise (RNAse H)
DNA ligase uses ATP to seal the nicks between fragments (ligation reaction)
Sliding clamp helps DNA polymerase not to fall off the template Molecular Biology of the Gene, 5th Edition
DNA polymerase needs a single-stranded DNA template: DNA helicase ‘opens’ the parental double helix
DNA polymerase needs a single-stranded DNA template: SSB proteins stabilize the unwound strands
The ‘winding’ problem Lehninger. Principles of Biochemistry, 3rd Edition
Topoisomerases remove positive supercoils Molecular Biology of the Gene, 6th Edition
The major types of proteins at a bacterial replication fork
The proteins involved in replication are arranged in a complex
Replication is initiated at the origins (ori) of replication
Mechanism of initiation in bacteria
Bacterial chromosomes are replicated from single origin
Eukaryotic chromosomes are replicated from many origins Molecular Biology of the Gene, 5th Edition
Eukaryotic chromosomes have redundancy of ori; all origins are inactivated by DNA replication
New nucleosomes are assembled right behind the replication fork
Patterns of histone modification can be faithfully inherited
Inheritance of chromatin structures is a mechanism of the EPIGENETIC INHERITANCE
The End Replication Problem Molecular Biology of the Gene, 6th Edition
Solving the end replication problem: TELOMERES & TELOMERASE Molecular Biology of the Gene, 5th Edition
Bacterial chromosomes have no ends & hence no end replication problem Molecular Biology of the Gene, 5th Edition
Single-stranded genomes (viruses) replicate through synthesis of complementary strands
Why is the genetic information stored in form of double-stranded DNA in all cells?