Eg pseudoknots 11 12 19032019 7 figure 320 the

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e.g. Pseudoknots1112
19/03/20197Figure 3.20The Central Dogma (Simple Version)The information flow in cells begins with DNA, which may either be replicated, giving a duplicate moleculeof DNA, or be transcribed to give RNA. The RNA is read (translated) as a protein is built.Central Dogma13
Cell and Molecular BiologyRBM2133Dr Christos StathisSlides prepared by DrCraig GoodmanSemester 1, 20201DNA Replication
DNA Replication and Cell Division
DNA Replication•When two DNA strandsseparate, each is able to formanother helix identical to theoriginal•Various proteins mustseparate double helix and thenadd correct bases to the newstrand over and over again.
Prokaryotic DNA replicationE. ColiDNA (bacterial) is a single, circular chromosome.Replication process begins at a certain sequence of nucleotides,theorigin of replication.Double helix is unwound at thereplication fork, and replicationproceeds in both directions away from origin of replication.origin of replicationreplication forks
Replication Occurs in Three Steps1.Double helix unravels2.Complementary binding of freebases to bases on the originalparent strands (via hydrogenbonding)3.Polymerization of nucleotidesby formation phosphodiesterbonds between sugar moietiesto form new strand backbone.template/parental strand
Replication Fork and ReplisomeThereplication forkis the site ofDNA replicationIncludes:DNA and associated proteins.Replisome– large protein complexthat creates the replication fork.Contains several enzymes:HelicasePrimaseDNA polymerase
7HelicaseDouble stranded DNA is melted by HelicaseUp to 1000 base pairs per secondPowered by the hydrolysis of ATP
Single-Strand DNA BindingProteins(SSBs)a.k.a. – Helix Destabilising Proteins
9Topoisomerase (Gyrase)“Unwinding/Winding problem”
10Topoisomerase (Gyrase)Topoisomerase I - breaks phosphodiesterase bonds inone strand (a ‘nick’)- prokaryotes & eukaryotesTopoisomerase II - breaks phosphodiesterase bonds inboth strands - prokaryotesBoth enzymes rejoin,or ligate, the twoends back together
Initiation of Replication
Initiation of ReplicationBacterial chromosomestypically have asingle origin of DNA replication specified byparticular DNA sequences.Sequences that attract initiator proteinsand relatively easy to open.i.e. A-T rich regionsWhy?Takes about 30 min to duplicate a bacterialgenome
Initiation of ReplicationEukaryotes have multiple origins of replicationThe average human chromosome contains a single linear DNAmolecular of ~150 million base pairs.At 0.02 sec/nucleotide x 150 million nucleotides, it would take~35 days to duplicate with a single origin of replication.

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DNA, Cell Molecular Biology

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