Genomes and DNA Replication

DNA polymerase are off to the races! - BI301

What is a Genome?

the entire compliment of an organism’s genes, but it’s limitation is that it won’t tell us what genes are being expressed at a given time; lets us look at genetic potential, organism’s relationships, virulence factors, antimicrobial targets

First genome sequence that was discovered? First genome from living organism?

RNA Virus MS2 (3569 bp); Haemophilus influenza (1.8 Mbp)

What does a genome sequence tell us?

Outlines the genetic potential for organisms, functions are assigned to genes (38.1% of e.coli has unknown functions)

ORFs (“Open reading frames”)

gene sequence predicted to code for a protein; note the positive/negative correlations (ex. more genes = more signalling necessary in the complex organism)

Characteristic of Bcaterial Chromosomes

Most are circular and covalently closed, cells are haploid (one copy of each gene), DNA is in nucleoid, one origin of replication, Most of DNA sequence codes for proteins

Flow of Biological Information

DNA→mRNA→Protein (aka. gene expression or Central Dogma)

Topoisomerases

Cause DNA packaging and condensation

Supercoiling/Chromosome Packaging in Nucleiod

A nick is made in a single strand of the nucleoid domain, supercoiling relaxes and DNA stretches; this is a back and fourth process

Replicating the Chromosome

Goal is to generate 2 identical copies of genetic information; partition in chromosome so that each daughter cell receives one

Issues when replicating the chromosome

• The speed of replication (doesn’t change) vs. speed of cell division (varying)

• Replication fidelity: no errors (?)

• Untangling chromosome to accommodate replication machinery

• Replicating DNA while genes are being translated/transcribed

Semi-conservative replication

DNA pol adds new nucleotides 5’→3’

DNA pol must have a 3’-OH as a substrate (open to add phosphodiester)

Primase - (RNA primer) provides 3’-OH to begin new strand synthesis

OriC

Origin of chromosome replication

DNA A protein

Initiator protein of replication, binds to the oriC

pol III

copies chDNA bi-directionally from the oriC until the sequence/terminator of replication