What are prokaryotes?
A prokaryote is a unicellular organism that lacks membrane-bound nucleus, mitochondria, or any other membrane-bound organelle.
Bacterial DNA Structure
- Bacterial DNA is usually a single circular, double-stranded DNA molecule Genome is compact with minimal noncoding (mostly regulatory) DNA
- The nucleoid is the region containing the chromosome, distinct from cytoplasm
- Chromosome is looped and compacted by Nucleoid-Associated Proteins (NAPs)
- SMC complexes help with chromosome structure and segregation during division
- Haploid – circular naked DNA.
- No introns, but small non-coding region as regulatory sequences.
- Some have small additional circular DNA that can replicate independently (plasmid).
- Genome is organized in a structure called Nucleoid.
- Operons: polycistronic transcription units
Extranuclear DNA (cytoplasmic DNA)
- Extranuclear DNA (cytoplasmic DNA) is any DNA that is found outside the nucleus of a cell.
- In eukaryotes it is primarily found in organelles, such as mitochondria and chloroplast.
- In prokaryotes, nonviral extranuclear DNA is primarily found in plasmids.
E. coli genome features:
- One origin of replication (Ori)
- A terminus (where replication ends)
- Genes distributed efficiently across the chromosome
- Plasmids (extra-chromosomal circular DNA):
- Present in one to thousands of copies
- Often carry survival genes (e.g., antibiotic resistance)
- Transfer via conjugation through a pilus
- Episomes are plasmids that can integrate into the host chromosome
- Environment-specific genes on plasmids and other types of mobile genetic elements
- Usually asexual reproduction (binary fission), great variety of recombination mechanisms
- Transcription and translation take place in the same compartment and simultaneously.