How a bacterial cell divides
Prokaryotic reproduction occurs via transverse binary fission. The trigger for this process is a change in intracellular proportions—specifically, reaching a certain ratio of the nucleoid volume (the region containing genetic material) to the cytoplasm volume. The process proceeds at a high rate, ensuring rapid colony growth.
Cell division itself is carried out in four strict stages:
- DNA replication — always precedes cell division so that each daughter cell receives a copy of the genome.
- Plasma membrane synthesis — preparation of membranes for future cells.
- Nucleoid division — segregation of the copied genetic material.
- Cytokinesis — formation of a transverse septum that ultimately divides the mother cell into two independent daughter cells.
Features of the prokaryotic sexual process
Bacteria lack the typical sexual process found in higher organisms: they do not form specialized sex cells (gametes) and do not fuse with each other. The entire process comes down exclusively to the transfer of genetic information.
For an individual bacterium, this event is quite rare. However, due to the enormous number of bacteria in a colony, gene exchange is observed relatively frequently on a population scale. The primary significance of genetic recombination is that it ensures genetic diversity and allows microorganisms to adapt rapidly to changing environmental conditions.
Three mechanisms of genetic recombination
Recombination is based on the transfer of a DNA fragment from a donor cell to a recipient cell. Bacteria use three fundamentally different pathways for this:
- Conjugation. Requires direct physical contact between cells. The transfer of genetic material proceeds in one direction: from the donor cell (designated as $F^+$) to the recipient cell ($F^-$). The mechanism is implemented through the formation of a special cytoplasmic bridge. A key condition for initiating conjugation is the presence of the F-factor (fertility factor) plasmid in the donor.
- Transformation. Occurs without any contact between cells. The recipient cell directly takes up isolated DNA extract (e.g., plasmids) from the environment.
- Transduction. The transfer of a DNA or RNA fragment from a donor to a recipient is carried out with the participation of intermediaries — bacteriophages (specific viruses that infect bacterial cells).
Briefly: answers to topical questions
Through which structural elements do bacteria form a cytoplasmic bridge during conjugation?
During conjugation, bacteria form a cytoplasmic bridge using sex pili.
- Sex pili (F-pili, sex pili) — specialized filamentous structures designed for the transfer of genetic material.
The formation of these structures is determined by the presence of a transmissible F-plasmid in the cell. Unlike common pili, sex pili are few in number (usually 1 to 3 per cell) and are present exclusively in "male" donor cells. Through the conjugation bridge they form, a targeted transfer of a DNA strand into the recipient cell takes place.
Due to what cell property or state does the uptake of DNA from the environment become possible during transformation?
The uptake of DNA from the surrounding environment becomes possible due to the cell entering a state of competence.
- State of competence is a specific state of a bacterial cell necessary for the uptake of naked DNA.
- Competence factor is a special low-molecular-weight protein that induces this state.
This factor promotes the synthesis of endonuclease, autolysin, and a DNA-binding protein, onto which the transforming DNA adsorbs before penetrating the cell. The maximum number of competent cells is usually observed at the end of the logarithmic growth phase.
It is easy to remember the three pathways of DNA transfer using associations: Transformation — the cell "absorbs" DNA from the environment; Transduction — a duet with a virus (phage) is at work; Conjugation — direct contact (cells build a cytoplasmic bridge).
Class and exam questions
What serves as the signal for the initiation of bacterial cell division?
The signal is a change in the ratio of the nucleoid volume to the cytoplasm volume.
Do bacteria fuse during the sexual process?
No, cell fusion and gamete formation do not occur. Only unidirectional transfer of genetic material from the donor to the recipient takes place.
How does transformation differ from conjugation?
During transformation, the cell takes up naked DNA from the environment without contact with other cells. Conjugation, however, requires direct physical contact and the formation of a cytoplasmic bridge.
What is the role of the F-factor?
The F-factor (fertility factor) is located in the plasmid of the donor cell ($F^+$) and is a prerequisite for conjugation.
What else to study on this topic
- Mechanisms of transverse septum formation during cytoplasmic division
- Structure and functions of the nucleoid during DNA replication
- Prokaryotic life cycle and generation turnover rate
- Interaction of bacteriophages with the bacterial cell during transduction
Master the entire topic in the "Biology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Bacterial Reproduction and Genetic Recombination" and 3,793 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 129 video lessons on the subject
Other topics in the section "The Cell — The Elementary Unit of Life"
Free video lessons: BiologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.