The bacterial cells which will take up the foreign DNA from the environment by a process called transformation are referred to as competent cells. Griffith first reported it in Streptococcus pneumoniae. In the case of wall alteration, E.coli cells are more likely to uptake the DNA. The cells are often made competent by salt and warmth shock therapy. The cells growing rapidly are often made competent more easily than those in other stages of growth. The cells may retain the acquired genetic information after the transformation procedure. The process is essentially used to introduce recombinant plasmid DNA into competent bacterial cells. This process does not require a donor cell but only DNA in the surrounding environment.

Principle of Competent Cells

Competent cells have altered cell walls that allow the DNA to simply undergo it. Some cells got to be exposed to some chemical or electrical treatments to transform them into competent cells. Treatment with calcium ions is the standard method for the preparation of those cells. Electroporation is the process in which cells take up DNA.

Methods of Preparation of Competent Cells

Competence is achieved in two ways:

Natural Competence
Artificial Competence

Natural Competence

Bacteria take up DNA from the environment by transformation, conjugation, and transduction. By the process of transformation, the foreign DNA directly enters into the bacterial cell. For this, the cells need to be in a competent state.

Frederich Griffith was the primary one to get natural competence. He injected the smooth strain of pneumococcus in mice, and the mice died. This strain is therefore referred to as virulent strain. But the mice didn't die when injected with the rough strain (non-virulent strain). Heat-killing abolishes the virulent nature of the graceful strain. The heat-killed smooth strain and therefore the rough strain were mixed. The rough strain acquired the graceful phenotype and has become virulent. This suggests that a heat stable, non-living material obtained from the graceful strain facilitated transformation.

Artificial Competence

In this, the cells are permeable to DNA in the laboratory. The competent cells are often prepared artificially in two ways, namely:

Calcium Chloride: This method was proposed by Mandel and Higa. The bacterial cells were treated with salt then suddenly exposed to high temperatures. This is known as the heat shock treatment method.

Electroporation: During this technique, an electrical field is applied to the cells to extend their permeability. It is also known as electropermeabilization.

What are the Characteristics of Cells?

Every cell consists of a single nucleus and membrane-bound organelles in the cytoplasm.

Some of the important characteristics of Cells are :

Cells help in providing structure and support to the body of an organism.
The cell interior comprises different individual organelles surrounded by a separate membrane.
The nucleus holds genetic information necessary for reproduction and cell growth.
Mitochondria is a double membrane-bound organelle that is mainly responsible for the energy transactions that are vital for the survival of the cell.
Lysosomes digest unwanted materials present in the cell.
Endoplasmic reticulum plays an important role within the internal organization of the cell by synthesizing selective molecules and processing, directing and putting them to their appropriate locations.

Types of Cells

Cells are similar to factories in which different departments work together to achieve a common goal. Different types of cells perform various functions. There are two types of cells based on cell structure.

Prokaryotic Cells

These cells have no cells. Some cells such as bacteria have free-floating or suspended genetic material in the cell space known as nucleoids.
Prokaryotic cells are found in single-celled organisms like bacteria, archaea, cyanobacteria, etc.
The size of the cell ranges from 0.1 micrometres to 0.5 micrometres in diameter.
Their hereditary or genetic material can either be RNA or DNA.
Single-celled organisms reproduce through asexual reproduction such as binary fission. They use conjugation, a form of reproduction that appears to be sexual but it’s not.

Eukaryotic Cells

Eukaryotic cells have a true nucleus.
Their cell size ranges from 10 to 100 micrometres in diameter.
Eukaryotic cells are found in organisms like fungi, plants, animals and protozoans.
The plasma membrane manages the transportation of nutrients in and out of the cell. It is also accountable for establishing cell to cell communication.
They reproduce through both methods of reproduction, asexual and sexual.
In eukaryotic cells, we can see some contrasting characteristics between animal and plant cells. For example, plant cells have cell walls, chloroplasts, plastids and central vacuoles but animal cells don’t have these organelles.

Cell Organelles

Cells consist of cell organelles that perform specific functions to carry out important life processes. Here are different cell organelles with their functions.

Nucleolus- It is the site of ribosome production. It controls cellular activities and reproduction.
Nuclear Membrane- It protects the nucleus from getting mixed with other cell organelles.
Chromosomes- It is a major factor that determines the sex of an individual. There are 23 pairs of chromosomes in each human cell.
Endoplasmic Reticulum- It is responsible for transporting substances throughout the cells. It helps in the metabolism of carbohydrates and the synthesis of steroids, proteins and lipids.
Golgi Bodies- These organelles are called the post office of the cells as they are involved in the transportation of materials within the cells.
Ribosomes- They help in protein synthesis.
Mitochondria- These are known as the powerhouse of the cell as they help to generate energy.
Lysosomes- They destroy the foreign particles immigrating to the cells by engulfing them. Therefore, they are known as suicidal bags of the cell.
Chloroplasts- These are involved in photosynthesis.
Vacuoles- They store water, nutrients and other waste materials in the cell.

What are the Different Functions of a Cell?

A cell performs these major functions which are essential for the growth and development of an organism. Some of the vital functions of a cell are :

To Provide Support and Structure to the Cell - All organisms consist of cells. They form the building blocks of all organisms. The cell wall and the cell membrane are the two main organelles whose function is to provide strength and support to the organism. For example, skin is built of a large number of cells, xylem is a vascular tissue in plants that is made up of cells that provides strength and support to the plant.
To Facilitate the Growth Mitosis - Mitosis is a process of cell growth in which the parent cell divides to form two daughter cells. Through this method, cells multiply and facilitate the growth and development of an organism.
To allow the Transport of Nutrients - Cells accept various nutrients inside them for carrying out different metabolic functions. During these processes, the waste is discarded by the cells through passive and active transport. Small molecules like carbon dioxide, oxygen and ethanol diffuse through the cell membrane along the concentration gradient. This process is known as passive transport. However, the larger molecules are transported through active transport in which the cell requires a lot of energy to carry out the process.
To Aid in Reproduction - A cell undergoes the process of reproduction through mitosis and meiosis. Mitosis is also known as asexual reproduction in which the parent cell divides to form daughter cells. However, in meiosis, the two daughter cells are genetically different from their parent's cells. Therefore, we can comprehend why cells are called functional and structural units of life. This is because they provide strength, support and stability to the organisms and perform different functions important for undergoing life processes.
To help in Energy Production - Cells need energy to perform important activities. This energy is generated by cells through a process called respiration in animals and photosynthesis in plants.

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FAQs on Competent Cells: Key Concepts, Methods, and Applications

1. What are competent cells in the context of biotechnology?

In biotechnology, competent cells are bacterial or yeast cells that have been specially treated to increase their ability to take up foreign DNA from the surrounding environment. This process, known as transformation, is fundamental in genetic engineering. Normally, the cell membrane is impermeable to large molecules like DNA, but making a cell 'competent' creates temporary pores or openings that allow plasmids or other DNA fragments to enter.

2. What is the difference between natural and artificial competence in bacteria?

The primary difference lies in how the ability to take up DNA is acquired.

Natural competence is a genetically programmed ability of some bacteria (like Streptococcus pneumoniae and Bacillus subtilis) to take up DNA from their environment under specific natural conditions, often as a response to stress.
Artificial competence is induced in a laboratory setting in bacteria that are not naturally competent, such as E. coli. Scientists use chemical treatments (e.g., calcium chloride) or electrical pulses (electroporation) to make the cell membranes temporarily permeable to DNA.

3. How are chemically competent cells prepared in a laboratory?

The most common method for preparing chemically competent cells, particularly E. coli, involves treating them with a cold solution of a divalent cation, typically calcium chloride (CaCl₂). The process involves several key steps:

Bacterial cells are grown to a specific density in the mid-log phase.
The cells are then harvested and washed with ice-cold calcium chloride.
The Ca²⁺ ions are thought to neutralize the negative charges on both the bacterial cell membrane and the DNA's phosphate backbone, reducing the electrostatic repulsion between them.
This allows the foreign DNA to adhere to the cell surface, preparing it for the next step, which is usually a heat shock.

4. Why is a 'heat shock' step required after treating cells with calcium chloride?

The 'heat shock' step is a critical part of the chemical transformation protocol. After the cells have been incubated with DNA on ice, they are briefly exposed to a higher temperature (typically 42°C for 30-60 seconds). This sudden temperature increase is believed to create a thermal imbalance across the cell membrane, which generates temporary pores. This allows the adhered plasmid DNA to be drawn into the cell's cytoplasm. Following the heat shock, the cells are immediately placed back on ice to close the pores and stabilise the membrane.

5. What is electroporation and how does it make cells competent?

Electroporation is a physical method used to introduce DNA into cells. In this technique, a mixture of cells and foreign DNA is exposed to a very brief, high-voltage electrical pulse. This pulse creates transient microscopic pores, called electropores, in the cell membrane. These pores are large enough for DNA molecules to pass through from the outside environment into the cell. It is a highly efficient method but can be harsher on the cells compared to chemical methods.

6. What is the primary function of competent cells in recombinant DNA technology?

The primary function of competent cells is to serve as a biological host for the amplification and replication of recombinant DNA. Once a plasmid containing a gene of interest is successfully introduced into a competent cell (transformation), the cell's own replication machinery is used to make millions of copies of that plasmid. This process, known as gene cloning, is essential for producing large quantities of a specific gene for study or for expressing the gene to produce a desired protein, such as insulin or growth hormones.

7. What happens if you try to introduce a plasmid into bacterial cells that are not competent?

If you attempt to introduce a plasmid into non-competent bacterial cells, the transformation will likely fail or have extremely low efficiency. The bacterial cell wall and membrane form a natural barrier that is impermeable to large, negatively charged molecules like DNA plasmids. Without the chemical or electrical treatments that induce competency, there are no pores or mechanisms to facilitate the DNA's entry, and the plasmid will remain outside the cell, unable to be replicated or expressed.

8. How do competency methods overcome the natural repulsion between DNA and the cell membrane?

Both DNA and the bacterial cell membrane are negatively charged, leading to a natural electrostatic repulsion that prevents DNA from getting close to the cell. Competency methods are designed to overcome this barrier. In the chemical method, the positive charge of divalent cations like Ca²⁺ acts as a shield, neutralizing the negative charges on both the DNA's phosphate backbone and the membrane's phospholipids. This allows the DNA to get much closer to the cell surface, where it can then be taken up during heat shock. Electroporation bypasses this issue entirely by using physical force (an electric field) to create temporary openings for the DNA to pass through.

9. What are some important real-world applications of using competent cells?

Competent cells are a cornerstone of modern molecular biology and have numerous applications, including:

Pharmaceutical Production: Manufacturing therapeutic proteins like insulin, human growth hormone, and vaccines by inserting the relevant human gene into competent bacteria.
Gene Cloning: Creating vast quantities of a specific gene or DNA fragment for research, sequencing (like in the Human Genome Project), or further manipulation.
Building DNA Libraries: Constructing genomic or cDNA libraries to store and catalogue the entire genetic makeup of an organism for future study.
Agriculture: Developing genetically modified crops with enhanced traits like pest resistance or drought tolerance by first cloning the desired genes in competent cells.