[Biology Class Notes] on R-Factor Pdf for Exam

R-factor, or resistance factor, are plasmids that allow specific bacteria to gain resistance against antibiotics. They are mostly available in a set of genetic codes which can transfer themselves from one cell to another of a bacterium via means of conjugation or non-conjugation. Through bacterial conjugation, many r-factors can pass from bacterium to another.

R factor is accountable for coding of antimicrobial resistance against specific drugs. Moreover, they often code restriction for more than a single antibiotic, up to eight different resistances at times. The standard means of spreading antimicrobial resistance among various bacterial species, chromosomes, etc. occur via conjugation. 

Define Plasmid

Plasmids are small, extra-chromosomal structure found in bacteria that can replicate itself. These circular molecules of DNA have a double-stranded format, and they are also found in multi-cellular organisms and archaea.

R plasmid is a DNA molecule that grants bacterial resistivity to one antibiotic or more. It comprises of two components primarily – a resistance transfer factor (RTF) and resistance determinants. RTF is a necessary factor responsible for the transmission of plasmids among bacteria, and r-determinants are genetic codes promoting antibiotic resistivity.

What are the Types of Plasmids?

1. Resistance or R Plasmid: These allow antimicrobial resistance against drugs. They have self-replication capabilities and can be resistant to multiple drugs. It comprises of two types – narrow and broad host range group. The narrow group enables replication within a species, whereas broad one allows transmission among different bacteria.

2. F-Plasmids: The fertility factor enables genetic coding transmission from one bacterium to another through conjugation. It is a form of a large plasmid and available mostly in Escherichia coli. The ones that contain F factor are termed as F+, and those lacking it are known as F–.

3. Virulence: They help bacteria to adapt efficiently with their surroundings. Similar to other plasmids, they can also travel from one bacterium to another.

4. Col Plasmids: They grant the bacteria a capacity to produce venomous proteins called colicines. Specific bacteria use these toxins to destroy other bacteria, thereby thriving in hostile environments.

5. Degradative: In contrast to other plasmids, they allow the host bacterium to decay xenobiotic components.

Structure of Resistance Plasmid

The resistance plasmid can be said to resemble a circular structure of DNA fragments, and its length varies in the spectrum of 80-95 kb and constitutes of the larger segment of a factor known as the R-RTF or Resistance Transfer Factor molecules. This plasmid is known to be majorly homologous to the F factor and contains quite like genes. It also constitutes a gene known as the fin 0 gene that restrains the task of transferring of the operon. These R factors come in varying sizes and also the kinds of resistance they offer to drugs. The R determinant is smaller in size as compared to the RTF. The RTF as well as the R determinants bind to develop a single unit and are split up from one another by the presence of IS 1 elements on both the sides. The presence of these IS 1 elements encourages the interchange of R determinant amongst the variants of R-RTF units present. 

Functions of Resistance Plasmid

Following are the functions of the resistance plasmid – 

• Resistance is also built to offer against the antibiotics and encourage bacteria to manufacture Pilli, by the resistance plasmids which contain a specific gene which promotes the above-mentioned function 

Horizontal Gene Transfer

Bacteria which consists of the F factors, can build a sex pilus which encourages the transmission of the horizontal gene between the bacteria, which is the donor and the bacteria, which is the recipient. The resistance to an antibiotic can quickly and without much hassle and expand amongst the rest of the bacterial community as well. This is because the F factor is present in several R factors too. Due to the presence of the gene known as the RTF or the Resistance Transfer Factor, several R factors can also be consumed by the DNA through the process of transduction or transformation. 

Fun Fact

There are more than 100 types of antibiotic drugs! Some most commonly used antibiotics are amoxicillin, azithromycin, penicillin, streptomycin, etc.

Wrack Your Brains

Here are specific questions on r factor and its functioning. Use your knowledge to crack them.

1. What does fertility plasmids grant to a host bacterium?

1. Antimicrobial resistance

2. Ability to conjugate

3. Multi-drug resistance ability

4. None of the above

2. For being able to exist simultaneously in a single cell, non-identical plasmids require 

1. Compatibility

2. Conjugation

3. Stability

4. High in numbers

5. None of them

From the above conversation, we hope now you will have an in-depth knowledge regarding r factor. If you wish to learn further about such fantastic biology topics, go through the course materials available in our website, or download ’s mobile application from Play Store now!