Microbial genetics, Biology tutorial


Microbial genetics is a subject part of microbiology and genetic engineering. It basically studies the genetics of extremely small (micro) organisms. This comprises the study of the genotype of microbial species and as well the expression system in the form of phenotypes. It as well comprises the study of the genetic processes occurring in these microorganisms that is, recombination and so on. The flow of genetic information in bacteria can be symbolized by:

There are two approaches by which genetic information can flow: 

1) Information is transferred among bacterial generations. This takes place if DNA duplicates and is distributed to two similar daughter cells via the procedure of binary fission. 

2) Information is transferred in the bacterial cell. The outcomes of this transfer are proteins required for metabolism and cell growth. Because DNA and protein encompass different chemical components, DNA should first be recorded into mRNA and then converted into a protein.  

Cell Division:

Bacteria reproduce by the process of binary fission. In this method, one cell splits to give two similar daughter cells. Mostly, the genetic information in bacteria is found on a single circular chromosome that comprises of proteins and DNA. This information should be distributed uniformly to each of the daughter cells. This is just possible as DNA is a self-replicating molecule and is capable to build an exact copy of it before cell division takes place. One copy will go to each and every daughter cell. The structure of DNA plays a significant role in the replication procedure. Two significant features to remember are: 

a) Complementation: DNA strands are complementary to one other. The base adenine will simply pair with the base thymine and base guanine will simply pair with the base cytosine. The two strands of DNA are held altogether through hydrogen bonds which exist among complementary bases.

b) Antiparallel: The two strands of DNA are as well antiparallel to one other. One strand runs in the 5' to 3' direction, while the other in 3' to 5' direction.


Replication starts on the bacterial chromosome at a particular series of nucleotides termed as the origin. Enzymes termed helicases identify this series and bind to this site. Helicases unwind those two strands by breaking the hydrogen bonds which hold the strand altogether. This region where DNA separates and the bases are exposed is termed as the replication fork. Single-stranded binding proteins join in chains all along the separated strands for stabilization and to prevent rewinding. Free nucleoside triphosphates in the cytoplasm are paired up with their complementary base on the exposed parental strand.

A nucleoside triphosphate is merely similar to a nucleotide except it consists of three phosphates rather than one. This makes it much reactive because of the cluster of negative charge. Once it is aligned correctly with its complementary base, the nucleoside triphosphate is combined to the growing strand by an enzyme termed as DNA polymerase. This enzyme catalyses the hydrolysis of phosphates as the nucleotide is added to the strand, making a phosphodiester bond.

DNA polymerase:

The DNA polymerases are enzymes which form DNA molecules by accumulating nucleotides, that is, the building blocks of DNA. Such enzymes are necessary to DNA replication and generally work in pairs to make two similar DNA strands from one original DNA molecule. Throughout this method, DNA polymerase 'reads' the existing DNA strands to form two new strands which match the existing ones.

Each and every time a cell divides; DNA polymerase is needed to assist duplicates the cell's DNA, in such a way that a copy of original DNA molecule can be passed to each of the daughter cells. In this manner, genetic information is conveyed from generation to generation.

Before replication can occur, an enzyme termed as helicase unwinds the DNA molecule from its strongly woven form. This opens up or unzips the double stranded DNA to provide two single strands of DNA which can be employed as templates for the replication.

DNA polymerase includes new free nucleotides to the 3' end of the newly-forming strand, lengthening it in a 5' to 3' direction. Though, DNA polymerase can't start the formation of this new chain on its own and can just add nucleotides to a pre-existing 3'-OH group. A primer is thus required, at which nucleotides can be added. Primers are generally composed of RNA and DNA bases and the first two bases are for all time RNA. Such primers are made by other enzyme termed as primase.


Transcription is a method by which the information in a strand of DNA is copied to a new molecule of messenger RNA (mRNA). DNA stably and safely stores genetic material in the nuclei of the cells as a reference, or template. In the meantime, mRNA is analogous to a copy from a reference book as it carries the similar information as DNA however is not employed for long-term storage and can freely depart the nucleus. However the mRNA includes the similar information, it is not a similar copy of the DNA segment, as its series is complementary to the DNA template.

It consists of three main events:

a) Initiation: Binding of RNA polymerase to double-stranded DNA; this step comprises a transition to single-strandedness in the area of binding; RNA polymerase binds at a series of DNA termed as the promoter. Initiation is the most important step in the gene expression.

b) Elongation: The covalent addition of nucleotides to 3' ends of the growing polynucleotide chain; this comprises the growth of a short stretch of DNA which is transiently single-stranded

c) Termination: It is the recognition of transcription termination series and the release of RNA polymerase.


Protein synthesis is termed as the translation as it translates the language of nucleic acids into the language of proteins. The language of mRNA is in codons, that is, groups of three nucleotides such as AUG. Each codon 'codes' for a specific amino acid. There are basically 64 possible codons, however just 20 amino acids.

Thus, an amino acid consists of more than one codon is termed to as degeneracy of the code.

Sense codons code for the amino acids; nonsense (or stop) codons signal the end of synthesis of a protein. The sites of translation are ribosome that moves all along mRNA. The amino acids are transported to the ribosome by transfer RNA (tRNA). Each and every tRNA molecule is made up of specific for an amino acid by an anticodon which is complementary to a codon. That is, the codon AUG would be complementary to the anticodon UAC.

Gene regulation:

Gene regulation can be stated as the informal term which is employed to explain any method employed by a cell to rise or reduce the production of particular gene products (that is, protein or RNA). Cells can transform their gene expression patterns to trigger developmental pathways, respond to ecological stimuli, or adapt to new food sources. The entire points of gene expression can be regulated. This comprises transcription, RNA processing and transport, translation and post-translational modification of a protein and degradation of mRNA.


A mutation is stated as a change in the structure or quantity of genetic material in an organism.  Mutations are extremely rare events and most are dangerous.  Though variations which let a population to adapt to a changing environment are the outcome of mutations. 

Devoid of mutations all the individuals would be homozygous and no variations would exist.  Harmful mutations tend to be removed from a population by chose against them. 

Most of the mutations are recessive and are thus not expressed until two take place altogether in the homozygous recessive individual.  If such a change takes place and the individual expresses the mutation in the phenotype that individual is identified as a mutant.

Types of mutations:

There are lots of different ways that DNA can be modified, resultant in various types of mutation.

  • Substitution
  • Insertion
  • Deletion
  • Frame-shift

Gene transfer:

Gene transfer is simply stated as a method to proficiently and stably introduce foreign genes into the genome of the target cells. Genes are the fundamental hereditary units of all life. It is our genes which give the blueprints essential to generate all proteins in our bodies, and our proteins that eventually carry out each and every biological function. Therefore, when a gene is stably introduced into a target cell the protein encoded through the gene is generated.

In bacteria genetic transfer can occur by three ways:

  • Transformation
  • Transduction
  • Conjugation

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