Skip to content

03 Genetic Regulation and the Process of Cloning

Genetic Regulation and the Process of Cloning

Introduction:

Gene Regulation : A mechanism that turns on certain genes while other genes remain turned off.

Cells with same genetic information can develop into different types of cells through gene regulation. Regulating gene activity within cells allows for specialization.

Genes determine the nucleotide sequence of specific mRNA molecules, and the mRNA in turn determines the specific sequence of amino acid in proteins. A gene that is being turned on is being transcribed into mRNA and that message is being translated into specific proteins. The overall process by which genetic information flows from genes to proteins is called Gene Expression. 

graph TD;
A(Genes)-->B(Nucleotide Sequence of mRNA);
B-->C(Sequence of Amino Acid Proteins);

Notice that genes for "housekeeping" enzymes such as those that provide energy via glycolysis are always "on". Whereas, more specific genes for some proteins like insulin and haemoglobin are expressed only by a particular kind of cell.

Gene Regulation in Bacteria:

Bacteria regulate their genes in response to environmental changes.

Natural Selection has favored bacterial that express only genes whose products are needed by the cell. For example, imagine eschericihia coli living in your intestine.

  • If you drink a milk shake, there will be a sudden rush of lactose.
  • In response, E.Coli will express only three genes for enzymes that will enable the bacterium to digest this sugar.
  • After the sugar has been digested, these genes are turned "off".

An operon is a sequence of DNA containing a cluster of genes under the control of a single promoter. An operon consists of a POS - promoter, operator and structural genes that function in a highly coordinated manner.

A lac-operon as discussed in the example given above is a segment of DNA containing adjacent genes including a SOR - structural gene, an operator gene and a regulatory gene.

Gene Regulation in Eukaryotes:

Eukaryotic chromosomes are highly condensed. This prevents gene expression as RNA polymerase and other transcription proteins cannot bind to DNA.

Introns : Sequence of a eukaryotes genes that are not transcribed into a protein.

Exons : Sequence of a gene's DNA that transcribes into protein's structures.

Genetic Regulation occurs at several levels: [UIRSTP]

  • Unpacking of DNA
  • Initiation of Transcription
  • RNA Processing
  • Stability of RNA
  • Translation

  • Protein Activation an Breakdown

  • Unpacking of DNA :

  • When lactose is absent the repressor remains bound to the operator and RNA Polymerase is therefore prevented from moving down the lac operon transcribing its genes.

  • When lactose is present the repressor is converted to its inactive form, which does not bind to the operator. RNA Polymerase can therefore move past the operator and transcribe the necessary genes into a single mRNA.

  • Initiation of Transcription :

  • Enhancers and Silencers : These are sequences on the DNA that are binding sites for proteins. Enhancers increase, Silencers decrease protein synthesis.

  • Transcription Factors (TFs) : Are proteins that control the available promoter sequence for transcription. TFs bind to DNA around the gene's promoter region and influence RNA polymerase's ability to start transcription. A particular gene will not be expressed if its TFs are not available.

  • Eukaryotic Transcription is so strictly regulated that TFs always guide RNA polymerase to the promoter sequence.

  • Prokaryotic cells also use proteins to block or encourage transcription but not to the extent that this stratergy is used in eukaryotic cells.

  • RNA Processing:

  • One gene can code for multiple RNAs, and thus multiple proteins.

  • Alternative splicing increases phenotype variation within species and among different species.

  • RNA Stability:

  • The lifespan of a mRNA molecule determines how much of a protein is made of microRNAs (miRNAs). These are small ss RNA molecules that bind to the complementary sequences on mRNA molecule in the cytoplasm. After binding, some miRNA trigger breakdown of their target mRNA, whereas others block translation.

Cells signal each other by direct contact or by the release of a substance from one cell that is taken up by another cell. The three stages are: [R.ST.R]

  • Reception, whereby the signal molecule binds to the receptor.
  • Signal Transduction, where the chemical signal results in a series of enzyme activations.
  • Response, which is cellular responses.

Cloning in Plants:

Tissues removed from the stem of Orchid Plant and placed in a growth medium may begin dividing and eventually grow into an adult plant. The new plant is a genetic duplicate of the parent plant. This process proves that mature plant cells can reverse their differentiation and develop in to all the specialized cells of an adult plant.

Reproductive Cloning of Animals:

This is achieved through Somantic Cell Nuclear Transplantation (SCNT) which involves replacing the nucleus of an egg cell or a zygote with a nucleus removed from an adult body cell. If the animal to be cloned is a mammal, further development of zygote requires implanting the early embryo in the uterus of a surrogate mother. The result will be the clone of the donor (not the surrogate mother).

Last Updated: 2023-03-31 ; Contributors: SivaaB

Comments