Difference between Prokaryotic and Eukaryotic Transcription

Transcription: Process by which RNA is synthesised from a DNA template.

Difference between : Prokaryotic vs Eukaryotic Transcription

	Prokaryotic Transcription	Eukaryotic Transcription
1	Coupled transcription-translation is the rule.	Coupled transcription translation is not possible.
2	Occurs in the cytoplasm.	Occurs in the nucleus.
3	There is no definite phase for its occurrence.	Take place in the G1 and G2 phases of cell cycle.
4	A single RNA polymerase synthesises all the three types of RNA (mRNA, tRNA, rRNA)	The RNA polymerases I, II and III synthesizes rRNA, mRNA and tRNA respectively.
5	RNAs are released and processed in the cytoplasm.	RNAs are released and processes in the nucleus.
6	Initiation of transcription does not need any proteins or initiation factors.	Initiation of transcription requires proteins called transcription factors. These are TFIIA, TFIIB, TFIID, TFIIE, TFIIF AND TFIIH. These recognise TATA BOX.
7	Pre RNA molecules are released and processed in the cytoplasm.	Pre RNA are released and processed in the nucleus.
8	RNA polymerases are complexes of five polypeptides.	RNA polymerases are complexes of 10-15 polypeptides.
9	The mRNA primary transcript has fewer surplus nucleotides.	The mRNA primary transcript has a large number of surplus nucleotides.
10	Transcriptional unit has one or more genes (Polycistronic).	Transcriptional unit has only one gene (Monocistronic).
11.	Transcription and translation nearly simultaneous. Little process of mRNA	Processing of hnRNA includes: ·        Addition of 5’cap(7 methylguanosine) ·        Addition of 3’poly A tail.
12	The 23S, 16S and 5S rRNAs are formed from a single primary transcript.	The 28S, 18S, 5.8S and 5S rRNAS are formed from two primary transcripts.
13.	Inhibitors: Rifampin: RNA polymerase binds to β subunit. Actinomycin-Intercalates to interrupt transcription.	Inhibitors: α amanitin: Inhibits RNA polymerase 2 most srongly

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How to Calculate Cotransformation Frequency with Examples?

Gene transfer in bacteria occurs by conjugation, transduction and transformation.

Transformation involves the uptake of genetic material from the surrounding medium and its incorporation into bacterial chromosome or plasmid.

Transformation is used to map bacterial genes. Cells that receive genetic material through transformation are called transformants. Genes can be mapped by looking at the rate at which two or more genes are co transformed in transformation. if two genes are close together on the same chromosomal fragment the chance of co transformation is more. 

Higher cotransformation frequency indicates a shorter distance between the two genes on the donor’s chromosome.

Cotransformation Frequency Problems

Problems 1

In a transformation experiment, donor DNA from an E.coli strain with the genotype Z’Y’ was used to transform a strain of genotype of genotype Z Y. The frequencies of transformed classes were:

Z+Y+               200

Z+Y                 400

Z-Y+                400

total               1000

what is the frequency (%) with which Y locus is co transformed with the Z locus?

Answer:

Cotransformation frequency=no. of transformed cells with Z+Y+ genotype/total number of transformed cells

that is 200/1000=0.2 or 20%

The frequency of co-transformation is 20%

Problem 2

DNA from a strain of Bacillus subtilis with the genotype trp+ tyr+ is used to
transform a recipient strain with the genotype trp tyr . The following numbers of
transformed cells were recovered:
Genotype Number of transformed cells

trp+ tyr 154
trp tyr+ 312
trp+ tyr+ 354
What do these results suggest about the linkage of the trp and tyr genes?
Answer:

Cotransformation frequency=no. of transformed cells with trp+ tyr+ genotype/total number of transformed cells

that is 354/820=0.43 or 43%

The frequency of co-transformation of trp and tyr genes are 43%

The high level of cotransformation indicates that these two genes are
closely linked.

Problem 3

DNA from a ‘c+ d+’ bacterial strain was used to transform a ‘c- d-’ strain.

The following transformants were obtained:
c+ d- : 300
c- d+ : 377
c+ d+: 223
Calculate the transformation and cotransformation frequencies ?

Answer:

Cotransformation frequency (%): Cotransformation frequency=no. of transformed cells with c+d+ genotype/total number of transformed cells x100

223/(300+377+223) X100 = 24.8%

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What are specialized cells? How do cells become specialized for different functions?

The genetic makeup of all cells in an adult body is the same. But nerve cell is different from muscle cell or cells of the eyes morphologically and functionally. How this happens?

By cell differentiation. It is the process by which genetically identical cells of an embryo become specialized or the process by which stable differences arise between cells of the embryo.

How specialization is achieved?
Let us make this concept clear by this figure given below.
All these cells have ~ 20000 genes distributed in 46 chromosomes.
Let us take the example of RBC. All these cells have haemoglobin gene in the nucleus.
This gene is not expressed in all cells… It is expressed or turned on only in RBCs where it has a role..

 

During the process of cell specialisation, in each cell only specific genes are “turned on” and transcribed to RNA and translated to proteins. Rest of the genes remain inactive. That is, genes active in the neurons may not be active in muscle cells. For instance, genes for actin and myosin filaments are present in all animal cells, but these genes are active only in muscle cells. Cell specialization involves the preferential synthesis of some specific proteins like antibodies in plasma cells or Hb in erythrocytes.

Smart genes and ‘house keeping’ genes

Remember, there are some genes that are expressed in all types of cells or genes essential for cell survival like genes making membranes. These genes are called ‘house keeping’ genes. But genes that are expressed in only certain types of cells or expressed differentially are called ‘luxury genes’ or smart genes’. Eg: IgG genes. This differential expression leads to cell specialization.

After fertilization, the first cell the zygote has nucleus of both the gametes where the cytoplasm is entirely provided by egg. Thus the zygote has only maternal effect genes contributed by egg cytoplasm only. This is conducive for the zygote development. On first division, zygotic gene are expressed that will trigger further development and differentiation.

In short: Zygote > determination > differentiation (to specialised cells and tissues).

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Types of Differentiated cells Based on their Proliferation Capacity

Cell differentiation is the process by which genetically identical cells of an embryo become specialized or the process by which stable differences arise between cells of the embryo.

Types of differentiated cells:

Differentiated cells can be categorized into three based on their proliferation and replacement capacity.

Type I: Cardiac cells, muscle cells, nerve cells, once differentiated these cells are incapable of division and cannot be replaced upon injury or cell death.

Type II: skin cells and liver cells, once differentiated enter G0 phase or resting phase of cell cycle and divide only upon injury or cell death. Mostly these cells have short life span and must be replaced by continuous division.

Type III: Blood cells once differentiated are incapable of division and undergo cell death. But these cells are replaced by the proliferation of less differentiated cells called stem cells.

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