Biology 5 Marks Questions

Four-ways of introducing the desired DNA segment into a bacterial cell are as follows:
i. Competent host (For transformation with recombinant DNA):
a. For transformation, bacterial cells are treated with a specific concentration of calcium which increases the efficiency with which DNA enters the bacterium through pores in its cell wall.
b. Cells with recombinant DNA are incubated on ice, followed by placing them briefly at 42°C (heat shock) and then putting them back into ice.
This enables the bacteria to take up recombinant DNA.
ii. Micro-injection: Recombinant DNA is directly injected into the nucleus of an animal cell.
iii. Biolistic or Gene gun: Plant cells are bombarded with high-velocity micro-particles of gold or tungsten coated with DNA.
iv. "Disarmed pathogen"vectors: (Ti- plasmid); retroviruses which when allowed to infect the cell, transfer the recombinant DNA into the host.

Two complexities that are observed in the process of transcription in eukaryotes and not in Prokaryotes are as follows
i. There are three RNA polymerases in the nucleus RNA polymerase I transcribes - rRNAs, RNA polymerase II transcribes - heterogenous nuclear RNA/hnRNA, RNA polymerase III transcribes - tRNA/5 srRNA/snRNA (small nuclear RNAs).
ii. Primary transcripts/hnRNA contain both the exons and non functional introns, subjected to splicing where introns are removed, exons are joined in a defined order, hnRNA undergoes processing called capping and tailing, In capping nucleotide methyl guanosine triphosphate is added to 5' end of hnRNA, In tailing adenylate residues (200-300) are added at 3"- end in a template independent manner, this fully processed hnRNA is now called mRNA (and transported out of the nucleus for translation).

i. Optimisation of the bioreactor system can be achieve by Temperature, pH, Substrate, Salts, Vitamins, Oxygen
ii. Log phase/Exponential phase is referred
iii. No
It needs separation and purification/down-streaming process/quality control testing/needs to be formulated with suitable preservatives/clinical trials.

a. In the first phase itself, amino acids are activated in the presence of ATP and linked to their cognate tRNA-a process commonly called as charging of tRNA or aminoacylation of tRNA to be more specific. If two such charged tRNAs are brought close enough, the formation of a peptide bond between them would be favored energetically.
b. Small subunit of ribosome binds to mRNA at start codon (AUG) at 5' end, in the two sites of large subunits of ribosome, the charged tRNA with the aminoacid corresponding to the codon on mRNA align, formation of peptide bond between the two closely placed amino acids in the two sites occur, with the help of ribozyme in the ribosome, peptide chain elongation continues till the stop codon (UAG, UGA, UAA) on the mRNA reach the big unit of ribosome.
c. Due to transcription error, ATG codon of DNA is transcribed into UAG in mRNA which translates a non-functional polypeptide chain in the ribosome. This means that due to transcription error i.e presence of G in place of C there will be a synthesis of incorrect protein. Since the codon, UAG stops codon and it will cause termination of the polypeptide chain synthesis.

Advantages of cross-pollination:
i. Cross-pollination brings about genetic recombinations and introduces the variations in the offsprings. Some of these variations are more useful and help the individuals in the struggle for existence and adapt to the changing environment.
ii. Plants are diseases resistant.
iii. New and improved varieties of plants can be produced by artificial cross-pollination.
iv. The yield is quite high and never falls below an average minimum.
v. The seeds are much better, usually larger, healthy and more vigorous due to the phenomenon of hybrid vigour.
Disadvantages of cross-pollination:
i. Cross-pollination is not a sure method as the chance factor is always there.
II. It is a less economical and highly wasteful method as plants have to spend a large amount of energy to produce a large number of pollen grains, develop many devices to promote and effect this kind of pollination by various pollinating agencies.
iii. Harmful or undesirable characters may be introduced in the individuals and may persist in the race permanently.
iv. The very good characters of the race are likely to be lost in the next generation.