RNA plays several important roles products. nd answer FOUR questions in complete
ID: 203057 • Letter: R
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RNA plays several important roles products. nd answer FOUR questions in complete sentences. important roles 1. in the processes that express genetic information from DNA into protein pt lko inmdiestrihe the events of transcription in a bacterial cell and indicate where RNA plays a role. that produce anticedibly resistant to multiple antibiotics, presumably as a response to competition from bacteria a. icate what role RNA plays in translation in bacterial cells. a. tare hre ways that these antibiotic resistant genes could move from soil bacteria species to other species of bacteria? Briefly describe each gene transfer process th 9 ou- ure 4. E 5. Imagine NASA sends you a specimen from a planet that they believe contains an extraterrestrial bacterial species You are the microbiologist in charge of determining how to grow the extraterrestrial bacteria. Many factors may affect the growth of extraterrestrial bacteria. a. Choose two and describe how you would test their effects.Explanation / Answer
1.a Transcription in bacteria involves three stages:
i) Initiation: The DNA is scanned by the RNA polymerase holoenzyme scans until the sigma factor identifies and recognizes the promoter sequence. Binding of sigma factor to -35 and -10 sequences on the promoter leads to formation of a closed complex. The DNA is denatured to form a bubble-like structure or open complex. RNA polymerase binds to promoter to initiate transcription.
ii) Elongation: RNA polymerase core enzyme slide along the DNA. RNA is synthesized as the RNA polymerase slides along the DNA. The RNA polymerase alpha subunit is required for contact with DNA while its beta subunit catalyses the synthesis of RNA. RNA is complementary to the template strand of DNA (3’-5’) and is synthesized in 5’-3’ direction. The nucleotides are same as DNA except, thymine is replaced by uracil.
iii) Termination: Transcription is terminated when RNA polymerase reaches a sequence at the end of the gene. In rho-independent termination, the rho protein recognizes a sequence within the RNA known as Rut site. It binds to this sequence and travels toward RNA polymerase by ATP hydrolysis. When it reaches the tsp (termination stop site) on RNA, it will utilize its helicase activity to dissociate the mRNA-DNA-RNA polymerase complex. Formation of stem loop structure in rho independent termination leads to halting of RNA polymerase and its removal from DNA.
RNA is involved in transcription termination process.
b) RNA is involved in translation in three ways:
i) The triplet nucleotide in messenger RNA or mRNA code for one amino acid. The initiation of translation occurs when AUG is encountered by ribosomes on the mRNA. This codon codes for formyl methionine. All AUG after this initiator codon will code for methionine. Each codon is complementary to the anticodon that is present on tRNA. There are 64 codons, each coding for one amino acid. One amino acid can be coded by different codon.
b) Transfer RNA or tRNA has anticodon in its structure. Each anticodon is complementary to the codon. The tRNA also binds to the amino acid that is defined by the anticodon sequence
c) Ribosomal RNA or rRNA associates with a set of proteins to form ribosomes. Ribosomes move along the mRNA and form proteins by assembly of amino acids. They also bind to tRNA an accessory molecules that bring in the amino acid. The large 60S and small 40S subunit of ribosomes is attached to 23S, 5S and 16S rRNA respectively.
2a. Resistance to antibiotics by bacteria can occur by mutations or Horizontal gene transfer (HGT) mechanism. There are three mechanism of HGT
i) Transduction: Transduction is the transfer of genetic material from the donor bacterium is transferred to a bacteriophage. When the bacteriophage infects a new host, it transfers the genes to that bacteria cell. Thus, the DNA is transferred between species by use of viral vectors. It does not require physical contact between the two bacteria. When a bacteriophage infects a bacterium, it will integrate its DNA into the host cell. It can remain integrated in the host cell and replicate its genome in a lysogenic cycle. If lytic cycle is induced, the viral DNA is excised from the host DNA. During this process, some host DNA is integrated into the viral genome. When lysis occurs, the phages will be released. The new phages will infect another bacterium and transfer this host genetic material when the genome integrates into the new host DNA.
ii) Transformation: Transformation is the transfer of free DNA into another host bacterium. The soli organism can die and release its DNA in the environment. For transformation to occur, the host cell must be competent to take in the antibiotic resistance gene DNA from the environment. Competence is the loosening of the cell membrane to accept the foreign DNA. The bacterial host will now take up the foreign DNA.
iii) Conjugation: Conjugation is the transfer of DNA through cell-cell contact via cell surface pili or adhesins. The soli bacterium is the donor while the other organism is a recipient. The donor bacterium has a F pilus that is coded by a F plasmid. The pilus attaches to the recipient F- cell and initiates contact. The donor cell will now transfer the antibiotic resistance DNA to the recipient bacteria.
5a. Extraterrestrial organisms are species that live outside the earth, in other planets. When an extraterrestrial bacterial species is sent to earth by NASA, various factors affect its growth on Earth.
i) Nutrition: Bacteria require specific types of carbon and nitrogen sources to live. The bacteria may be autotrophic and synthesize its own food. It can be a heterotroph and requires external carbon and nitrogenous sources for growth. In order to study whether it is an autotroph or heterotrophy, the species can be grown on minimal media and minimal media that are supplemented with different carbon and nitrogen sources.
ii) Temperature: In order to identify the temperature at which it grown, it can be inoculated in complete nutrient rich medium containing all nutrients and subjected to different temperatures from 00C, 250C,370C, 450C, 600C, 750C. The temperature at which it grows optimally is its ideal temperature.
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