21. Mistakes may happen during every copying process. The same is true for DNA replication. Are there correction systems in cells that try to fix those mistakes? Under which situation are the mistakes carried only by the individual owner of the cell within which the mistake has occurred and in which situation are they transmitted to other individuals?
The cell is equipped with an enzymatic system that tries to fix mistakes of the DNA replication process. This system however is not completely efficient.
The cell is equipped with an enzymatic system that tries to fix mistakes of the DNA replication process. This system however is not completely efficient.
DNA replication mistakes are kept in the original individual where the failure occurred when the phenomenon affects somatic cells. If a replication mistake occurs in the formation of a germline cell (e.g., in gametes) the DNA alteration may be transmitted to the offspring of the individual.
22. Where can RNA be found within cells?
In the eukaryote cell nucleus RNA can be found dispersed in the nuclear fluid, along with DNA, and as the main constituent of the nucleolus. In cytosol (in eukaryotes or in bacteria) RNA molecules can be found free, as structural constituent of ribosomes (organelles specialized in protein synthesis) or even associated to them in the process of making proteins.
In the eukaryote cell nucleus RNA can be found dispersed in the nuclear fluid, along with DNA, and as the main constituent of the nucleolus. In cytosol (in eukaryotes or in bacteria) RNA molecules can be found free, as structural constituent of ribosomes (organelles specialized in protein synthesis) or even associated to them in the process of making proteins.
Mitochondria and chloroplasts also have their own DNA and RNA.
23. Does RNA molecule have two polynucleotide chains like DNA?
Only DNA has two polynucleotide chains. RNA is formed by just one polynucleotide chain.
24. What is the production of RNA called and what is the enzyme that catalyzes the process?
Only DNA has two polynucleotide chains. RNA is formed by just one polynucleotide chain.
24. What is the production of RNA called and what is the enzyme that catalyzes the process?
The making of RNA from information contained in DNA is called transcription. The enzyme that catalyzes the process is the RNA polymerase.
25. What are similarities and differences between the transcription process and the replication processes?
25. What are similarities and differences between the transcription process and the replication processes?
A DNA polynucleotide chain serves as a template in replication (DNA duplication) as well as in transcription (RNA formation). In both processes the pairing of the two polynucleotide chains of the original DNA molecule is broken by the breaking of hydrogen bonds for the chains to be exposed as templates. The reaction is catalyzed by specific enzymes in transcription and in replication.
In replication the enzyme DNA polymerase catalyzes the formation of a new polynucleotide chain using free nucleotides in solution and putting them in the new chain according to the DNA template exposed and to the rule A-T, C-G. In transcription the enzyme RNA polymerase makes a new polynucletide chain according to the DNA template exposed obeying, however, the rule A-U, C-G.
In replication the original template DNA chain is kept bound by hydrogen bonds to the newly formed DNA chain and a new DNA molecule is then created. In transcription the association between the template DNA chain and the newly formed RNA is undone and RNA constituted of only one polynucleotide chain is liberated.
26. What are the three main types of RNA? What is meant by heterogeneous RNA?
26. What are the three main types of RNA? What is meant by heterogeneous RNA?
Messenger RNA, or mRNA, transfer RNA, or tRNA, and ribosomal RNA, or rRNA, are the three main types of RNA.
The newly formed RNA molecule, a precursor of mRNA, is called heterogeneous RNA (hnRNA). The heterogenous RNA bears portions called introns and portions called exons. The hnRNA is processed in many chemical steps, introns are removed and mRNA is created formed only of exons, the biologically active nucleotide sequences.
27. Concerning their biological function what is the difference between DNA and RNA?
DNA is the source of information for RNA production (transcription) and thus for protein synthesis. DNA is still the basis of heredity due to its replication capability.
The messenger RNA is the template for protein synthesis (translation). In this process tRNA and rRNA also participate since the first carries amino acids for the polypeptide chain formation and the second is a structural constituent of ribosomes (the organelles where proteins are made).
28. Is there any situation in which DNA is made based on a RNA template? What is the enzyme involved?
The process in which DNA is synthesized having as template a RNA chain is called reverse transcription. In cells infected by retroviruses (RNA viruses, like the AIDS or SARS viruses) reverse transcription occurs and DNA is made from information contained in the viral RNA.
The process in which DNA is synthesized having as template a RNA chain is called reverse transcription. In cells infected by retroviruses (RNA viruses, like the AIDS or SARS viruses) reverse transcription occurs and DNA is made from information contained in the viral RNA.
Viral RNA within the host cell produces DNA with the help of an enzyme called reverse transcriptase. Based on that DNA the host cell then makes viral proteins, new viruses are assembled and viral replication occurs.
29. Do the phosphate and the pentose groups give homogeneity or heterogeneity to the nucleic acid chains? What about the nitrogen-containing groups? Supported by that, which of those groups is expected to directly participate in the highly diverse and heterogeneous genetic coding, i.e., which of those groups is the basis of the information for protein production?
29. Do the phosphate and the pentose groups give homogeneity or heterogeneity to the nucleic acid chains? What about the nitrogen-containing groups? Supported by that, which of those groups is expected to directly participate in the highly diverse and heterogeneous genetic coding, i.e., which of those groups is the basis of the information for protein production?
The phosphate and the pentose groups are the same in every nucleotide that forms the nucleic acid and so they give homogeneity to the molecule. The nitrogen-containing bases however can vary among adenine, thymine, cytosine, guanine (in DNA) and uracil (in RNA). These variations provide the heterogeneity of the nucleic acid molecule.
Homogeneous portions of a molecule seldom would store any information, by the same reason that a sequence of the same letter of the alphabet cannot make many words with different meanings. The nitrogen-containing bases, on the other hand, because they are different (four different types for RNA or DNA), can make different sequences and combinations that allow the diversity of the genetic code.
Compiled by My Preparation of Maharashtra Public Service Commission (MPSC) Examination for the blog http://maharashtrapublicserviceexams.blogspot.com
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