DNA and RNA Review
1. What are nucleic acids? What is the historic origin of this name?
DNA and RNA, the nucleic acids, are the molecules responsible for the hereditary information that commands the protein synthesis in living beings. The name “nucleic” derives from the fact that they were discovered (by the Swiss biochemist Friedrich Miescher, in 1869) within the cell nucleus. In that time it was not known that those substances contained the hereditary information.
2. Of what units are nucleic acids constituted? What are the chemical entities that compose that unit?
2. Of what units are nucleic acids constituted? What are the chemical entities that compose that unit?
Nucleic acids are formed by sequences of nucleotides.
Nucleotides are constituted by one molecule of sugar (deoxyribose in DNA and ribose in RNA) bound to one molecule of phosphate and to one nitrogen-containing base (adenine, uracil, cytosine or guanine, in RNA, and adenine, thymine, cytosine and guanine, in DNA).
3. What are pentoses? To what organic group do pentoses belong? Are nucleotides formed of only one type of pentose?
3. What are pentoses? To what organic group do pentoses belong? Are nucleotides formed of only one type of pentose?
Pentoses are carbohydrates made of five carbons. Deoxyribose is the pentose that constitutes DNA nucleotides and ribose is the pentose that is part of RNA nucleotides.
4. Into which two groups can the nitrogen-containing bases that form DNA and RNA be classified? What is the criterion used in that classification?
4. Into which two groups can the nitrogen-containing bases that form DNA and RNA be classified? What is the criterion used in that classification?
The nitrogen-containing bases that form DNA and RNA are classified as pyrimidine and purine bases.
By the analysis of the structural formulae of those nitrogen-containing bases it is possible to realize that three of them, cytosine, thymine and uracil, have only one nitrogenized carbon ring. The others, adenine and guanine, have two nitrogenized associated carbon rings.5. Concerning the nitrogen-containing bases that participate in nucleotides, what is the difference between DNA and RNA?
In DNA nucleotides can be formed of adenine (A), thymine (T), cytosine (C) or guanine (G). In RNA nucleotides can also contain adenine (A), cytosine (C) or guanine (G), however, instead of thymine (T) there is uracil (U).
6. Which are the nucleotides “portions” that bind in the formation of nucleic acids? What is meant by the 5’ and 3’ extremities of nucleic acids?
6. Which are the nucleotides “portions” that bind in the formation of nucleic acids? What is meant by the 5’ and 3’ extremities of nucleic acids?
The phosphate group of one nucleotide binds to the pentose of the other nucleotide and so on to make the polynucleotide chain.
Each extremity of a DNA or RNA chain can be distinguished from the other extremity according to their terminal chemical entity. The phosphate-ended extremity is called 5’-extremity and the pentose-ended extremity is called 3’-extremity. So DNA or RNA chains can be run along the 5’-3’ way or along the 3’-5’ way. These ways are important in several biological functions of DNA and RNA since some reactions specifically occur following one way or the other way.
7. Bacteria are prokaryotic cells, i.e., they do not have a membrane-delimited nucleus. Eukaryotes have cells with a delimited nucleus. Where in these types of cells can DNA be found?
7. Bacteria are prokaryotic cells, i.e., they do not have a membrane-delimited nucleus. Eukaryotes have cells with a delimited nucleus. Where in these types of cells can DNA be found?
In eukaryotic cells DNA is found within the cell nucleus. In prokaryotic cells DNA is found dispersed in the cytosol, the fluid space inside the cell.
Other DNA molecules can also be found within mitochondria and chloroplasts, specialized organelles of eukaryotic cells.
8. Who were James Watson, Francis Crick and Maurice Wilkins?
8. Who were James Watson, Francis Crick and Maurice Wilkins?
Watson (North American), Crick (British) and Wilkins (New Zealander) were the discoverers of the molecular structure of DNA, the double helix made of two polynucleotide chains paired by their nitrogen-containing bases. They won the Nobel prize in Medicine in 1962 for the discovery.
9. According to the Watson-Crick model how many polynucleotide chains does a DNA molecule have?
9. According to the Watson-Crick model how many polynucleotide chains does a DNA molecule have?
The DNA molecule is formed by two polynucleotide chains bound in antiparallel mode (5’-3’ to 3’-5’) and forming a helical structure.
10. What is the rule for the pairing of nitrogen-containing bases in the DNA molecule? And in the RNA? Is this last question appropriate?
10. What is the rule for the pairing of nitrogen-containing bases in the DNA molecule? And in the RNA? Is this last question appropriate?
The rule for the pairing of nitrogen-containing bases of the polynucleotide chains that form the DNA molecule is pyrimidine base binds to purine base, under the condition that thymine (T) binds to adenine (A) and cytosine (C) binds to guanine (G).
In RNA there is no binding between nitrogen-containing bases. That is because RNA is formed of only one polynucleotide chain; differently, DNA is formed of two chains. It is therefore not correct to question base pairing in RNA.
Compiled by My Preparation of Maharashtra Public Service Commission (MPSC) Examination for the blog http://maharashtrapublicserviceexams.blogspot.com
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