Concept explainers
Newsdate: March 1, 2030. A unique creature has been discovered during exploration of outer space. Recently, its genetic material has been isolated and analyzed. This material is similar in some ways to DNA in its chemical makeup. It contains in abundance the 4-carbon sugar erythrose and a molar equivalent of phosphate groups. In addition, it contains six nitrogenous bases: adenine (A), guanine (G), thymine (T), cytosine (C), hypoxanthine (H), and xanthine (X). These bases exist in the following relative proportions:
X-ray diffraction studies have established a regularity in the molecule and a constant diameter of about 30 Å. Together, these data have suggested a model for the structure of this molecule.
- (a) Propose a general model of this molecule. Describe it briefly.
- (b) What base-pairing properties must exist for H and for X in the model?
- (c) Given the constant diameter of 30 Å, do you think that either (i) both H and X are purines or both pyrimidines, or (ii) one is a purine and one is a pyrimidine?
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Concepts of Genetics (12th Edition)
- In DNA the nucleic acid bases form hydrogen bonds between them, which are responsible for the formation of the double-stranded helix. A hydrogen bond donor is defined as any hydrogen atom that can participate in a hydrogen bond, whereas a hydrogen bond acceptor is defined as any atom that can “receive” that hydrogen atom to form a hydrogen bond. How many hydrogen bond acceptors does guanine (shown below) have? a) 3, b) 5 c) 4 d) 6 e) 7arrow_forwardLactose sugar is hydrolyzed to produce two monosaccharides.(ii) Why can't we store Vitamin C in our bodies?The distinction between a nucleoside and nucleotide is explained in (iii).arrow_forwardThe following define nucleic acids EXCEPT A) They are polyionic molecules of high molecular weight composed of subunits or monomers called nucleosides. B) They are chainlike macromolecules that function in the storage and transfer of genetic information. C They are polynucleotides. They contain genes that encode for polypeptides and RNAS.arrow_forward
- RNA differs from DNA in that: a) The ribose in RNA nucleotides contains fewer oxygen atoms than does deoxyribose DNA nucleotides. b) It is always single stranded and cannot form base pairs. c) It contains the nucleotide uracil, which pairs with thymine. d) It is single-stranded but can fold into a variety of structures, some of which are double-stranded. e) RNA can only be found in the cytoplasm whereas DNA can only be found in the nucleus.arrow_forwardCells contain two types of nucleic acids: DNA and RNA. Which of the following statements about DNA and RNA is the most accurate? DNA contains uracil whereas RNA contains thymine. All three of the other options are correct. The sugar component of DNA nucleotides contains one less oxygen molecule than is found in the sugar component of RNA nucleotides. Hydrogen bonding can occur between bases in DNA molecules, whereas this does not occur in RNA molecules.arrow_forwardDna is composed of a phosphate back bone, a sugar and four nitrogenous bases. Of the following bases: adenine, cytosine, guanine, and thymine; which are the hydrogen bond donors and which are the acceptors?arrow_forward
- Section B: True / False The diagram shows an amino acid in L-configuration. NH, 1. H- CO,H CH,OH This sugar can be found in DNA. ҫнон он 2. но CH,OH 3. Base pairing can be found between two purines in DNA. The relation between the following two sugars is epimers. сно сно но C-OH HCOH OH но C-H HC он HC- он он он CH,OH CH,OHarrow_forwardSelect all of the true statements regarding the molecule below: NH2 NH OH NH, H,N ОН `NH ОН ОН ОН O This is RNA O This is DNA This chain is a polymer. O The backbone of these nucleotides is a ribose sugar O This nucleic acid is the hereditary material for humans. O This nucleic acid is the hereditary material for coronaviruses. O This type of nucleic acid is never found in healthy human cells. O This nucleic acid contains the nucleobase thymine.arrow_forwardBoth RNA and DNA have negatively charged phosphate groups as part of their structure. Would you expect ions that bind to nucleic acids to be positively or negatively charged? Why?arrow_forward
- Intramolecular ______ are responsible for formation of the most common three-dimensional shape in proteins, the alpha helix. a) van der waals forces b) hydrogen bonds c) covalent bonds d) ionic (electrostatic) interactionsarrow_forwardA molecule contains adenine, deoxyribose, and one phosphate. Is it a nucleoside or a nucleotide? Would it be found in DNA or RNA?arrow_forwardThe human eye is a remarkable organ. It forms a high-resolution image by focusing light through a transparent lens made of living tissue. The lens is made up largely of proteins called crystallins. Where did they originate?arrow_forward
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