a)
Interpretation:
Long strand of DNA have the higher melting temperature than a shorter one, the reason has to be explained.
Concept Introduction:
Composition of
Base pairing in DNA: The two strands of the DNA double helix run in the opposite directions: one in 5’ to 3’ direction and other from 3’ to 5’ direction (complementary strand). The hydrogen bonding between two strands enhances the stability of the DNA; where the alignment of hydrophobic nitrogenous bases in the interior and hydrophilic phosphate and sugar groups on the exterior, is present that enhance the stability too. Adenine and thymine gives a pair forming two hydrogen bonds and cytosine and guanine gives rise to another pair forming three hydrogen bonds.
Melting temperature of DNA: On Heating DNA, (the process of denaturing the strand) the strand is unfolded or uncoiled.
b)
Interpretation:
The higher melting point is for either DNA with high percentage of G – C base pairs or high percentage of A – T base pairs has to be accounted.
Concept Introduction:
Composition of nucleic acid: Nucleic acid is a polymer of nucleotides. Each nucleotide has three parts: a sugar, a nitrogenous base, and a phosphate group. Two nucleotides are joined by phosphate diester linkage where a free phosphate on 5’ carbon of one nucleotide and a free –OH group on 3’ carbon of another nucleotide is linked.
Base pairing in DNA: The two strands of the DNA double helix run in the opposite directions: one in 5’ to 3’ direction and other from 3’ to 5’ direction (complementary strand). The hydrogen bonding between two strands enhances the stability of the DNA; where the alignment of hydrophobic nitrogenous bases in the interior and hydrophilic phosphate and sugar groups on the exterior, is present that enhance the stability too. Adenine and thymine gives a pair forming two hydrogen bonds and cytosine and guanine gives rise to another pair forming three hydrogen bonds.
Melting temperature of DNA: On Heating DNA, (the process of denaturing the strand) the strand is unfolded or uncoiled.
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Fundamentals of General, Organic, and Biological Chemistry (8th Edition)
- The A and G compositions (mole percent) of one of the strands of a duplex DNA is A = 27 and G = 30. (a) What would be the T and C compositions of the complementary strand? (b) What can be said about the A and G compositions of its complementary strand?arrow_forwardHow Can Fragments of DNA Be Separated From One Another? Agarose gel electrophoresis is a procedure used to separate DNA fragments based on their sizes. DNA is an acid and has many negative electrical charges due to the negatively charged phosphate-deoxyribose backbone. Scientists have used this fact to modify chromatography to separate pieces of DNA. A solution containing a mixture of DNA fragments of variable sizes is placed into a small well formed in an agarose gel (that has a texture similar to gelatin). An electric current causes the negatively-charged DNA molecules to move towards the positive electrode. Imagine the gel as a strainer with tiny pores that allow small particles to move through it very quickly. The larger the size of the particles, however, the slower they are strained through the gel. After a period of exposure to the electrical current, the DNA fragments will sort themselves out by size. Fragments that are the same size will tend to move together through the gel…arrow_forwardWhen DNA is heated, it denatures; that is, the strands separate because hydrogen bonds are broken and some base-stacking and hydrophobic interactions are disrupted. The higher the temperature, the larger the number of hydrogen bonds that are broken. After reviewing DNA base pair structure, determine which of the following molecules will denature first as the temperature is raised. Explain your reasoning. a. 5′-GCATTTCGGCGCGTTA-3′ 3′-CGTAAAGCCGCGCAAT-5′ b. 5′-ATTGCGCTTATATGCT-3′ 3′-TAACGCGAATATACGA-5′arrow_forward
- The ratio of (A+T) to (G+C) in a particular DNA is 1.0. Is this sufficient data to determine whether the DNA is double-stranded or single-stranded please explain why or why not.arrow_forwardFor some DNAs, it is possible to separate the two strands, after denaturation,in a CsCl gradient.(a) What property of any DNA determines where it will band in a CsClgradient?(b) What kind of DNA might have two strands that differ sufficiently in thisproperty that they could be separated after denaturation?arrow_forwardIn a DNA Double helix ,why doesn't an A or T form two hydrogen bonds(out of the three possible) with G or C? Explain in detail.arrow_forward
- A solution contains DNA polymerase and the Mg ²+ salts of dATP, dGTP, dCTP, and TTP. The following DNA molecules are added to aliquots of this solution. Which of them would lead to DNA synthesis? (a) A single-stranded closed circle containing 1000 nucleotide units. (b) A double-stranded closed circle containing 1000 nucleotide pairs. (c) A single-stranded closed circle of 1000 nucleotides base-paired to a linear strand of 500 nucleotides with a free 3' -OH terminus. (d) A double-stranded linear molecule of 1000 nucleotide pairs with a free 3’-OH group at each end.arrow_forward(a) (b) (c) The figure shown below is the mechanism of a DNA nuclease. The DNA molecule is in blue while the protein residues are in black (M1 and M2 are metal ions, they are irrelevant to this question). 3' Base reaction. M² 5' 00 3' Glu 357 M¹ Draw the structure of the final DNA product for this reaction. Draw a square around the nucleophile and draw a circle around the leaving group in this Does this depict the reaction of an endonuclease or an exonuclease?arrow_forwardThe melting temperature Tm of DNA can be predicted by calculation without actually measuring it. Calculate the Tm of the DNA double strand shown in (1) to (3), and discuss the results. The numbers in parentheses indicate the degree of polymerization of nucleotides.(1) A(10) + T(10), (2) A(15) + T(15), (3) G(10) + C(10)arrow_forward
- DNA structure depends on base pairing of its four nucleotides, A, C, T, and G. Nucleotide A pairs with T, and nucleotide C pairs with G. This forms a four-letter DNA “alphabet." Because DNA codes for amino acids in sets of three nucleotides, there are 4 cubed (4'), or 64, possible combinations, coding for 20 different amino acids. What is the best explanation for why there is no selective advantage for DNA to have five nucleotides (e.g., A, C, T, G, and E) with C pairing with either G or functionally equivalent E? It would be impossible to form the DNA molecule, because it must have an equal number of Cs and Gs. Because G and E have the same role, there would still be four functional letters of the alphabet. Replication would be inaccurate because sometimes C would bond with G and sometimes C would bond with E. There would be a five-letter alphabet with 125 combinations, which is too numerous. It is impossible because there are not five known nucleotides in the cell.arrow_forwardWhich conformation of DNA – (i) totally double helix, (ii) minimally unwound or (iii) largely unwound – would have the highest relative absorbance at 260 nm. Would a molecule of DNA having a higher content of guanine and cytosine than of adenine and thymine have a higher or lower melting temperature (Tm) than one with the reverse composition?arrow_forwardIf a DNA double helix contains 28% T nucleotides, then what is the percentage of A nucleotides?arrow_forward
- Human Heredity: Principles and Issues (MindTap Co...BiologyISBN:9781305251052Author:Michael CummingsPublisher:Cengage Learning