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You are watching: The weak chemical bonds important in holding the dna double helix together is the:

Griffiths AJF, miller JH, Suzuki DT, et al. An introduction to genetic Analysis. 7th edition. Brand-new York: W. H. Freeman; 2000.

By agreement with the publisher, this book is available by the search feature, but cannot it is in browsed.

1. Explain the varieties of chemistry bonds and forces of the DNA twin helix.

The DNA dual helix has actually two species of bonds, covalent and also hydrogen. Covalentbonds exist in ~ each straight strand and strongly shortcut bases, sugars, andphosphate groups (both within each component and also between components). Hydrogenbonds exist in between the two strands and form between a base, indigenous one strand anda base from the 2nd strand in complementary pairing. This hydrogen bond areindividually weak yet collectively rather strong.

2. Describe what is supposed by the terms conservative andsemiconservative replication.

3. What is meant by a primer, and also why space primers essential for DNAreplication?

A inside wall is a short segment that RNA that is synthesized by primase making use of the DNAas a template during DNA replication. After the primer has been synthesized, DNA polymerase climate adds DNA come the 3′ finish of the RNA. Primers are compelled becausethe major DNA polymerase catalyzing DNA replication is unable to initiate DNAsynthesis and, rather, calls for a 3′ end. The RNA is subsequently removed andreplaced through DNA so that no gaps exist in the last product.

4. What room helicases and also topoisomerases?

5. Why is DNA synthesis continuous on one strand and also discontinuous on the oppositestrand?

Because the DNA polymerase is capable of adding new nucleotides just at the 3′end of a DNA strand and because the two strands are antiparallel, at the very least twomolecules of DNA polymerase have to take part in the replication of any kind of specificregion the DNA. As soon as a region becomes solitary stranded, the two strands have anopposite orientation. Imagine a single-stranded an ar that runs from left toright. At the left end, the 3′ finish of one strand points come the right, andsynthesis have the right to initiate and continue toward the right finish of that region. Theother strand has actually a 5′ end pointing towards the right, and also synthesis cannotinitiate and continue towards the right finish of the single-stranded an ar at the5′ end. Instead, synthesis have to initiate what to the ideal of the left endof the single-stranded region and relocate toward the left end of the region. As first strand continues synthesis (continuous synthesis), the single-strandedregion extends towards the right. This now leaves the second strand unreplicatedin this brand-new region the single-strandedness, and there must be a second initiationof DNA synthesis moving from the existing right finish of the single-stranded regiontoward the first initiation suggest on that strand. This results in discontinuoussynthesis along that strand.

6. If thymine renders up 15 percent of the bases in a certain DNA molecule, whatpercentage the the bases is cytosine?

7. If the GC contents of a DNA molecule is 48 percent, what space the percentages ofthe four bases (A, T, G, and also C) in this molecule?

The frequency that both A and also T is (52%) = 26%.

8. E. Coli chromosomes in which every nitrogen atom is labeled(that is, every nitrogen atom is the heavy isotope 15N instead of thenormal isotope 14N) are allowed to replicate in an environment inwhich all the nitrogen is 14N. Using a solid line to represent aheavy polynucleotide chain and also a dashed line for a light chain, sketch thefollowing:


The heavy parental chromosome and the commodities of the an initial replicationafter transport to a 14N medium, assuming the the chromosomeis one DNA dual helix and that replication is semiconservative.


Repeat part a, yet assume that replication is conservative.


Repeat component a, however assume the the chromosome is in truth two side-by-sidedouble helices, every of i m sorry replicates semiconservatively.


Repeat part c, but assume the each side-by-side dual helix replicatesconservatively and that the in its entirety chromosomereplication is semiconservative.


Repeat component d, but assume the the overall chromosome replication isconservative.


If the daughter chromosomes native the first department in 14N arespun in a cesium chloride (CsCl) thickness gradient and a single band isobtained, i beg your pardon of possibilities in components a through e can be rule out?Reconsider the Meselson-Stahl experiment: what does itprove?

9. R. Okazaki found that the immediate commodities of DNA replication in E.coli incorporate single-stranded DNA fragments around 1000nucleotides in size after the freshly synthesized DNA is extracted and also denatured(melted). As soon as he enabled DNA replication to proceed for a longer period oftime, he discovered a lower frequency of these quick fragments and longsingle-stranded DNA chains after extraction and denaturation. Define how thisresult could be pertained to the fact that all recognized DNA polymerases synthesizeDNA just in a 5′ → 3′ direction.

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The results indicate that the DNA is replicated in brief segments that aresubsequently joined by enzymatic activity (DNA ligase). Because DNA replication isbidirectional, because there are multiple points follow me the DNA wherein replicationis initiated, and also because DNA polymerases occupational only in a 5′ → 3′ direction, onestrand that the DNA is always in the dorn orientation for the enzyme. Thisrequires synthetic in fragments.

10. Once plant and animal cells are offered pulses that <3H>thymidine atdifferent times during the cabinet cycle, heterochromatic regions on thechromosomes room invariably shown to be “late replicating.” deserve to you imply what,if any, biological significance this observation might have?

11. On the planet of Rama, the DNA is of six nucleotide types: A, B, C, D, E, and F.A and also B are called marzines, C and D areorsines, and also E and F space pirines. Thefollowing rules room valid in all Raman DNAs: