Genetics: Essential Points and Now Solve This Exam I

Now Solve This 17.3 You have just created the world's first genomic library from the African okapi, a relative of the giraffe. No genes from this genome have been previously isolated or described. You wish to isolate the gene encoding the oxygen-transporting protein β-globin from the okapi library. This gene has been isolated from humans, and its nucleotide sequence and amino acid sequence are available in databases. Using the information available about the human β-globin gene, what two strategies can you use to isolate this gene from the okapi library?

A probe can be created only from a nucleotide sequence of the human B-globin protein that screens the African okapi library. Also, in human b-globin protein, the amino acid sequence can be used to construct a complementary DNA probe. The probe will then identify the DNA sequences in the African okapi genomic library that is complementary to the b- globin. Once identified, the cells with the clone are seperated and the plasmid isolated.

Essential Point 9.2

Although both proteins and nucleic acids were initially considered as possible candidates, proteins were initially favored to serve as the genetic material

Essential Point 10.2

Arthur Kornberg isolated the enzyme DNA polymerase I from E. coli and showed that it is capable of directing in vitro DNA synthesis, provided that a template and precursor nucleoside triphosphates were supplied

Essential Point 9.6

As proposed by Watson and Crick, DNA exists in the form of a right-handed double helix composed of two long antiparallel polynucleotide chains held together by hydrogen bonds formed between complementary, nitrogenous base pairs

Essential Point 9.6 part II

Based on the model of DNA put forward by Watson and Crick in 1953, the gene was viewed for the first time in molecular terms as a sequence of nucleotides in DNA helix that encodes genetic information

10.3 Now Solve This An alien organism was investigated. When DNA replication was studied, a unique feature was apparent: No Okazaki fragments were observed. Create a model of DNA that is consistent with this observation

Basically you would have two leading strands. On one strand the primer replicated in the direction towards the replication fork and on the other stand the primer would replicate away from the fork.

Essential Point 9.3

By 1952, transformation studies and experiments using bacteria infected with bacteriophages strongly suggested that DNA is the genetic material in bacteria and most viruses

Essential Point 10.3 II

Concurrent DNA synthesis occurs continuously on the leading strand and discontinuously on the opposite lagging strand, resulting in short Okazaki fragments that are later joined by DNA ligase

Now solve this 10.1 In the Meselson-Stahl experiment, which of the three modes of replication could be ruled out after one round of replication? After two rounds?

Conservative and Dispersive

Essential Point 10.6

DNA replication in eukaryotes is more complex than replication in prokaryotes, using multiple reaction origins, multiple forms of DNA polymerases, and factors that disrupt and assemble nucleosomal chromatin

Essential Point 10.3

During the initiation of DNA synthesis, the double helix unwinds, forming a replication fork at which synthesis begins. Proteins stabilize the unwound helix and assist in relaxing the coiling tension created ahead of the replication fork

Essential Point 11.4

Eukaryotic chromatin is nucleoprotein organized into repeating unit called nucleosomes, which are composed of 200 BP of DNA, an octamer of four types of histones, plus one linker histone.

Essential Point 11.5

Eukaryotic genomes demonstrate complex sequence organization characterized by numerous categories of repetitive DNA, consisting of either tandem repeats clustered in various regions of the genome or single sequences repeatedly interspersed at random throughout the genome.

Now Solve This 9.6: In sea urchin DNA, which is double stranded, 17.5 percent of the bases were shown to be cytosine (C). What percentages of the other three bases are expected to be present in this DNA?

G= 17.5 A= 32.5 T= 32.5

Essential Point 11.4 II

Heterochromatin, prematurely condenses in interphase and for the most part genetically inert, is illustrated by the centromeric and telomeric regions of eukaryotic chromosomes, the Y chromosome, and the Barr body

Essential Point 10.1

In 1958, Meselson and Stahl resolved the question of which of the three potential modes of replication is utilized by E. coli during the duplication of DNA in favor of semiconservative replication, showing that newly synthesized DNA consists of one old strand and one new strand

Essential Point 11.1

In contrast to eukaryotes, bacteriophage and dbacterial chromosomes are largely devoid of associated proteins, are much smaller size, and most often consist of circular DNA

Essential Point 11.2

Mitochondria and chloroplasts contain DNA that is remarkably similar in for and appearance to some bacterial and bacteriophage DNA

Essential Point 17.3

PCR allows DNA to be amplified, or copied, without cloning and is a rapid and sensitive method with wide-ranging applications

Essential Point 17.1

Recombinant DNA technology was made possible by the discovery of proteins called restriction enzymes, which cut DNA at specific sequences, producing fragments that can be joined with other DNA fragments to form recombinant DNA molecules

Essential Point 10.7

Replication at the ends of linear chromosomes in eukaryotes poses a special problem that can be solved by the presence of telomeres and by unique RNA- containing enzyme called telomerase

Now Solve This 11.1 In bacteriophages and bacteria, the DNA is almost always organized into circular chromosomes. Phage (Lambda) is an exception, maintaining its DNA in a linear chromosome within the viral particle. However, as soon as this DNA is injected into a host cell, it circularizes before replication begins. What advantage exists in replicating circular DNA molecules compared to linear molecules, characteristic of eukaryotic chromosomes?

Replication occurs faster due to no missing fragments. Also, there is no need for a lagging and leading strand, it is all done on one strand.

Essential Point 10.1 II

Taylor, Woods, and Hughes demonstrated semiconservative replication in eukaryotes using the root tips of the broad bean as the source of dividing cells

Essentail Point 10.2 II

The discovery of the polA1 mutant strain of E. coil, capable of DNA replication despite its lack of polymerase I activity, cast doubt on the enzyme's hypothesized in vivo replication function. Polymerase III has been identified as the enzyme responsible for DNA replication in vivo

Essential Point 17.1 II

Vectors replicate autonomously in host cells and facilitate the cloning and manipulation of newly created recombinant DNA molecules

Now Solve this 9.3 Would an experiment similar to that performed by Hershey and Chase work if the basic design were applied to the phenomenon of transformation? Explain why or why not

Yes, the results of the Hershey Chase experiment showed that 32P injected its genetic material into the infected bacteria. This is transformation

Now Try This 17.1 An ampicillin-resistant, tetracycline-resistant plasmid, pBR322, is cleaved with PstI, which cleaves within the ampicillin resistance gene. The cut plasmid is ligated with PstI-digested Drosophila DNA to prepare a genomic library, and the mixture is used to transform E. coli K12. a) Which antibiotic should be added to the medium to select cells that have incorporated a plasmid? b) If recombinant cells were plated on medium containing ampicillin or tetracycline and medium with both antibiotics, on which plates would you expect to see growth of bacteria containing plasmids with Drosophila DNA inserts? C) How can you explain the presence of colonies that are resistant to both antibiotics?

a) Tetracycline should be added to the medium to select cells that have incorporated the plasmid b) The recombinant bacteria would produce colonies in a medium containing tetracucline. c) If there is imcomplete cleavage by the PstI endonuclease would maintain the plasmid's ampicillin resistance. Also the cut sits could have ligated back together without the insert, maintaining ampicillin resistance.