hw 6 chapter 13 DNA structure

What did the structure of DNA's double helix suggest about DNA's properties?

DNA can be replicated by making complementary copies of each strand. DNA stores genetic information in the sequence of its bases. DNA can change. Errors in copying can result in changes in the DNA sequence that could be inherited by future generations. The structure of DNA suggested that the order of bases contains information. Because A is always paired with T and G with C, the order of bases on one strand determines the order on the other strand. Thus, if a DNA molecule were unwound, each strand could be copied into a complementary strand, producing an exact replica of the original molecule.

Gel Electrophoresis of DNA

An electrical current is generated across the gel, and DNA molecules migrate from the negative end toward the positive end. The shorter the DNA molecule, the farther it moves.

DNA is a self-replicating molecule. What accounts for this important property of DNA?

The nitrogenous bases of the double helix are paired in specific combinations: A with T and G with C. Because of the specificity of the pairing of the nitrogenous bases, each strand of the double helix specifies the matching sequence of bases on the other strand. During replication, when the strands separate, each strand serves as a template for the replication of other strand.

In the 1950s, when Watson and Crick were working on their model of DNA, which concepts were well accepted by the scientific community?

Chromosomes are made up of protein and nucleic acid. Genes are located on chromosomes. Chromosomes are found in the nucleus. When Watson and Crick began working on their model, scientists knew that genes were found on chromosomes in the nucleus and that chromosomes were composed of proteins and nucleic acid. Watson and Crick were two of the few to focus on the nucleic acid, DNA, instead of proteins.

In his work with pneumonia-causing bacteria and mice, Griffith found that __________.

some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic

In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules?

A + G = C + T

In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.

1' ... 5' The nitrogenous base is attached to the sugar's 1' carbon and the phosphate group is attached to the sugar's 5' carbon.

How many DNA molecules would there be after four rounds of PCR if the initial reaction mixture contained two molecules?

32 DNA molecules are produced if two molecules are doubled four times.

Hershey and Chase used _____ to radioactively label the T2 phage's proteins.

35 S Hershey and Chase used radioactive sulfur to label the phage's proteins.

Nucleic acids are assembled in the _____ direction.

5' to 3' New nucleotides are added to the 3' end of a growing polynucleotide.

In an analysis of the nucleotide composition of DNA, which of the following will be found?

A + C = G + T

What is the polymerase chain reaction (PCR)?

A method to amplify a fragment of DNA. PCR is an in vitro DNA synthesis reaction that produces many copies of a single DNA fragment.

The building blocks or monomers of nucleic acid molecules are called _____.

A nucleotide is a nucleic acid monomer consisting of a nitrogen base, a pentose sugar, and a phosphate group. Nucleotides joined together by covalent bonds called phosphodiester linkages form nucleic acid molecules.

Early, flawed DNA models proposed by Watson and Crick and by Linus Pauling correctly described which property of DNA?

DNA is composed of sugars, phosphates, and bases. The composition of DNA was well established by the 1950s. Models showed different arrangements of the components and sometimes introduced additional ones (such as magnesium), but all contained sugars, phosphates, and bases.

Which of these is a difference between a DNA and an RNA molecule?

DNA is double-stranded, whereas RNA is single-stranded.

The radioactive isotope 32P labels the T2 phage's _____.

DNA. The T2 phage consists of a protein coat and DNA. It is the DNA that contains P.

Who demonstrated that DNA is the genetic material of the T2 phage?

Hershey and Chase did a series of classic experiments demonstrating that DNA is the genetic material of the T2 phage.

In the early 1950s, many researchers were racing to describe the structure of DNA using different approaches.

Jim Watson and Francis Crick built theoretical models, incorporating current knowledge about chemical bonding and X-ray data. Different scientists took different approaches to understanding the structure of DNA, based upon their training and the tools available. In the end, the problem was solved using all these different approaches.

During which step in the PCR cycle are nucleotides used?

Nucleotides are used to synthesize the complementary strand to the DNA template during the extension step.

During which step in the PCR cycle do primers form bonds with a single-stranded template?

Primers form hydrogen bonds with the single-stranded DNA template during the annealing step.

In the Hershey and Chase experiment that helped confirm that DNA, not protein, was the hereditary material, what was the key finding?

Radioactively labeled phosphorus was present inside the infected bacteria. When the bacteria had been infected with T2 phage whose DNA was tagged with radioactive phosphorus, the pellet of mainly bacterial material contained most of the radioactivity, indicating that the labeled phage DNA had entered the cells.

Who conducted the X-ray diffraction studies that were key to the discovery of the structure of DNA?

Rosalind Franklin conducted these X-ray diffraction studies of DNA.

True or false? Comparison of the sequences of the same gene across species can give some insight into the existence of a common ancestor with that gene.

true

Erwin Chargaff observed that the proportions of adenine (A) and thymine (T) bases were always equal, as were the proportion of guanine (G) and cytosine (C). Chargaff's observation suggests which of the following statements?

The data suggest that A would always pair with T and G would always pair with C in a DNA molecule. Chargaff's observation was an important clue to the A-T and G-C pairings that Watson and Crick eventually proposed.

You are a member of the jury for a murder case. The prosecution has presented DNA evidence linking the defendant to the crime scene. The defense claims that DNA evidence using STR analysis with 13 markers is not sufficient to reliably distinguish between people. What do you think?

The prosecution is right. STR analysis with 13 markers gives a 1 in 10 billion or greater chance that two people will have the same pattern. This person was at the crime scene. Given the current population of the Earth, STR analysis with 13 markers should be sufficient to distinguish between any two people (excluding identical twins, of course) on the planet.

Griffith's experiments with S. pneumoniae were significant because they showed that traits could be transferred from one organism to another. What else did he find that was significant?

The transferred traits were heritable. The fact that offspring of transformed bacteria also showed the pathogenic trait meant that the transforming agent had to be involved with the genetic material.

What information can not be obtained from the sequence of a gene?

Whether the gene is methylated. Although the gene's sequence may reveal the presence of methylation targets like cytosine (C), it does not give information about whether such bases have been methylated.

True or false? The Taq enzyme is a type of DNA polymerase that allows researchers to separate the DNA strands during the annealing step of the PCR cycle without destroying the polymerase.

false Taq polymerase is derived from a species of bacteria living in hot springs, which makes it stable at the high temperature required for the denaturation step of PCR.

Gel electrophoresis separates DNA fragments on the basis of what characteristic?

length As the DNA fragments move through the gel, longer fragments are impeded more than shorter fragments, producing characteristic banded patterns in the gel.

What are the chemical components of a DNA molecule?

nitrogenous bases sugars phosphate groups DNA is composed of a sequence of subunits, each containing a phosphate, a deoxyribose sugar, and one of four nitrogenous bases: adenine (A), thymine (T), guanine (G), or cytosine (C).

Hershey & Chase grew phages with bacteria in a medium that contained 32P or 35S. Then they separated out the radioactive viruses and used them to infect a different batch of bacterial cells. After a period of time, Hershey and Chase used a centrifuge to separate the phage "ghosts" (the empty protein coats) from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage's genetic material.

radioactive DNA ... DNA Since the phage DNA entered the bacterial cells, it makes sense that DNA is the genetic material.

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.

thymine ... cytosine This is referred to as specific base pairing.

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.

thymine ... cytosine specific base pairing