"line of best fit" for a scatterplot must pass through at least ____

Bacteriophages (phages) are viruses that infect only bacteria and do not infect mammalian or plant cells. Phages are ubiquitous in the environment. Phages or bacteriophages were chosen as a model system for their simplicity, as they only contained protein-coated nucleic acid. Alfred D. Hershey and Martha Chase (who were part of the bacteriophage group) in 1952 studying the infection of the bacterium Escherichia coli by the T2 phage show that the information definitely resides in the DNA. They used phage with either [32P] -labeled DNA or [35S] -labeled proteins to infect the bacteria. Immediately afterwards, they centrifuged the sample so that the infected bacteria remain in the pellet and the virus capsids (proteins) remain in the supernatant. [35S] is found in the supernatant, whereas [32P] is found in bacteria. After one cycle of infection, it was observed that when phage labeled in the [35S] proteins were used, only 1% of the radioactivity was incorporated into the progeny. But when phages were [32P] labeled, more than 30% of the radioactivity was in the progeny. They showed directly that what is transmitted from one progeny to another is the DNA and not the proteins, despite having first "diluted" in a bacterium.

Explanation:

Bacteriophages are viruses that infect bacteria in a specific way. Bacteriophages, like other known viruses, are found in an intermediate zone between living organisms and inert matter. Bacteriophages bind to the host pathogenic bacterium, introduce their genetic material, replicate inside it and destroy it. Hersey, along with his assistant Martha Chase, used phages because they knew that T2 phages were made up of 50% proteins and 50% nucleic acids and that phages entered bacteria and reproduced. As the progeny carried the same infection traits, the genetic material of this had to be transmitted to the offspring, but the mechanism was unknown. These scientists carried out an experimental work with the T2 virus, a bacteriophage that infects the bacterium Escherichia coli, which it reproduces by attaching itself to the outer wall of the bacterium, injecting its DNA into it where it replicates and directs the synthesis of the phage's own proteins. Phage DNA is encapsulated within proteins and produces phages, which lyse or disrupt the cell and release phage from progeny. They infected a culture of bacteria with radioactively labeled phages: the protein coat with sulfur (35S) and its DNA with phosphorus (32P). After infection, they separated the phages from the bacteria by violent shaking using a mixer (hence the name of the experiment). By centrifugation the much smaller phages remained in the supernatant and the much larger bacteria in the pellet. 85% of the radioactivity corresponding to DNA appeared in the pellet and 82% of the protein in the supernatant. This result supported the idea that DNA was the only component of the bacteriophage that penetrated the interior of the bacteria and, having the ability to form new phages, constituted the genetic material.

5 0

3 years ago

Match the scientist(s) with their contribution to what we now know about DNA.

Lerok [7]

Hi,

Here are the answers:

1) Rosalind Franklin and Maurice Wilkens

Found DNA to be a helix structure because of their x-ray crystallography

During 1953, Rosalind Franklin and Maurice Wilkens attempted to explore the structure of DNA by firing the x-rays on the fibres of DNA. X-rays were scattered when they hit the DNA and later detected on the photographic film. The image on photographic film indicated that DNA had a helical structure. This served as a basis for further analysis of DNA structure by coming scientists, most importantly Watson and Crick.

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2) Alfred Hershey and Martha Chase:

Conclusively proved DNA is the hereditary molecule with their work with bacteriophages.

Harshey and Chase, did experimentation on a bacteriophage called T2. During their experiment, they infected some bacteria E-coli with T2. They used radioactively labelled S and P atoms in the protein coat and DNA of virus respectively. When the virus infected bacteriophage, they found that the radioactively labelled P atoms were found in bacteriophage but S were not found. Now, as we know that S- Sulphur atoms become part of protein coat of virus and when virus infects bacteria, protein remains outside. Only DNA containing P-Phosphorus is injected in bacteria. They, proved that hereditary molecule was DNA and not proteins. Their experimentation was a great breakthrough in the field of Biology and it paved the paths for better understanding of DNA by coming generation of scientists.

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3) Avery, McLoed and McCarty:

Determined Griffith's transforming factor was DNA

Avery, McLoed and McCarty proceeded the experimentation of a scientist Griffith. Griffith used two strains of bacteria Steptococcus pneumonia for his experimentation i.e S strain and R strain. S strain bacteria had capsule of polysaccharide around them and they produced smooth colonies while R strain did not have and produce rough colonies. Griffith killed S strain bacteria and injected in mice, but mice stayed alive. This depicted that polysaccharide coat was not responsible for the death of mice.

He then injected the mice with live S strains along with some dead R strains. The mice died of pneumonia. So Griffith thought that something was transferred from dead R strains into the S strains due to which they became infectious.

In 1944, Avery, McLoed and McCarty, continued his experimentation and proved that the molecule that was transferred from R strain to S stain was DNA and DNA is basically the transforming factor.

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4) James Watson and Frances Crick:

Determined DNA to be double helix structure

In 1953, using the work of Rosalind and Franklin, two scientists James Watson and Frances Crick got successful in creating a perfect three dimensional structure of a DNA molecule. They described their model as double helix that is composed of backbones of sugar and phosphate molecules that are held together through bonding between nitrogenous bases. They also proposed that there exists hydrogen bonding between nitrogenous bases, purines and pyrimidines.

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5) Erwin Chargaff:

Determined base pair ruling and that percentages of bases is species specific.

Erwin Chargaff studied the DNA of different living organisms and gave out a rule called Chargaff's rule. His rule also contributed and helped in the understanding and preparation of DNA structure by Watson and Crick. According to his rule, In the DNA of any cell at any time, the amount of guanine units is equal to the amount of cytosine units, and the amount of adenine units is equal to the amount of thymine units. This gave an important clue about the complementary bonding of bases i.e Adenine always pairs with Thymine and Guanine always pairs with Cytosine.

Hope it helps! :)

8 0

3 years ago

7. Phytochrome prevents seeds of some plants from germinating when they are in deep shade by the: absorption of far-red waveleng

SIZIF [17.4K]

<h2>Function of Phytochrome </h2>

Explanation:

The color of light that they absorb maximally by the two types such as Pfr is a blue-green structure that ingests far-red light (730 nm) and Pr is a blue structure that retains red light (660 nm)
Pfr assimilates far-red light, it is changed over to the Pr structure
Pfr can spontaneously revert to the Pr form structure in obscurity dark over time = dark reversion Pfr is additionally helpless to proteinases
Pfr contains some red light, so in red light 15% Pr and there is a parity of 85% Pfr.
The phytochrome (Pr) is changed over to the organically dynamic structure red light with the Pfr under illumination
Darkness and Far -red light convert the particle back to the inactive form.

4 0

4 years ago

"line of best fit" for a scatterplot must pass through at least _____ of the data points in the data set.