Answer:
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.
Answer:organs
Explanation:the body of multicellular organisms are organised into levels of organization.these levels increases in complexity.
The macromolecules makes up the organelles . organelles in turn makes up the cell.A group of similar cells at a certain location makes up an organ.for example the heart consists of a number of cells.
A group of organs which work together to achieve a specific function in the body , makes up the organs system.
For example the circulatory system of a while is made up of different connected organs - heart, blood vessels,to perform the function of transporting blood around it's body.this makes it an organ system.
Our central nervous system is made up of two tissues: the gray matter and the white matter. The gray matter is composed of the dendrites and the axon terminals where synapses are. These synapses are the links between neurons that transmits electrochemical signals. The white matter, on the other hand, is composed of axons that connect all the gray matter together. Therefore, the answer is: <span>white matter is primarily in the CNS in the presence of myelinated axons</span>
Answer:
Yes.
Explanation:
In the tropical Pacific, like the western coast of central and south America, the surface of the sea is cooler than normal and that results in reduced rainfall, drought and increased fires. This definitely brings about a negative effect on wildlife, as there is less water and food available.
However, in South East Asia, a higher than normal rainfall is commonly experienced, which is good for agriculture.
Answer:
An extraneous variable is eliminated, for example, if background noise that might reduce the audibility of speech is removed as Unknown extraneous variables can be controlled by randomization.
