Why did Hershey and Chase use radioactively labelled phosphorous and sulphur only? Would they have got the same result if they use radiolabelled carobon and nitrogen?
Why did Hershey and Chase use radioactively labelled phosphorous and sulphur only? Would they have got the same result if they use radiolabelled carobon and nitrogen?
Text Solution
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(i) Alfred Hershey and Martha Chase (1952) conducted experiments on bacteriophages that infect bacteria.
(ii) Hershey and Chase wanted to observe whether it was DNA or protein that entered the bacteria.
(iii) All nucleic acids contain phosphorus and contain sulphur (in the amino acid cysteine and methionine)
(iv) Hershey and Chase used radioactive isotopes of Sulphur (`""^(35)S)` and phosphorus (`""^(32)P`) to keep separate track of the viral protein and nucleic acids during the infection process.
(v) The phages were allowed to infect bacteria in culture medium which contained the radioactive isotopes `""^(35)S` or `""^(32)P`.
(vi) The bacteriophage that grew in the presence of `""^(35)S` had labelled proteins and bacteriophages grown in the presence of `""^(32)P` had labelled DNA.
(vii) The differential labelling thus enabled them to identify DNA and proteins of the phage.
(viii) Hershey and Chase mixed the labelled phages with unlabelled E.coli and allowed bacteriophages to attack and inject their genetic material.
(ix) It was observed that only `""^(32)P` was found associated with bacterial cells and `""^(35)S` was in the surrounding medium and not in the bacterial cells. When phage progeny was studied for radioactivity, it was found that it carried only `""^(32)P` and not `""^(35)S`.
(x) Hershey and Chase thus conclusively proved that it was DNA, not protein, which carries the hereditary information from virus to bacteria.
(xi) If they had used radioactive labelled carbon and nitrogen they would have not got the same result because carbon and nitrogen are found in DNA and protein.
(xii) If they had used radioactive labelled carbon and nitrogen these labelled molecules would have been found in DNA and proteins and they would never be able to prove whether DNA or protein of a virus causes the heredity information.
(ii) Hershey and Chase wanted to observe whether it was DNA or protein that entered the bacteria.
(iii) All nucleic acids contain phosphorus and contain sulphur (in the amino acid cysteine and methionine)
(iv) Hershey and Chase used radioactive isotopes of Sulphur (`""^(35)S)` and phosphorus (`""^(32)P`) to keep separate track of the viral protein and nucleic acids during the infection process.
(v) The phages were allowed to infect bacteria in culture medium which contained the radioactive isotopes `""^(35)S` or `""^(32)P`.
(vi) The bacteriophage that grew in the presence of `""^(35)S` had labelled proteins and bacteriophages grown in the presence of `""^(32)P` had labelled DNA.
(vii) The differential labelling thus enabled them to identify DNA and proteins of the phage.
(viii) Hershey and Chase mixed the labelled phages with unlabelled E.coli and allowed bacteriophages to attack and inject their genetic material.
(ix) It was observed that only `""^(32)P` was found associated with bacterial cells and `""^(35)S` was in the surrounding medium and not in the bacterial cells. When phage progeny was studied for radioactivity, it was found that it carried only `""^(32)P` and not `""^(35)S`.
(x) Hershey and Chase thus conclusively proved that it was DNA, not protein, which carries the hereditary information from virus to bacteria.
(xi) If they had used radioactive labelled carbon and nitrogen they would have not got the same result because carbon and nitrogen are found in DNA and protein.
(xii) If they had used radioactive labelled carbon and nitrogen these labelled molecules would have been found in DNA and proteins and they would never be able to prove whether DNA or protein of a virus causes the heredity information.
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Take a small stone. Hold it in your hand. We know that the force gravity due to the earth acts on each and every object. When we were holding the stone in our hand, the stone was experiencing this force, but it was balanced by a force that we were applying onn it in the opposite direction. As a result, the stone remained at rest. Once we release the stone from our hands the only force that acts onit is the gravitational force of the earth and the stone falls down under its influence. Whenever an object moves under the influence of the force of gravity alone, it is said to be falling freely. Thus the released stone is in a free fall. In free fall, the initial velocity of the object is zero and goes on increasing due to acceleration due to gravity of the earth. During free fall, the frictional force due to air opposes the motion of the object anda buoyant force also acts on the object. Thus, true free fall is posible only in vacuum. For a freely falling object, the velocity on reachign the earth and the time taken for it can be calculated by using Newton's eqwuations of motion. For free fall the initial velocity u=0 and the acceleration a=g . Thus, we can write the equations as v="gt",s=1/2"gt"^(2),v^(2)=2gs For calculating the motion of an object thrown upwards, acceleration is negative, i.e. in a direction opposite ot the velocity and is taken to be -g. The magnitude of g is the same but the velocity of the object decreases due to -ve acceleration. The moon and the artificial satellites are moving only under the influence of the gravitational field of the earth. Thus they are in free fall. Write kinematic equations used in free fall?
Take a small stone. Hold it in your hand. We know that the force gravity due to the earth acts on each and every object. When we were holding the stone in our hand, the stone was experiencing this force, but it was balanced by a force that we were applying onn it in the opposite direction. As a result, the stone remained at rest. Once we release the stone from our hands the only force that acts onit is the gravitational force of the earth and the stone falls down under its influence. Whenever an object moves under the influence of the force of gravity alone, it is said to be falling freely. Thus the released stone is in a free fall. In free fall, the initial velocity of the object is zero and goes on increasing due toi acceleration due to gravity of the earth. During free fall, the frictional force due to air opposes the motion of the object anda buoyant force also acts on the object. Thus, true free fall is posible only in vacuum. For a freely falling object, the velocity on reachign the earth and the time taken for it can be calculated by using Newton's eqwuations of motion. For free fall the initial velocity u=0 and the acceleration a=g . Thus, we can write the equations as v="gt",s=1/2"gt"^(2),v^(2)=2gs For calculating the motion of an object thrown upwards, acceleration is negative, i.e. in a direction opposite ot the velocity and is taken to be -g. The magnitude of g is the same but the velocity of the object decreases due to -ve acceleration. The moon and the artificial satellites are moving only under the influence of the gravitational field of the earth. Thus they are in free fall. Which force acts on the stone when held in the hand?
Take a small stone. Hold it in your hand. We know that the force gravity due to the earth acts on each and every object. When we were holding the stone in our hand, the stone was experiencing this force, but it was balanced by a force that we were applying on it in the opposite direction. As a result, the stone remained at rest. Once we release the stone from our hands the only force that acts on it is the gravitational force of the earth and the stone falls down under its influence. Whenever an object moves under the influence of the force of gravity alone, it is said to be falling freely. Thus the released stone is in a free fall. In free fall, the initial velocity of the object is zero and goes on increasing due to acceleration due to gravity of the earth. During free fall, the frictional force due to air opposes the motion of the object and a buoyant force also acts on the object. Thus, true free fall is possible only in vacuum. For a freely falling object, the velocity on reaching the earth and the time taken for it can be calculated by using Newton's equations of motion. For free fall the initial velocity u=0 and the acceleration a=g . Thus, we can write the equations as v="gt",s=1/2"gt"^(2),v^(2)=2gs For calculating the motion of an object thrown upwards, acceleration is negative, i.e. in a direction opposite to the velocity and is taken to be -g. The magnitude of g is the same but the velocity of the object decreases due to -ve acceleration. The moon and the artificial satellites are moving only under the influence of the gravitational field of the earth. Thus they are in free fall. Which force acts on the stone in free fall after you release it?
Take a small stone. Hold it in your hand. We know that the force gravity due to the earth acts on each and every object. When we were holding the stone in our hand, the stone was experiencing this force, but it was balanced by a force that we were applying onn it in the opposite direction. As a result, the stone remained at rest. Once we release the stone from our hands the only force that acts onit is the gravitational force of the earth and the stone falls down under its influence. Whenever an object moves under the influence of the force of gravity alone, it is said to be falling freely. Thus the released stone is in a free fall. In free fall, the initial velocity of the object is zero and goes on increasing due to acceleration due to gravity of the earth. During free fall, the frictional force due to air opposes the motion of the object anda buoyant force also acts on the object. Thus, true free fall is posible only in vacuum. For a freely falling object, the velocity on reachign the earth and the time taken for it can be calculated by using Newton's eqwuations of motion. For free fall the initial velocity u=0 and the acceleration a=g . Thus, we can write the equations as v="gt",s=1/2"gt"^(2),v^(2)=2gs For calculating the motion of an object thrown upwards, acceleration is negative, i.e. in a direction opposite ot the velocity and is taken to be -g. The magnitude of g is the same but the velocity of the object decreases due to -ve acceleration. The moon and the artificial satellites are moving only under the influence of the gravitational field of the earth. Thus they are in free fall. What is free fall?
Take a small stone. Hold it in your hand. We know that the force gravity due to the earth acts on each and every object. When we were holding the stone in our hand, the stone was experiencing this force, but it was balanced by a force that we were applying on it in the opposite direction. As a result, the stone remained at rest. Once we release the stone from our hands the only force that acts on it is the gravitational force of the earth and the stone falls down under its influence. Whenever an object moves under the influence of the force of gravity alone, it is said to be falling freely. Thus the released stone is in a free fall. In free fall, the initial velocity of the object is zero and goes on increasing due to acceleration due to gravity of the earth. During free fall, the frictional force due to air opposes the motion of the object and buoyant force also acts on the object. Thus, true free fall is possible only in vacuum. For a freely falling object, the velocity on reaching the earth and the time taken for it can be calculated by using Newton's equations of motion. For free fall the initial velocity u=0 and the acceleration a=g . Thus, we can write the equations as v="gt",s=1/2"gt"^(2),v^(2)=2gs For calculating the motion of an object thrown upwards, acceleration is negative, i.e. in a direction opposite to the velocity and is taken to be -g. The magnitude of g is the same but the velocity of the object decreases due to -ve acceleration. The moon and the artificial satellites are moving only under the influence of the gravitational field of the earth. Thus they are in free fall. What is the initial velocity and what is the effect of gravitational acceleration on the object in free fall?
a. What happens if a bar magnet is cut into two pieces : (i) transverse to its length , (ii) along its length ? b. A magnetised needle in a uniform magnetic field experiences a torque but no net force . An iron nail near a bar magnet , however , experiences a force of attraction in addition to a torque . Why ? c. Must every magnetic configuration have a north pole and a south pole ? What about the field due to a toroid ? d. Two identical looking iron bars A and B are given , one of which is definitely known to be magnetised. (We do not know which one ) . How would one ascertain whether or not both are magnetised ? If only one is magnetised , how does one ascertain which one ? [Use nothing else but the bars A and B ]
(b) (i) Mention the uses of phosphorous ? (ii) Why bleaching action of sulphur dioxide is temporary?
We have log_(2)32 = 5 . Show that we get the same result by writing 32 = 2^(5) and then using power rules. Verify the answer.
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