What is the genetic code? (1 point)
a:The order of amino acids in proteins makes up the genetic code.
b:The order of amino acids in mRNA makes up the genetic code.
c:The order of nitrogen bases in tRNA makes up the genetic code.
d:The order of nitrogen bases in DNA makes up the genetic code.
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The genetic code is the order of nitrogenous bases in DNA as stated in answer D. Early in the 20th century, it was thought that DNA or protein contained the genetic code. A scientist named Frederick Griffith in 1928 did a famous experiment with mice and bacteria. He injected mice with a harmful bacteria that caused pneumonia and those died. He injected mice with heat-- killed harmful bacteria and they lived. When he injected a mixture of dead heat-- killed harmful bacteria mixed with a harmless strain, the mice died. The harmless strain was somehow changed into a harmful pathogenic strain and Griffith called the process transformation.
Later research by Oswald Avery removed the parts of the harmful strain of bacteria and tested each one to see which molecule was able to transform harmless bacteria into harmful ones. He tested the DNA, RNA and the protein components of the cells. Only DNA could transform the harmless cells into the harmful ones.
Another later experiment to prove DNA held the genetic code was performed by Alfred Hershey and Martha Chase. They worked with a virus known as the T2 phage, which consists of an external protein coat with a viral DNA molecule inside. It attacks a bacteria known as E. coli by attaching to the bacteria, injecting its DNA inside and taking over the bacteria's replication machinery causing the production of more viral DNA and more protein coats, eventually releasing many new T2 phages. By testing to see which part of the phage--the protein coat or the DNA carried genetic information into a bacteria, one could solve the question as to whether DNA or protein carried the genetic code.
By radioactively labeling the protein coat with radioactive sulfur, the proteins were marked. A different batch of phages was radioactively labeled with phosphorus which marked the DNA molecule. Both batches were allowed to infect different cultures of E. coli. The results obtained after centrifuging the batches was that in the culture of E. coli infected by phages labeled with radioactive sulfur, the sulfur ended up in the liquid, not in the bacterial cells. And in the batch labeled with radioactive phosphorus, the radioactivity was found in the pellet containing the bacteria cells indicating that DNA is the transforming substance that carries the genetic code.
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