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12.3 Gene Expression: RNA and the Genetic Code
A DNA polymerase makes a mistake about once per 100,000 base pairs.
Many errors would accumulate over the course of several cell divisions as a result of this error rate.
The daughter strand it is making can be checked for accuracy.
It can reverse direction and remove several nucleotides from a daughter strand.
It changes direction again once it has removed the wrong nucleotide.
In the 1900s, there was evidence that metabolic disorders can be passed on.
George Beadle and Edward Tatum were working with red bread mold when they came up with the idea of the "one gene, one enzyme hypothesis."
In the remainder of this chapter, we will look at the flow of information from DNA, toRNA, and then onto an expressed protein.
In this section, we will see that the genetic code plays an important role in this process.
The ribonucleic acid in RNA is similar to DNA.
The base uracil is replaced by the sugar ribose and the bases adenine, cytosine, and guanine in RNA.
A double helix is not formed in the same way as a single helix.
RNA is similar to DNA in that it is a strand of nucleotides.
One of the bases is ribose, while the other is single-stranded.
There are three major classes ofRNA.
Page 217 is a part of the process of regulating the expression of genes.
In the genetic flow of information, two major steps are needed to convert the information stored in DNA into aProtein that supports body function.
A writing is a process in which a DNA template is used to make an RNA molecule.
One strand of DNA acts as a template for the synthesis of messenger RNA and the sequence of bases in it determines the sequence of a polypeptide.
The ribosome reads the transcript and converts it into a sequence of amino acids.
Like a translator, the cell changes a sequence into an acid sequence.
The flow of information between genes is known as the of molecular biology.
Now that we know the sequence of the genes in a gene is transcribed into an RNA molecule, it is necessary to identify the specific parts of the genes that code for a specific type of molecule.
The discovery was made in the 1960s.
Each coding unit needs to be made up of three nucleotides.
The reason is that there isn't enough variety in the 20 different amino acids.
The groundwork for cracking the genetic code was laid in an experiment performed in 1961.
They found that a cellularidase could be used to make a syntheticRNA, and then they found that the syntheticRNA could be translated into a test tube that contained the contents of a cell.
Their first syntheticRNA was composed of uracil, while theprotein that resulted was composed of phenylalanine.
The codon for phenylalanine was known as UUU.
It was possible to assign an acid to each of the mRNA codons using just three nucleotides at a time.
The first, second, and third base are represented in the codons in this chart.
The first base and second base intersect in this example.
U, C, A, or G can be the third base.
The bases CAU and CAC are codons for histidine and glutamine, respectively.
The genetic code seen in Figure 12.11 is a masterpiece of scientific discovery because it is a key that unlocks the very basis of biological life.
The term means that most amino acids have more than one codon.
The code helps protect against harmful changes.
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