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< "clear" >
each mRNA molecule in the primary nucleocyte often has multiple functionally relevantprotein encoding information, arranged in the form of a multi-shun inverse, in the translation process can be synthesized several proteins at the same time, and in the true nuclei, Each mRNA usually comes with only one protein-coded information, in the form of a sing-shun anti-sub. mRNA carries genetic information from >DNA in the order ofnucleotides in its molecules, which determines the order ofamino acids in protein molecules as a direct template for protein biosynthetics. Different proteins have different mRNAs, and mRNA contains non-coding regions at both ends in addition to coding regions. Non-coding zones are necessary for template activity of mRNA, especially where 5' end non-coding zones are considered to bind to RNA in protein synthesis. See Figure 18-2.
Figure 18-2 (a) primary nuclear biomRNA) is a multi-shun antigen
(b)) EunucleotymRNA is a single-shun antigen
mRNA molecule in the direction of 5'→3', starting from AUG every three consecutive nucleotides to form a cryptone, mRNA four bases can form 64 cryptones. These passwords not only represent 20 amino acids, but also determine the start and end of the translation process. Each amino acid has at least one coder, up to six. From inferences about the nature of genetic codes to determining the meaning of individual cryptones, and then fully clarifying genetic codes, is one of the most outstanding achievements in science, scientists designed a very good genetics andbiochemistry" experiment, in 1966 compiled a genetic code dictionary. See table 18-1.
Table 18-1 amino acid password (code)
intermediate base (second base)
, located at the starting site of mRNA AUG is the starting signal of the amino acid synthesis peptide chain. The celebrics represent methionine, represented by mammals, and the primary nuclei, represented bymicroorganisms represent methyl methionine.
genetic code has the following characteristics:
(1) start code and termination code (starting code and termination code):
password sub-AUG is the starting password, representing synthetic peptides The location of the first amino acids of the chain, they are located at the end of mRNA5', and it is also a cryptoneth of methionine, so the primary and ebony organismspolypeptides chain synthesis of the first amino acids are methionine, of course, a few bacteria also use GUG as the starting code. The nucleus CUG is also occasionally used as the code for the starting methionine. The cryptics UAA, UAG, UGA are termination codes made up of peptide chains and do not represent any amino acids that exist individually or jointly at the end of mRNA3'. Therefore, the translation is carried out in the direction of the → 5' and 3' of the mRNA molecule.
(2) password without punctuation: there are no nucleotides between the two codes every other day, so starting from the starting code AUG, the three base generations have an amino acid, which constitutes a continuous reading box until the termination code. If a base is inserted or missing in the middle of the reading box, it will cause a change in the code, resulting in an error in the arrangement of aminos downstream of the mutation point.
(3) password degemeracy:
An amino acid has several sets of codes, or groups of cryptics represent a phenomenon called an amino acid phenomenon called The simplicity of the cocoon, this simplicity is mainly due to the third base of the cocoon swing phenomenon formed, that is to say, the specificity of the cocoon is mainly determined by the first two bases, even if the third base mutation can translate the correct amino acids, which is to ensure the stability of species has a certain significance. For example: GCU, GCC, GCA, GCG all represent alanine.
(4) password versatility:
A large number of facts show that the world of life from low to high, using a set of passwords, that is, genetic codes remain unchanged over a long period of evolution. So this cryptric table is biologically common. However, unexpectedly, the true nuclear mitochondrial code has many different from the universal password, for example, in human mitochondrials, UGA is not a termination code, but tryptophan code, AGA, AGG is not a coder of arginine, but a termination cryptone, plus the universal password UAA and UAG, mitochondrials in a total of four sets of termination code. There are two internal methionine codes, AUG and AUA, and there are four groups of starting methionine codes, or AON.
< p class " "tt1" > between the structure of the p-code substructur and the amino acid side chain analysis. (1) The polarity of the amino acid side chain is determined in most cases by the second base of the section. When the second base is niacin (Y), the amino acid side chain is non-polar, the second base is radon, and the amino acid side chain is polar. (2) When the first base is U or A, the second base is C, and the third base is not specific, the determined amino acid side chain is polar without electricity. (3) When the first base is not U and the second base is P, the amino acid side chain is charged. Under this premise, if a C or A, indicating positively charged amino acids, the first and second bases are G, A, this amino acid is negatively charged, but there are individual exceptions to the above relationship.The fact that an amino acid is encoded by multiple cophers makes one think: Is a group of cocoons of the same amino acid used the same frequency? Many experiments have confirmed that the same group of cophers is used differently in primary and higher-level nuclear organisms. High-frequency cryptors are found in proteins with high expressionsgenes such as the ucose protein gene, the RecA protein gene, and so on. Table 18-2. This frequency of use is associated with different tRNA content in a group of tRNAs in cells.
