TAILIEUCHUNG - Biochemistry, 4th Edition P100

Biochemistry, 4th Edition P100. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | How Is an Amino Acid Matched with Its Proper tRNA 953 3. The base sequence is read from a fixed starting point without punctuation. That is the mRNA sequences contain no commas signifying appropriate groupings of triplets. If the reading frame is displaced by one base it remains shifted throughout the subsequent message no commas are present to restore the correct frame. 4. The code is degenerate meaning that in most cases each amino acid can be coded by any of several triplets. Recall that a triplet code yields 64 codons for 20 amino acids. Most codons 61 of 64 code for some amino acid. Codons Specify Amino Acids The complete translation of the genetic code is presented in Table . Codons like other nucleotide sequences are read 5 3 . Codons represent triplets of bases in mRNA or replacing U with T triplets along the nontranscribed nontemplate strand of DNA. Several noteworthy features characterize the genetic code 1. All the codons have meaning. Of the 64 codons 61 specify particular amino acids. The remaining 3 UAA UAG and UGA specify no amino acid and thus they are nonsense codons. Nonsense codons serve as termination codons they are stop signals indicating that the end of the protein has been reached. 2. The genetic code is unambiguous. Each of the 61 sense codons encodes only one amino acid. 3. The genetic code is degenerate. With the exception of Met and Trp every amino acid is coded by more than one codon. Several Arg Leu and Ser are represented by six different codons. Codons coding for the same amino acid are called synonymous codons. 4. Codons representing the same amino acid or chemically similar amino acids tend to be similar in sequence. Often the third base in a codon is irrelevant so for example all four codons in the GGX family specify Gly and the UCX family specifies Ser Table . This feature is known as third-base degeneracy. Note also that codons with a pyrimidine as second base likely encode amino acids with hydrophobic side chains

• Sinh học
• Nền tảng của hóa sinh học
• trao đổi chất protein
• RNA trao đổi chất
• nguyên tắc của hóa sinh
• Axit amin
• công nghệ DNA