Concept explainers
Interpretation:
The case of a protein that does not include methionine as its first amino acid has to be accounted.
Concept Introduction:
RNA synthesis: The process of RNA synthesis is Transcription. A small section of DNA unwinds, only one of the two strands act as template and the other strand as informational strand. The complementary bases are attached one by one by the action of RNA polymerase at template strand on moving down. The newly generated RNA is the exact copy of the informational strand, with the exception that a U replaces each T in the template DNA. The RNA synthesised carries genetic information and directs protein synthesis.
Codon: A sequence of three ribonucleotides in the mRNA chain that codes for a specific amino acid; also a three-
Genetic code: The sequence of nucleotides, coded in triplets (codons) in mRNA that determines the sequence of amino acids in protein synthesis.
Illustrated relationships are:
DNA informational strand: 5’ ATG CCA GTA GGC CAC TTG TCA 3’
DNA Template strand: 3’ TAC GGT CAT CCG GTG AAC AGT 5’
mRNA: 5’ AUG CCA GUA GGC CAC UUG UCA 3’
protein: Met Pro Val Gly His Leu Ser
Notice: 5’ end of the mRNA strand codes for the N-terminal amino acid, whereas the 3’ end of the mRNA strand codes for the C-terminal amino acid. Proteins are always written N-terminal to C-terminal, reading left to right.
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FUND.OF GEN CHEM CHAP 1-13 W/ACCESS
- Several experiments were conducted to obtain information about how the eukaryotic ribosome recognizes the AUG start codon. In one experiment, the gene that encodes methionine initiator tRNA (tRNAiMet) was located and changed; specifically, the nucleotides that specify the anticodon on tRNAiMet were mutated so that the anticodon in the tRNA was 5′ –CCA–3′ instead of 5′ CAU–3′. When this mutated gene was placed in a eukaryotic cell, protein synthesis took place, but the proteins produced were abnormal. Some of these proteins contained extra aminoacids, and others contained fewer amino acids than normal. a. What do these results indicate about how the ribosome recognizes the starting point for translation in eukaryotic cells? Explain your reasoning. b. If the same experiment had been conducted on bacterial cells, what results would you expect? c. Explain why some of the proteins produced contained extra amino acids while others contained fewer amino acids than normal.arrow_forwardAccording to wobble rules, what codons should be recognized by the following anticodons? What amino acid residues do these correspond to?(a) 5′ ¬ICC ¬ 3′ (b) 5′ ¬GCU ¬3′arrow_forwardThe following pattern has been observed in the genetic code. For many codons, the first base specifies a biosynthetic precursor: U = pyruvate, C = α-ketoglutarate, A = oxaloacetate, G = any of a number of simple precursors. The second base of the codon tends to be associated with water solubility: water-soluble amino acids have a G, A, or C as the middle position, whereas five of seven of the most hydrophobic amino acids have U as the middle base. The third base in a codon is often information free; that is, many of the codons for the same amino acid differ only with the third base. Review amino acid biosynthesis and determine which amino acids obey these rules. What are the exceptions?arrow_forward
- How many cases are there in which it would be possible to identify the first two nucleotides of a codon if the amino acid specified by it is known?arrow_forwardThe amino acid glycine is encoded by four codons: GGA, GGC, GGG, and GGU. Which of the following statements correctly explains this fact? The glycine anticodon contains the sequence CC, but the 5' base of the anticodon can pair nonspecifically with the 3' base of the codon. The glycine anticodon contains the sequence CC, but the 3' base of the anticodon can pair nonspecifically with the 5' base of the codon. Glycine tRNA has four anticodons, and the appropriate anticodon specifically pairs with the correct codon. There are four tRNAs for glycine, each of which has an anticodon that specifically pairs with the correct codon. all of the abovearrow_forwardA gene contains 141 codons. How many nucleotides are present in the gene’s coding sequence? How many amino acids are expected to be present in the polypeptide encoded by this gene?arrow_forward
- Several experiments were conducted to obtain information about how the eukaryotic ribosome recognizes the AUG start codon. In one experiment, the gene that encodes methionine initiator tRNA (tRNAiMet) was located and changed; specifically, the nucleotides that specify the anticodon on tRNAiMet were mutated so that the anticodon in the tRNA was 5′ –CCA–3′ instead of 5′ –CAU–3′. When this mutated gene was placed in a eukaryotic cell, protein synthesis took place, but the proteins produced were abnormal. Some of these proteins contained extra amino acids, and others contained fewer amino acids than normal. Q. What do these results indicate about how the ribosome recognizes the starting point for translation in eukaryotic cells? Explain your reasoning.arrow_forwardSeveral experiments were conducted to obtain information about how the eukaryotic ribosome recognizes the AUG start codon. In one experiment, the gene that encodes methionine initiator tRNA (tRNAiMet) was located and changed; specifically, the nucleotides that specify the anticodon on tRNAiMet were mutated so that the anticodon in the tRNA was 5′ –CCA–3′ instead of 5′ –CAU–3′. When this mutated gene was placed in a eukaryotic cell, protein synthesis took place, but the proteins produced were abnormal. Some of these proteins contained extra amino acids, and others contained fewer amino acids than normal. Q. If the same experiment had been conducted on bacterial cells, what results would you expect?arrow_forwardSeveral experiments were conducted to obtain information about how the eukaryotic ribosome recognizes the AUG start codon. In one experiment, the gene that encodes methionine initiator tRNA (tRNAiMet) was located and changed; specifically, the nucleotides that specify the anticodon on tRNAi Met were mutated so that the anticodon in the tRNA was 5′ –CCA–3′ instead of 5′ –CAU–3′. When this mutated gene was placed in a eukaryotic cell, protein synthesis took place, but the proteins produced were abnormal. Some of these proteins contained extra amino acids, and others contained fewer amino acids than normal. a. What do these results indicate about how the ribosome recognizes the starting point for translation in eukaryotic cells? Explain your reasoning. b. If the same experiment had been conducted on bacterial cells, what results would you expect? c. Explain why some of the proteins produced contained extra amino acids while others contained fewer amino acids than normalarrow_forward
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