Concept explainers
HOW DO WE KNOW?
In this chapter, we focused on the translation of mRNA into proteins as well as on protein structure and function. Along the way, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions:
(a) What experimentally derived information led to Holley's proposal of the two-dimensional cloverleaf model of tRNA?
(b) What experimental information verifies that certain codons in mRNA specify chain termination during translation?
(c) How do we know, based on studies of Neurospora nutritional mutations, that one gene specifies one enzyme?
(d) On what basis have we concluded that proteins are the end products of genetic expression?
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Essentials of Genetics (9th Edition) - Standalone book
- I are studying pancreatic islet cells and have isolated, cloned, and sequenced a novel protein that you postulate has 4 transmembrane segments. Explain why the sequence would lead to this hypothesis (what procedure would I have applied).arrow_forwardThe protein Xpot transports tRNAs out of the nucleus so that they can be aminoacylated in the cytosol. (a) What tRNA structural features is Xpot likely to recognize? (b) How does Xpot distinguish mature tRNAs from pre-tRNAs?arrow_forwardAs we focused on the genetic code and the transcription of genetic information stored in DNA into complementary RNA molecules. Along the way, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions: Question: How do we know that the initial transcript of a eukaryotic gene contains noncoding sequences that must be removed before accurate translation into proteins can occur?arrow_forward
- The genetic code was deciphered by experiments in which synthetic polyribonucleotides of known repeating sequences were used as mRNAs to direct protein synthesis in cell - free extracts . What type or types of polypeptides would you expect to be synthesized if poly (AAG) n (A) AAGAAGAAG ) used as the template for in vitro peptide synthesis ?arrow_forwardPosition on the small and large ribosomal subunits which the peptidyl-tRNA occupies prior to peptide bond formation Group of answer choices a)No answer text provided. b)A Site c)P Sitearrow_forwardExplain (in one or two lines) the function of the followings:(a) Promoter(b) tRNA(c) Exonsarrow_forward
- Sickle cell anemia is a widespread disease in many African countries and can be caused by a change in the amino acid sequence from glutamic acid to valine. A patient is diagnosed with the disease and a genetic fingerprint reveals the following DNA sequence for the gene: (a) (b) (c) (d) (e) Write down the mRNA sequence for the given DNA sense strand indicating the polarity. Derive the polypeptide from the mRNA molecule using the table of the genetic code (Table Q1 below) again indicating the polarity of the peptide chain. Indicate the position in the DNA molecule that could have caused the disease and write down all possible point mutations in the DNA sequence that could have caused it. [ The polypeptide chain is polymerized at the ribosomes using t-RNA molecules. Write down all possible t-RNA molecules with their anti-codons that are used to polymerize the amino acid VAL. Indicate the polarity. 3'-TAC TGA GCA AGA TTA CAT ACT-5' Explain what is meant by redundancy of the genetic code.…arrow_forwardWhich of the following statements regarding Anfinsen's denaturing experiments with ribonuclease A are valid? (i) Exposing the denatured protein to air oxidation and then dialysis to remove urea restored the protein to its original functionality. (ii) Removing urea by dialysis and then allowing air oxidation of the denatured protein restored the protein to its original functionality. (iii) Denaturing the protein with both urea and β-mercaptoethanol yielded an inactive protein. (iv) Protein folding is determined by its primary sequence.arrow_forwardWhat two reaction steps are required for the formation of an aminoacyl-tRNA?arrow_forward
- How does the cell ensure that a specific amino acid (say, valine) attaches itself only to the one tRNA molecule that is specific for valine? (A) Proteins called aminoacyl DNA synthetases are responsible for bringing together the proper pair. The enzymes match the amino acid and one of the correct DNA molecules carrying the right anticodon. (B) Lipids called aminoacyl tRNA synthetases are responsible for bringing together the proper pair. The lipid binds the amino acid and one of the correct tRNA molecules carrying the right codon. (C) Enzymes called aminoacyl tRNA synthetases are responsible for bringing together the proper pair. The enzymes match the amino acid and one of the correct tRNA molecules carrying the right anticodon. (D) Enzymes called peptidyl mRNA synthetases are responsible for bringing together the proper pair. The enzymes match the amino acid and one of the correct mRNA molecules carrying the right anticodon.arrow_forwardThe genetic code was solved partly by the use of in vitro systems to translate synthetic RNAs into peptides. In these systems, ribosomes, amino acids, and buffers that support translation are added and there is no control of where translation begins. AAA = Lys; AUA = Ile; AAU = Asn; UAA = stop. What peptides would NOT be produced in an in vitro system if the following oligonucleotide were added: AAAAAAAAAUAAAAAAAA Select one: a) Lys-Lys-Lys-Lys-Lys-Lys-Lys-Lys b) Lys-Lys-Ile-Lys-Lys c) Lys-Lys-Asn-Lys-Lysarrow_forwardDescribe what two reaction steps are required for the formation of an aminoacyl-tRNA?arrow_forward
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