Question

Name: ста втAссатсАс TUTTUTUU This assignment has two parts. Print this page and complete the labeling of this figure. I started it for you. Label everything. Turn in your NEXT class This is the essay portion of the assignment: Then answer the questions below. Use good organization skills, spelling, sentence structure and grammar. Save electronically as an attachment in the assignment dropbox as a doc. This is also due the day of your next lecture class. Essay What is the uppermost strand? What is the second strand? What is the process going from upper stand to second strand? The row of "guitars" represents what? What do each tan ball represent? What do the multi-color "piano keys" represent? Describe the various differences between second strand and the first (upper) strand? Describe the differences between the second strand and the "guitars"? Focusing on the sequence of the colored "keys, what are the differences between the first (upper) strand and the "guitars"? Identify the process going from the second strand to the "guitars

Answer 1

The uppermost strand is that of a DNA.The chemical nature of the monomeric deoxynucleotide units of DNA—deoxyadenylate, deoxyguanylate, deoxycytidylate, and thymidylate. These monomeric units of DNA are held in polymeric form by 3′,5′-phosphodiester bonds constituting a single strand, as depicted in Figure 34–1. The informational content of DNA (the genetic code) resides in the sequence in which these monomers—purine and pyrimidine deoxyribonucleotides—are ordered. The polymer as depicted possesses a polarity; one end has a 5′-hydroxyl or phosphate terminal while the other has a 3′-phosphate or hydroxyl terminal. The importance of this polarity will become evident. Since the genetic information resides in the order of the monomeric units within the polymers, there must exist a mechanism of reproducing or replicating this specific information with a high degree of fidelity. That requirement, together with x-ray diffraction data from the DNA molecule and the observation of Chargaff that in DNA molecules the concentration of deoxyadenosine (A) nucleotides equals that of thymidine (T) nucleotides (A = T), while the concentration of deoxyguanosine (G) nucleotides equals that of deoxycytidine (C) nucleotides (G = C), led Watson, Crick, and Wilkins to propose in the early 1950s a model of a double-stranded DNA molecule.

The second strand is that of a RNA. The process of conversion of DNA to RNA is called transcription.T he strand that is transcribed or copied into an RNA molecule is referred to as the template strand of the DNA. The other DNA strand, the non-template strand, is frequently referred to as the coding strand of that gene. It is called this because, with the exception of T for U changes, it corresponds exactly to the sequence of the RNA primary transcript, which encodes the (protein) product of the gene. In the case of a doublestranded DNA molecule containing many genes, the template strand for each gene will not necessarily be the same strand of the DNA double helix . Thus, a given strand of a double-stranded DNA molecule will serve as the template strand for some genes and the coding strand of other genes.

The guitars signify a codon and the tan balls signify the amino acid coded by a codon.

The letters A, G, T, and C correspond to the nucleotides found in DNA. Within the protein coding genes these nucleotides are organized into three-letter code words called codons, and the collection of these codons makes up the genetic code.

DNA and RNA synthesis do differ in several important ways, including the following: (1) ribonucleotides are used in RNA synthesis rather than deoxyribonucleotides; (2) U replaces T as the complementary base for A in RNA; (3) a primer is not involved in RNA synthesis as RNA polymerases have the ability to initiate synthesis de novo; (4) only portions of the genome are vigorously transcribed or copied into RNA, whereas the entire genome must be copied, once and only once during DNA replication; and (5) there is no highly active, efficient proofreading function during RNA transcription. T he process of synthesizing RNA from a DNA template has been characterized best in prokaryotes. Although in mammalian cells the regulation of RNA synthesis and the processing of the RNA transcripts are different from those in prokaryotes, the process of RNA synthesis per se is quite similar in these two classes of organisms. Therefore, the description of RNA synthesis in prokaryotes, where it is best understood, is applicable to eukaryotes even though the enzymes involved and the regulatory signals, though related, are different.

T hree of the 64 possible codons do not code for specific amino acids; these have been termed nonsense codons. These nonsense codons are utilized in the cell as termination signals; they specify where the polymerization of amino acids into a protein molecule is to stop. The remaining 61 codons code for 20 amino acids. Thus, there must be “degeneracy” in the genetic code—ie, multiple codons must decode the same amino acid. Some amino acids are encoded by several codons; eg, six different codons specify serine. Other amino acids, such as methionine and tryptophan, have a single codon. In general, the third nucleotide in a codon is less important than the first two in determining the specific amino acid to be incorporated, and this accounts for most of the degeneracy of the code. However, for any specific codon, only a single amino acid is indicated; with rare exceptions, the genetic code is unambiguous—ie, given a specific codon, only a single amino acid is indicated. The distinction between ambiguity and degeneracy is an important concept. T he unambiguous but degenerate code can be explained in molecular terms. The recognition of specific codons in the mRNA by the tRNA adapter molecules is dependent upon their anticodon region and specific base-pairing rules. Each tRNA molecule contains a specific sequence, complementary to a codon, which is termed its anticodon. For a given codon in the mRNA, only a single species of tRNA molecule possesses the proper anticodon. Since each tRNA molecule can be charged with only one specific amino acid, each codon therefore specifies only one amino acid. However, some tRNA molecules can utilize the anticodon to recognize more than one codon. With few exceptions, given a specific codon, only a specific amino acid will be incorporated—although, given a specific amino acid, more than one codon may be used. As discussed below, the reading of the genetic code during the process of protein synthesis does not involve any overlap of codons. Thus, the genetic code is nonoverlapping. Furthermore, once the reading is commenced at a specific codon, there is no punctuation between codons, and the message is read in a continuing sequence of nucleotide triplets until a translation stop codon is reached.