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Reading Notes Chapter 17 p. 326 One the basis of experiments with mutants of Bread mold, Beadle and Tatum proposed the one gene ____ _________________ hypothesis. Basic Principles of Transcription and Translation, p. 328 Transcription is the synthesis of ________ under the direction of _______. ______________________ _______ (mRNA) carries a genetic message from the ______ to the protein-synthesizing machinery of the cell. ______________________ is the actual synthesis of a polypeptide , which occurs under the direction of the mRNA. During this stage the cell must translate the sequence of an mRNA molecule into the amino acid sequence of a polypeptide. Copy Figure 17.3 summarizing the differences between transcription and translation in prokaryotic and eukaryotic cells. In Eukaryotes, the RNA is undergoes ________________ to yield the finished RNA. The initial RNA transcript is called the ______________ _____________________. p. 328 The Genetic Code The flow of genetic information from gene to protein is based a __________ code. In other words, codons of consisting of ____ bases specify one amino acid. DNA strand that is transcribed is called the _________________ strand. An mRNA is _____________________ rather than identical to the DNA template. mRNA base triplets are called ___________. Copy Figure 17.4 Bottom of p. 330: There is redundancy in the genetic code, but no _______________. Top of p. 331: In order to interpreted correctly the symbols must read in the correct ______________ ________________. Evolution of the Genetic Code p. 331 The genetic code is nearly ________________________, shared by organisms from the simplest bacteria to the most complex plants and animals. 17.2 Transcription is the DNA-directed synthesis of RNA, p. 331 mRNA is transcribed from the template strand of the gene by the enzyme ______ ________________________. (p. 332) RNA polymerases can only assemble a polynucleotide in the _____ to ______ direction. Since RNA polymerases are able to start a strand from scratch they do not need a primer. Specific _____________ of nucleotides along the DNA mark where transcription of a gene _________ and ______. The region of DNA where RNA polymerase attaches and initiates transcription is known as the _____________________. In bacteria, the sequence that signals the end of transcription is called the ____________________. Molecular biologists refer to the direction of transcription as “ ___________________” and the other direction as “upstream”. Synthesis of an RNA Transcript The three stages of transcription are ______________________,_______________________ and ____________________. Using Fig. 17.7, briefly describe each stage. RNA Polymerase Binding and Initiation of Transcription The promoter of the a gene includes within it the transcription ____________ __________ (the nucleotides where RNA synthesis actually begins) and typically extends several dozen nucleotides upstream from the start point. In addition to serving as a binding site for ________ __________________ and determining where transcription ______________, the promoter determines which of the two strands of the DNA helix is used as the _____________________. In prokaryotes the RNA _______________ itself specifically recognizes and binds to the promoter. In eukaryotes, by contrast a collection of specific collection of proteins called __________________________ ________________ mediate the binding of RNA polymerase and the initiation of transcription. Only after certain transcription factors are attached to the promoter does RNA polymerase II bind to it. The whole complex of transcription factors and RNA polymerase II bound to the promoter is called the ______________________ ______________________ complex. Copy Figure 17.8 Elongation of the RNA Strand p. 333 As RNA polymerase moves along the DNA, it continues to untwist the double helix, exposing 10 to 20 DNA bases at a time for pairing with RNA molecules. The enzyme adds nucleotides to the ______ end of the growing RNA molecule. Termination of Transcription, p. 333 The mechanism of termination differs between bacteria and eukaryotes. In bacteria, transcription procedes through a ______________________ sequence of DNA. The transcribed (RNA) terminator sequence functions as a termination signal, causing polymerase to _____________ from the DNA and ________________ the transcript. In eukaryotes, RNA polymerase II transcribes a sequence on the DNA called the _____________________________ signal sequence, which codes for a polyadenylation signal ( ___ ____ ____ _____ ____ ) in the pre mRNA. Then at a point about ____ to ____ nucleotides downstream from the AAUAAA signal, proteins associated with the RNA transcript cut it free from the polymerase, _________________ the pre-mRNA. 17.3 p. 334: Eukaryotic cells modify RNA after transcription Enzymes in the eukaryotic _______________ modify _____- ________ in specific ways before genetic messages are dispatched to the cytoplasm. RNA Processing Alteration of mRNA ends: Each end of a pre-mRNA molecule is modified in a particular way. The 5’ end, the end made first during transcription is immediately capped of with a _______________ form of a ____________ (G) nucleotide. The other end of the RNA molecule, the 3’ end is also modified before the message exits the nucleus.To the 3’ end an enzyme adds a _________ tail consisting of 50 to 250 _________________ nucleotides. The 5’ cap and poly-A tail seem to 3 important functions: 1) 2) 3) Split Genes and RNA splicing, p. 334 Eukaryotic genes have long stretches of noncoding segments called intervening sequences or ______________. The coding regions are called _____________, because they are expressed. Introns are removed by an assembly of small nuclear RNA (snps) and proteins called a ________________________. The spliceosome interacts with the splice sites at the ends of the intron. Copy Figure 17.10 Copy Figure 17.11 p. 336 Ribozymes – RNA molecules can function as ________________. The Functional and Evolutionary Importance of Introns, p. 336 One consequence of the presence of introns is that a ____________ gene can encode more than one kind of ________________________. Alternative RNA splicing – different segments of RNA are treated as ____________ Presence of introns in a gene may facilate the ____________________ of new and potentially useful by ____________ shuffling. Exon shuffling could lead to new proteins with novel combinations of functions. 17.4, p. 337 TRANSLATION IS THE RNA-DIRECTED SYNTHESIS OF A POLYPEPTIDE Molecular Components of Translation The function of transfer RNA (tRNA) is to ____________ ___________ __________ from the cytoplasm’s amino acid pool to a ribosome. Molecules of tRNA are not all identical. Differ in which amino acid is attached at one end and in the _____________ attached at the other end. The anticodon is a nucleotide _____________ which binds according to base pairing rules to the ____________________ ______________ on mRNA. Sketch figure 17.13 The Structure and Function of Transfer RNA, p.337 Sketch Fig. 17.14 – Label the amino-acid attachment site and the anticodon site Aminoacyl –tRNA Synthetases p. 338 The accurate translation of a genetic message requires two processes that involve molecular recognition. First a t-RNA that binds to an mRNA ______- specifying a particular ________ ______ must carry that amino acid and no other, to the ribosome. The correct matching up of t- RNA and amino acid is carried out by a family of enzymes called _______________________ - ______ ____________________> Ribosomes, p. 339 Ribosomes facilitate the specific coupling of tRNA _____________ with mRNA ___________. A ribosome if made up of two subunits: _______________ and ____________ Ribosomal subunits are constructed of ____________ and RNA called _________________________. Describe the Roles of the P, A and E sites P site: A site: E site: Draw figure 17.16- Anatomy of a ribosome Draw figure 17.17- Initiation of translation, p. 340 Draw figure 17.18- The elongation cycle of translation, p. 341 Draw figure 17.19- Termination translation p. 342 Polyribosome A polyribosome is From Polypeptide to Functional Protein Chemical modification of protein by attachment of sugar, lipids, phosphate groups or cleaving of amino acid groups or cleavage of the chain are all examples of ______________________________ modifications. Signal peptides target some Eukaryotic polypeptides to specific destinations in the cell. Polypeptides destined for the endomembrane system or for secretion are marked by a ____________ __________, which targets the protein to the endoplasmic reticulum(ER). The signal peptide, a sequence of about _____ amino acids at or near the ______________ ( ) end of the polypeptide is recognized as it emerges from the ribosome by a protein-RNA complex called a _____________________________ _____________________ (SRP). p. 344 Point mutations can affect protein structure and function Mutations are Point mutations are chemical changes in just ______ or a few base pairs in a single gene. Types of Point Mutations Substitutions A base-pair substitution is Nonsense mutations are Insertion and deletions are A frame shift mutation is