BIOL 1140 Chapters 15-16 Review Worksheet KEY Define transcription Transcription is the process of creating RNA from DNA. Describe how only one strand of DNA is used as the template in transcription. Only one of the strands (3’-5’ strand) serves as a template; the other strand is unused. Identify the three steps of transcription and briefly what is happening in each step. Initiation - in this step, the enzyme *RNA polymerase attaches to a region of the gene called a promoter, and transcription starts Elongation – In elongation, the enzyme RNA polymerase zips along the DNA strand adding complementary nucleotides to the DN template. The newly made RNA is fed out the back of the enzyme, and the two DNA strands re-anneal (re-zip). Remember that adenine, guanine, and cytosine are used in making RNA, but uracil is used in place of thymine. Termination - in this step, RNA polymerase reaches a sequence of nucleotides on the DNA template called a terminator. RNA polymerase then detaches from the newly synthesized RNA and the DNA. *before RNA polymerase binds, a series of proteins called transcription factors first bind to the promoter. Once they bind, they “recruit” RNA polymerase to the promoter. The binding of RNA polymerase starts the transcription process Which of the following statements regarding transcription is not true? A. The three stages of transcription are initiation, elongation and termination B. The key enzyme responsible for transcription is RNA polymerase C. Transcription is the conversion of information from DNA nucleotides into RNA nucleotides D. Transcription in eukaryotes is regulated (in part) by the binding of transcription factors to the promoter E. All are true statements What is the name of the enzyme used in transcription? Where does this enzyme bind? RNA polymerase…it binds to the gene’s promoter (though it doesn’t bind directly to the DNA strand) Indicate if the following statements about codons, amino acids and the genetic code are true or false: ____True______ A codon is a three nucleotide sequence that codes for a specific amino acid ____ True ______ In the genetic code, a codon will code for only one amino acid; that is there is specificity on the genetic code. ____False______ Some codons consist of only two nucleotides. 🡪 all are three nucleotides _____False_____ Some amino acids are not specified by any codons. 🡪 all amino acids have their own set of codons ____ True ______ Some codons (“stop codons”) do not code for any amino acid. ____ True ______ More than one codon can code for the same amino acid; that is, there is redundancy in the genetic code. Define translation. Translation is the process of creating proteins from RNA. Match the key players in translation with their function Answers B_____ tRNA A) The kind of RNA that makes up a ribosome. D______ mRNA B) Acts as the ‘interpreter’ in translation, by bringing in amino acids. C_______ DNA C) The genetic information in a cell. A_______ rRNA D) The kind of RNA that codes for amino acids. E_______ Ribosome E) Where translation takes place. Identify the three steps of translation and briefly describe what is happening in each step. Initiation – First an mRNA molecule binds to the small ribosomal subunit. A special initiator tRNA binds to a specific codon called the start codon (AUG = methionine). The initiator tRNA which carries the amino acid methionine, binds its anticodon (UAC) to the start codon . Second, a large ribosomal subunit binds to the small one, creating a function ribosome. The initiator tRNA binds to one of two tRNA binding sites on the ribosome. Elongation - In elongation amino acids are added one-by-one to the first amino acid. Each addition occurs in a three-step process: 1st: the anticodon of an incoming tRNA molecule, carrying its amino acid, pairs with the mRNA codon. 2nd: the incoming amino acid attaches by peptide bond to the amino acid already present – the formation of the bond is catalyzed by the ribosome. 3rd : The tRNA already present moves over to the next site (the codon and anticodon remain hydrogen bonded and the mRNA and tRNA move over as a unit), allowing another tRNA to move in. The second amino acid is then added to the growing polypeptide chain. The process is repeated - the first tRNA leaves the ribosome, the second tRNA moves over, allowing room for the next to move in…the process is repeated over and over again Termination - Elongation continues until a stop codon reaches the ribosome (recall that a stop codon does not code for any amino acid). The completed polypeptide is freed from the tRNA and the ribosome splits back into two separate subunits. Which of the following statements regarding translation is not true? A. Translation is the conversion of information from nucleic acids to proteins B. Translation takes place in the nucleus C. During translation, amino acids are linked to one another by peptide bonds D. Polypeptides made during translation must still be modified to become fully-functioning mature proteins E. All are true statements