ch11 - Chapter 11 11.1 Distinguish between DNA and RNA (a)...

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Chapter 11 11.1 Distinguish between DNA and RNA (a) chemically, (b) functionally, and (c) by location in the cell. ANS: (a) RNA contains the sugar ribose, which has an hydroxyl (OH) group on the 2- carbon; DNA contains the sugar 2-deoxyribose, with only hydrogens on the 2-carbon. RNA usually contains the base uracil at positions where thymine is present in DNA. However, some DNAs contain uracil, and some RNAs contain thymine. DNA exists most frequently as a double helix (double-stranded molecule); RNA exists more frequently as a single-stranded molecule. But, some DNAs are single-stranded and some RNAs are double-stranded. (b) The main function of DNA is to store genetic information and to transmit that information from cell to cell and from generation to generation. RNA stores and transmits genetic information in some viruses that contain no DNA. In cells with both DNA and RNA: (1) mRNA acts as an intermediary in protein synthesis, carrying the information from DNA in the chromosomes to the ribosomes (sites at which proteins are synthesized). (2) tRNAs carry amino acids to the ribosomes and function in codon recognition during the synthesis of polypeptides. (3) rRNA molecules are essential components of the ribosomes. (4) snRNAs are important components of spliceosomes, and (5) miRNAs play key roles in regulating gene expression (see Chapter 20). (c) DNA is located primarily in the chromosomes, which are found in the nucleus of eukaryotic cells; however, some DNA is also found in cytoplasmic organelles, such as mitochondria and chloroplasts. RNA is located throughout cells. FEEDBACK: 11.1 DIFFICULTY: medium 11.2. What bases in the mRNA transcript would represent the following DNA template sequence: 5 -TGCAGACA-3 ? ANS: 3 -ACGUCUGU-5 FEEDBACK: 11.1 DIFFICULTY: easy 11.3 What bases in the transcribed strand of DNA would give rise to the following mRNA base sequence: 5 -CUGAU-3 ?
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ANS: 3 —GACTA—5 FEEDBACK: 11.1 DIFFICULTY: easy 11.4. On the basis of what evidence was the messenger RNA hypothesis established? ANS: The genetic information of cells is stored in DNA, which is located predominantly in the chromosomes. The gene products (polypeptides) are synthesized primarily in the cytoplasm on ribosomes. Some intermediate must therefore carry the genetic information from the chromosomes to the ribosomes. RNA molecules (mRNAs) were shown to perform this function by means of RNA pulse-labeling and pulse chase experiments combined with autoradiography (see Figure 11.6). The enzyme RNA polymerase was subsequently shown to catalyze the synthesis of mRNA using chromosomal DNA as a template. Finally, the mRNA molecules synthesized by RNA polymerase were shown to faithfully direct the synthesis of specific polypeptides when used in in vitro protein synthesis systems. FEEDBACK:
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This note was uploaded on 11/26/2011 for the course BIOLOGY 2c03 taught by Professor Dej during the Spring '11 term at McMaster University.

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ch11 - Chapter 11 11.1 Distinguish between DNA and RNA (a)...

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