ch12 - Chapter 12 12.1 In a general way, describe the...

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Chapter 12 12.1 In a general way, describe the molecular organization of proteins and distinguish proteins from DNA, chemically and functionally. Why is the synthesis of proteins of particular interest to geneticists? ANS: Proteins are long chainlike molecules made up of amino acids linked together by peptide bonds. Proteins are composed of carbon, hydrogen, nitrogen, oxygen, and usually sulfur. They provide the enzymatic capacity and much of the structure of living organisms. DNA is composed of phosphate, the pentose sugar 2-deoxyribose, and four nitrogen-containing organic bases (adenine, cytosine, guanine, and thymine). DNA stores and transmits the genetic information in most living organisms. Protein synthesis is of particular interest to geneticists because proteins are the primary gene products—the key intermediates through which genes control the phenotypes of living organisms. FEEDBACK: 12.1 DIFFICULTY: easy 12.2. At what locations in the cell does protein synthesis occur? ANS: Protein synthesis occurs on ribosomes. In eukaryotes, most of the ribosomes are located in the cytoplasm and are attached to the extensive membranous network of endoplasmic reticulum. Some protein synthesis also occurs in cytoplasmic organelles such as chloroplasts and mitochondria. FEEDBACK: 12.1 DIFFICULTY: easy 12.3 Characterize ribosomes in general as to size, location, function, and macromolecular composition. ANS: Ribosomes are from 10 to 20 nm in diameter. They are located primarily in the cytoplasm of cells. In bacteria, they are largely free in the cytoplasm. In eukaryotes, many of the ribosomes are attached to the endoplasmic reticulum in the cytoplasm. Ribosomes are complex structures composed of over 50 different polypeptides and three to five different RNA molecules. In both prokaryotes and eukaryotes, ribosomes are the site of translation. FEEDBACK: 12.1
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DIFFICULTY: easy 12.4. (a) Where in the cells of higher organisms do ribosomes originate? (b) Where in the cells are ribosomes most active in protein synthesis? ANS: (a) The nucleus, specifically the nucleoli. (b) The cytoplasm. FEEDBACK: 12.1 DIFFICULTY: easy 12.5 Identify three different types of RNA that are involved in translation and list the characteristics and functions of each. ANS: Messenger RNA (mRNA) molecules carry genetic information from the chromosomes (where the information is stored) to the ribosomes in the cytoplasm (where the information is expressed during protein synthesis). The linear sequence of triplet codons in an mRNA molecule specifies the linear sequence of amino acids in the polypeptide(s) produced during translation of that mRNA. Transfer RNA (tRNA) molecules are small (about 80 nucleotides long) molecules that carry amino acids to the ribosomes and provide the codon-recognition specificity during translation. Ribosomal RNA (rRNA) molecules provide part of the structure and function of ribosomes; they represent an important part of the machinery required for the synthesis of polypeptides. 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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ch12 - Chapter 12 12.1 In a general way, describe the...

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