b. Glycolipids form part of the structural component of the cell c. Carbohydrates form part of the structural framework of DNA and a. Glycoprotein function in a variety of l-molecule 1. Which of the recognition process membrane RNA molecules d. All of the above 2. Carbohydrates have a general formula of what? a. (CH2O) n b. (CeH22011) n c. (CSH22O6) n d. (CsHsO6) n 3. Which among the following is the systematic name for maltose? a. B-D-glucopyrnosyl-(1→4) -D-glucopyranose b. a-D-glucopyrnosyl-(1→4) -D-glucopyranose c. a-D-glucopyrnosyl-(1→6) -D-glucopyranose d. B-D-glucopyrnosyl-(1→4) -D-glucopyranose 4. Sugars that differ in configuration of one carbon only is called a. Anomer b. Diastereomer c. Epimer d. Enantiomer 5. Immunoglobulins are used by our immune system to fight off infectious a pathogenic agents. These complex molecules are glycoconjugates which are a. Glycobiose b. Proteoglycans c. Glycoprotein d. Glycolipid S. All of the following are reducing sugars except a. glucose b. sucrose C. maltose d. lactose 7. Carbohydrates differ from nucleic acids and proteins in that carbohydrates a. have the capacity to form polymeric substances TAR ARCYHO B. The functionality of carbohydrate is increased through b. have a branched monomer c. have cyclic monomeric units d. have both linear and branching polymer a. formation of sugar acids b. formation of amino sugars C. formation of glycoconjugates d. formation of ester phosphates AMI Asparagine is linked through carbohydrate in the formation of glycoproteim a. a-D glycosidic linkage b. N-linkage c. B-L glycosidic linkage d. O-linkage

Figure 15.16 Many antibiotics inhibit bacterial protein synthesis. For example, tetracycline blocks the A site on the bacterial ribosome, and chloramphenicol blocks peptidyl transfer. What specific effect would you expect each of these antibiotics to have on protein synthesis? Tetracycline would directly affect: tRNA binding to the ribosome ribosome assembly growth of the protein chain Chloramphenicol would directly affect tRNA binding to the ribosome ribosome assembly growth of the protein chain

Antibiotics and Protein Synthesis Antibiotics are molecules produced by microorganisms as defense mechanisms. The most effective antibiotics work by interfering with essential biochemical or reproductive processes. Many antibiotics block or disrupt one or more stages in protein synthesis. Some of these are mentioned here. Tetracyclines are a family of chemically related compounds used to treat several types of bacterial infections. Tetracyclines interfere with the initiation of translation. The tetracycline molecule attaches to the small ribosomal subunit and prevents binding of the tRNA anticodon during initiation. Both eukaryotic and prokaryotic ribosomes are sensitive to the action of tetracycline, but this antibiotic cannot pass through the plasma membrane of eukaryotic cells. Because tetracycline can enter bacterial cells to inhibit protein synthesis, it will stop bacterial growth, helping the immune system fight the infection. Streptomycin is used in hospitals to treat serious bacterial infections. It binds to the small ribosomal subunit but does not prevent initiation or elongation; however, it does affect the efficiency of protein synthesis. Binding of streptomycin changes the way mRNA codons interact with the tRNA. As a result, incorrect amino acids are incorporated into the growing polypeptide chain, producing nonfunctional proteins. In addition, streptomycin causes the ribosome to randomly fall off the mRNA, preventing the synthesis of complete proteins. Puromycin is not used clinically but has played an important role in studying the mechanism of protein synthesis in the research laboratory. The puromycin molecule is the same size and shape as a tRNA/amino acid complex. When puromycin enters the ribosome, it can be incorporated into a growing polypeptide chain, stopping further synthesis because no peptide bond can be formed between puromycin and an amino acid, causing the shortened polypeptide to fall off the ribosome. Chloramphenicol was one of the first broadspectrum antibiotics introduced. Eukaryotic cells are resistant to its actions, and it was widely used to treat bacterial infections. However, its use is limited to external applications and serious infections. Chloramphenicol destroys cells in the bone marrow, the source of all blood cells. In bacteria, this antibiotic binds to the large ribosomal subunit and inhibits the formation of peptide bonds. Another antibiotic, erythromycin, also binds to the large ribosomal subunit and inhibits the movement of ribosomes along the mRNA. Almost every step of protein synthesis can be inhibited by one antibiotic or another. Work on designing new synthetic antibiotics to fight infections is based on our knowledge of how the nucleotide sequence of mRNA is converted into the amino acid sequence of a protein. Questions Why is targeting protein synthesis an effective strategy for preventing infection?

Exploring the Structure of the 30S Ribosomal Subunit Go to www.pdh.org and bring up PDB file 1GIX, which shows the 30S ribosomal subunit, the three tRNAs, and mRNA. In the box on the right titled ‘Biological Assembly.� click “More Images.� and then scroll down to look at the Interactive Vic By moving your cursor over the image, you can rotate it to view it from any perspective. a. How are the ribosomal proteins represented in the image? b. How is the 16S rRNA portrayed? c. Rotate the image to see how the tRNAs stick out from the structure. Which end of the tRNA is sticking out? d. Where will these ends of the tRNAs lie when the 50S subunit binds to this complex?