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Bio Exam 3 Key - EXAM II I 1(6 pts Cellular respiration...

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EXAM III 1. (6 pts) Cellular respiration occurs in three phases. A) Describe the function of the process that occurs in the cytoplasm (not in the mitochondria) that is necessary to initiate cellular respiration. B) Describe the function of one of the stages that occurs in the mitochondria. For both A) and B), explain what the important starting and ending molecules are, and what the relative energy yield is. A) Glycolysis: Important to convert sugars to pyruvate, the molecule that is necessary to carry out further cellular respiration reactions. Thus it starts with sugar and ends with pyruvate and produces a small amount of ATP B If oxygen is present, pyruvate gets taken into the mitochondria (and gets converted to acetyl CoA) so the Krebs cycle reactions can occur. This is important to make the electron donor molecules for further respiration reactions. Start: pyruvate (though not technically correct), produces NADH, FADH 2 and a small amount of ATP. OR The electron transport chain (ETC) in the inner mitochondrial membrane where the majority of ATP is made. As molecules get reduced, H ions are released in the intermembrance space. Oxygen is necessary because it is at the bottom of the ETC and helps to pull electrons all the way down. When H ions diffuse back in to the interior of the mitochondrion, they go through ATP synthase, which speeds up the reaction of adding phosphate to ADP. Start: NADH, FADH 2 to produce an abundance of ATP . 2. (8 pts) a) What is the function of translation and where does it occur? Translation uses the information in mRNA to direct the production of a protein (polypeptide/string of amino acids). It occurs at ribosomes in the cell cytoplasm (1 pt for function, 1 pt for location) b) Briefly describe three sequential steps (they must be in the correct order) that occur during translation. Identify any molecules that are necessary to carry out these steps. (2 pts for each step; 1.5 for correct general idea (the sequences may be missing a step in between (e.g. my #1 to #4), 0.5 if sequence is incorrect.) 1. mRNA that has been edited moves through the cytoplasm to a ribosome 2. a tRNA with the anticodon to the start codon (group of 3 bases, specifically AUG) on the mRNA delivers a methionine to the ribosome (this defines the P site) 3. the large ribosomal subunit comes together with the small subunit, sandwiching the mRNA in between 4. based on the mRNA codons tRNAs with the appropriate anticodon deliver amino acids to the ribosome (at the A site) 5. covalent (peptide) bonds form between amino acids on the growing polypeptide chain that is on the tRNA 6. Ribosome is translocated. Empty tRNA is in E site. 7. Cycle continues as long as mRNA in A site has a non-stop codon. 8. when a stop codon is reached on the mRNA, a termination factor, instead of a tRNA binds (at the A site), causing the ribosomal subunits to come apart and the polypeptide to be released.
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