Question

Wings of Eagles Ranch in the final condensation step that produces glutamine, mis replaced with a) OH, NH b) ADP, NH2 c) ATP, NH2 d) phosphate, NH2 e) H20, a covalent bond 18) In the cell, activated carrier molecules are used to: a) transfer chemical energy from catabolic reactions to anabolic reactions b) transfer chemical energy from anabolic reactions to catabolic reactions c) transport ions and other low molecular weight molecules across the cell membrane d) reduce the activation energy to promote a chemical reaction e) change +AG reactions into -AG reactions 19) Within a protein, which of the amino acid residues (shown below) is the most probable target for post translational covalent modification by phosphorylation? a) serine b) glycine c) phenylalanine d) methionine sorina (Ser, or S) glycine (Gly, or G) phenylalanine (Phe, or F) methionine (Met, or M) Ho -N-C-C- 1 CHE -N-C-0- HH -N-CC- H CH2 нҫн, CH, S-CH₃ 20) Consider the Central Dogma and the fact that ribosomal subunits (small and large) are assembled in the nucleolus of eukaryotic cells. In terms of protein trafficking in eukaryotic cells, how many times do the proteins that make up each ribosome cross the nuclear envelope before becoming active in translation? a) Zero times, ribosomes occur in the cytosol b) Once, during export of assembled ribosomes out of the nucleus c) Twice, the proteins must move into the nucleus for ribosome assembly and then out again into the cytosol d) Impossible to say - ribosomes regularly move into and out of the eukaryou nucleus Cell Bio Practice Exam 1 Page 5

Answer 1

Ans-17- in the final step of glutamine synthesis catalyzed by the glutamine synthetase, terminal phosphate group from the gamma-glutamyl phosphate, an intermediate in glutamine biosynthesis is replaced by amine group.

option D (phosphate, NH₂) is correct.

Ans-18- the main function of carrier molecules is to transport hydrophilic and charged molecules across the cell membrane because hydrophilic compounds can not cross the lipid bilayer.

option C is the correct answer.

Ans-19- out of 20 amino acids only 3 amino acids tyrosine, serine, threonine undergoes phosphorylation most frequently.

Serine is the correct answer.

Ans-20- protein for the assembly of ribosomes are synthesized in the cytosol. once the synthesis is complete these proteins send to the nucleus for the assembly of ribosomes. once the synthesis of ribosomes is complete proteins along associated with ribosomes are send back to the cytoplasm for the synthesis of proteins. So total of 2 times proteins crosses the nuclear envelope. option C is the correct answer.