CHEM 120 Unit 7 Lab Practicum

CHEM 120 Unit 7 Lab Practicum CHEM 120 UNIT 7 LAB PRACTICUM Expanded Original Q&A; Study Guide Protein Synthesis • Gene Expression • Protein Structure • MALDI-TOF Mass Spectrometry • Recombinant EPO Purpose: This guide is an original, expanded study resource built from the publicly visible topic information associated with the linked Stuvia listing. It is designed to help you understand and reason through Unit 7 laboratory concepts rather than reproduce a paid document. Source orientation: The linked Stuvia page identifies the item as a 1-page CHEM-120 Unit 7 Lab Practicum Q&A; resource, uploaded May 2, 2022, for Chamberlain College of Nursing. The related CHEM 120 Unit 7 lab material publicly describes a Protein Synthesis lab involving translation, post-translational modification, protein structure, recombinant erythropoietin (EPO), and MALDI-TOF mass spectrometry. Important: This is not a reproduction of the paid/locked material, and no claim is made that these are the original practicum questions or guaranteed answers. The practice questions below are newly written. How to use this guide ● First learn the process maps; then test yourself with the Q&A; sections. ● For lab-practicum questions, explain the mechanism, not just the vocabulary. ● When a question presents a sequence, identify what happens first, what molecule is involved, and where the event occurs. ● For mass spectrometry, keep the central idea in mind: the instrument separates detected ions according to mass-to-charge ratio (m/z). ● Use the rapid-fire section at the end for final review. CHEM 120 • Unit 7 Lab Practicum • Expanded Original Study Guide Page 2 1. Unit 7 Big Picture: What the Lab Is Testing The central theme is how genetic information becomes a functional protein and how laboratory methods can be used to study the resulting protein. The topic chain is: DNA → transcription → mRNA → translation → polypeptide → folding/processing → functional protein The lab context connects that biology to recombinant protein production and analytical chemistry. Recombinant EPO is useful as an example because it illustrates how the same encoded protein can be produced in different host systems and how post-translational processing can affect the final product. The publicly visible course/lab descriptions emphasize five learning targets: translation from mRNA to amino acids, post-translational modification, ribosomal protein synthesis, the four levels of protein structure, and the basic principle of MALDI-TOF mass spectrometry. citeturn1search0turn1search1 Q: What is the single best mental model for Unit 7? A: Think of the unit as a pipeline. DNA stores the information, transcription makes an RNA copy, translation converts the RNA message into an amino-acid sequence, and folding/processing produces a functional protein. The laboratory portion then asks how we can recognize or compare proteins experimentally. Exam tip: If you can draw the pipeline from memory, many individual questions become much easier. Q: What is the difference between transcription and translation? A: Transcription uses a DNA template to produce RNA. Translation uses the nucleotide sequence of mRNA to determine the amino-acid sequence of a polypeptide. In simple terms, transcription is DNA → RNA, while translation is RNA → protein. Exam tip: Do not say that DNA is directly translated into protein. The mRNA intermediate matters. 2. Gene Expression: DNA → RNA → Polypeptide In a typical eukaryotic cell, transcription occurs in the nucleus. RNA polymerase uses one DNA strand as a template to synthesize a complementary RNA transcript. For a protein-coding gene, the resulting pre-mRNA is processed before mature mRNA is exported to the cytoplasm. Translation then occurs on ribosomes. A common exam trap is confusing template and coding strands. The RNA sequence is complementary to the DNA template strand and closely corresponds to the coding strand except that RNA uses U instead of T. Q: What bases are used in DNA and RNA? A: DNA uses adenine (A), thymine (T), cytosine (C), and guanine (G). RNA uses adenine (A), uracil (U), cytosine (C), and guanine (G). Thus, U replaces T in RNA. Exam tip: A quick memory cue is: DNA has T; RNA has U. Q: What happens to a eukaryotic pre-mRNA before it becomes mature mRNA? A: Major processing events include addition of a 5′ cap, removal of introns by splicing, and addition of a 3′ poly(A) tail. These changes help with RNA stability, export, and translation. Exam tip: The exact processing details may vary by organism and transcript, but the cap/splicing/poly(A) framework is high yield. Q: What is a codon? A: A codon is a three-nucleotide sequence in mRNA that specifies an amino acid or a translation stop signal. Because codons are read in groups of three, the reading frame matters. Exam tip: Changing the reading frame changes every downstream codon. Q: Why are AUG and UAA/UAG/UGA important? CHEM 120 • Unit 7 Lab Practicum • Expanded Original Study Guide Page 3 A: AUG commonly functions as the start codon and specifies methionine. UAA, UAG, and UGA are stop codons that signal termination of translation. Exam tip: A start codon establishes the reading frame; a stop codon ends the polypeptide. CHEM 120 • Unit 7 Lab Practicum • Expanded Original Study Guide Page 4 3. Translation: How mRNA Becomes a Polypeptide Translation is carried out by ribosomes using mRNA, transfer RNA (tRNA), and amino acids. The ribosome reads mRNA codons while tRNAs deliver amino acids through complementary anticodon-codon pairing. Core sequence: initiation → elongation → termination. Q: What is the role of tRNA? A: tRNA acts as an adaptor. One region contains an anticodon that base-pairs with an mRNA codon, while the other end carries the corresponding amino acid. Exam tip: Think 'tRNA = transporter/adaptor' rather than a source of genetic information. Q: What happens during initiation? A: The ribosomal subunits assemble on the mRNA, the initiator tRNA pairs with the start codon, and the translation machinery becomes positioned to begin elongation. Exam tip: The start codon is more than a signal to begin; it establishes the reading frame. Q: What happens during elongation? A: The ribosome repeatedly accepts a charged tRNA, forms a peptide bond between amino acids, and moves along the mRNA so the next codon can be read. The growing chain therefore reflects the order of codons in the mRNA. Exam tip: If asked what directly determines amino-acid order, answer: the sequence of mRNA codons. Q: What happens at termination? A: When a stop codon enters the ribosome's decoding site, no normal tRNA supplies an amino acid for that codon. Release factors promote release of the completed polypeptide and disassembly of the translation complex. Exam tip: Stop codons terminate translation; they do not encode amino acids. Q: What is a peptide bond? A: A peptide bond is the covalent linkage formed between the carboxyl group of one amino acid and the amino group of another during protein synthesis. Repeated peptide-bond formation creates the polypeptide backbone. Exam tip: The amino-acid sequence is also called the primary structure of a protein. Mini Practice: Reading a Codon Sequence Suppose an mRNA segment is 5′-AUG-GCU-AAA-UAA-3′. AUG is the start codon, GCU specifies alanine, AAA specifies lysine, and UAA terminates translation. The conceptual output is therefore Met–Ala–Lys, followed by termination. The important skill is not memorizing every codon. It is recognizing the workflow: locate the start, read in triplets, translate each codon in order, and stop at the first in-frame stop codon. 4. Protein Structure: Four Levels You Must Distinguish Level What it describes High-yield clue Primary Linear amino-acid sequence Peptide-bonded sequence Secondary Local backbone folding α-helices and β-sheets Tertiary Overall 3D shape of one polypeptide Side-chain interactions CHEM 120 • Unit 7 Lab Practicum • Expanded Original Study Guide Page 5 Level What it describes High-yield clue Quaternary Association of multiple polypeptide subunits More than one chain Q: What defines primary protein structure? A: The exact linear sequence of amino acids in the polypeptide chain. Exam tip: If the question asks 'sequence,' think primary structure. Q: What are common examples of secondary structure? A: Alpha helices and beta sheets. These are stabilized largely by hydrogen bonding involving the peptide backbone. Exam tip: Secondary structure describes local folding patterns, not the full 3D shape. Q: What determines tertiary structure? A: Tertiary structure is the overall three-dimensional conformation of a single polypeptide, influenced by interactions among amino-acid side chains and with the surrounding environment. Hydrophobic interactions, ionic interactions, hydrogen bonds, van der Waals forces, and disulfide bonds can contribute. Exam tip: Disulfide bonds are covalent; many other stabilizing interactions are noncovalent. Q: When should you choose quaternary structure? A: Choose quaternary structure when a functional protein contains multiple polypeptide subunits that associate to form one larger protein complex. Exam tip: One chain can have primary, secondary, and tertiary structure without having quaternary structure. CHEM 120 • Unit 7 Lab Practicum • Expanded Original Study Guide Page 6 5. Post-Translational Modification and Protein Processing Translation produces a polypeptide, but the polypeptide is not always the final functional form. Proteins can be folded, cleaved, chemically modified, transported to a specific cellular location, or assembled with other subunits. Examples of post-translational modification include phosphorylation, glycosylation, acetylation, methylation, lipid attachment, and disulfide-bond formation. Which modifications occur depends on the protein and cellular context. Q: Why can two proteins with the same amino-acid sequence behave differently after synthesis? A: Different processing, folding, chemical modification, cellular localization, or association with other proteins can alter activity and stability. Protein function depen