BBMB 405 1nd Edition Lecture 34Outline of Last Lecture XVI. Chapter 30: Protein SynthesisC. The ribosome is the site of protein synthesisOutline of Current Lecture XVI. Chapter 30: Protein SynthesisD. Eukaryotic protein synthesis differs from prokaryotic protein synthesis primarily in translation initiationE. A variety of antibiotics and toxins can inhibit protein synthesisF. Ribosomes bound to endoplasmic reticulum manufacture secretory and membrane proteinsXVII. Chapter 31: The control of gene expression in prokaryotesA. IntroductionCurrent LectureXVI. Chapter 30: Protein SynthesisD. Eukaryotic protein synthesis differs from prokaryotic protein synthesis primarily intranslation initiation1. Selenocysteine: the 21st amino acida. Lower pka so deprotonated at body pH, has a lower reduction potentialb. Used in antioxidantsc. Binds to stop codon, can bind to tRNA like cysteineThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Cap-independent translationa. Internal Ribosome Entry Site (IRES) is recognized by translation components and is translatedb. Direct recruitment of 40S of eIFsc. Often found in viruses: hijack cellular translation machineryd. Cellular mRNAs involved in stress responseE. A variety of antibiotics and toxins can inhibit protein synthesis1. Inhibition of protein synthesis: a potent drug targeta. Streptomycin: highly basic, interferes with ability of initiator tRNA to bind to 30S subunitb. Puromycin mimics aminoacyl-tRNA and can be incorporated at end of nascent peptide2. Ricin cleaves 28S rRNA and renders ribosome inactivea. Deadly toxin: single molecule can kill cell, extracted from castor beansb. Two protein chains: chain B binds cell surface and injects toxin, chain A cleaves sarcin/ricin loop of 28S rRNAF. Ribosomes bound to endoplasmic reticulum manufacture secretory and membrane proteins1. Synthesis of secretory and membrane proteinsa. Ribosomes must be directed to membranes for insertion or secretionb. In eukaryotes, ribosomes are directed to rough endoplasmic reticulum2. A signal sequence marks proteins for translocation across the ER membrane3. The signal sequence is recognized by signal recognition particle (SRP)a. SRP binds signal sequence as it emerges from ribosomeb. SRP diffuses to ER and binds to SRP receptorc. SRP targeting to membrane: process dependent on GTP hydrolysisd.4. Transport vesicles (refer to picture below)a. Most membrane proteins will already be inserted into membrane of vesicle (protein inserted in plasma membrane)b. Signal traffic proteins to lysosome (lysosome)c. Protein modification (cis-golgi)d.XVII. Chapter 31: The control of gene expression in prokaryotesA. Introduction1. Regulation of gene expressiona. What factors control gene expression?b. DNA: Cis-regulatory elements, trans-acting factors, epigenetic controlc. RNA: processing, degradation, sequenstrationd. Protein: modification, degradation2. Gene regulation in prokaryotes vs eukaryotes: transcriptiona. General prokaryotic features: operon structures, polycistronic transcripts, no mRNA processing, activators and repressorsb. General eukaryotic features: operon structures uncommon, monocistronic transcripts, mRNA processing, activators and repressors3. The lac operon: a classic example of transcriptional
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