BIOL 23373 - General Genetics Lecture 10 - Translation I PDF

BIOL 23373 – General Genetics Fall 2024 Lecture 10 Translation I Announcements Exam 1 was last Friday (Sept. 13). You will be able to view your submission and the answers after the last student completes the makeup exam (Wed. evening). We will d...

BIOL 23373 – General Genetics Fall 2024 Lecture 10 Translation I Announcements Exam 1 was last Friday (Sept. 13). You will be able to view your submission and the answers after the last student completes the makeup exam (Wed. evening). We will discuss class scores (mean, median, SD, distribution, etc.) in class on Friday, Sept. 20. Don’t forget that you get to drop your lowest exam score among the four hour exams and the final exam. If you want to meet (in person or via Zoom), email me 3 or 4 meeting day/time options. Tutoring Tutoring @ the CORD offers 1-on-1 and small group assistance in over 100 U of A courses. Students can meet with tutors in person or online by scheduling an appointment or accessing drop-in services. Learn more about Tutoring services and book an appointment at: https://success.uark.edu/academic-initia tives/tutoring.php Corresponding Readings Chapter sections: 14.1-14.4 The Flow of Genetic Information Transcription Synthesis of a single-stranded RNA molecule (transcript) from a DNA template (gene) This messenger RNA (mRNA) specifies the amino acid sequence of a polypeptide (protein) Translation Process of synthesizing a polypeptide using the mRNA template Mature Messenger RNA The sequence of the mRNA coding region dictates the amino acid sequence of the polypeptide. This is the region that is translated. The 5 untranslated region (5 UTR) and 3 UTR flank the translated region. 6 Translating Messenger RNA Boundaries of translation are defined by a start codon that corresponds to the N-terminus (amino terminus) of the protein and a stop codon that corresponds to the C-terminus (carboxyl terminus) 7 The Flow of Genetic Information Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Coding strand 5′ 3′ A C T G C C C A T G A G C G A C C C C T T C G G G C T C G G G G A A T G A A T C G T G A C G G G T A C T C G C T G G G G A A G C C C G A G C C C C T T A C T T A G C DNA 3′ 5′ Template strand Transcription 5′ 3′ mRNA A C U G C C C A U G A G C G A C C C C U U C G G G C U C G G G G A A U G A A U C G 5′ Untranslated Start Codon Stop 3′ Untranslated region codon codon region Anticodon Translation U A C U C G C U G G G G A A G C C C G A G C C C C U U tRNA Polypeptide NN3+ C-terminus N-terminus COO– (amino terminus) (carboxyl terminus) Met Ser Asp Pro Phe Gly Leu Gly Glu Peptide Amino bond acids The Genetic Code Translates Messenger RNA into a Polypeptide The term “genetic code” describes the correspondence between mRNA nucleotide sequences and the amino acid sequences of the resulting polypeptides During translation, tRNAs act as adaptor molecules that interpret and act on information in mRNA tRNAs have anticodons that are complementary and antiparallel to mRNA codons 9 Transfer RNAs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3′ Amino acid attachment site at the 3′ single-stranded 5′ region Different tRNA molecules are encoded by different Hydrogen bonds Stem-loop structure genes G G C Anticodon tRNASer carries serine (a) Two-dimensional structure of tRNA Common features 5′ 3′ single Cloverleaf structure stranded region Acceptor stem for amino acid binding Anticodon Anticodon (b) Three-dimensional structure of tRNA Charging tRNA Molecules tRNAs used during translation are called charged tRNAs, whereas tRNAs without amino acids attached are uncharged Correct charging of each tRNA molecule is critical for the integrity of the genetic code Enzymes called tRNA synthetases catalyze the addition of the correct amino acid to tRNAs 11 tRNA Synthetases tRNA synthetase contacts several points on the tRNA in the recognition process The acceptor stem of the correct tRNA fits into the active site of the enzyme The active site contains the amino acid to be added to the tRNA; ATP provides the energy for attachment tRNA synthetase uses a proofreading system to maintain a very low error rate 12 Ribosomes Are Translation Machines Ribosomes assemble strings of amino acids called polypeptides Ribosomes are composed of multiple ribosomal RNAs (rRNAs) and proteins Ribosomes translate mRNA in the 5 – 3 direction, reading each codon and assembling the amino acids in the order specified by the codons Codon = series of 3 ribonucleotides (triplet) 13 Bacterial and Eukaryotic Ribosome Structures Ribosomes in bacteria and eukaryotes perform three tasks: 1. Bind mRNA and identify the start codon where translation begins 2. Facilitate complementary base pairing of mRNA codons and the corresponding tRNA anticodons 3. Catalyze formation of peptide bonds between amino acids on the growing polypeptide chain 14 Ribosome Composition Ribosomes are composed of two subunits, the large ribosomal subunit and the small ribosomal subunit Ribosomal subunit size is measured in Svedberg units (S), a property based on size, shape, and hydration state 15 Ribosomes of E. coli Ribosomes of E. coli are the most thoroughly studied bacterial ribosomes The small subunit is 30S and contains 21 proteins and one 16S rRNA molecule The large subunit is 50S and contains 31 proteins, a small 5S rRNA, and a large 23S rRNA The fully assembled ribosome is 70S 16 Eukaryotic Ribosomes Mammalian ribosomes are the most fully characterized eukaryotic ribosomes The small (40S) subunit contains about 35 proteins and one 18S rRNA The large subunit (60S) contains 45 – 50 proteins and three rRNA molecules: 5S, 5.8S, 28S The fully assembled ribosome is 80S 17 Important Regions of Ribosomes The aminoacyl site (A site) binds a new tRNA containing an amino acid to be added to the growing polypeptide chain 18 Important Regions of Ribosomes The peptidyl site (P site) holds the tRNA to which the polypeptide is attached 19 Important Regions of Ribosomes The exit site (E site) provides an avenue for the tRNA to exit after its amino acid has been added to the polypeptide chain 20 Important Regions of Ribosomes Ribosomes also have a polypeptide channel from which the polypeptide chain emerges 21 X