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Protein Synthesis Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Protein Synthesis DNA serves as master blueprint for protein synthesis Genes are segments of DNA carrying instructions for a polypeptide chain Triplets of nucleotide bases form the genetic library Each triplet specifies coding for an amino acid Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings From DNA to Protein Nuclear envelope DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Polypeptide Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.33 From DNA to Protein DNA Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.33 From DNA to Protein Transcription Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings DNA Figure 3.33 From DNA to Protein DNA Transcription Pre-mRNA RNA Processing mRNA Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.33 From DNA to Protein Nuclear envelope DNA Transcription Pre-mRNA RNA Processing mRNA Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.33 From DNA to Protein Nuclear envelope DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Polypeptide Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.33 Roles of the Three Types of RNA 1. 2. 3. Messenger RNA (mRNA) – carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm Transfer RNAs (tRNAs) – bound to amino acids base pair with the codons of mRNA at the ribosome to begin the process of protein synthesis Ribosomal RNA (rRNA) – a structural component of ribosomes Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Transcription Transfer of information from the sense strand of DNA to RNA Transcription factor Loosens histones from DNA in the area to be transcribed Binds to promoter, a DNA sequence specifying the start site of RNA synthesis Mediates the binding of RNA polymerase to promoter Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Transcription: RNA Polymerase An enzyme that oversees the synthesis of RNA Unwinds the DNA template Adds complementary ribonucleoside triphosphates on the DNA template Joins these RNA nucleotides together Encodes a termination signal to stop transcription Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Coding strand Termination signal Promoter Template strand Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA polymerase bound to promoter RNA nucleotides mRNA RNA nucleotides RNA polymerase mRNA synthesis begins RNA polymerase moves down DNA; mRNA elongates mRNA synthesis is terminated DNA (a) mRNA transcript Coding strand RNA polymerase Unwinding of DNA Rewinding of DNA Template strand RNA nucleotides mRNA RNA-DNA hybrid region (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Termination signal Promoter Template strand Transcription unit (a) Coding strand RNA polymerase Unwinding of DNA Rewinding of DNA Template strand RNA nucleotides mRNA RNA-DNA hybrid region (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Termination signal Promoter Template strand Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA polymerase bound to promoter (a) Coding strand RNA polymerase Unwinding of DNA Rewinding of DNA Template strand RNA nucleotides mRNA RNA-DNA hybrid region (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Termination signal Promoter Template strand Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA polymerase bound to promoter RNA nucleotides mRNA synthesis begins (a) Coding strand RNA polymerase Unwinding of DNA Rewinding of DNA Template strand RNA nucleotides mRNA RNA-DNA hybrid region (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Termination signal Promoter Template strand Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA polymerase bound to promoter RNA nucleotides mRNA synthesis begins mRNA (a) Coding strand RNA polymerase Unwinding of DNA Rewinding of DNA Template strand RNA nucleotides mRNA RNA-DNA hybrid region (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Termination signal Promoter Template strand Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA polymerase bound to promoter RNA nucleotides mRNA RNA nucleotides mRNA synthesis begins RNA polymerase moves down DNA; mRNA elongates (a) Coding strand RNA polymerase Unwinding of DNA Rewinding of DNA Template strand RNA nucleotides mRNA RNA-DNA hybrid region (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Termination signal Promoter Template strand Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA polymerase bound to promoter RNA nucleotides mRNA RNA nucleotides RNA polymerase mRNA synthesis begins RNA polymerase moves down DNA; mRNA elongates mRNA synthesis is terminated DNA (a) mRNA transcript Coding strand RNA polymerase Unwinding of DNA Rewinding of DNA Template strand RNA nucleotides mRNA RNA-DNA hybrid region (b) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Initiation of Translation A leader sequence on mRNA attaches to the small subunit of the ribosome Methionine-charged initiator tRNA binds to the small subunit The large ribosomal unit now binds to this complex forming a functional ribosome Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nucleus Nuclear membrane RNA polymerase Nuclear pore mRNA Template strand of DNA Amino acids Released mRNA 1 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. tRNA Aminoacyl-tRNA synthetase Small ribosomal subunit Codon 15 Codon 16 Codon 17 Direction of ribosome advance Portion of mRNA already translated tRNA “head” bearing anticodon Large ribosomal subunit 2 4 Once its amino acid is released, tRNA is ratcheted to the E site and then released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid. 3 As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Incoming aminoacyltRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. Figure 3.36 Nucleus Nuclear membrane RNA polymerase Nuclear pore mRNA Template strand of DNA Released mRNA Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.36 Nucleus Nuclear membrane RNA polymerase Nuclear pore mRNA Template strand of DNA Released mRNA 1 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Small ribosomal subunit Codon 15 Codon 16 Codon 17 Direction of ribosome advance Portion of mRNA already translated Large ribosomal subunit Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.36 Nucleus Nuclear membrane RNA polymerase Nuclear pore mRNA Template strand of DNA Amino acids Released mRNA 1 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Aminoacyl-tRNA synthetase Small ribosomal subunit Codon 15 Codon 16 Codon 17 tRNA Direction of ribosome advance Portion of mRNA already translated Large ribosomal subunit Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. Figure 3.36 Nucleus Nuclear membrane RNA polymerase Nuclear pore mRNA Template strand of DNA Amino acids Released mRNA 1 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. tRNA Aminoacyl-tRNA synthetase Small ribosomal subunit Codon 15 Codon 16 Codon 17 Direction of ribosome advance Portion of mRNA already translated tRNA “head” bearing anticodon Large ribosomal subunit 2 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Incoming aminoacyltRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. Figure 3.36 Nucleus Nuclear membrane RNA polymerase Nuclear pore mRNA Template strand of DNA Amino acids Released mRNA 1 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. tRNA Aminoacyl-tRNA synthetase Small ribosomal subunit Codon 15 Codon 16 Codon 17 Direction of ribosome advance Portion of mRNA already translated tRNA “head” bearing anticodon Large ribosomal subunit 2 3 As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Incoming aminoacyltRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. Figure 3.36 Nucleus Nuclear membrane RNA polymerase Nuclear pore mRNA Template strand of DNA Amino acids Released mRNA 1 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. tRNA Aminoacyl-tRNA synthetase Small ribosomal subunit Codon 15 Codon 16 Codon 17 Direction of ribosome advance Portion of mRNA already translated tRNA “head” bearing anticodon Large ribosomal subunit 2 4 Once its amino acid is released, tRNA is ratcheted to the E site and then released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid. 3 As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Incoming aminoacyltRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. Figure 3.36 Genetic Code RNA codons code for amino acids according to a genetic code Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.35 Information Transfer from DNA to RNA DNA triplets are transcribed into mRNA codons by RNA polymerase Codons base pair with tRNA anticodons at the ribosomes Amino acids are peptide bonded at the ribosomes to form polypeptide chains Start and stop codons are used in initiating and ending translation Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Information Transfer from DNA to RNA Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.38 Other Roles of RNA Antisense RNA – prevents protein-coding RNA from being translated MicroRNA – small RNAs that interfere with mRNAs made by certain exons Riboswitches – mRNAs that act as switches regulating protein synthesis in response to environmental conditions Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cytosolic Protein Degradation Nonfunctional organelle proteins are degraded by lysosomes Ubiquitin attaches to soluble proteins and they are degraded in proteasomes Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Extracellular Materials Body fluids and cellular secretions Extracellular matrix Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Developmental Aspects of Cells All cells of the body contain the same DNA but develop into all the specialized cells of the body Cells in various parts of the embryo are exposed to different chemical signals that channel them into specific developmental pathways Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Developmental Aspects of Cells Genes of specific cells are turned on or off (i.e., by methylation of their DNA) Cell specialization is determined by the kind of proteins that are made in that cell Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Developmental Aspects of Cells Development of specific and distinctive features in cells is called cell differentiation Cell aging Wear and tear theory attributes aging to little chemical insults and formation of free radicals that have cumulative effects throughout life Genetic theory attributes aging to cessation of mitosis that is programmed into our genes Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings