Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 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 Figure 3.33 Nuclear envelope DNA Pre-mRNA mRNA Ribosome Polypeptide Translation RNA Processing Transcription

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings From DNA to Protein Figure 3.33 DNA

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings From DNA to Protein Figure 3.33 DNA Transcription

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings From DNA to Protein Figure 3.33 DNA Pre-mRNA RNA Processing Transcription mRNA

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings From DNA to Protein Figure 3.33 DNA Pre-mRNA RNA Processing Transcription mRNA Nuclear envelope

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings From DNA to Protein Figure 3.33 Nuclear envelope DNA Pre-mRNA mRNA Ribosome Polypeptide Translation RNA Processing Transcription

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Roles of the Three Types of RNA 1. Messenger RNA (mRNA) – carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm 2. Transfer RNAs (tRNAs) – bound to amino acids base pair with the codons of mRNA at the ribosome to begin the process of protein synthesis 3. 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 Figure 3.34 Coding strand Template strand Promoter Termination signal 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 nucleotides RNA polymerase bound to promoter mRNA synthesis begins RNA polymerase moves down DNA; mRNA elongates RNA nucleotides mRNA synthesis is terminated RNA polymerase mRNA DNA mRNA transcript (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Template strand Promoter Termination signal Transcription unit (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Template strand Promoter Termination signal 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) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Template strand Promoter Termination signal 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 nucleotides RNA polymerase bound to promoter mRNA synthesis begins (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Template strand Promoter Termination signal 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 nucleotides RNA polymerase bound to promoter mRNA synthesis begins mRNA (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Template strand Promoter Termination signal 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 nucleotides RNA polymerase bound to promoter mRNA synthesis begins RNA polymerase moves down DNA; mRNA elongates RNA nucleotides mRNA (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.34 Coding strand Template strand Promoter Termination signal 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 nucleotides RNA polymerase bound to promoter mRNA synthesis begins RNA polymerase moves down DNA; mRNA elongates RNA nucleotides mRNA synthesis is terminated RNA polymerase mRNA DNA mRNA transcript (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 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 Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase tRNA “head” bearing anticodon Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus 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. Incoming aminoacyl- tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. 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. Codon 16Codon 15Codon 17 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.36 Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Nucleus

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Codon 16Codon 15Codon 17 1

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Codon 16Codon 15Codon 17 1 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase tRNA “head” bearing anticodon Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Incoming aminoacyl- tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. Codon 16Codon 15Codon 17 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. 1 2

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase tRNA “head” bearing anticodon Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Incoming aminoacyl- tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. 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. Codon 16Codon 15Codon 17 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase tRNA “head” bearing anticodon Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus 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. Incoming aminoacyl- tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. 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. Codon 16Codon 15Codon 17 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Genetic Code  RNA codons code for amino acids according to a genetic code Figure 3.35

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 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 Figure 3.38

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 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