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Human Anatomy and Physiology Eleventh Edition Chapter 3 Cells: The Living Units Slides have been modified and edited by C. Youngson PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Com...
Human Anatomy and Physiology Eleventh Edition Chapter 3 Cells: The Living Units Slides have been modified and edited by C. Youngson PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 1 Pre-lecture Questions 1. What are the different parts of the cell (organelles) and what are their functions? 2. How do molecules get into and out of the cell? 3. What is the cell cycle? Define all the phases of the cell cycle and what is happening in each phase. 4. What is DNA replication? 5. What is transcription? 6. What is translation? 2 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cells: The Smallest Living Units Cell theory – A cell is the structural and functional unit of life – How well the entire organism functions depends on individual and combined activities of cells ▪ Cells can arise only from other preexisting cells Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cells: The Smallest Living Units Generalized cell – All cells have some common structures and functions – Human cells have three basic parts: 1. Plasma membrane: flexible outer boundary 2. Cytoplasm: intracellular fluid containing organelles 3. Nucleus: DNA containing control center Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Part 1 – Plasma Membrane Acts as an active barrier separating intracellular fluid (ICF) from extracellular fluid (ECF) Plays dynamic role in cellular activity by controlling what enters and what leaves cell Also known as the “cell membrane” Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of Plasma Membrane Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Membrane Proteins Perform Many Tasks Figure 3.3a Membrane proteins perform many tasks. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 7 Membrane Proteins Perform Many Tasks Figure 3.3b Membrane proteins perform many tasks. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 8 Membrane Proteins Perform Many Tasks Figure 3.3c Membrane proteins perform many tasks. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 9 Membrane Proteins Perform Many Tasks Figure 3.3d Membrane proteins perform many tasks. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 10 Membrane Proteins Perform Many Tasks Figure 3.3e Membrane proteins perform many tasks. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 11 Membrane Proteins Perform Many Tasks Figure 3.3f Membrane proteins perform many tasks. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 12 Cell Junctions While some cells not bound to any other cells (eg blood cells, sperm cells), most cells are bound together to form tissues and organs Three ways cells can be bound to each other – Tight junctions – Desmosomes – Gap junctions Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 13 Transport across the plasma membrane The plasma membrane is selectively permeable allowing only certain molecules to cross Two essential ways substances cross plasma membrane: – Passive transport: no energy is required – Active transport: energy (ATP) is required Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 14 1. Passive Membrane Transport Passive transport requires no energy input Three types of passive transport – Simple Diffusion – Facilitated diffusion – Osmosis All types involve diffusion – natural movement of molecules from areas of high concentration to areas of low concentration – Also referred to as moving down a concentration gradient Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 15 Simple Diffusion Simple diffusion – Nonpolar lipid-soluble (hydrophobic) substances diffuse directly through phospholipid bilayer – Examples: oxygen, carbon dioxide, steroid hormones, fatty acids – Small amounts of very small polar substances, such as water, can even pass Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 16 Animation: Diffusion Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 17 Diffusion Through The Plasma Membrane Figure 3.6a Diffusion through the plasma membrane. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 18 Diffusion Through The Plasma Membrane Figure 3.6b Diffusion through the plasma membrane. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 19 Diffusion Through The Plasma Membrane Figure 3.6c Diffusion through the plasma membrane. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 20 Osmosis Osmosis – Movement of water across a selectively permeable membrane – Water diffuses across plasma membranes ▪ through lipid bilayer (even though water is polar, it is so small that some molecules can sneak past nonpolar phospholipid tails) ▪ through specific water channels called aquaporins (AQPs) – Flow occurs when water concentration is different on the two sides of a membrane Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 21 Diffusion Through The Plasma Membrane Figure 3.6d Diffusion through the plasma membrane. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 22 Osmosis Osmolarity: measure the concentration of the total number of solute particles in solvent Water concentration varies with number of solute particles because solute particles displace water molecules – When solute concentration goes up, water concentration goes down, and vice versa Water moves by osmosis from areas of low solute (high water) concentration to high areas of solute (low water) concentration Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 23 Influence of Membrane Permeability on Osmosis Figure 3.7b Influence of membrane permeability on diffusion and osmosis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 24 Osmosis Tonicity – Ability of a solution to change the shape or tone of cells by altering the cells’ internal water volume ▪ Isotonic solution has same osmolarity as inside the cell, so volume remains unchanged ▪ Hypertonic solution has higher osmolarity than inside cell, so water flows out of cell, resulting in cell shrinking – Shrinking is referred to as crenation ▪ Hypotonic solution has lower osmolarity than inside cell, so water flows into cell, resulting in cell swelling – Can lead to cell bursting, referred to as lysing Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 25 The Effect of Solutions of Varying Tonicities on Living Red Blood Cells Figure 3.8 The effect of solutions of varying tonicities on living red blood cells. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 26 2. Active Membrane Transport Two major active membrane transport processes – Active transport – Vesicular transport Both require ATP to move solutes across a plasma membrane for any of these reasons: – Solute is too large for channels, or – Solute is not lipid soluble, or – Solute is not able to move down concentration gradient Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 27 Active Transport Requires carrier proteins (solute pumps) – Bind specifically and reversibly with substance being moved – Some carriers transport more than one substance ▪ Antiporters transport one substance into cell while transporting a different substance out of cell ▪ Symporters transport two different substances in the same direction Moves solutes against their concentration gradient (from low to high) – This requires energy (ATP) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 28 Active Transport Two types of active transport: - Primary active transport ▪ Required energy comes directly from ATP hydrolysis - Secondary active transport ▪ Required energy is obtained indirectly from ionic gradients (mostly by Na+) created by primary active transport Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 29 Vesicular Transport Involves transport of large particles, macromolecules, and fluids across membrane in membranous sacs called vesicles Requires cellular energy (usually ATP) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 30 Vesicular Transport Vesicular transport processes include: – Endocytosis: transport into cell ▪ 3 different types of endocytosis: phagocytosis, pinocytosis, receptor-mediated endocytosis – Exocytosis: transport out of cell – Vesicular trafficking: transport from one area or organelle in cell to another Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 31 Comparison of Three Types of Endocytosis Figure 3.11a Comparison of three types of endocytosis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 32 Comparison of Three Types of Endocytosis Figure 3.11b Comparison of three types of endocytosis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 33 Comparison of Three Types of Endocytosis Figure 3.11c Comparison of three types of endocytosis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 34 Exocytosis Figure 3.12a Exocytosis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 35 Exocytosis Figure 3.12b Exocytosis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 36 Part 2 – Cytoplasm All cellular material that is located between the plasma membrane and the nucleus – Composed of: ▪ Cytosol: gel-like solution made up of water and soluble molecules such as proteins, salts, sugars, etc. ▪ Organelles: metabolic machinery structures of cell; each with specialized function; either membranous or nonmembranous Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cytoplasmic Organelles Membranous Nonmembranous – Mitochondria – Ribosomes – Endoplasmic reticulum – Cytoskeleton – Golgi apparatus – Centrioles – Peroxisomes – Lysosomes Membranes allow compartmentalization, which is important to cell functioning Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Membranous Organelles: Mitochondria Called the “power plant” of cells because they produce most of cell’s energy molecules (ATP) via aerobic (oxygen-requiring) cellular respiration Enclosed by double membranes; inner membrane has many folds, called cristae – Cristae are embedded with membrane proteins that play a role in cellular respiration Mitochondria contain their own DNA, RNA, and ribosomes Resemble bacteria Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Endoplasmic Reticulum (ER) ER is continuous with outer nuclear membrane Two varieties: – Rough ER: ▪ Site of synthesis of proteins that will be secreted from cell ▪ Site of synthesis of many plasma membrane proteins and phospholipids – Proteins enter cisterns as they are synthesized and are modified as they wind through fluid-filled tubes – Final protein is enclosed in vesicle and sent to Golgi apparatus for further processing – Smooth ER – Enzymes found in its plasma membrane (integral proteins) function includes: ▪ Lipid metabolism; cholesterol and steroid-based hormone synthesis; making lipids for lipoproteins ▪ Converting of glycogen to free glucose ▪ Storage and release of calcium Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Golgi Apparatus Stacked and flattened membranous cistern sacs Modifies, concentrates, and packages proteins and lipids received from rough ER Three steps are involved: 1. Transport vesicles from ER fuse with cis (inner) face of Golgi 2. Proteins or lipids taken inside are further modified, tagged, sorted, and packaged 3. Golgi is “traffic director,” controlling which of three pathways final products will take as new transport vesicles pinch off trans (outer) face Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Sequence of Events from Protein Synthesis on the Rough ER to the Final Distribution of those Proteins Figure 3.17 Processing and distribution of newly synthesized proteins. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Peroxisomes Membranous sacs containing powerful detoxifying substances that neutralize toxins – Free radicals: toxic, highly reactive molecules that are natural by-products of cellular metabolism; can cause havoc to cell if not detoxified – Two main detoxifiers: oxidase uses oxygen to convert toxins to hydrogen peroxide (H2O2), which is itself toxic; however, peroxisome also contains catalase, which converts H2O2 to harmless water Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Lysosomes Spherical membranous bags containing digestive enzymes (acid hydrolases) – Considered “safe” sites because they isolate potentially harmful intracellular digestion from rest of cell Digest ingested bacteria, viruses, and toxins Degrade nonfunctional organelles Metabolic functions: break down and release glycogen Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Clinical – Homeostatic Imbalance Lysosomal storage diseases result when one or more lysosomal digestive enzymes are mutated and do not function properly Tay-Sachs disease is a condition in which the patient lacks a lysosomal enzyme needed to break down glycolipids in brain cells – Glycolipids build up as a result of this defect, interfering with nervous system functioning Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Animation: Endomembrane System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 46 Non-membranous Organelles: Ribosomes Nonmembranous organelles that are site of protein synthesis Made up of protein and ribosomal RNA (rRNA) Two switchable forms found in cell: – Free ribosomes: free floating; site of synthesis of soluble proteins that function in cytosol or other organelles – Membrane-bound ribosomes: attached to membrane of endoplasmic reticulum (ER); site of synthesis of proteins to be incorporated into membranes or lysosomes, or exported from cell Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cytoskeleton Elaborate network of rods that run throughout cytosol Hundreds of different kinds of proteins link rods to other cell structures Also act as cell’s “bones, ligaments, and muscle” by playing a role in movement of cell components Three types: Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Examples of cytoskeleton The spindle apparatus during cell division: an area of the cell called the centrosome is a microtubule organizing center, consisting of centrioles—a pair of barrel-shaped microtubular organelles that lie at right angles to each other. During cell division, newly assembled microtubules radiate from centrosome to the cellular poles forming a spindle Centrioles form the basis of cilia and flagella Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Animation: Cilia and Flagella Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 50 Microvilli Figure 3.24 Microvilli. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Part 3 – Nucleus Contains the genetic library of blueprints for synthesis of nearly all cellular proteins – Responds to signals that dictate the kinds and amounts of proteins that need to be synthesized Most cells are uninucleate (one nucleus), but skeletal muscle, certain bone cells, and some liver cells are multinucleate (many nuclei) – Red blood cells are anucleate (no nucleus) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of the Nucleus The nucleus has three main structures: – Nuclear envelope – Nucleoli: Dark-staining spherical bodies within nucleus (usually only one or two) that are involved in ribosomal RNA (rRNA) synthesis and ribosome subunit assembly – Chromatin Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Chromatin Consists of 30% threadlike strands of DNA, 60% histone proteins, and 10% RNA Arranged in fundamental units called nucleosomes, which consist of DNA wrapped around histones – histones help regulate gene expression Chromosomes are condensed chromatin – Condensed state helps protect fragile chromatin threads during cell division Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Chromosome Structure Figure 3.26b Chromatin and chromosome structure. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 55 Cell Cycle Series of changes a cell undergoes from the time it is formed until it reproduces Two major periods of cell cycle: – Interphase ▪ Cell grows and carries on its usual activities – Cell division (mitotic phase) ▪ Cell divides into two Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 56 Interphase DNA replication (S Phase) – Prior to division, the cell makes a copy of DNA – Double-stranded DNA helices unwind and unzip ▪ Replication fork: point where strands separate ▪ Replication bubble: active area of replication ▪ Each strand acts as a template for a new complementary strand – RNA starts replication by laying down short strand that acts as a primer – DNA polymerase attaches to primer and begins adding nucleotides to form new strand ▪ DNA polymerase synthesizes both new strands at one time (one leading and one lagging strand) – Another enzyme, DNA ligase, then splices short segments of discontinuous lagging strand together Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved No definition of economics can adequately capture the subject. For that reason, some teachers don’t like definitions and skip right over them. If you are one of these teachers, go ahead. Not much is lost. Other teachers regard a basic definition as essential, and the textbook takes this view. The definition in the text…“the social science that studies the choices that individuals, businesses, and governments, and entire societies make as they cope with scarcity,” is a modern language version of Lionel Robbins famous definition, “Economics is the science which studies human behavior as a relationship between ends and scarce means that have alternative uses.” Some teachers like to play with definitions a bit more elaborately. If you are one of these, here are four more, all of which add some useful insight and the last one a bit of fun: 57 John Maynard Keynes: “The theory of economics does not furnish a body of settled conclusions immediately applicable to policy. It is a method rather than a doctrine, an apparatus of the mind, a technique of thinking, which helps its possessors to draw correct conclusions.” Alfred Marshall: “Economics is a study of mankind in the ordinary business of life; it examines that part of individual and social action which is most closely connected with the attainment and with the use of the material requisites of wellbeing.” Jacob Viner: “Economics is what economists do.” Jim Duesenberry: “Economics is all about how people make choices. Sociology is about why there isn’t any choice to be made.” Animation: Replication of DNA Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cell Division Most cells need to replicate continuously for growth and repair purposes – Skeletal, cardiac, and nerve cells do not divide efficiently; damaged cells are replaced with scar tissue M (mitotic) phase of cell cycle is phase in which division occurs; consists of 2 distinct events: – Mitosis – Cytokinesis Control of cell division is crucial, so cells divide when necessary, but do not divide unnecessarily Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 59 Cell Division M phase – Mitosis is the division of nucleus, in which the duplicated DNA is distributed to new daughter cells Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 60 Animation: Mitosis Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Control of Cell Division “Go” and “Stop” signals direct when a cell should and should not divide ▪ Go signals include: – Critical surface-to-volume ratio of cell, when area of membrane becomes inadequate for exchange – Chemicals (example: growth factors, hormones) ▪ Stop signals include: – Availability of space; normal cells stop dividing when they come into contact with other cells Referred to as contact inhibition Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 62 Two groups of proteins are crucial to cell’s ability to accomplish S phase and enter mitosis: – Cyclins: regulatory proteins that accumulate during interphase – Cdks (Cyclin-dependent kinases) that activate cyclins when they bind to them – Cyclin-Cdk complex in turn activates enzyme cascades that prepare cell for division – Cyclins are destroyed after mitotic cell division, and process begins again Checkpoints are key events In the cell cycle where cell division processes are checked and, if faulty, stopped until repairs are made – G1 checkpoint (restriction point) is the most important of the three major checkpoints – If cell does not pass, it enters G0, in which no further division occurs Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 63 Protein Synthesis DNA is master blueprint that holds the code for protein synthesis – DNA directs the order of amino acids in a polypeptide A segment of DNA that holds the code for one polypeptide is referred to as a gene The code is determined by the specific order of nitrogen bases (Adenine, Guanine, Thymine, and Cytosine) in the gene – Code consists of three sequential bases (triplet code) ▪ Example: GGC codes for amino acid proline, whereas GCC codes for arginine – Each triplet specifies the code for a particular amino acid Genes are composed of exons and introns – Exons are part of gene that actually codes for amino acids – Introns are noncoding segments interspersed amongst exons Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 64 Animation: DNA and RNA Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Role of RNA Messenger RNA (mRNA) – Single stranded – Code from DNA template strand is copied with complementary base pairs, resulting in a strand of mRNA ▪ Process is referred to as transcription – mRNA maintains the triplet code (codon) from DNA Ribosomal RNA (rRNA) – Structural component of ribosomes, the organelle where protein synthesis occurs – Along with tRNA, helps to translate message from mRNA into polypeptide Transfer RNA (tRNAs) – Carrier of amino acid – Have special areas that contain a specific triplet code (anticodon) that allows each tRNA to carry only a specific amino acid – Anticodon of tRNA will complementary base-pair with codon of mRNA at ribosome, adding its specific amino acid to growing polypeptide chain ▪ Process is referred to as translation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 66 Protein Synthesis Occurs in two steps: – Transcription ▪ DNA information coded in mRNA – Translation ▪ mRNA decoded to assemble polypeptides Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 67 Transcription Transcription is broken down into three phases: 1. Initiation ▪ RNA polymerase separates DNA strands 2. Elongation ▪ RNA polymerase adds complementary nucleotides to growing mRNA matching sequence of based on DNA template strand – Short, 12-base-pair segment where DNA and mRNA are temporarily bonded is referred to as DNA-RNA hybrid 3. Termination ▪ Transcription stops when RNA polymerase reaches special termination signal code Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 68 Translation Role of tRNA – tRNA binds a specific amino acid at one end (stem); once amino acid is loaded onto tRNA, molecule is now called an aminoacyl-tRNA – Anticodon at other end (head) is triplet code that determines which amino acid will be bound at stem ▪ Example: tRNA with anticodon UAU will only be able to load a methionine amino acid to its stem region Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Translation Sequence of events in translation – Translation occurs in three phases that require ATP, protein factors, and enzymes 1. Initiation 2. Elongation 3. Termination Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 70 Translation 1. Initiation – Small ribosomal subunit binds to a special initiator tRNA (methionine) and then to the mRNA to be decoded ▪ Ribosome scans mRNA looking for first methionine codon, which is referred to as the start codon – When anticodon of initiator tRNA binds to start codon, large ribosomal unit can then attach to small ribosomal unit forming a functional ribosome – At end of initiation, initiator tRNA is in P site of ribosome, and A and E sites are empty Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 71 Translation 2. Elongation: involves three steps: 2a. Codon recognition: tRNA binds complementary codon in A site of ribosome 2b. Peptide bond formation: Ribosomal enzymes transfer and attach growing polypeptide chain from tRNA in P site over to amino acid of tRNA in A site 2c. Translocation: ribosome shifts down three bases of mRNA, displacing tRNAs by one position tRNA in A site moves into P site tRNA in P site moves into E site tRNA in E site is ejected from ribosome – Once A site is empty, a new tRNA can enter, bringing its amino acid cargo, and whole process starts over Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 72 Translation 3. Termination – When one of three stop codons (UGA, UAA, UAG) on mRNA enters A site, translation ends Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 73 Rough ER Processing of Proteins A short amino acid segment, called the ER signal sequence, present on a growing polypeptide chain, signals associated ribosome to dock on rough ER surface Signal-recognition particle (SRP) on ER directs mRNA–ribosome complex where to dock Once docked, forming polypeptide enters ER Protein is then enclosed in vesicle for transport to Golgi apparatus Figure 3.33 Rough ER processing of proteins. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 74 Summary: From DNA to Proteins Complementary base pairing directs transfer of genetic information in DNA into amino acid sequence of protein – DNA triplets are coded to mRNA codons – mRNA codons are base-paired with tRNA anticodons to ensure correct amino acid sequence ▪ Anticodon sequence of tRNA is identical to DNA sequence, except uracil is substituted for thymine Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 75 Information Transfer From DNA to RNA to Polypeptide Figure 3.34 Information transfer from DNA to RNA to polypeptide. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 76 Independent Reading Developmental Aspects of Cells pg 109-110 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved
