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Resp & Cell Comm Review Two main catabolic processes: • fermentation: partial degradation of sugars in the absence of oxygen. • cellular respiration: uses oxygen to complete the breakdown of many organic molecules. • more efficient and widespread • Most steps occur in mitochondria. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Introduction • Photosynthetic organisms store energy in organic molecules. • These are available to… • themselves, and … • others that eat them. Fig. 9.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 2. Cells recycle the ATP they use for work • ATP (adenosine triphosphate): • chemical equivalent of a loaded spring. • trio of PO4- groups are unstable, high-energy. • ATP ADP + PO4 powers most cellular work • ATP must be constantly recycled from ADP and PO4 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • What’s different in the electron sharing of the reactants vs. the products? • Where does this energy come from? • Which atoms got oxidized/reduced? Fig. 9.3 high energy e- positions low energy e- positions Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings glycolysis, the Krebs cycle, the electron transport chain, and chemiosmosis via ATP synthase & H+ gradient. • substrate-level phosphorylation generates the few ATP’s produced in glycolysis and the Krebs cycle. • How is this different from oxidative phosphorylation? • no e- transport chain. Fig. 9.7 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • energy investment phase: 2 ATP create reactants with high free energy by phosphorylating glucose. • energy payoff phase: BIG PICTURE • 4 ATP via substratelevel phosphorylation • NAD+ is reduced to NADH. • Net Production? • 2 ATP + 2 NADH • 2 pyruvate • NOT used? • O2 Fig. 9.8 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • More than ¾ of the original energy in one glucose is still present in two molecules of pyruvate. Fig. 9.10 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • For each Acetyl CoA that goes in... • Lots of high energy electron carriers are produced… Know THIS one! • Net of 2 NADH • 1 FADH2 • Also produced? • one ATP Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 9.12 • electron transport chain: • Thousands of copies in the cristae of each mitochondrion. • Most parts are proteins that accept electrons, then pass them along. • Electrons drop in free energy as they pass down the chain. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Note the location! Note what is being pumped! + 2 H+ Fig. 9.15 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • ATP synthase in the cristae makes ATP from ADP & Pi. • osmos – “to push” • chemiosmosis*: using a chemical’s “push” • Push of H+ gradient powers ATP synthase • http://www.youtube.com/watch?v=xbJ0nbzt5Kw • • start at 40 seconds, watch next 3:10 http://www.youtube.com/watch?v=FFBr3ANCkb4 • 5 min of Ninja Respiration fun! * vs. substrate level phosphorylation Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 9.14 Big Picture Fig. 9.16 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • alcohol fermentation: • performed by yeast; used in brewing and winemaking. Fig. 9.17a Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • lactic acid fermentation: • Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt. • Muscle cells switch from aerobic respiration to lactic acid fermentation to generate ATP if O2 is scarce. • lactate is converted back to pyruvate in the liver. Fig. 9.17b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Some organisms (facultative anaerobes), including yeast and many bacteria, can survive using either fermentation or respiration. • human muscle cells too. Fig. 9.18 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 9.19 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • ex: phosphofructokinase catalizes 3rd glycolysis step • high ATP levels enzyme inhibition • high ADP/AMP levels enzyme activation. • inhibition by citrate slows glycolysis until Krebs cycle “catches up”. Fig. 9.20 Chapter 11 Cell Communication PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution of Cell Signaling • Yeast cells – Identify their mates by cell signaling 1 Exchange of mating factors. Each cell type secretes a mating factor that binds to receptors on the other cell type. 2 Mating. Binding of the factors to receptors induces changes in the cells that lead to their fusion. factor Receptor a Yeast cell, mating type a factor a 3 New a/ cell. Figure 11.2 The nucleus of the fused cell includes all the genes from the a and a cells. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Yeast cell, mating type a/ • In local signaling, animal cells – May communicate via direct contact Figure 11.3 (b) Cell-cell recognition. Two cells in an animal may communicate by interaction between molecules protruding from their surfaces. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In other cases, animal cells – Communicate using local regulators Local signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse Secretory vesicle Local regulator diffuses through extracellular fluid (a) Paracrine signaling. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Target cell is stimulated (b) Synaptic signaling • In long-distance signaling Long-distance signaling Endocrine cell – Both plants and animals use hormones – Why do only certain cells respond? Blood vessel Hormone travels in bloodstream to target cells Target cell Figure 11.4 C Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells. • Overview of cell signaling EXTRACELLULAR FLUID 1 Reception CYTOPLASM Plasma membrane 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule Figure 11.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • G-protein-linked receptors Signal-binding site Some good animations Segment that interacts with G proteins G-protein-linked Receptor Plasma Membrane Activated Receptor Signal molecule GDP CYTOPLASM G-protein (inactive) Enzyme GDP GTP Activated enzyme GTP GDP Pi Figure 11.7 Cellular response Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inactive enzyme • Receptor tyrosine kinases – what’s happening? Signal-binding sitea Signal molecule Signal molecule Helix in the Membrane Tyr Tyrosines Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Receptor tyrosine kinase proteins (inactive monomers) CYTOPLASM Tyr Dimer Activated relay proteins Figure 11.7 Tyr P Tyr P Tyr Tyr P Tyr P Tyr P Tyr Tyr P Tyr Tyr Tyr Tyr 6 ATP Activated tyrosinekinase regions (unphosphorylated dimer) 6 ADP Fully activated receptor tyrosine-kinase (phosphorylated dimer) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings P Tyr P Tyr P Tyr Tyr P Tyr P Tyr P Inactive relay proteins Cellular response 1 Cellular response 2 Signal molecule (ligand) • Ion channel receptors – critical in nerve cells Gate closed Ligand-gated ion channel receptor Ions Plasma Membrane Gate open Cellular response Gate close Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 11.7 • A phosphorylation cascade Signal molecule Receptor Activated relay molecule Inactive protein kinase 1 1 A relay molecule activates protein kinase 1. 2 Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase. Active protein kinase 1 Inactive protein kinase 2 ATP Pi PP Inactive protein kinase 3 5 Enzymes called protein phosphatases (PP) catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse. Figure 11.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings P Active protein kinase 2 ADP 3 Active protein kinase 2 then catalyzes the phosphorylation (and activation) of protein kinase 3. ATP ADP Pi Active protein kinase 3 PP Inactive protein P 4 Finally, active protein kinase 3 phosphorylates a protein (pink) that brings about the cell’s response to the signal. ATP ADP Pi PP P Active protein Cellular response 1 A signal molecule binds 2 Phospholipase C cleaves a to a receptor, leading to plasma membrane phospholipid activation of phospholipase C. called PIP2 into DAG and IP3. • “2nd Messenger” is a general term, it may actually be applied to a 3rd or 4th messenger. EXTRACELLULAR FLUID 3 DAG functions as a second messenger in other pathways. Signal molecule (first messenger) G protein DAG GTP PIP2 G-protein-linked receptor Phospholipase C IP3 (second messenger) IP3-gated calcium channel Endoplasmic reticulum (ER) Various proteins activated Ca2+ Cellular response Ca2+ (second messenger) Figure 11.12 4 IP3 quickly diffuses through the cytosol and binds to an IP3– gated calcium channel in the ER membrane, causing it to open. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5 Calcium ions flow out of the ER (down their concentration gradient), raising the Ca2+ level in the cytosol. 6 The calcium ions activate the next protein in one or more signaling pathways. Reception Binding of epinephrine to G-protein-linked receptor (1 molecule) • Amplification of a transduced signal: Transduction Inactive G protein Active G protein (102 molecules) Inactive adenylyl cyclase Active adenylyl cyclase (102) ATP Cyclic AMP (104) Inactive protein kinase A Active protein kinase A (104) Inactive phosphorylase kinase Active phosphorylase kinase (105) Inactive glycogen phosphorylase Active glycogen phosphorylase (106) Response Figure 11.13 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycogen Glucose-1-phosphate (108 molecules) Growth factor Reception Receptor • Many pathways regulate genes by activating transcription factors that turn genes on or off Phosphorylation cascade Transduction CYTOPLASM Inactive transcription Active factor transcription factor P Response DNA Gene NUCLEUS Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings mRNA • Branching and “cross-talk” further help the cell coordinate incoming signals Signal molecule Cell A. Pathway leads to a single response Receptor Relay molecules Response 1 Response Response 2 Cell B. Pathway branches, leading to two responses 3 Cell C. Cross-talk occurs between two pathways Activation or inhibition Response 4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Response 5 Cell D. Different receptor leads to a different response Signaling Efficiency: Scaffolding Proteins and Signaling Complexes • Scaffolding proteins – Can increase the signal transduction efficiency Signal molecule Plasma membrane Receptor Scaffolding protein Figure 11.16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Three different protein kinases