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Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hole’s Essentials of Human Anatomy & Physiology David Shier Jackie Butler Ricki Lewis Power Points prepared by Melanie Waite-Altringer Biology Faculty Member of Anoka-Ramsey Community College APR Enhanced Lecture Outlines Chapter 4 Cellular Metabolism CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Introduction A. A living cell is the site of enzyme-catalyzed metabolic reactions that maintain life. 3 The Composite Cell CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metabolic Reactions A. Metabolic reactions are of two types: 1. anabolic reactions, larger molecules are constructed from smaller ones, a process requiring energy. 2. catabolic reactions, larger molecules are broken down, releasing energy. The reactions of metabolism are often reversible. 5 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. B. Anabolism 1. Anabolism provides the substances needed for growth and repair. 2. These reactions occur by dehydration synthesis, removing a molecule of water to join two smaller molecules. 6 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Polysaccharides, lipids, and proteins are constructed via dehydration synthesis. a. To form fats, glycerol and fatty acids bond. b. The bond between two amino acids is a peptide bond; two bound amino acids form a dipeptide, while many joined form a polypeptide. 7 Fig04.01 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CH2OH CH2OH O H HO OH H O H H H OH H H + H OH Monosaccharide CH2OH O H H HO OH OH Monosaccharide CH2OH OH H O H H HO OH H H O H OH Disaccharide H H H2O OH H H OH + OH Water 8 Fig04.02 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H H C O OH HO C H (CH 2)14 CH3 H C O O O H C OH HO C C OH HO C (CH 2)14 CH3 H C O C H2O H2O H2O (CH2)14 CH3 O (CH 2)14 CH3 H Glycerol (CH2)14 CH3 O O H C H C O C (CH2)14 CH3 H + 3 fatty acid molecules Fat molecule (triglyceride) + 3 water molecules 9 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Catabolism 1. Catabolism breaks apart larger molecules into their building blocks. 2. These reactions occur by hydrolysis, wherein a molecule of water is inserted into a polymer which is split into two smaller molecules. 10 Fig04.03 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Peptide bond H H N H C C R Amino acid H H O N H H + C H O C R Amino acid N H H H O C C R R N C H H Dipeptide molecule O C OH H2O + Water 11 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Control of Metabolic Reactions: A. Enzymes control the rates of all the metabolic reactions of the cell. B. Enzyme Action 1. Enzymes are complex proteins that function to lower the activation energy of a reaction so it may begin and proceed more rapidly. Enzymes are called catalysts. 12 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. 3. 4. 5. Enzymes work in small quantities and are recycled by the cell. Each enzyme is specific, acting on only one kind of substrate. Active sites on the enzyme combine with the substrate and a reaction occurs. The speed of enzymatic reactions depends on the number of enzyme and substrate molecules available. 13 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Factors That Alter Enzymes 1. Enzymes (proteins) can be denatured by heat, pH extremes, chemicals, electricity, radiation, and by other causes. Enzymes that only become active when they combine with a nonprotein component are cofactors. Small organic cofactors are called coenzymes. 14 Fig04.04 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Substrate molecules Product molecule Active site Enzyme molecule (a) Enzyme-substrate complex (b) (c) Unaltered enzyme molecule CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Energy for Metabolic Reactions: A. Energy is the capacity to do work. B. Common forms of energy include heat, light, sound, electrical energy, mechanical energy, and chemical energy. 16 C. D. Release of Chemical Energy 1. Release of chemical energy in the cell often occurs through the oxidation of glucose. Cellular Respiration consists of 3 reactions: glycolysis, citric acid cycle & electron transport chain 1. ATP a. ATP molecules contain three phosphates in a chain. b. A cell uses ATP for many functions including active transport and synthesis of various compounds. Fig04.05 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glucose High-energy electrons (e–) Cytosol Glycolysis 1 The 6-carbon sugar glucose is broken down in the cytosol into two 3-carbon pyruvic acid molecules with a net gain of 2 ATP and the release of high-energy electrons. 2 ATP Glycolysis 2 Pyruvic acids (Each enters separately) 3 Each acetyl CoA combines with a 4-carbon oxaloacetic acid to form the 6-carbon citric acid, for which the cycle is named. For each citric acid, a series of reactions removes 2 carbons (generating 2 CO2’s), synthesizes 1 ATP, and releases more high-energy electrons. The figure shows 2 ATP, resulting directly from 2 turns of the cycle per glucose molecule that enters glycolysis. High-energy electrons (e–) CO2 Mitochondrion Citric Acid Cycle 2 The 3-carbon pyruvic acids generated by glycolysis enter the mitochondria separately. Each loses a carbon (generating CO2) and is combined with a coenzyme to form a 2-carbon acetyl coenzyme A (acetyl CoA). More high-energy electrons are released. Acetyl CoA Citric acid Oxaloacetic acid Citric acid cycle High-energy electrons (e–) 2 CO2 2 ATP Electron Transport Chain 4 The high-energy electrons still contain most of the chemical energy of the original glucose molecule. Special carrier molecules bring the high-energy electrons to a series of enzymes that store much of the remaining energy in more ATP molecules. The other products are heat and water. The function of oxygen as the final electron acceptor in this last step is why the overall process is called aerobic respiration. Electron transport chain 32–34 ATP 2e– and 2H+ ½ O2 H2O 18 c. Energy is stored in the last phosphate bond of ATP. d. Energy is stored while converting ADP to ATP; when energy is released, ATP becomes ADP, ready to be regenerated into ATP. 19 Fig04.06 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P ATP P P Fig04.07 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P Energy transferred from cellular respiration used to reattach phosphate P P Energy transferred and utilized by metabolic reactions when phosphate bond is broken ATP P P P P ADP CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Glycolysis a. The first part of cellular respiration is the splitting of 6-C glucose that occurs through a series of enzymecatalyzed steps called glycolysis. b. Glycolysis occurs in the cytosol and does not require oxygen (is anaerobic). c. Energy from ATP is used to start the process but there is a net gain of energy as a result. 22 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Aerobic Respiration 1. Oxygen is needed for aerobic respiration, which occurs within the mitochondria. 2. There is a much greater gain of ATP molecules from aerobic respiration. 3. The final products of glucose oxidation are carbon dioxide, water, and energy. 23 Mitochondrion Cristae of Mitochondrion Fig04.09 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Food © Royalty-Free/Corbis Proteins (egg white) Carbohydrates (toast, hash browns) Amino acids Simple sugars (glucose) Glycolysis Fats (butter) Glycerol 2 Breakdown of simple molecules to acetyl coenzyme A accompanied by production of limited ATP and high-energy electrons Acetyl coenzyme A 3 Complete oxidation of acetyl coenzyme A to H2O and CO2 produces high-energy electrons, which yield much ATP via the electron transport chain CO2 ATP High-energy electrons Electron transport chain Fatty acids ATP Pyruvic acid Citric acid cycle 1 Breakdown of large molecules to simple molecules ATP 2e– and 2H+ –NH2 CO2 ½ O2 H2 O Waste products 26 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metabolic Pathways: A. B. The enzymes controlling either an anabolic or catabolic sequence of reactions must act in a specific order. A sequence of enzyme-controlled reactions is called a metabolic pathway. 27 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Regulation of Metabolic Pathways 1. The rate of a metabolic pathway is determined by a regulatory enzyme responsible for one of its steps. 2. A rate-limiting enzyme is the first step in a series. 28 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA (Deoxyribonucleic acid): A. Deoxyribonucleic acid (DNA) contains the genetic code needed for the synthesis of each protein (including enzymes) required by the cell. B. Genetic Information 1. A gene is a portion of a DNA molecule that contains the genetic information for making a single protein. The complete set of instructions is the genome. 29 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. DNA Molecules 1. The nucleotides of DNA form a sugar-phosphate backbone with bases extending into the interior of the DNA molecule. 2. The nucleotides of one DNA strand are compatible to those in the other strand (adenine pairs with thymine; cytosine with guanine) and so exhibit complementary base pairing. 30 Fig04.10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. The DNA molecule twists to form a double helix and may be millions of base pairs long. A T C G G C C G T A C G C G A T C G A T G C T A T A CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. D. DNA Replication 1. Each new cell must be provided with an exact replica of the parent cell's DNA. 2. DNA replication occurs during interphase. a. The DNA molecule splits. b. Nucleotides form complementary pairs with the original strands. 3. Each new DNA molecule consists of one parental strand and one newlysynthesized strand of DNA. 32 Fig04.11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A T C G G C C G Original DNA molecule A T C G C G A T A C T G A T G C C Region of replication G T A A T A T A G C C A G A T T T C T A T T G A G G A Newly formed DNA molecules C G A 33 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protein Synthesis: A. The Genetic Code- Instructions for making proteins 1. The genetic code is the correspondence of gene and protein building block sequences. 2. DNA molecules are trapped within a cell’s nucleus 3. Protein synthesis occurs in the cytoplasm 4. Genetic information must be carried from the nucleus to the cytoplasm 34 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Transcription a. RNA molecules are singlestranded and contain ribose rather than deoxyribose, and uracil rather than thymine. b. Messenger RNA (mRNA) molecules are synthesized in the nucleus in a sequence complementary to the DNA template in a process called transcription. 35 Nucleus Nuclear Pores CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Translation a. Each amino acid corresponds to a triplet of DNA nucleotides; a triplet of nucleotides in messenger RNA is called a codon. b. Messenger RNA can move out of the nucleus and associate with ribosomes in the cytoplasm where the protein will be constructed in a process called translation. 38 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. c. d. In the cytoplasm, a second kind of RNA, called transfer RNA, has a triplet of nucleotides called the anticodon, which is complementary to nucleotides of the messenger RNA codon. The ribosome holds the messenger RNA in position while the transfer RNA carries in the correct amino acid in sequence, with anticodons matching up to codons. 39 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. e. The ribosome contains enzymes needed to join the amino acids together. f. As the amino acids are joined, the new protein molecule into its unique shape. 40 Membrane-bound Ribosomes Free Ribosomes Rough Endoplasmic Reticulum Fig04.13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3 Translation begins as tRNA anticodons recognize complementary mRNA codons, thus bringing the correct amino acids into position on the growing polypeptide chain Cytoplasm DNA double helix T Nucleus A T G A C T A G C G T A G C A T C T A G C A T G C G T A G C A T C T A A T G C T A G C A T G DNA strands pulled apart C T A T G G G C T C C G C A A C G G C A G G C T C C A T G A C G C G T A G C T U A 2 mRNA leaves the nucleus and attaches Messenger to a ribosome RNA 6 tRNA molecules can pick up another molecule of the same amino acid and be reused Polypeptide chain G C G C G C C G U A C G C G G C C G A T A T C G G C G C C G A T G C G C C G U A C G C G A U A G C A T C G C 5 At the end of the mRNA, the ribosome releases the new protein Direction of “reading” 1 DNA information is copied, or transcribed, into mRNA following complementary base pairing 4 As the ribosome moves along the mRNA, more amino acids are added Amino acids represented A U Codon 1 Methionine Codon 2 Glycine Codon 3 Serine Codon 4 Alanine Codon 5 Threonine Codon 6 Alanine Codon 7 Glycine G G G C U C C Messenger RNA A G Amino acids attached to tRNA C A G C A C G C A T G G C G C C G A G Transcription U C G C DNA strand C A G Translation G G C 44 Fig04.14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 The transfer RNA molecule for the last amino acid added holds the growing polypeptide chain and is attached to its complementary codon on mRNA. 1 2 Growing polypeptide chain 3 4 Next amino acid 5 6 Transfer RNA Anticodon U G C C G U A U G G G C U C C G C A A C G G C A G G C A A G C G U 1 2 3 4 5 6 Messenger RNA 7 Codons Peptide bond 1 2 2 A second tRNA binds complementarily to the next codon, and in doing so brings the next amino acid into position on the ribosome. A peptide bond forms, linking the new amino acid to the growing polypeptide chain. Growing polypeptide chain 3 Next amino acid 4 5 6 Transfer RNA Anticodon U G C C G U A U G G G C U C C G C A A C G G C A G G C A A G C G U 1 2 3 4 5 6 Messenger RNA 7 Codons 1 2 3 The tRNA molecule that brought the last amino acid to the ribosome is released to the cytoplasm, and will be used again. The ribosome moves to a new position at the next codon on mRNA. 3 4 7 5 Next amino acid 6 Transfer RNA C G U A U 1 G G C U C C G C A A C G G C A G G C A A G C G U 2 3 4 5 6 7 Messenger RNA Ribosome 1 2 3 4 A new tRNA complementary to the next codon on mRNA brings the next amino acid to be added to the growing polypeptide chain. 4 5 6 7 Next amino acid Transfer RNA C G U C C G A U G G G C U C C G C A A C G G C A G G C A A G C G U 1 2 3 4 5 6 7 Messenger RNA 45