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Chapter 4 Cellular Metabolism

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4.1 Introduction A.The total of chemical reactions in a cell -> Metabolism B.Special type of protein called enzymes control the rate of these reactions. 2

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4.2 Metabolic Processes A.Metabolic reactions are of two types: 1. Anabolic reactions -> larger molecules are constructed from smaller ones (requires energy) 2. Catabolic reactions -> larger molecules are broken down (releasing energy) *The reactions of metabolism are often reversible.* 3

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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. 4

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5 3. Polysaccharides, lipids, and proteins are constructed by dehydration synthesis. a. To form fats, glycerol and fatty acids bond.

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b. The bond between two amino acids is a peptide bond; two bound amino acids form a dipeptide, while many joined form a polypeptide.

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7 c. Monosaccharides are bonded to produces a disaccharide.

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C.Catabolism 1. Catabolism breaks apart larger molecules into their building blocks. 2. These reactions occur by hydrolysis, where a molecule of water is inserted into a polymer which is split into two smaller molecules. 8

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3. Hydrolysis is the reverse of dehydration synthesis. 4. Like dehydration synthesis, hydrolysis requires specific enzymes, discussed in the next section.

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4.3 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.* 10

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2. Each enzyme is specific, acting on only one kind of substrate. ~ Enzyme names are often derived from the name of their substrate, with the suffix ase added. ex. Sucrase - sucrose, maltase maltose & lactase - lactose. 11

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3. Active sites on the enzyme combine with the substrate and a reaction occurs. 12

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4. Enzymes work in small quantities and are recycled by the cell. 5. The speed of enzymatic reactions depends on the number of enzyme and substate molecules available.

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C. Factors That Alter Enzymes 1. Enzymes (proteins) can be denatured by heat, pH extremes, chemicals, electricity, radiation, and by other causes. 2. extremophiles, live in conditions of high or low heat, salinity, or pH. * Their enzymes have evolved under these conditions and are useful in industrial processes that are too harsh to use other enzymes.* 14

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D. Cofactors & Coenzymes 1. An enzyme may be inactive until it combines with a non-protein component that either helps the active sit change shape or helps bind the enzyme to its substrate. ~ cofactor ion of an element, such as copper, iron, or zinc ~ coenzyme small organic molecule

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2. Vitamins are essential organic molecules that humans cannot synthesize (or may not make in sufficient quantities) and must come from the diet. ~ Vitamins provide coenzymes & are required in very small quantities. ~ Why such small amounts?

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4.4Energy for Metabolic Reactions: A.Energy is the capacity to do work. 1. Forms include heat, light, sound, and electrical, mechanical, and chemical energy. 2. Energy can be changed from one form to another. 17

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ex. Engine changes chemical energy in fuel to heat & mechanical energy ? Light bulb 18

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B.Release of Chemical Energy 1. Release of chemical energy in the cell often occurs through the oxidation of glucose. 2. Burning glucose requires energy to begin the process. (enzymes reduce activation energy) 19

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3. The end-products of these reactions are heat (maintain body temperature) as well as stored energy. 4. About of the energy is captured in special energy- carrying molecules such as ATP. 20

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C. Cellular Respiration ~ Series of three reactions glycolysis citric acid cycle electron transport chain ~ Products Carbon Dioxide Water Energy ~ Energy is used to create ATP

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1. ATP Molecules a. Up to 38 molecules of ATP are produced for each molecule of glucose oxidized. b. Adenosine triphosphate (ATP) is a molecule that carries energy in a form that the cell can use. 22

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c. Each ATP molecule consists of three main parts: adenine, ribose and 3 phosphates in a chain.

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d. Release & storage of energy is in the form of high energy bonds between the phosphate groups.

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2. Anaerobic Respiration a. The first part of cellular respiration is the splitting of 6-C glucose that occurs through a series of enzyme-catalyzed steps called glycolysis. b. The result is two 3-C molecules of pyruvate. 25

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c. Glycolysis occurs in the cytosol and does not require oxygen (anaerobic). d. Energy from ATP is used to start the process but there is a net gain of energy as a result. 2 ATP start 4 ATP result 2 ATP - net 26

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3. Aerobic Respiration a. Oxygen is needed for aerobic respiration in the mitochondria. 1. Pyruvic acid is converted into an intermediate molecule called acetyl-CoA. 2. The citric acid cycle (Hans Kreb German-British biochemist) releases carbon dioxide & H+ resulting in the formation of ATP. 27

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3. Carrier molecules move e- from the citric acid cycle to the e- transport chain, where water & more ATP are formed. Summary Glycolosis 2 ATP Cytric Acid Cycle 2 ATP Electron Transport34 ATP Yield38 ATP

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b. There is a much greater gain of ATP molecules from aerobic respiration. c. The actual number of ATP varies for different types of cells. ex. Brain cells 32 ATP

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4.5 Metabolic Pathways: A.The enzymes controlling either an anabolic or catabolic sequence of reactions must act in a specific order. B.A sequence of enzyme-controlled reactions is called a metabolic pathway. 30

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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. 32

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4.6 Nucleic Acids ~Deoxyribonucleic acid (DNA) contains the genetic code needed for the synthesis of each protein (including enzymes). A. Genetic Information 1. A gene is a portion of a DNA that contains the genetic information for making a single protein. 33

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34 2. Because enzymes control synthesis reactions, all four groups of organic molecules depend on proteins. 3. The genome is all the DNA (genetic instructions) in a cell.

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B. DNA Molecules 1. Nucleotides are the building blocks of nucleic acids. 35

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2. A polynucleotide chain consists of nucleotides connected by a sugar-phosphate backbone. (Model) 3. A DNA molecule consists of two polynucleotide chains. (Model) ~ Notice that the sugars point in opposite directions 36

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4. Nitrogen bases project from the backbone of one strand and bind by hydrogen bonds to the base of the 2 nd strand. (Model) a. Four types of Bases A, T, G, C b. Pairing A T, C G ~ Called complementary base pairs 37

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5. The DNA molecule twists to form a double helix and may be millions of base pairs long. Hint: DNA profiling p. 82

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4.7DNA 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. (DNA Polymerase) 42

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3. Each new DNA molecule consists of one parental strand and one newly synthesized strand of DNA. Hint: Topic of interest p. 83 Mutations Topic of interest p. 87Proteomics 44

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4.8 Protein Synthesis ~Genetic Code 1. The sequence of nucleotides in a DNA molecule gives the order of aa for a protein. 2. This method of storing information for protein synthesis is the genetic code. 3. RNA molecules copy & transfer this information to the cytoplasm where proteins are manufactured. 45

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A. Transcription 1. RNA Molecules a. RNA molecules are single- stranded 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. 46

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c. Each amino acid corresponds to a triplet of DNA nucleotides; a triplet of nucleotides in mRNA is called a codon. 48

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d. Messenger RNA can move out of the nucleus and attach to a ribosomes in the cytoplasm where the protein will be made in a process called translation. 50

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B. Translation 1. In the cytoplasm transfer RNA has a triplet of nucleotides called the anticodon, which is complementary to nucleotides of the mRNA codon. 2. The ribosome holds the mRNA in position while the tRNA carries in the correct amino acid in sequence, with anticodons matching up to codons. 51

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3. The ribosome contains enzymes needed to join the amino acids together. 4. As the amino acids are joined, the new protein molecule changes into its unique shape. 53

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