hapter 4 ellular Metabolism
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. Introduction. living cell is the site of enzyme-catalyzed metabolic reactions that maintain life. 2
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. Metabolic Reactions. 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. he reactions of metabolism are often reversible. 3
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. B. nabolism 1. nabolism provides the substances needed for growth and repair. 2. hese reactions occur by dehydration synthesis, removing a molecule of water to join two smaller molecules. 4
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. 3. Polysaccharides, lipids, and proteins are constructed via dehydration synthesis. a. o form fats, glycerol and fatty acids bond. b. he bond between two amino acids is a peptide bond; two bound amino acids form a dipeptide, while many joined form a polypeptide. 5
Fig04.01 2 O O opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. 2 O 2 O 2 O O O O O O O O O O O O O O O 2 O O O O O Monosaccharide + Monosaccharide Disaccharide + Water 6
Fig04.02 O opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. O O O ( 2 ) 14 3 O ( 2 ) 14 3 O O 2 O O O ( 2 ) 14 3 O ( 2 ) 14 3 2 O O O 2 O O O ( 2 ) 14 3 O ( 2 ) 14 3 lycerol + 3 fatty acid molecules Fat molecule (triglyceride) + 3 water! molecules! 7
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display.. atabolism 1. atabolism breaks apart larger molecules into their building blocks. 2. hese reactions occur by hydrolysis, wherein a molecule of water is inserted into a polymer which is split into two smaller molecules. 8
Fig04.03 opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. Peptide! bond! O O O R O N N N N O 2 O R R R mino acid + mino acid Dipeptide molecule + Water 9
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. ontrol of Metabolic Reactions:. Enzymes control the rates of all the metabolic reactions of the cell. B. Enzyme ction 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
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. 2. Enzymes work in small quantities and are recycled by the cell. 3. Each enzyme is specific, acting on only one kind of substrate. 4. ctive sites on the enzyme combine with the substrate and a reaction occurs. 5. he speed of enzymatic reactions depends on the number of enzyme and substrate molecules available. 11
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display.. Factors hat lter Enzymes 1. Enzymes (proteins) can be denatured by heat, p 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. 12
Fig04.04 Substrate molecules opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. Product molecule ctive site Enzyme! molecule! Enzyme-substrate! complex! (a) (b) (c) Unaltered! enzyme! molecule!
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. Energy for Metabolic Reactions:. Energy is the capacity to do work. B. ommon forms of energy include heat, light, sound, electrical energy, mechanical energy, and chemical energy. 14
. Release of hemical Energy - 1. Release of chemical energy in the cell often occurs through the oxidation of glucose. D. ellular Respiration consists of 3 reactions: glycolysis, citric acid cycle & electron transport chain 1. P a. P molecules contain three phosphates in a chain. b. cell uses P for many functions including active transport and synthesis of various compounds.
Fig04.05 opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. lucose 1 lycolysis! he 6-carbon sugar glucose is broken down in the cytosol! into two 3-carbon pyruvic acid molecules with a net gain! of 2 P and the release of high-energy electrons.! ytosol igh-energy electrons (e ) lycolysis 2 P 2 Pyruvic acids! (Each enters separately)! 2 3 itric cid ycle! he 3-carbon pyruvic acids generated by glycolysis enter! the mitochondria separately. Each loses a carbon! (generating O 2 ) and is combined with a coenzyme to! form a 2-carbon acetyl coenzyme (acetyl o). More! high-energy electrons are released.! Each acetyl o 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 O 2 s), synthesizes! 1 P, and releases more high-energy electrons.! he figure shows 2 P, resulting directly from 2! turns of the cycle per glucose molecule that enters! glycolysis. Mitochondrion igh-energy electrons (e ) igh-energy electrons (e ) cetyl o Oxaloacetic acid itric acid! cycle! O 2 itric acid 2 O 2 2 P 4 Electron ransport hain! he 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 P molecules. he other products are! heat and water. he function of oxygen as the final! electron acceptor in this last step is why the overall! process is called aerobic respiration. ½ O 2! Electron! transport! chain! 2e and 2 + 32 34! P 2 O 16
c. Energy is stored in the last phosphate bond of P. d. Energy is stored while converting DP to P; when energy is released, P becomes DP, ready to be regenerated into P. 17
Fig04.06 opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. P P P P
Fig04.07 opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. P P P Energy transferred! from cellular! respiration used! to reattach! phosphate P P P P P Energy transferred! and utilized by! metabolic! reactions when! phosphate bond! is broken DP
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. 2. lycolysis a. he first part of cellular respiration is the splitting of 6- glucose that occurs through a series of enzymecatalyzed steps called glycolysis. b. lycolysis occurs in the cytosol and does not require oxygen (is anaerobic). c. Energy from P is used to start the process but there is a net gain of energy as a result. 20
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. 3. erobic Respiration 1. Oxygen is needed for aerobic respiration, which occurs within the mitochondria. 2. here is a much greater gain of P molecules from aerobic respiration. 3. he final products of glucose oxidation are carbon dioxide, water, and energy. 21
Fig04.09 opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. Food Royalty-Free/orbis Proteins! (egg white)! arbohydrates! (toast, hash browns)! Fats! (butter)! 1 Breakdown of large! molecules to! simple molecules mino acids Simple sugars! (glucose)! lycerol Fatty acids! lycolysis P Pyruvic acid cetyl coenzyme 2 Breakdown of simple! molecules to acetyl! coenzyme! accompanied by! production of limited! P and high-energy! electrons itric! acid! cycle igh-energy! electrons! O 2 P 3 omplete oxidation! of acetyl coenzyme! to 2 O and O 2 produces! high-energy electrons,! which yield much P! via the electron transport! chain Electron! transport! chain P 2e and 2 + N 2 ½ O 2 2 O O 2 Waste products 22
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. Metabolic Pathways:. he enzymes controlling either an anabolic or catabolic sequence of reactions must act in a specific order. B. sequence of enzyme-controlled reactions is called a metabolic pathway. 23
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display.. Regulation of Metabolic Pathways 1. he rate of a metabolic pathway is determined by a regulatory enzyme responsible for one of its steps. 2. rate-limiting enzyme is the first step in a series. 24
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. DN (Deoxyribonucleic acid):. Deoxyribonucleic acid (DN) contains the genetic code needed for the synthesis of each protein (including enzymes) required by the cell. B. enetic Information 1. gene is a portion of a DN molecule that contains the genetic information for making a single protein. he complete set of instructions is the genome. 25
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display.. DN Molecules 1. he nucleotides of DN form a sugar-phosphate backbone with bases extending into the interior of the DN molecule. 2. he nucleotides of one DN strand are compatible to those in the other strand (adenine pairs with thymine; cytosine with guanine) and so exhibit complementary base pairing. 26
3. he DN molecule twists to form a double helix and may be millions of base pairs long. 27
Fig04.10 opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. 28
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. D. DN Replication 1. Each new cell must be provided with an exact replica of the parent cell's DN. 2. DN replication occurs during interphase. a. he DN molecule splits. b. Nucleotides form complementary pairs with the original strands. 3. Each new DN molecule consists of one parental strand and one newlysynthesized strand of DN. 29
30 Fig04.11 Newly formed! DN molecules! Region of! replication! Original DN! molecule! opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display.
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. Protein Synthesis:. he enetic ode- Instructions for making proteins 1. he genetic code is the correspondence of gene and protein building block sequences. 31
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. 2. ranscription a. RN molecules are singlestranded and contain ribose rather than deoxyribose, and uracil rather than thymine. b. Messenger RN (mrn) molecules are synthesized in the nucleus in a sequence complementary to the DN template in a process called transcription. 32
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. 3. ranslation a. Each amino acid corresponds to a triplet of DN nucleotides; a triplet of nucleotides in messenger RN is called a codon. b. Messenger RN can move out of the nucleus and associate with ribosomes in the cytoplasm where the protein will be constructed in a process called translation. 33
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. c. In the cytoplasm, a second kind of RN, called transfer RN, has a triplet of nucleotides called the anticodon, which is complementary to nucleotides of the messenger RN codon. d. he ribosome holds the messenger RN in position while the transfer RN carries in the correct amino acid in sequence, with anticodons matching up to codons. 34
opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. e. he ribosome contains enzymes needed to join the amino acids together. f. s the amino acids are joined, the new protein molecule into its unique shape. 35
Fig04.13 opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. DN! double! helix Nucleus DN! strands! pulled! apart ranscription ytoplasm U U U U Direction of reading Messenger! RN 2 mrn leaves! the nucleus! and attaches! to a ribosome 1 DN! information! is copied, or! transcribed,! into mrn! following! complementary! base pairing Messenger! RN U 3 ranslation begins as trn anticodons! recognize complementary mrn codons,! thus bringing the correct amino acids into! position on the growing polypeptide chain DN! strand! Polypeptide! chain! Direction of reading 4 s the ribosome! moves along the! mrn, more amino! acids are added ranslation mino acids! attached to trn 6 trn molecules! can pick up another! molecule of the! same amino acid! and be reused 5 t the end of the mrn,! the ribosome releases! the new protein U U odon 1 odon 2 odon 3 odon 4 odon 5 odon 6 odon 7 mino acids! represented! Methionine lycine Serine lanine hreonine lanine lycine 36
Fig04.14 opyright he Mcraw-ill ompanies, Inc. Permission required for reproduction or display. 1 he transfer RN molecule! for the last amino acid added! holds the growing polypeptide! chain and is attached to its! complementary codon on mrn. 1 2 rowing! polypeptide! chain nticodon 3 4 5 6 U U U U Next amino acid ransfer! RN U 1 2 3 4 5 6 7 Messenger! RN odons 2 second trn binds! complementarily to the! next codon, and in doing! so brings the next amino! acid into position on the ribosome.! peptide bond forms, linking! the new amino acid to the! growing polypeptide chain. 1 2 rowing! polypeptide! chain 1 nticodon 2 3 3 4 4 5 5 6 U U U U 6 Peptide bond! Next amino acid! 7 ransfer! RN U Messenger! RN odons 3 he trn molecule that! brought the last amino acid! to the ribosome is released! to the cytoplasm, and will be! used again. he ribosome! moves to a new position at! the next codon on mrn. 1 2 3 4 5 U 6 U U U 7 Next! amino acid ransfer! RN U 1 2 3 4 5 6 7 Messenger! RN Ribosome 4 new trn complementary to! the next codon on mrn brings! the next amino acid to be added! to the growing polypeptide chain. 1 2 3 4 5 6 7 U U U Next! amino acid ransfer! RN U 1 2 3 4 5 6 7 Messenger! RN 37