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Chapter 4


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Cell Metabolism for Ivy Tech Community College

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Chapter 4

  1. 1. Cellular Metabolism• Metabolism = Sum of all reactions in the body
  2. 2. Metabolic reactions are of two types Anabolism • Synthesizes smaller molecules into larger molecules • Provides materials for growth and repair • Consumes energy Catabolism • Large molecules decompose into smaller molecules • Releases energy for cellular use ATP = energy
  3. 3. Dehydration Synthesis• Type of anabolic reaction• Joins triglycerides, polysaccharides, and proteins• Water is formed from dehydration synthesisDehydration synthesis joiningamino acids together
  4. 4. Dehydration Synthesis• Synthesizes polysaccharides from monosaccharides• Synthesizes proteins from amino acids• Joins fatty acids to glycerol, forming form fats• Synthesizes nucleic acids from nucleotides
  5. 5. Catabolism• Reverse of Anabolism• Breaks down molecules• Releases energy from chemical bonds• Example: Hydrolysis
  6. 6. Hydrolysis• Type of Catabolic reaction• Reverse of dehydration synthesis• Requires water to break bonds
  7. 7. Hydrolysis• Decomposes Polysaccharides into monosaccharides & disaccharides• Decomposes proteins into amino acids• Decomposes Fats into fatty acids & glycerol• Decomposes Nucleic Acids into nucleotides
  8. 8. Anabolism & Catabolism are reversible reactionsEnzymes control direction & rate of reactions
  9. 9. Enzyme ActionsEnzymes• Are biological catalyst• They greatly reduce the activation energy required to start a reaction.Substrate• Target molecule of an enzyme• Each enzyme acts on a specific substrate
  10. 10. Enzyme Characteristics• Most all are Proteins• Catalyze reactions - Increases the rate of reactions• Reusable - Not consumed by reaction• Specificity – Able to “recognize” a specific substrate
  11. 11. Enzyme Names• Named for substrate they act upon• Usually end with ____ ase.• Examples: • Lipase: decomposes lipids • Protease: decomposes proteins • Nuclease: decomposes nucleic acids • ATP Synthase: synthesizes ATP molecules
  12. 12. b. Enzyme- Enzyme releases a. Active site Substrate product Complex• Region of enzyme • Enzyme temporarily binds to • Enzyme is reused that binds to substrate to join new substrate substrates
  13. 13. Rates of reactions are limited by:• The concentration of substrate• The concentration of enzyme• The efficiency of enzymes • Some enzymes handle 2-3 molecules per second • Other enzymes handle thousands per second
  14. 14. Metabolic Pathways • Complex series of reactions leading to a product • Pathways are controlled by several enzymesExample: Catabolic pathway forthe breakdown of glucose
  15. 15. Metabolic Pathways • The product of each reaction becomes the substrate of next reaction. • Each step requires its own enzyme • “Rate-Limiting Enzyme” • Least efficient enzyme in group • Rate-limiting enzyme is usually first in sequence• Enzyme A = Rate-limiting Enzyme
  16. 16. Negative Feedback in Metabolic Pathway• Product of reaction often inhibits the rate-limiting enzyme.• Negative feedback prevents the overproduction of a product.
  17. 17. Cofactor• Combines with and activates some enzymes • Exposes the active site of enzyme to substrate• Cofactors are non-proteins• Include ions (zinc, iron, copper) and coenzymesCoenzymes = organic cofactors• Coenzymes include Vitamins (Vitamin A, B, D)• Reusable – required in small amounts
  18. 18. Vitamins• Essential organic molecules that humans cannot synthesize - must come from diet• Many vitamins are coenzymes• Vitamins can function repeatedly, so can be used in small amounts.• Example: Coenzyme A
  19. 19. Energy for Metabolic ReactionsEnergy: is the capacity to change something, orability to do work. Common forms of energy: Heat Light Sound Chemical energy Mechanical energy Electrical energy
  20. 20. Energy cannot be created or destroyed. Only transferred from one form to another Think of a combustion engineFuel (chemical energy) = Kinetic Energy + CO2 + H2O + Oxygen
  21. 21. Cellular Respiration• Cell Respiration: is the transfer of energy from food to make available for cellular use• Energy is stored in the electrons of food molecules• Oxidation: “controlled burning” of food molecules to release their energy• Cellular respiration requires enzymes
  22. 22. Cellular RespirationGlucose (C6H12O6) + 6O2 → Energy for ATP + H2O + CO2 ATP Energy from foods such as glucose is used to make ATP End of Section 1, Chapter 4
  23. 23. Mitochondria
  24. 24. Cellular RespirationGlucose (C6H12O6) + 6O2 → Energy for ATP + H2O + CO2 ATP Energy from Energy for Chemical bonds ATP synthesis
  25. 25. Currency of Energy for cells AdenosineTriphosphate
  26. 26. Diphosphate Adenosine
  27. 27. ATP ADP hydrolysis Products: ADP + Phosphate + Energy
  28. 28. Phosphorylation of ADP resynthesizes ATP
  29. 29. ATP provides energy For metabolic reactionsCell Respiration Figure 4.8Regenerates ATP
  30. 30. Cell RespirationAnaerobic Aerobic• No oxygen required • Requires oxygen• Yields little energy • Much greater energy yield• Yields 2 ATP per glucose • Up to 38 ATP per glucose
  31. 31. glycolysis Acetyl CoA synthesis Citric Acid CycleElectron Transport Chain
  32. 32. Glycolysis• Series of 10 reactions• Breaks down glucose into 2 Pyruvic Acid molecules• Occurs in Cytoplasm of Cell• Anaerobic Reaction (no oxygen required)• Yields • 2 ATP (net gain) per glucose • 2 NADH molecule • 2 Pyruvic Acid molecules
  33. 33. • 2 Phosphates are added to end of glucose• Glucose is a 6-carbon sugar• Primes glucose for further reactions• Consumes 2 ATP
  34. 34. • 6-Carbon glucose is split into 2 3-carbon Pyruvic Acid molecules• Produces 4 ATP total• Produces 2 NADH molecules
  35. 35. +4 ATP produced- 2ATP consumed
  36. 36. •1 NADH •2 FADH2 2 electrons attached to 2 electrons attached to hydrogen NADH1. NAD+ + 2H+ H NADH + H+ 2 electrons attached to 2. FAD + 2H FADH2 FADH2 NADH & FADH2 carry electrons to the electron transport chain
  37. 37. No oxygen toreceive electronsfrom NADH
  38. 38. Without Oxygen, NADH donates its electrons to pyruvic acidThis regenerates NAD+, which is used again for glycolysisLactic Acid is formed as waste 2 electronsPyruvic Acid + NADH Lactic Acid + NAD+
  39. 39. Once oxygen is available:Lactic Acid is converted back to glucose by the liverAnaerobic Respiration• Inefficient reaction; yields only 2 ATP• Consumes a great deal of glucose• Quick source of energy; for intense exercise
  40. 40. If Oxygen is available, pyruvic acid can continue through aerobic respiration inside the mitochondria Pyruvic Acid (3 Carbon)Aerobic Pathways Include:1. Acetyl CoA synthesis Mitochondria2. Citric Acid Cycle3. Electron Transport Chain (ETC)
  41. 41. Mitochondria• Powerhouse of cell• Synthesizes ATP• 2 layers – Outer Membrane – Inner Membrane• Cristae • highly folded inner membrane • Greatly increases surface area for reactions
  42. 42. Synthesis of Acetyl CoAPyruvic Acid is converted into Acetyl CoA Acetyl CoA = substrate for Citric Acid Cycle
  43. 43. Synthesis of Acetyl CoA Pyruvic Acid (3 Carbon)1 carbon is lost as CO2 CO2 (waste) Acetic Acid CoA (2 Carbon) (coenzyme A) Acetyl CoA (Enters Citric Acid Cycle)
  44. 44. Products from Acetyl CoA Synthesis• 1 molecule of CO2• Acetyl CoA
  45. 45. Citric Acid Cycle Begins when Acetyl CoA combines with Oxaloacetic Acid to form Citric Acid. Acetyl CoA + Oxaloacetic Acid → Citric Acid (2 carbons) (4 carbons) (6 carbons)Citric Acid = Oxaloacetic acid =Start molecule of cycle end molecule of cycle Citric Acid is converted back to Oxaloacetic acid through a series of 8-9reactions
  46. 46. Acetyl CoA (2 carbons) Oxaloacetic Acid (4 carbons) + Oxaloacetic acid is regenerated Citric Acid2CO2 (6 Carbons)(waste) 2ADP Citric Acid Cycle 8-9 reactions FADH2 2 ATP FAD 3 NADH 3NAD+
  47. 47. Products of Citric Acid Cycle• 2 ATP• 3 NADH = transports electrons to ETC• 1 FADH2 = transports electrons to ETC• 2 CO2
  48. 48. Electron transport chain (ETC)• Occurs on inner membrane of mitochondria• ATP synthase (enzyme): phosphorylates ADP → ATP• Involves a chain of 3 enzymes (protein complexes)• Produces 32-34 ATP per glucose• Requires Oxygen to accept electrons
  49. 49. Enzyme Complexes in ETC• Transport Complex Proteins – 3 Membrane proteins on inner membrane of Mitochondria – NADH & FADH2 transfer electrons to complex proteins – Electrons are passed from one complex to the next complex – Transfer of electrons releases energy to power ATP Synthase• ATP Synthase – Phosphorylates ADP into ATP – Powered by Transport Complex Proteins
  50. 50. ADP + P ATP Synthase ATP 2 electrons energy NADH energy Complex I energy Complex II NAD+ 2H+ (reused) Complex III + ½ O2 H2O (final electron acceptor)Without Oxygen to accept electrons, ETC would grind to a halt!
  51. 51. Products of Electron Transport Chain• H2O• 32-34 ATP
  52. 52. Lipids & Proteins can also be broken down for ATP synthesis Summary of catabolism of proteins, fats, & carbohydrates Most common entry point toaerobic respiration is into citric acid cycle as acetyl coA
  53. 53. End of Section 3, Chapter 4
  54. 54. Pathway of Protein Synthesis transcription translationDNA RNA ProteinsDNA Replication (DNA Synthesis) replicationDNA DNA Copy of original
  55. 55. backbone backboneAntiparallel Hydrogen bonds Strand 1 Strand 2
  56. 56. Properties of DNA4 nitrogenous bases Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Adenine & Guanine = Purines • 2 organic rings Thymine & Cytosine = Pyrimidines • 1 organic ring
  57. 57. Complementary Base PairsPurine pairs with Pyrimidine: Adenine pairs with Thymine Guanine pairs with Cytosine A & T = complimentary base pair G & C = complementary base pair
  58. 58. H-bonds stabilize complimentary base pairsDNA is twisted into a double helix
  59. 59. Overview of DNA Replication• Occurs during S-phase• Original DNA strand is used as a template to synthesize a new complimentary DNA strand.• Catalyzed by DNA Polymerase – Synthesizes new DNA strand• Semi-Conservative – One strand of the replicated DNA is new, the other is the original molecule.
  60. 60. Original DNA strand Strand 1 sugar phosphate backbone A C T A A T A A C G G A T G A T C T G A T T A T T G C C T A C T A G Strand 2 Hydrogen Bonds
  61. 61. Step 1. Hydrogen bonds break, and strands separate T A A C G G A T DNA A C T A A Polymerase G A T C T G A T T DNA C T A G Polymerase A T T G C C T A Replication bubbleStep 2. DNA Polymerases attach to open strands
  62. 62. Step 3. DNA Polymerase adds new bases T A A C G G A T A T T G C C T A A C T A A G A T C T G A T T T A A C G G A T C T A GH bonds continue to break A T T G C C T A Replication bubble
  63. 63. Step 3. DNA Polymerase adds new bases A C T A A T A A C G G A T G A T C T G A T T A T T G C C T A C T A G A C T A A T A A C G G A T T T T C T G A T T A T T G C C T A C T A G
  64. 64. A C T A A T A A C G G A T G A T CT G A T T A T T G C C T A C T A GA C T A A T A A C G G A T T T T CT G A T T A T T G C C T A C T A G 2 Complete DNA molecules Each with 1 original strand & 1 new strand
  65. 65. The two DNA molecules separate during mitosis End of Section 4, Chapter 4
  66. 66. Transcription & Translation Section 5, Chapter 4
  67. 67. 3 RNA Molecules• Messenger RNA (mRNA): • Transcribed from DNA in nucleus• Transfer RNA (tRNA): •Translates a codon of MRNA into an amino acid •Carries amino acids to mRNA •Anticodons on tRNA are complimentary to codons of mRNA •• Ribosomal RNA (rRNA): • Provides structure and enzyme activity for ribosomes 76
  68. 68. mRNA MoleculesMessenger RNA (mRNA):•Delivers genetic information from DNA DNA mRNA nucleus to the cytoplasm S P A U P S• Single polynucleotide chain S Direction of “reading” code P T A P S•Formed beside a strand of DNA S P C G P S• RNA nucleotides are complementary P Sto DNA nucleotides (exception – no C G P Sthymine in RNA; replaced with uracil) P S G C P S Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  69. 69. Step 1. RNA Polymerase attaches to DNA strands & breaks Hydrogen bonds Strand 1 A C T A C T A A C G G A T G A T C RNA Polymerase T G A T G A T T G C C T A C T A G Strand 2
  70. 70. Step 2. Strands Separate T A C C G G A T G A T C RNA A U G G C C U A C U A G A C T A A Polymerase mRNA T G A T T A T G G C C T A C T A G Replication bubbleStep 3. RNA Polymerase synthesizes mRNA using DNA strand as a template
  71. 71. T A C C G G A T G A T C RNA A U G G C C U A C U A G A C T A A Polymeras mRNA T G A T T A T G G C C T A C T A GStep 4. RNA Polymerase releases mRNA& DNA resumes original structure
  72. 72. A C T A A T A C C G G A T G A T C T G A T T A T G G C C T A C T A G A U G G C C U A C U A G mRNAStep 5. mRNA is undergoes further processing & leaves nucleus
  73. 73. • Codon = 3 letter sequence that encodes for an amino acid• All mRNA begin with AUG “Start Codon” Start Codon A U G G C C U A C U A G mRNA
  74. 74. Note:• Codons are redundant - Each amino acid corresponds to more than one codon• e.g. UCU, UCC, and UCA all encode for Serine•Start Codon (AUG)initiates translation•Stop Codons terminatetranslation
  75. 75. Protein SynthesisThe codon sequence of mRNAdetermines the amino acid sequenceof a protein. Figure 4.23
  76. 76. 2. Amino acid tRNA binding siteClover-leaf shapeRNA with 2important regions 1. Anticodon
  77. 77. Ribosomes• Small particle of protein & ribosomal RNA (rRNA)• Ribosomes have 2 subunits • Small subunit binds to mRNA • Large subunit holds tRNA & amino acids• Small subunit has 2 binding sites for adjacent mRNA codons• Ribosomes link amino acids by peptide bonds
  78. 78. Ribosomes Peptide bond forming large subunitanticodons small subunit Binding sites with codons
  79. 79. 1. mRNA binds to the small subunit of a Ribosome.2. The ribosome „reads‟ the mRNA sequence3. tRNA brings amino acids to the ribosomes, aligning their anticodons with mRNA codons4. The Ribosome links the amino acids together5. Polypeptide chain lengthens
  80. 80. Anchors polypeptide.
  81. 81. tRNA released
  83. 83. After translation Chaperone proteinsfold protein into its configurationEnzymes may further modify proteinsafter translation = post-translational modification• Phosphorylation – adding a phosphate to the protein• Glycosylation – adding a sugar to the protein
  84. 84. End of Section 5, Chapter 4