Transcript Slide 1
Section 1, Chapter 4 Chapter 4, Metabolism Cellular Metabolism metabolism is the sum of all reactions in the body metabolic reactions are of two types Anabolism In anabolic reactions energy is used to synthesize large molecules from smaller molecules. Anabolic reactions create materials for growth and repair. Catabolism In catabolic reactions large molecules are decomposed into smaller molecules Catabolic reactions release energy for cellular use Dehydration Synthesis Dehydration synthesis is a type of anabolic reaction. triglycerides, polysaccharides, and proteins are synthesized through dehydration synthesis A molecule of water is released from dehydration synthesis. Amino acids are joined by dehydration synthesis Dehydration Synthesis Synthesizes polysaccharides from monosaccharides proteins from amino acids nucleic acids from nucleotides fats by joining fatty acids to glycerol dehydration synthesis Hydrolysis hydrolysis is the reverse of dehydration synthesis water is used to break apart molecules hydrolysis releases energy from chemical bonds hydrolysis Hydrolysis Decomposes Polysaccharides into monosaccharides & disaccharides Decomposes proteins into amino acids Decomposes Fats into fatty acids & glycerol Decomposes Nucleic Acids into nucleotides The critical amount of energy required for a reaction to occur is called the activation energy. Enzymes are biological catalysts They greatly reduce the activation energy required to start a reaction. Characteristics of enzymes Most enzymes are Proteins Enzymes lower the activation energy of a reaction Enzymes catalyze reactions – they increase the rate of reactions, but are not consumed by the reaction Enzymes are specific to one substrate. A substrate is the target molecule of an enzyme Enzyme Names Enzymes are named for substrate they act upon and their name usually ends with _____ase. Examples of enzymes: Lipase: decomposes lipids Protease: decomposes proteins Nuclease: decomposes nucleic acids ATP Synthase: synthesizes ATP molecules Enzymes The Active site of an enzyme is the region that binds to the substrate The enzyme temporarily binds to the substrate forming an Enzyme-Substrate Complex The Enzyme releases the product and enzyme is reused for a new reaction. Rate of enzyme-catalyzed reactions The rate of a reaction is limited by: 1. The concentration of substrate 2. The concentration of enzyme 3. The efficiency of enzymes Some enzymes handle 2-3 molecules per second Other enzymes handle thousands per second Metabolic Pathways A metabolic pathway is a complex series of reactions leading to a product Metabolic Pathways are controlled by several enzymes Example: The catabolic pathway for the breakdown of glucose is highly complex. Metabolic Pathways The product of each reaction becomes the substrate of next reaction. Each step requires its own enzyme The least efficient enzyme is the “Rate-Limiting Enzyme” Rate-limiting enzyme is usually first in sequence • Enzyme A = Rate-limiting Enzyme Negative Feedback in Metabolic Pathway Negative feedback prevents too much product from being produced. The product of the metabolic pathway often inhibits the rate-limiting enzyme. Cofactor substance that increases the efficiency of an enzyme Cofactors include ions (zinc, iron, copper) and coenzymes Coenzymes are organic cofactors Coenzymes include Vitamins (Vitamin A, B, D) Reusable – required in small amounts Vitamins are essential organic molecules that humans cannot synthesize, so they must come from diet Many vitamins are coenzymes Vitamins can function repeatedly, so can be used in small amounts. Example: Coenzyme A Energy for Metabolic Reactions Energy: is the capacity to change something, or ability to do work. Common forms of energy: Heat Light Sound Chemical energy Mechanical energy Electrical energy Energy cannot be created or destroyed, but it may be transferred from one form to another. example of energy transfer: combustion engine The combustion of fuel converts chemical energy in the gasoline into kinetic energy, heat, sound. Water and CO2 are produced as waste. Fuel (chemical energy) + Oxygen = Kinetic Energy + CO2 + H2O Cellular Respiration Cell Respiration is the transfer of energy from food molecules into a form the cells can use Energy from foods such as glucose is used to make ATP for the cell. Reaction of Cell Respiration Initial fuel or energy source End of Section 1, Chapter 4 ATP = Energy currency for cells Section 2, Chapter 4 Overview of Cell Respiration Initial fuel or energy source ATP = energy currency used by cells Glucose is broken down to make ATP Oxidation- transfer of electrons away from a molecule. Glucose is oxidized in cell respiration. Energy from the transfer of e- away from glucose is used to make ATP. Cells break down ATP into ADP for cell activity. Adenosine Triphosphate (ATP) Adenosine Diphosphate (ATP) Currency of Energy for cells ATP is converted to ADP by hydrolyzing one of the phosphorus bonds ADP ATP hydrolysis Energy is released by hydrolyzing 3 rd phosphate group of ATP Cells quickly use their ATP supplies for cell activity, so the ATP must be replenished. Cell respiration regenerates ATP supplies by adding a phosphate to ADP ATP provides energy for cell activity Cell Respiration regenerates ATP Figure 4.8 Cell Respiration anaerobic respiration (glycolysis) occurs in the cytoplasm does not require oxygen yields 2 ATP per glucose aerobic respiration occurs in mitochondria requires oxygen yields up to 38 ATP per glucose Cell Respiration involves 3 reactions 1. Glycolysis Glycolysis is a series of anaerobic reactions that occur in the cytoplasm. Glucose is broken down into 2 molecules of pyruvic acid Only 2 molecules of ATP are produced per glucose molecule. 2. Citric Acid Cycle (Kreb’s Cycle) If oxygen is present respiration continues into the Citric Acid Cycle within the matix of the mitochondrion. 3. Electron Transport Chain Aerobic respiration is complete in the electron transport chain. ETC occurs on the inner membrane of the mitochondrion. Overview of Cell Respiration 2 ATP If O2 available glucose 1. glycolysis Without O2 Lactic acid 2. citric acid cycle 3. ETC Up to 36 ATP Overview of Cell Respiration cell glucose mitochondrion 1. Glycolysis (anaerobic ) pyruvic acid O2 available pyruvic acid O2 not available Lactic acid 2. CAC 3. ETC Electron Carriers: NADH & FADH2 During respiration electrons are removed from glucose and transported to the ETC by electron carriers. Energy from the electrons is used to synthesize ATP in the ETC. glucose 2e- 2e- NAD+ NADH 2e- FAD FADH2 NADH carries 2e- from glucose into the ETC, where its worth 2-3 ATP FADH2 carries 2e- into the ETC, where its worth 2 ATP glucose Summary of Glycolysis Phase 1: phosphorylation of glucose 2 phosphates are added to glucose. 2 ATP are hydrolyzed into 2 ADP molecules in this step. ATP ATP ADP ADP Phase 1 Phase 2 Phase 2: lysing of glucose Glucose is split into 2 3-carbon molecules Phase 3: oxidation of glucose glucose is oxidized into 2 molecules of pyruvic acid Phase 3 produces 4 ATP, 2 NADH 2 molecules of pyruvic acid. 2ADP 2ADP 2 ATP 2ATP Phase 3 NAD+ NAD+ NADH NADH pyruvic acid pyruvic acid +4 ATP are produced in the third phase - 2ATP are used in the first phase Glycolysis produces a net gain of 2 ATP The overall products of glycolysis includes: 2ATP 2 Pyruvic Acids 2 NADH (these carry e- to the ETC) pyruvic acid If O2 is not available pyruvic acid completes anaerobic respiration in the cytoplasm. If O2 is available pyruvic acid enters mitochondria for aerobic respiration. Anaerobic Respiration The electron carriers (NADH) from glycolysis cannot enter into the ETC if oxygen is not available. Without oxygen NADH donates its electrons to pyruvic acid, forming Lactic acid. 2e- NADH NAD+ 2e- pyruvic acid lactic acid This replenishes NAD+ supplies, so they can be used to remove electrons from additional glucose molecules. Anaerobic Respiration Without O2, Lactic acid builds up as glucose is burned During exercise when there isn’t sufficient O2 for aerobic respiration, lactic acid (Lactate) accumulates in the cells. Anaerobic Respiration Once oxygen is available (eg after exercise), then Lactic Acid is converted back to glucose by the liver Oxygen debt is the amount of O2 required to convert the lactic acid back to glucose after exercise. Anaerobic respiration yields only 2 ATP per glucose, but it provides cells with a quick source of energy; for exercise End of section 2, chapter 4 Glycolysis Glycolysis breaks down glucose into 2 Pyruvic Acid molecules Occurs in Cytoplasm of Cell Anaerobic Reaction (no oxygen required) Glycolysis Yields 2 ATP (net gain) per glucose 2 NADH molecule (worth 2-3 ATP in the ETC) 2 Pyruvic Acid molecules If oxygen is available, pyruvic acid can continue through aerobic respiration inside the mitochondria Pyruvic Acid (3 Carbon) Aerobic Pathways Includes 1. Citric Acid Cycle 2. Electron Transport Chain (ETC) Mitochondrion mitochondria Mitochondria are the powerhouse of cell. Most ATP are synthesized within mitochondria Mitochondria consists of two layers Outer Membrane Inner Membrane – the inner membrane is highly folded into cristae. Cristae greatly increase the surface area for the ETC Priming Pyruvic Acid for the Citric Acid Cycle Before pyruvic acid can enter the CAC it must first be converted into acetyl CoA For each pyruvic acid, this reaction produces 1 CO2 molecule 1 NADH molecule 1 Acetyl CoA pyruvic acid 1 molecule of CO2 is released Acetyl CoA is the substrate for the citric acid cycle. NAD+ NADH Coenzyme A acetyl CoA Citric Acid Cycle The citric acid cycle occurs in the matrix of the mitochondrion. pyruvic acid Citric Acid Cycle Conenzyme A released Acetyl CoA combines with oxaloacetic acid to form citric acid. acetyl coA Citric acid is converted back to oxaloacetic acid + oxaloacetic acid acetic acid citric acid FADH2 Citric Acid Cycle 3 NAD+ FAD 3 NADH 2CO2 ATP ADP + P Products of the citric acid cycle include: 1 ATP 3 NADH = transports electrons to ETC 1 FADH2 = transports electrons to ETC 2 CO2 electron transport chain (ETC) The ETC is located on the inner membrane of mitochondria An enzyme called ATP synthase forms ATP by attaching a phosphate to ADP ATP synthase is powered by the transfer of e- along a chain protein complexes that form the ETC. The ETC produces 32-34 ATP per glucose Oxygen removes electrons from the final complex protein, so it is the final e- acceptor ETC Electron Transport Chain 1. NADH (and FADH2) transfer their electrons to the first complex protein. 2. e- are transported along the protein complexes of the ETC. Products of Electron Transport Chain include 32-34 ATP and Water. 5. The H+ gradient established by the ETC is used to power ATP Synthase. 3. Energy from the etransfer is used to pump H+ into the inner membrane space. 4. Oxygen removes efrom the last complex protein. Water is formed in this reaction. 6. ATP Synthase generates new ATP by adding a phosphate to ADP. catabolism of proteins, fats, & carbohydrates Lipids & Proteins can also be broken down and used for ATP synthesis Most organic molecules are converted into acetyl CoA and enter the citric acid cycle as acetyl coA End of Section 3, Chapter 4 Section 4, Chapter 4 DNA Replication & Protein Synthesis Pathway of Protein Synthesis DNA transcription RNA translation transcript DNA Replication (DNA Synthesis) DNA replication DNA Copy of original Protein Definitions Gene = portion of DNA that encodes one protein Genetic code = 3 letter DNA sequence that encodes for 1 amino acid Genome = complete set of genetic instructions for an organism Human genome = 46 chromosomes in diploid pairs DNA encodes the genetic instructions for protein synthesis It is a double-stranded helix Strand 1 The two strands run in opposite directions and therefore are anti-parallel. Strand 2 The two strands are held together by hydrogen bonds Properties of DNA DNA contains 4 nitrogenous bases Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Adenine & Guanine are purines 2 organic rings Thymine & Cytosine are pyrimidines 1 organic ring Purine pairs with Pyrimidine Complimentary Base Pairs A pairs with T G pairs with C Example of complimentary base pairs. H-bonds stabilize complimentary base pairs DNA is twisted into a double helix Overview of DNA Replication DNA replication occurs during S-phase (within interphase) The original DNA strand is used as a template to synthesize a new complimentary DNA strand. DNA replication is catalyzed by the enzyme DNA Polymerase DNA replication is Semi-Conservative – One strand of the replicated DNA is new, the other is the original molecule. DNA Replication The two DNA molecules separate during mitosis End of Section 4, Chapter 4 Section 5, Chapter 4 Transcription & Translation There are several kinds of RNA Messenger RNA (mRNA): Conveys genetic information from DNA to the ribosomes Transfer RNA (tRNA): Transfers amino acids to the ribosomes during translation. Ribosomal RNA (rRNA): Provides structure and enzyme activity for ribosomes 61 Messenger RNA (mRNA): Delivers genetic information from the DNA inside the nucleus to the cytoplasm mRNA is formed beside a strand of DNA RNA nucleotides are complementary to DNA nucleotides with one exception – no thymine in RNA; replaced with uracil) mRNA DNA S P A U T A G C C G G C P Direction of “reading” code S S P P S S P P S S P P S S P S Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P 5. mRNA undergoes further processing & leaves the nucleus A Codon is the 3 letter nucleotide sequence of mRNA that encodes for 1 amino acid. AUG is the first codon in protein synthesis, so it’s it’s called the start codon Protein Synthesis The codon sequence of mRNA determines the amino acid sequence of a protein. Figure 4.23 The start codon marks the site at which translation into protein sequence begins, and the stop codon marks the site at which translation ends. amino acid tRNA Clover-leaf shape RNA with 2 important regions Amino acid binding site Anticodon Ribosomes Small particle of protein & ribosomal RNA (rRNA) Ribosomes have 2 subunits Large subunit holds tRNA & amino acids Small subunit binds to mRNA Small subunit has 2 binding sites for adjacent mRNA codons Ribosomes link amino acids by peptide bonds Ribosomes Peptide bond forming large subunit anticodons small subunit Binding sites with codons 1. mRNA binds to the small subunit of a Ribosome. 2. The ribosome ‘reads’ the mRNA sequence 3. tRNA brings amino acids to the ribosomes, aligning their anticodons with mRNA codons 4. The Ribosome links the amino acids together 5. Polypeptide chain lengthens Anchors polypeptide. tRNA released Figure 4.23 overview of protein synthesis TRANSCRIPTION Once translation is complete chaperone proteins fold the protein into its configuration post-translational modification enzymes may further modify proteins after translation phosphorylation – adding a phosphate to the protein glycosylation – adding a sugar to the protein End of Chapter 4