Chapter 5Chapter 5Chapter 5Chapter 5Cell Respiration and MetaboliCell Respiration and Metaboli

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All reactions that involve energy transformationsDivided into 2 Categories

CatabolicCatabolicRelease energyBreakdown larger molecules into smaller molecules

b lAnabolicRequire input of energySynthesis of large energy-storage moleculesy g gy g

MetabolismMetabolism

Oxidation-reduction reactions◦ Break down of molecules for energy◦ Electrons are transferred to intermediate car

i th t th fi l l t t riers, then to the final electron acceptor: oxygen◦ Oxygen is obtained from the blood◦ Oxygen is obtained from the blood

Aerobic Cell RespirationAerobic Cell Respiration

Breakdown of glucose for energy in the cytoplasmGlucose is converted to 2 molecules of pyruvicacid

Each pyruvic acid contains◦ 3 carbons3 carbons◦ 3 oxygens◦ 4 hydrogens4 hydrogens are removed from intermediates4 hydrogens are removed from intermediates

GlycolysisGlycolysis

Gl l iGl l iGlycolysisGlycolysis

Each pair of H+ reduces a molecule of NADProduces◦ 2 molecules of NADH and 2 unbound H+

◦ 2 ATP

Glycolysis PathwayGlycolysis PathwayGlucose + 2NAD + 2ADP + 2Pi 2 pyruvic acid + 2NADH + 2ATP

Glycolysis is exergonic◦ Energy released used to drive endergonic reactiongy g◦ ADP + Pi ATP

Glucose must be activated first before energy can be oGlucose must be activated first before energy can be obtained◦ ATP consumed at the beginning of glycolysis◦ ATP ADP + PiATP ADP + Pi

Pi is not released but added to intermediate molecules (phosphorylation)p p y )Phosphorylation of glucose, traps the glucose inside cellNet gain of 2 ATP and 2 NADH

Anaerobic respiration: Oxygen is not used in the processNADH + H+ + pyruvic acid lactic acid and NADProduce 2 ATP/ glucose moleculeProduce 2 ATP/ glucose molecule

Lactic Acid PathwayLactic Acid Pathway

S ti d t d t bi t b liSome tissues adapted to anaerobic metabolism◦ Skeletal muscle: normal daily occurrence◦ RBCs do not contain mitochondria and only use lactic aRBCs do not contain mitochondria and only use lactic a

cid pathway

C di l i h iCardiac muscle: ischemia

Glycogenesis and GlycogenolysisGlycogenesis and Glycogenolysis

Increase glucose intracellularly would increase osmotic prIncrease glucose intracellularly, would increase osmotic pressureMust store carbohydrates in form of glycogen

Glycogenesis: formation of glycogen from glucoseGlycogenolysis: conversion of glycogen to glucose-6-phosphate◦ Glucose-6-phosphate can be utilized through glycolysis

Glucose-6-phosphate cannot leak out of the cellSkeletal muscles generate glucose-6-phosphate for own glycolyticneedsLiver contains glucose-6-phosphatase that can produce free glucose

Lactic acid produced by anaerobic respiration delivered to the liverLDH converts lactic acid to pyruvic acidPyruvic acid converted to glucose-6-phosphatePyruvic acid converted to glucose-6-phosphate◦ Intermediate for glycogen◦ Converted to free glucose

Gluconeogenesis: conversion to non-carbohydrate molecules throg yugh pyruvic acid to glucose

Cori CycleCori Cycle

Aerobic respiration of glucose, pyruvic acid is formed by glycolysis, then converted into acetyl coenzyme A (acetyl CoA)Energy is released in oxidative reactions, and is captured as ATPPyruvic acid enters interior of mitochondriaConverted to acetyl CoA and 2 C02y 2Acetyl CoA serves as substrate for mitochondrial enzymes

Aerobic RespirationAerobic RespirationAcetyl CoA enters the Krebs Cycle

Acetyl CoA combines with oxaloacetic acid to form citric acidCitric acid enters the Krebs CycleProduces oxaloacetic acid to continue the pathway1 GTP, 3 NADH, and 1 FADH2NADH and FADH2 transport electrons to Electron Transport Cy2 p p ycle

Krebs CycleKrebs Cycle

Cristae of inner mitochondrial membrane contain molecules that serve as electron transport systemules that serve as electron transport system

Electron transport chain consists of FMN, coenzyme Q, and cytochromes

Electron TransportElectron Transport

Each cytochrome transfers electron pairs from NADH and FADH2 to next cytochrome2

Oxidized NAD and FAD are regenerated and shuttle electrons from the Krebs Cycle to the ETCy

Cytochrome receives a pair of electronsIron reduced then oxidized as electrons are transferredIron reduced, then oxidized as electrons are transferred

Cytochrome a3 transfers electrons to O2 (final electron accept )tor)Oxidative phosphorylation occurs. Energy derived is used to phosphorylate ADP to ATP

ETC ChainETC Chain

Chemiosmotic theoryETC powered by transport of electrons, pumps H+ from mitochondria matrix into space between inner and outer mitocochondria matrix into space between inner and outer mitochondrial membranes

Proton pumps◦ NADH-coenzyme Q reductase complex: Transports 4H+ fo

r every pair of electronsy p◦ Cytochrome C reductase complex: Transports 4H+

◦ Cytochrome C oxidase complex: Transports 2H+

Coupling ETC to ATPCoupling ETC to ATP

Higher [H+] in inter-membrane spaceg [ ] pRespiratory assemblies permit the passage of H+

Phosphorylation is coupled to oxidation when H+ diffuse Phosphorylation is coupled to oxidation, when H+ diffuse through the respiratory assemblies◦ ADP and Pi ATP

Oxygen functions as the last electron acceptor◦ Oxidizes cytochrome a◦ Oxidizes cytochrome a3

Oxygen accepts 2 electrons: O2 + 4 e- + 4 H+ 2 H 0 H20

Metabolism of LipidsMetabolism of Lipids

When more energy is taken in than consumed glycolysis inhibihan consumed, glycolysis inhibited

Glucose converted into glycogeGlucose converted into glycogen and fat

LipogenesisLipogenesis

Formation of fatOccurs mainly in adipose ti d liissue and liver

Acetic acid subunits from Acetic acid subunits from acetyl CoA converted into various lipids

Lipolysis: Breakdown of fatTriglycerides glycerol + fa

F f bl d b i

lipase

Free fa serve as blood-borne energy carriers

BetaBeta--oxidationoxidation

Enzymes remove acetic acid from acid end of faForms acetyl CoAAcetyl CoA enters Krebs Cycle

Nitrogen is ingested primarily as proteinExcess nitrogen must be excretedNitrogen balance: Amount of nitrogen ingested minus amount Nitrogen balance: Amount of nitrogen ingested minus amount excreted+ N balance: Amount of nitrogen ingested more than amountg gexcreted

- N balance: Amount of nitrogen excreted greater than ingested

Metabolism of ProteinsMetabolism of Proteins

Adequate amino acids are required for growth and repairq q g pA new amino acid can be obtained by transamination: Amino group (NH2) transferred from one amino acid to form another

P b hi h i id li i t dProcess by which excess amino acids are eliminatedAmine group from glutamic acid removed, forming ammonia and excreted as urea

DeaminationDeamination

Energy conversion: amino acid is deaminatedKetoacid can enter the Krebs CycleKetoacid can enter the Krebs Cycle