Chapter 5Chapter 5

Ground Rules Of Ground Rules Of

MetabolismMetabolism

Energy and the World of LifeEnergy and the World of Life

Energy Energy –– Capacity to do workCapacity to do work

Two Forms Of energyTwo Forms Of energy

��Kinetic Energy Kinetic Energy –– is the energy an object has is the energy an object has

because it is movingbecause it is moving

��Potential Energy Potential Energy –– is the energy of an object is the energy of an object

because of its position and shapebecause of its position and shape

Two Laws Of thermodynamicsTwo Laws Of thermodynamics

1 Energy cannot be created or destroyed1 Energy cannot be created or destroyed

��It can be converted from one form to another and It can be converted from one form to another and

transferred between objects or systemtransferred between objects or system

��E.g. Chemical (potential )energy in food will be E.g. Chemical (potential )energy in food will be

converted to the kinetic energy by movementconverted to the kinetic energy by movement

2 Entropy tends to increase2 Entropy tends to increase

��Energy tends to disperse spontaneously Energy tends to disperse spontaneously

��Some energy disperses at each energy transfer, usually Some energy disperses at each energy transfer, usually

in the form of heatin the form of heat

��Entropy is the measure of energy dispersalEntropy is the measure of energy dispersal

Energy In, Energy OutEnergy In, Energy Out

ReactantReactant -- Molecule that enter in a reactionMolecule that enter in a reaction

Product Product –– A molecule remaining at the end of the A molecule remaining at the end of the

reactionreaction

ExergonicExergonic & & EndergonicEndergonic Reactions in Reactions in

metabolismmetabolism

►► ExergonicExergonic reactions (energyreactions (energy--releasing)releasing)

Aerobic respirationAerobic respiration

►► EndergonicEndergonic reactions (energyreactions (energy--requiring)requiring)

�� PhotosynthesisPhotosynthesis

Exergonic and Endergonic ReactionsExergonic and Endergonic Reactions

Energy Flows in One DirectionEnergy Flows in One Direction

►►Energy is not cycled Energy is not cycled

�� In from the sun; into and out of ecosystemsIn from the sun; into and out of ecosystems

►►All living things harvest external energyAll living things harvest external energy

�� Producers and consumers use energy to Producers and consumers use energy to

assemble, rearrange, and dispose of substancesassemble, rearrange, and dispose of substances

�� All organisms survive by tapping into the one All organisms survive by tapping into the one ––

way flow from sunway flow from sun

OneOne--Way Energy FlowWay Energy Flow

ATP in MetabolismATP in Metabolism

Adenosine Adenosine triphosphatetriphosphate (ATP) (ATP)

►►Main energy carrier in cellMain energy carrier in cell

►► ATP accepts energy released by ATP accepts energy released by exergonicexergonic

reactions, and delivers to reactions, and delivers to endergonicendergonic reactionsreactions

PhosphorylationPhosphorylation

�� PhosphatePhosphate--groups transfer to and from ATPgroups transfer to and from ATP

�� When ATP gives up one of its phosphate, an ADP is When ATP gives up one of its phosphate, an ADP is

formedformed

�� ATP/ADP cycle drives most metabolic reactionsATP/ADP cycle drives most metabolic reactions

ATP: Energy Currency of LifeATP: Energy Currency of Life

Enzymes in MetabolismEnzymes in Metabolism

Enzymes Enzymes -- Molecules that make chemicalMolecules that make chemical reactions reactions

occur much faster than they would on their ownoccur much faster than they would on their own

Activation energyActivation energy

Minimum energy needed to start a reactionMinimum energy needed to start a reaction

Enzyme Structure & FunctionEnzyme Structure & Function

EnzymesEnzymes are catalysts are catalysts

CatalystCatalyst-- Chemical agent that speeds up a reactionChemical agent that speeds up a reaction

Enzymes lowers the activation energyEnzymes lowers the activation energy

Activation EnergyActivation Energy

Enzyme Structure & FunctionEnzyme Structure & Function

Substrate Substrate

A reactant molecule that is specifically A reactant molecule that is specifically

acted upon by an enzymeacted upon by an enzyme

Active siteActive site

Small cleft in enzymeSmall cleft in enzyme’’s surface wheres surface where

reactions occur reactions occur

�� Microenvironment is more favorable for Microenvironment is more favorable for

reaction than the surroundingsreaction than the surroundings

EnzymeEnzyme-- substratesubstrate

Enzyme ActionEnzyme Action

►►Transition State Transition State –– The state in a chemical The state in a chemical reaction when the reactants bond are at reaction when the reactants bond are at breaking pointbreaking point

►►How enzymes lower How enzymes lower activation energyactivation energy�� By concentrating By concentrating substratesubstrate molecules molecules

�� By orienting substrates to favor reaction By orienting substrates to favor reaction

�� By By inducing fitinducing fit between substrate and between substrate and active active sitesite

�� By excluding water from active siteBy excluding water from active site

Induced Fit modelInduced Fit model

Controls Over EnzymesControls Over Enzymes

►► AllostericAllosteric sitessites

AlloAllo –– Other, Other, StericSteric -- StructureStructure

�� Enzyme binding site other than active siteEnzyme binding site other than active site

�� Alters shape of enzyme to enhance or Alters shape of enzyme to enhance or

inhibit functioninhibit function

Feedback InhibitionFeedback Inhibition

Mechanism by which a change that results Mechanism by which a change that results

from some activity stops that activityfrom some activity stops that activity

Allosteric ControlAllosteric Control

Feedback InhibitionFeedback Inhibition

Enzymes and the EnvironmentEnzymes and the Environment

►► Each enzyme functions best within a characteristic Each enzyme functions best within a characteristic

range of temperature, salt concentration and pH range of temperature, salt concentration and pH

CofactorsCofactors

►►Many enzymes require non Many enzymes require non –– protein helpers for protein helpers for

catalytic activity, these are called cocatalytic activity, these are called co--factorsfactors

►► Some are inorganic metal ionsSome are inorganic metal ions

►► Organic coOrganic co--factors are called coenzymesfactors are called coenzymes

►► All vitamins are coenzymesAll vitamins are coenzymes

►► Co factors bind loosely or tightly with enzymesCo factors bind loosely or tightly with enzymes

►► Example:Example: CatalaseCatalase (Antioxidant)(Antioxidant)

�� Cofactor:Cofactor: IronIron

Metabolism Metabolism ––

Organized, EnzymeOrganized, Enzyme--Mediated ReactionsMediated Reactions

►►Cells concentrate, convert, and dispose of Cells concentrate, convert, and dispose of most substances in orderly, enzymemost substances in orderly, enzyme--mediated reaction sequences called mediated reaction sequences called metabolic pathwaysmetabolic pathways

Types of metabolic PathwaysTypes of metabolic Pathways

►► Biosynthetic (anabolic) pathwayBiosynthetic (anabolic) pathway

►► Pathways construct large molecules from smaller Pathways construct large molecules from smaller

onesones

�� Require energy Require energy

DegradativeDegradative (catabolic) pathway(catabolic) pathway

►► Break down of large molecules into smaller Break down of large molecules into smaller

productsproducts

►► Release usable energyRelease usable energy

Types of metabolic PathwaysTypes of metabolic Pathways

PhotosynthesisPhotosynthesis

�� Main biosynthetic pathway in the Main biosynthetic pathway in the biospherebiosphere

�� AutotrophsAutotrophs or Producersor Producers

►►Aerobic respiration Aerobic respiration

�� Main Main degradativedegradative pathway in the pathway in the biospherebiosphere

�� HeterotrophsHeterotrophs

Main Metabolic PathwaysMain Metabolic Pathways

Chemical EquilibriumChemical Equilibrium

►► It is attained when the concentration of reactants It is attained when the concentration of reactants

and products no longer changeand products no longer change

RedoxRedox reactionsreactions

Oxidation Oxidation –– Loss of electronsLoss of electrons

Reduction Reduction –– Gain of electronsGain of electrons

Coenzymes and electron transfer chains Coenzymes and electron transfer chains

Take part in organized sequences of Take part in organized sequences of

reactions in photosynthesis and aerobic reactions in photosynthesis and aerobic

respirationrespiration

Controlled Energy ReleaseControlled Energy Release

Diffusion, Membranes, Diffusion, Membranes,

and Metabolismand Metabolism

►►Concentration of a substance Concentration of a substance

�� Number of atoms or molecules in a given Number of atoms or molecules in a given

volume volume

►►Concentration gradient of a substanceConcentration gradient of a substance

�� A difference in concentration between two A difference in concentration between two

regionsregions

Concentration gradientConcentration gradient

DiffusionDiffusion

►►Diffusion Diffusion

�� Net movement of molecules to a region where Net movement of molecules to a region where

they are less concentrated they are less concentrated

►►Diffusion rates are influenced by:Diffusion rates are influenced by:

�� Temperature Temperature

�� Molecular sizeMolecular size

�� Gradients of pressure, charge, and Gradients of pressure, charge, and

concentration concentration

Diffusion and Membrane Diffusion and Membrane

PermeabilityPermeability

►►Selective permeability Selective permeability –– Cell membrane Cell membrane

allows some substance, but not others to allows some substance, but not others to

cross itcross it

Diffusion and Membrane Diffusion and Membrane

PermeabilityPermeability

►►Selective PermeabilitySelective Permeability

How Substances Cross Membranes:How Substances Cross Membranes:

Diffusion, Passive and Active TransportDiffusion, Passive and Active Transport

EndocytosisEndocytosis and and ExocytosisExocytosis

►►EndocytosisEndocytosis –– Process by which a cell takes Process by which a cell takes

in substances by engulfing it in a vesicle in substances by engulfing it in a vesicle

formed from a bit of plasma membraneformed from a bit of plasma membrane

►►ExocytosisExocytosis –– A vesicle that formed in the A vesicle that formed in the

cytoplasm fuses with the plasma membrane cytoplasm fuses with the plasma membrane

How Substances Cross Membranes:How Substances Cross Membranes:

Endocytosis and ExocytosisEndocytosis and Exocytosis

Working With and Against GradientsWorking With and Against Gradients

Many solutes cross membranes through Many solutes cross membranes through

transport proteins (open or gated channels)transport proteins (open or gated channels)

Passive transport (Facilitated diffusion)Passive transport (Facilitated diffusion)

►►Does not require energy inputDoes not require energy input

�� Solute diffuses down its concentration gradient Solute diffuses down its concentration gradient

through a transporter through a transporter

�� Example:Example: Glucose transportersGlucose transporters

passivetransportprotein

glucosetransporter

ExtracellularFluid

glucose, moreconcentratedoutside cellthan inside

Cytoplasm

Lipid Bilayer

Fig. 5.19, p. 85

Active TransportActive Transport

►►Active transporters require ATP energy to Active transporters require ATP energy to

move a solute move a solute againstagainst its concentration its concentration

gradient gradient

�� Specific solutes can bind to the active Specific solutes can bind to the active

transportertransporter

�� Example:Example: Calcium pumpsCalcium pumps

►►CotransportersCotransporters move two substances at the move two substances at the

same timesame time

�� Example:Example: SodiumSodium--potassium pumppotassium pump

Movement of waterMovement of water

►►Osmosis Osmosis –– Diffusion that involves the Diffusion that involves the

movement of water molecules across a semi movement of water molecules across a semi

permeable membranepermeable membrane

►►Water molecules follow their concentration Water molecules follow their concentration

gradient, influenced by solute concentrationgradient, influenced by solute concentration

OsmosisOsmosis

TonicityTonicity

►►Relative concentrations of two solutes Relative concentrations of two solutes

separated by a semipermeable membraneseparated by a semipermeable membrane

�� Hypertonic fluid (higher solute concentration)Hypertonic fluid (higher solute concentration)

�� Hypotonic fluid (lower solute concentration)Hypotonic fluid (lower solute concentration)

�� Isotonic solutions (two solutions with the same Isotonic solutions (two solutions with the same

tonicity)tonicity)

Effects of Fluid PressureEffects of Fluid Pressure

Hydrostatic pressure (Hydrostatic pressure (turgorturgor))

�� Exerts pressure on cell walls of plantsExerts pressure on cell walls of plants

�� supports plantssupports plants

Osmotic pressureOsmotic pressure

�� The amount of hydrostatic pressure that can The amount of hydrostatic pressure that can

stop water from diffusing into a hypertonic stop water from diffusing into a hypertonic

solutionsolution

Membrane Traffic To and From the Membrane Traffic To and From the

cell surfacecell surface

►►By the process of By the process of exocytosisexocytosis and and

endocytosisendocytosis, vesicles move substances to , vesicles move substances to

and from the plasma membraneand from the plasma membrane

Three Types of EndocytosisThree Types of Endocytosis

►►ReceptorReceptor--mediated endocytosismediated endocytosis

�� Substance binds to surface receptorsSubstance binds to surface receptors

�� Pit forms Pit forms endocytoticendocytotic vesiclevesicle

►►Phagocytosis (Phagocytosis (““cell eatingcell eating””))

�� Amoebas use pseudopods to engulf preyAmoebas use pseudopods to engulf prey

►►BulkBulk--phase endocytosisphase endocytosis

�� Vesicle forms around extracellular fluidVesicle forms around extracellular fluid

Some vesiclesare routed to thenuclear envelopeor ER membrane.Others fuse withGolgi bodies.

Endocytosis Exocytosis

coated pit

Molecules getconcentrated insidecoated pits at theplasma membrane.

The pitssink inwardand becomeendocyticvesicles.

Vesiclecontentsare sorted.

Some vesiclesand their contentsare delivered tolysosomes.

Many ofthe sortedmoleculescycle tothe plasmamembrane.

Night LightsNight Lights

►►Bioluminescence Bioluminescence -- Fluorescent light released Fluorescent light released

by enzymeby enzyme--mediated reactions in organismsmediated reactions in organisms