05_lecture_presentation cell membrane and energy

8/3/2019 05_Lecture_Presentation Cell Membrane and Energy

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Copyright 2009 Pearson Education, Inc.

PowerPoint Lectures for

Biology: Concepts & Connections, Sixth EditionCampbell, Reece, Taylor, Simon, and Dickey

Chapter 5 The Working Cell

Lecture by Richard L. MyersEdited by: Glen R. Mangali


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1. Describe the cell membrane within the context ofthe fluid mosaic model

2. Explain how spontaneous formation of a

membrane could have been important in theorigin of life

3. Describe the passage of materials across a

membrane with no energy expenditure4. Explain how osmosis plays a role in maintenance

of a cell


You should be able to


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5. Explain how an imbalance in water between thecell and its environment affects the cell

6. Describe membrane proteins that facilitate

transport of materials across the cell membranewithout expenditure of energy

7. Discuss how energy-requiring transport proteins

move substances across the cell membrane8. Distinguish between exocytosis and endocytosis

and list similarities between the two




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9. Explain how energy is transformed during lifeprocesses

10. Define the two laws of thermodynamics and

explain how they relate to biological systems11. Explain how a chemical reaction can either

release energy or store energy

12. Describe ATP and explain why it is considered tobe the energy currency of a cell




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13. Describe enzyme and how enzymes cause achemical reaction to speed up

14. Discuss the specificity of enzymes

15. Distinguish between competitive inhibitors andnoncompetitive inhibitors



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Introduction: Turning on the Lights to Be Invisible

Some organisms use energy-converting reactionsto produce light

Examples are organisms that live in the ocean and uselight to hide themselves from predators

Energy conversion involves not only energy butalso membranes and enzymes

So, production of light involves all of the topicscovered in this chapter



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MEMBRANE STRUCTURE ANDFUNCTION



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5.1 Membranes are a fluid mosaic ofphospholipids and proteins

Membranes are composed of phospholipids andproteins

Membranes are commonly described as a fluid mosaic

the surface appears mosaicbecause of the proteinsembedded in the phospholipids and fluidbecause theproteins can drift about in the phospholipids



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Phospholipidbilayer

Hydrophobic regionsof protein Hydrophilicregions of protein


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Many phospholipids are made from unsaturatedfatty acids that have kinks in their tails

This prevents them from packing tightly together, whichkeeps them liquid

This is aided by cholesterol wedged into the bilayer tohelp keep it liquid at lower temperatures



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Hydrophilichead

WATER

Hydrophobictail

WATER


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Cholesterol

Glycoprotein

Glycolipid

Carbohydrate ofglycoprotein

Phospholipid

Microfilaments

of cytoskeleton

Integrin


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Some glycoproteins in the membrane serve asidentification tags that are specifically recognizedby membrane proteins of other cells

For example, cell-cell recognition enables cells of theimmune system to recognize and reject foreign cells,such as infectious bacteria

Carbohydrates that are part of the extracellular matrixare significantly involved in cell-cell recognition



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membrane proteins function as I. enzymes,II. signal transduction, III. transport

membranes allow some substances to cross or betransported more easily than others, they exhibit

selectively permeability

Nonpolar molecules (carbon dioxide and oxygen) cross easily

Polar molecules (glucose and other sugars) do not crosseasily


Animation: Overview of Cell Signaling

Animation: Signal Transduction Pathways
http://05_01signaltransduction_a.html/http://05_01csignalingoverview_a.html/


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Enzymes

Figure 5.1B Enzyme activity.


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Messenger molecule

Activatedmolecule

Receptor

Figure 5.1C Signal transduction.


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Figure 5.1D Transport.


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Water

Water

Figure 5.2 Diagram of a section of a membrane sac.


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5.3 Passive transport is diffusion across amembrane with no energy investment

Diffusion is a process in which particles spreadout evenly in an available space

Particles move from an area of more concentratedparticles to an area where they are less concentrated

This means that particles diffuse down theirconcentration gradient

Eventually, the particles reach equilibrium where theconcentration of particles is the same throughout



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5.3 Passive transport is diffusion across amembrane with no energy investment

Diffusion across a cell membrane does not requireenergy, so it is called passive transport

The concentration gradient itself represents potentialenergy for diffusion


Animation: Membrane Selectivity

Animation: Diffusion
http://05_03diffusion_a.html/http://05_03membraneselectivity_a.html/


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Molecules of dye Membrane Equilibrium

Figure 5.3A Passive transport of one type of molecule.


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Two differentsubstances

Membrane Equilibrium

Figure 5.3B Passive transport of two types of molecules.


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5.4 Osmosis is the diffusion of water across amembrane

It is crucial for cells that water moves across theirmembrane

Water moves across membranes in response to soluteconcentration inside and outside of the cell by a process

called osmosis

Osmosis will move water across a membrane down itsconcentration gradient until the concentration of soluteis equal on both sides of the membrane


Animation: Osmosis

L E lHi h
http://05_04osmosis_a.html/


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Selectivelypermeablemembrane

Solutemolecule

Lowerconcentration

of solute

H2O

Solute molecule withcluster of water molecules

Net flow of water

Watermolecule

Equalconcentration

of solute

Higherconcentration

of solute


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5.5 Water balance between cells and theirsurroundings is crucial to organisms

Tonicity is a term that describes the ability of asolution to cause a cell to gain or lose water

Tonicity is dependent on the concentration of anonpenetrating solute on both sides of the membrane

Isotonic =same on both sides

Hypertonic =higher outside the cell

Hypotonic =higher inside the cell



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5.5 Water balance between cells and theirsurroundings is crucial to organisms

Many organisms are able to maintain waterbalance within their cells by a process calledosmoregulation

This process prevents excessive uptake or excessiveloss of water

Plant, prokaryotic, and fungal cells have different issueswith osmoregulation because of their cell walls


Video: ParameciumVacuole

Video: ChlamydomonasVideo: Turgid Elodea

Video: Plasmolysis
http://05_05plasmolysis_sv.mpg/http://05_05turgidelodea_sv.mpg/http://05_05chlamydomonas_sv.mpg/http://05_05parameciumvacuole_sv.mpg/


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Isotonic solution

(B) Lysed (C) Shriveled

(D) Flaccid (E) Turgid (F) Shriveled

Hypertonic solutionHypotonic solution

Plantcell

Animalcell

(A) Normal

Plasmamembrane

(plasmolyzed)

Figure 5.5 How animal and plant cells behave in different solutions.

5 6 T i f ili diff i


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5.6 Transport proteins may facilitate diffusionacross membranes

Many substances that are necessary for viability ofthe cell do not freely diffuse across the membrane

They require the help of specific transport proteinscalled aquaporins

These proteins assist in facilitated diffusion, a typeof passive transport that does not require energy


5 6 T i f ili diff i


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5.6 Transport proteins may facilitate diffusionacross membranes

Some proteins function by becoming a hydrophilictunnel for passage

Other proteins bind their passenger, change shape, andrelease their passenger on the other side

In both of these situations, the protein is specific for

the substrate, which can be sugars, amino acids, ions,and even water



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Solute

molecule

Transportprotein

Figure 5.6 Transport protein providing a channel for the diffusion of a specific solute across a membrane.

5 8 C ll d i th ti t t f


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5.8 Cells expend energy in the active transport ofa solute against its concentration gradient

Cells have a mechanism for moving a soluteagainst its concentration gradient

It requires the expenditure of energy in the form of ATP

The mechanism alters the shape of the membraneprotein through phosphorylation using ATP


Animation: Active Transport
http://05_08activetransport_a.html/


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Transportprotein

Solute

Solute binding1

Figure 5.8 Active transport of a solute across a membrane.


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Transportprotein

Solute

Solute binding1 Phosphorylation2



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Transportprotein

Solute

Solute binding1 Phosphorylation2 Transport3

Proteinchanges shape


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Transportprotein

Solute

Solute binding1 Phosphorylation2 Transport3

Proteinchanges shape

Protein reversion4

Phosphatedetaches


5 9 E t i d d t i t t l


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5.9 Exocytosis and endocytosis transport largemolecules across membranes

A cell uses two mechanisms for moving largemolecules across membranes

Exocytosis is used to export bulky molecules, such asproteins or polysaccharides

Endocytosis is used to import substances useful to thelivelihood of the cell

In both cases, material to be transported is

packaged within a vesicle that fuses with themembrane


5 9 E oc tosis and endoc tosis transport large


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5.9 Exocytosis and endocytosis transport largemolecules across membranes

There are three kinds of endocytosis1. Phagocytosis = engulfment of a particle by wrapping

cell membrane around it, forming a vacuole

2. Pinocytosis = fluids are taken into small vesicles

3. Receptor-mediated endocytosis =receptors in areceptor-coated pit interact with a specific protein,initiating formation of a vesicle


Animation: Exocytosis and Endocytosis Introduction

Animation: Phagocytosis

Animation: Exocytosis

Animation: Receptor-Mediated Endocytosis

Animation: Pinocytosis

Phagocytosis
http://05_09pinocytosis_a.html/http://05_09receptmedendocyt_a.html/http://05_09exocytosis_a.html/http://05_09phagocytosis_a.html/http://05_09_exocytendointro_a.html/


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EXTRACELLULARFLUID

Pseudopodium

CYTOPLASM

Foodvacuole

Food or

other particle

Pinocytosis

Plasmamembrane

Vesicle

Coatedvesicle

Coatedpit

Specificmolecule

Receptor-mediated endocytosis

Coat proteinReceptor

Coatedpit

Material bound

to receptor proteins

Plasma membrane

Foodbeingingested

Figure 5.9 Three kinds of endocytosis.


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ENERGY AND THE CELL


5 10 Cells transform energy as they perform work


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5.10 Cells transform energy as they perform work

Cells are small units, a chemical factory, housing

thousands of chemical reactions The result of reactions is maintenance of the cell,

manufacture of cellular parts, and replication




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Energy is the capacity to do work and causechange

Work is accomplished when an object is moved againstan opposing force, such as friction

There are two kinds of energy

Kinetic energy is the energy of motion

Potential energy is energy that an object possesses as a

result of its location




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Kinetic energy performs work by transferringmotion to other matter

For example, water moving through a turbine generateselectricity

Heat, or thermal energy, is kinetic energy associatedwith the random movement of atoms




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An example of potential energy is water behind adam

Chemical energy is potential energy because of itsenergy available for release in a chemical reaction


Animation: Energy Concepts
http://05_10energyconcepts_a.html/


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Figure 5.10A Kinetic energy, the energy of motion.Figure 5.10B Potential energy, stored energy as a result of location or structure.

5 11 Two laws govern energy transformations


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5.11 Two laws govern energy transformations

Energy transformations within matter are studiedby individuals in the field ofthermodynamics

Biologists study thermodynamics because an organismexchanges both energy and matter with itssurroundings


5 11 Two laws govern energy transformations


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5.11 Two laws govern energy transformations

It is important to understand two laws that governenergy transformations in organisms

The first law ofthermodynamicsenergy in theuniverse is constant

The second law ofthermodynamicsenergyconversions increase the disorder of the universe

Entropy is the measure of disorder, or randomness


Fuel Waste productsEnergy conversion


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Fuel

Gasoline

Energy conversion in a cell

Energy for cellular work

Cellular respiration

Waste productsEnergy conversion

Combustion

Energy conversion in a car

Oxygen

Heat

Glucose

Oxygen Water

Carbon dioxide

Water

Carbon dioxide

Kinetic energyof movement

Heatenergy

5 12 Chemical reactions either release or store


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5.12 Chemical reactions either release or storeenergy

An exergonic reaction is a chemical reactionthat releases energy

This reaction releases the energy in covalent bonds ofthe reactants

Burning wood releases the energy in glucose, producingheat, light, carbon dioxide, and water

Cellular respiration also releases energy and heat

and produces products but is able to use the releasedenergy to perform work



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Reactants

Amount of

energyreleased

Potentialenergyo

fmolecules

Energy released

Products

Figure 5.12A Exergonic reaction, energy released.

5 12 Chemical reactions either release or store


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An endergonic reaction requires an input ofenergy and yields products rich in potential energy

The reactants contain little energy in the beginning, but

energy is absorbed from the surroundings and stored incovalent bonds of the products

Photosynthesis makes energy-rich sugar moleculesusing energy in sunlight



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Reactants

Potentialenergyo

fmolecules

Energy required

Products

Amount of

energyrequired

Figure 5.12B Endergonic reaction, energy required.

5.12 Chemical reactions either release or store


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A living organism produces thousands ofendergonic and exergonic chemical reactions

All of these combined is called metabolism

Ametabolic pathway is a series of chemical reactionsthat either break down a complex molecule or build upa complex molecule


5.12 Chemical reactions either release or store


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A cell does three main types of cellular work Chemical workdriving endergonic reactions

Transport workpumping substances acrossmembranes

Mechanical workbeating of cilia

To accomplish work, a cell must manage its energy

resources, and it does so by energycouplingthe use of exergonic processes to drive anendergonic one


5.13 ATP shuttles chemical energy and drives


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ATP, adenosine triphosphate, is the energycurrency of cells.

ATP is the immediate source of energy that powersmost forms of cellular work.

It is composed of adenine (a nitrogenous base), ribose(a five-carbon sugar), and three phosphate groups.


5.13 ATP shuttles chemical energy and drivescellular work



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5.13 ATP shuttles chemical energy and drivescellular work

Hydrolysis of ATP releases energy by transferringits third phosphate from ATP to some other

molecule

The transfer is called phosphorylation

In the process, ATP energizes molecules


Triphosphate (ATP)Adenosine


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Ribose

Adenine

Phosphategroup

Triphosphate (ATP)Adenosine


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Ribose

Adenine

Phosphategroup

Hydrolysis

Diphosphate (ADP)Adenosine

+


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Chemical work

Solute transportedMolecule formed

Product

Reactants

Motorprotein

Membraneprotein

Solute

Transport workMechanical work

Protein moved

Figure 5.13B How ATP powers cellular work.



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5. 3 s utt es c e ca e e gy a d d vescellular work

ATP is a renewable source of energy for the cell

When energy is released in an exergonic reaction, such

as breakdown of glucose, the energy is used in anendergonic reaction to generate ATP



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Energy fromexergonic

reactions

Energy forendergonic

reactions

Figure 5.13C The ATP cycle.


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HOW ENZYMES FUNCTION


5.14 Enzymes speed up the cells chemical


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y p preactions by lowering energy barriers

Although there is a lot of potential energy inbiological molecules, such as carbohydrates andothers, it is not released spontaneously

Energy must be available to break bonds and form newones

This energy is called energy of activation (EA

)


5.14 Enzymes speed up the cells chemical


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y p preactions by lowering energy barriers

The cell uses catalysis to drive (speed up)biological reactions

Catalysis is accomplished by enzymes, which areproteins that function as biological catalysts

Enzymes speed up the rate of the reaction by loweringthe EA, and they are not used up in the process

Each enzyme has a particular target molecule called the

substrate


Animation: How Enzymes Work
http://05_14howenzymeswork_a.html/


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Reactionwithoutenzyme

EA withenzyme

ReactantsReaction withenzyme

EA withoutenzyme

Netchangein energy(the same)

Products

Progress of the reaction

5.15 A specific enzyme catalyzes each cellular


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p y yreaction

Enzymes have unique three-dimensional shapes

The shape is critical to their role as biological catalysts

As a result of its shape, the enzyme has an active sitewhere the enzyme interacts with the enzymes substrate

Consequently, the substrates chemistry is altered toform the product of the enzyme reaction


Enzyme available1


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with empty activesite

Active site

Enzyme

(sucrase)

Figure 5.15 The catalytic cycle of an enzyme.

Enzyme available1


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Active site

Enzyme

(sucrase)

Substrate bindsto enzyme withinduced fit

2

Substrate

(sucrose)


Enzyme availablei h i

1


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Active site

Enzyme

(sucrase)


2

Substrate

(sucrose)

Substrate isconverted toproducts

3


Enzyme availablei h i

1


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Active site

Enzyme

(sucrase)


2

Substrate

(sucrose)

Substrate isconverted toproducts

3

Products arereleased

4

Fructose

Glucose



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reaction

For optimum activity, enzymes require certainenvironmental conditions

Temperature is very important, and optimally, human

enzymes function best at 37C, or body temperature High temperature will denature human enzymes

Enzymes also require a pH around neutrality for best

results




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reaction

Some enzymes require nonprotein helpers

Cofactors are inorganic, such as zinc, iron, or copper

Coenzymes are organic molecules and are oftenvitamins


5.16 Enzyme inhibitors block enzyme action and


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can regulate enzyme activity in a cell

Inhibitors are chemicals that inhibit an enzymesactivity

One group inhibits because they compete for theenzymes active site and thus block substrates fromentering the active site

These are called competitive inhibitors


S b t t


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Substrate

Enzyme

Active site

Normal binding of substrate

Competitiveinhibitor

Enzyme inhibition

Noncompetitiveinhibitor



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Other inhibitors do not act directly with the activesite

These bind somewhere else and change the shape ofthe enzyme so that the substrate will no longer fit theactive site

These are called noncompetitive inhibitors




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Enzyme inhibitors are important in regulating cellmetabolism

Often the product of a metabolic pathway can serve as

an inhibitor of one enzyme in the pathway, amechanism called feedback inhibition

The more product formed, the greater the inhibition,and in this way, regulation of the pathway is

accomplished


Requires no energy Requires energy


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Diffusion

Requires no energy

Passive transport

Higher solute concentration

Facilitateddiffusion

OsmosisHigher water

concentration

Higher soluteconcentration

Requires energy

Active transport

Solute

Water

Lower soluteconcentration

Lower waterconcentration

Lower soluteconcentration

05_lecture_presentation cell membrane and energy

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