05 Lecture Presentation

7/25/2019 05 Lecture Presentation

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Chapter 5:

THE WORKING CELL



Chapter 5: THE WORKING CELL

•Some organisms use energy-convertingreactions to produce light

–Examples are organisms that live in the oceanand use light to hide themselves from predators

•Energy conversion involves not only energy

but also membranes and enzymes

Copyright © 2009 Pearson Education, Inc.



Bioluminescent

anglerfish

Cookiecutter shark

Firefly squid



MEMBRANE STRUCTURE ANDFUNCTION




Phospholipidbilayer

Hydrophobic regionsof protein

Hydrophilicregions of protein

•Membranes are composed of phospholipids and proteins

–Membranes are commonly described as afluid mosaic

5.1 Membranes are a fluid mosaic of phospholipids and proteins



Cholesterol

Glycoprotein

Glycolipid

Carbohydrate of glycoprotein

Phospholipid

Microfilamentsof cytoskeleton

Integrin

Integrins give themembrane a

strongerframework-attach to theextracellular matrixon the outside of the

cell-Glycoproteins

serve asidentification tagsspecificallyrecognized bymembrane proteinsof other cells



•Many membrane proteins function asenzymes,others insignal transduction, while others areimportant intransport

–Because membranes allow some substances to cross

or be transported more easily than others, they exhibitselectively permeability

–Nonpolar molecules (carbon dioxide and oxygen) cross easily

–Polar molecules (glucose and other sugars) do not cross easily




Enzymes

Enzyme Actiity



Messenger molecule

Actiatedmolecule

!eceptor

"ignal #ransduction



#ransport



5.2EVOLUTION CONNECTION: Membranesform spontaneously, a critical step in the

origin of life

•Phospholipids, the key component of biologicalmembranes, spontaneously assemble into simplemembranes


$ater%filledbubble made of

phospholipids

$ater

$ater



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


Diffusion across a cell membrane does notrequire energy, so it is calledpassivetransport



Molecules of dye Membrane E&uilibrium



#'o differentsubstances

Membrane E&uilibrium



5.4 Osmosis is the diffusion of wateracross a membrane

•It is crucial for cells thatwater moves across theirmembrane

–Water moves across membranes in response tosolute concentration inside and outside of the cell by a process

calledosmosis–Osmosis will move water across a membrane down itsconcentration gradient until theconcentration of solute is equal on both sides of the membrane




"electielypermeablemembrane

"olutemolecule

(o'er concentration

of solute

H)*

"olute molecule 'ithcluster of 'ater molecules

+et flo' of 'ater

$ater molecule

E&ualconcentration

of solute

Higher concentration

of solute



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 indicates that the concentration of a solute is the sameon both sides

–Hypertonic indicates that the concentration of solute is higheroutside the cell

–Hypotonic indicates a higher concentration of solute inside the

cell


•Osmoregulation:maintain water balance

–prevents excessive uptake or excessive loss of water



Isotonic solution

,B- (ysed ,C- "hrieled

,.- /laccid ,E- #urgid ,/- "hrieled

Hypertonic solutionHypotonic solution

Plant

cell

Animalcell

,A- +ormal

Plasmamembrane

,plasmolyzed-



5.6 Transport proteins may facilitatediffusion across membranes

•Many substances do not freely diffuseacross the membrane

–Specific transport proteins (aquaporins)

–These proteins assist infacilitated diffusion, atype of passive transport that does not requireenergy

–the protein is specific for the substrate, which

can be sugars, amino acids, ions, and evenwater




"olute

molecule

#ransportprotein



#ransportprotein

"olute

"olute binding0 Phosphorylation) #ransport1

Proteinchanges shape

Protein reersion2

Phosphatedetaches

•Cells have a mechanism for moving a solute against itsconcentration gradient

–It requires energy in the form of ATP

–The mechanism alters the shape of the membrane protein through

phosphorylation using ATP

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

9E i d d i



5.9 Exocytosis and endocytosis transportlarge molecules across membranes

•A cell uses two mechanisms for movinglarge molecules across membranes

–Exocytosis is used to export bulky molecules,

such as proteins or polysaccharides–Endocytosis is used to import substancesuseful to the livelihood of the cell

•In both cases, material to be transported is

packaged within a vesicle that fuses with themembrane


Th th kid f d ti



PhagocytosisE3#!ACE((4(A!/(4I.

Pseudopodium

C5#*P(A"M

/ood

acuole

6/ood7 or other particle

/oodbeingingested

•There are three kinds of endocytosis

–Phagocytosis is engulfment of a particle by wrapping

cell membrane around it, forming a vacuole



Pinocytosis

Plasmamembrane

8esicle

Plasma membrane

Pinocytosis is the same thing except that fluidsare taken into small vesicles

R di d d i h



Coatedesicle

Coatedpit

"pecificmolecule

!eceptor%mediated endocytosisCoat protein

!eceptor

Coatedpit

Material boundto receptor proteins

Plasma membrane

Receptor-mediated endocytosis is where receptors in areceptor-coated pit interact with a specific protein,

initiating formation of a vesicle



ENERGY AND THE CELL


510Cllt f



5.10 Cells transform energy asthey perform work

•Energy is the capacity to do work andcause change

–Work is accomplished when an object is movedagainst an 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 possessesas a result of its location


Cells are small units, a chemical factory, housing thousands of chemical reactions

510Cllt f



5.10 Cells transform energy asthey perform work

•Kinetic energy performs work by transferringmotion to other matter

–For example, water moving through a turbinegenerates electricity


510Cll f



5.10 Cells transform energyas they perform work

•An example of potential energy is water behind adam


–Chemical energy is potential energy because of its energy

available for release in a chemical reaction



5.11 Two laws govern energytransformations

•Thermodynamics: the study of Energytransformations–Biologists study thermodynamics because an organism exchangesboth energy and matter with its surroundings


–Thefirst law of thermodynamics—energy in the universe is

constant: can be transferred or transformed but can’t be

created or destroyed

–Thesecond law of thermodynamics—energy conversionsincrease the disorder of the universe

–Entropy is the measure of disorder, or randomness



/uel

Gasoline

Energy conersion in a cell

Energy for cellular 'ork

Cellular respiration

$aste productsEnergy conersion

Combustion

Energy conersion in a car

*9ygen

Heat

Glucose

*9ygen $ater

Carbon dio9ide

$ater

Carbon dio9ide

:inetic energyof moement

Heatenergy

512Chemicalreactionseitherreleaseor



5.12 Chemical reactions either release orstore energy

•Anexergonic reaction is a chemicalreaction that releases energy

–Burning wood releases the energy in glucose,

producing heat, light, carbon dioxide, and water–Cellular respiration also releases energy andheat and produces products but is able to usethe released energy to perform work




!eactants

Amount of

energyreleased

P o t e n t

i a l e n e r g y o

f m o l e c u l e s

Energy released

Products





•Anendergonic 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




!eactants

P o t e n t i a l e n e r g y o

f m o l e c u l e s

Energy re&uired

Products

Amount of energy

re&uired





•A living organism produces thousands ofendergonic and exergonic chemical reactions

–All of these combined is calledmetabolism

–Ametabolic pathway is a series of chemical reactionsthat either break down a complex molecule or build up acomplex molecule






•A cell does three main types of cellular work–Chemical work—driving endergonic reactions

–Transport work—pumping substances acrossmembranes

–Mechanical work—beating of cilia

•To accomplish work, a cell must manage itsenergy resources, and it does so byenergy coupling—the use of exergonic processesto drive an endergonic one


513ATPshuttleschemicalenergyand



•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 anddrives cellular work

•Hydrolysis of ATP releases energy by transferring its thirdphosphate from ATP to some other molecule

–The transfer is calledphosphorylation

–In the process, ATP energizes molecules

#riphosphate ,A#P-Adenosine



!ibose

Adenine


Phosphategroup




!ibose

Adenine


Phosphategroup

Hydrolysis

.iphosphate ,A.P-Adenosine



Chemical 'ork

"olute transportedMolecule formed

Product

!eactants

Motor protein

Membraneprotein

"olute

#ransport 'orkMechanical 'ork

Protein moed

•ATPisarenewablesourceofenergyforthecell



Energy frome9ergonic

reactions

Energy for endergonic

reactions

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 an endergonic

reaction to generate ATP



HOW ENZYMES FUNCTION


514Enzymesspeedupthecell’schemical



5.14 Enzymes speed up the cells chemicalreactions by lowering energy barriers

•Although there is a lot ofpotential energy in

biological molecules, such as carbohydratesand others, it is not released spontaneously

–Energy must be available to break bonds andform new ones

–This energy is calledenergy of activation (EA)


514Enzymesspeedupthecell’schemical



5.14 Enzymes speed up the cells chemicalreactions by lowering energy barriers

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

–Catalysis is accomplished byenzymes,

–Enzymes speed up the rate of the reaction bylowering the EA, and they are not used up in the

process

–Each enzyme has a particular target molecule

called thesubstrate




!eaction'ithoutenzyme

EA 'ith

enzyme

E n e r g y !eactants

!eaction 'ithenzyme

EA 'ithout

enzyme

+etchangein energy,the same-

Products

Progress of the reaction

515Aspecificenzymecatalyzeseach



5.15 A specific enzyme catalyzes eachcellular reaction

•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 anactive site where the enzyme interacts with the enzyme’s substrate

–Consequently, the substrate’s chemistry is altered toform the product of the enzyme reaction


Enzyme aailable0



Enzyme aailable'ith empty actiesite

Actie site

0

Enzyme

,sucrase-

"ubstrate bindsto enzyme 'ithinduced fit

)

"ubstrate

,sucrose-

"ubstrate isconerted toproducts

1

Products arereleased

2

/ructose

Glucose

5.15Aspecificenzymecatalyzeseach



5.15 A specific enzyme catalyzes eachcellular reaction

•For optimum activity, enzymes requirecertain environmental conditions

–Temperature is very important, and optimally,human enzymes function best at 37ºC, or body

temperature–High temperature will denature human enzymes

–Enzymes in animals also require a pH around neutralityfor best results


•Some enzymes require nonprotein helpers

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

–Coenzymes are organic molecules and are often vitamins

516Enzymeinhibitorsblockenzymeactionand



5.16 Enzyme inhibitors block enzyme action andcan regulate enzyme activity in a cell

•Inhibitors are chemicals that inhibit anenzyme’s activity

–competitive inhibitors:

compete for the enzyme’s active site and thusblock substrates from entering the active site


-noncompetitive inhibitors:

bind somewhere else and change the shape

of the enzyme so that the substrate will no longer

fit the active site



"ubstrate

Enzyme

Actie site

+ormal binding of substrate

Competitieinhibitor

Enzyme inhibition

+oncompetitieinhibitor

516Enzymeinhibitorsblockenzymeactionand



5.16 Enzyme inhibitors block enzyme action andcan regulate enzyme activity in a cell

•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, a mechanismcalledfeedback inhibition

–The more product formed, the greater the inhibition, andin this way, regulation of the pathway is accomplished




Youshouldnowbeableto



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

6.Describe membrane proteins that facilitatetransport of materials across the cell membrane

without expenditure of energy

7.Discuss how energy-requiring transport proteinsmove substances across the cell membrane

8.Distinguish between exocytosis and endocytosisand list similarities between the two


You should now be able to




9.Explain how energy is transformed during lifeprocesses

10.Define the two laws of thermodynamics andexplain how they relate to biological systems

11.Explain how a chemical reaction can eitherrelease energy or store energy

12.Describe ATP and explain why it is considered to

be the energy currency of a cell







13.Define enzyme and explain how enzymescause a chemical reaction to speed up

14.Discuss the specificity of enzymes

15.Distinguish between competitive inhibitorsand noncompetitive inhibitors

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05 Lecture Presentation