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
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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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You should be able to
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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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You should be able to
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You should be able to
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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5.1 Membranes are a fluid mosaic ofphospholipids and proteins
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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5.1 Membranes are a fluid mosaic ofphospholipids and proteins
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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5.1 Membranes are a fluid mosaic ofphospholipids and proteins
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
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Animation: Overview of Cell Signaling
Animation: Signal Transduction Pathways
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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
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Animation: Membrane Selectivity
Animation: Diffusion
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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
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Animation: Osmosis
L E lHi h
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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
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Video: ParameciumVacuole
Video: ChlamydomonasVideo: Turgid Elodea
Video: Plasmolysis
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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
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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
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Animation: Active Transport
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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
Figure 5.8 Active transport of a solute across a membrane.
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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
Figure 5.8 Active transport of a solute across a membrane.
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
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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
Copyright 2009 Pearson Education, Inc.
Animation: Exocytosis and Endocytosis Introduction
Animation: Phagocytosis
Animation: Exocytosis
Animation: Receptor-Mediated Endocytosis
Animation: Pinocytosis
Phagocytosis
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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
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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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5 10 Cells transform energy as they perform work
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5.10 Cells transform energy as they perform work
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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5 10 Cells transform energy as they perform work
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5.10 Cells transform energy as they perform work
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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5 10 Cells transform energy as they perform work
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5.10 Cells transform energy as they perform work
An example of potential energy is water behind adam
Chemical energy is potential energy because of itsenergy available for release in a chemical reaction
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Animation: Energy Concepts
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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
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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
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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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5.12 Chemical reactions either release or storeenergy
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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5.12 Chemical reactions either release or storeenergy
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
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5.12 Chemical reactions either release or store
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5.12 Chemical reactions either release or storeenergy
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
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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.
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5.13 ATP shuttles chemical energy and drivescellular work
5.13 ATP shuttles chemical energy and drives
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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
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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.
5.13 ATP shuttles chemical energy and drives
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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
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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
)
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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
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Animation: How Enzymes Work
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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
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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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with empty activesite
Active site
Enzyme
(sucrase)
Substrate bindsto enzyme withinduced fit
2
Substrate
(sucrose)
Figure 5.15 The catalytic cycle of an enzyme.
Enzyme availablei h i
1
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with empty activesite
Active site
Enzyme
(sucrase)
Substrate bindsto enzyme withinduced fit
2
Substrate
(sucrose)
Substrate isconverted toproducts
3
Figure 5.15 The catalytic cycle of an enzyme.
Enzyme availablei h i
1
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with empty activesite
Active site
Enzyme
(sucrase)
Substrate bindsto enzyme withinduced fit
2
Substrate
(sucrose)
Substrate isconverted toproducts
3
Products arereleased
4
Fructose
Glucose
5.15 A specific enzyme catalyzes each cellular
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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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5.15 A specific enzyme catalyzes each cellular
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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
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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
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S b t t
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Substrate
Enzyme
Active site
Normal binding of substrate
Competitiveinhibitor
Enzyme inhibition
Noncompetitiveinhibitor
5.16 Enzyme inhibitors block enzyme action and
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can regulate enzyme activity in a cell
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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5.16 Enzyme inhibitors block enzyme action and
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can 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, amechanism called feedback inhibition
The more product formed, the greater the inhibition,and in this way, regulation of the pathway is
accomplished
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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