© 2010 pearson education, inc. functions of cells the sum total of all chemical reactions that...
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© 2010 Pearson Education, Inc.
Functions of cells
The sum total of all chemical reactions that occur in organisms is called “metabolism”
More specifically, building proteins and other products is called anabolism
Breaking molecules down is called catabolism
Enzymes are used to lower the activation energy for reactions to occur, thereby using less energy
Remember, enzymes catalyze specific reactions
Figure 5.00
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SOME BASIC ENERGY CONCEPTS• Energy makes the world go around.• But what is energy?• We need to discuss energy because that’s what cells use to run
themselves and ultimately the organism which they comprise• The first rule of energy is:• ENERGY CAN NEITHER BE CREATED NOR DESTROYED – this is
known as a principle called “conservation of energy”• So what does that mean? Well, the suggestion is that the
Universe has all of the energy that it will ever have, no more, no less.
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Conservation of Energy• Energy is defined as the capacity to perform work.
• Kinetic energy is the energy of motion.
• Potential energy is stored energy.
Climbing the stepsconverts kineticenergy of musclemovement topotential energy.
On the platform,the diver has morepotential energy.
Diving convertspotential energyto kinetic energy.
In the water, thediver has lesspotential energy.
Figure 5.1
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• Machines and organisms can transform kinetic energy to potential energy and vice versa.
• In all such energy transformations, total energy is conserved.
– Energy cannot be created or destroyed.
– This is the principle of conservation of energy.
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Remember calories?
The small calorie or gram calorie (symbol: cal) is the approximate amount of energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere.
The large calorie, kilogram calorie, dietary calorie, nutritionist's calorie, nutritional calorie, Calorie (capital C) or food calorie (symbol: Cal) is approximately the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius.
The large calorie is thus equal to 1000 small calories or one kilocalorie (symbol: kcal). These are food calories on food labels
So ten kilocalories are equivalent to how many calories?
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Cellular RespirationCellular Respiration (covered in next chapter) is the process of converting the energy stored in food molecules to energy stored in ATP
An adaptation of animal cells for increasing the surface area for more cellular respiration to occur is the cristae of a mitochondria
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Entropy• Every energy conversion releases some randomized energy in
the form of heat.
• Entropy is a scientific concept that measures disorder: the higher the entropy, the higher the disorder. Unless energy is added, entropy will take over and the energy in the system will decrease. It’s like a log decaying in the woods.
• Heat is a
– Type of kinetic energy
– Product of all energy conversions
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• Scientists use the term entropy as a measure of disorder, or randomness.
• All energy conversions increase the entropy of the universe.
• This is theory of course and recent advancements in physics tend to support an alternate theory that order dominates the universe, not randomness.
• However, just focus on entropy and just remember that there are other ideas out there and lots for you to discover
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Chemical Energy• Molecules store varying amounts of potential energy in the
arrangement of their atoms. (in the bonds between molecules or atoms)
• Organic compounds are relatively rich in such chemical energy.
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• Living cells and automobile engines use the same basic process to make chemical energy do work.
Fuel rich inchemicalenergy
Energy conversionWaste productspoor in chemicalenergy
Gasoline
Oxygen
Carbon dioxide
WaterEnergy conversion in a car
Energy for cellular work
Energy conversion in a cell
Heatenergy
Heatenergy
Carbon dioxide
Water
Food
Oxygen
Combustion
Cellularrespiration
Kinetic energyof movement
ATP
Figure 5.2
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• Cellular respiration is the energy-releasing chemical breakdown of fuel molecules that provides energy for cells to do work.
• Humans convert about 40% of the energy in food to perform useful work, such as the contraction of muscles and sending action potentials (electrical currents) in nerves
• Do you remember carbohydrates? Well, carbohydrates come from plants. Photosynthesis in particular. They take carbon dioxide from the atmosphere along with water and sunlight, and make fruits and vegetables! Whoa!
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Food Calories• A calorie is the amount of energy that raises the temperature of
one gram of water by 1 degree Celsius.
• Food Calories are kilocalories, equal to 1,000 calories.
(a) Food Calories (kilocalories) invarious foods
(b) Food Calories (kilocalories) weburn in various activities
Cheeseburger
Spaghetti with sauce (1 cup)
Pizza with pepperoni (1 slice)
Peanuts (1 ounce)
Apple
Bean burrito
Fried chicken (drumstick)
Garden salad (2 cups)
Popcorn (plain, 1 cup)
Broccoli (1 cup)
Baked potato (plain, with skin)
Food Calories Food
295
241
220
193
181
166
81
56
189
31
25
Activity Food Calories consumed perhour by a 150-pound person*
979
510
490
408
204
73
61
245
28
Running (7min/mi)
Sitting (writing)
Driving a car
Playing the piano
Dancing (slow)
Walking (3 mph)
Bicycling (10 mph)
Swimming (2 mph)
Dancing (fast)
*Not including energy necessary for basic functions, suchas breathing and heartbeat
Figure 5.3
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ATP AND CELLULAR WORK• Chemical energy is
– Released by the breakdown of organic molecules during cellular respiration
– Used to generate molecules of ATP
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• ATP is a nucleotide! Oh yeah, I know what that is.
– Acts like an energy shuttle
– Stores energy obtained from food
– Releases it later as needed
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The Structure of ATP• ATP (adenosine triphosphate)
– Consists of adenosine plus a tail of three phosphate groups
– Is broken down to ADP and a phosphate group, releasing energy
– Watch This: http://youtu.be/5GMLIMIVUvo
Triphosphate Diphosphate
Adenosine Adenosine
Energy
ATP ADP
P P P P P P
Phosphate(transferred to
another molecule)
Figure 5.4
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Phosphate Transfer• ATP energizes other molecules by transferring phosphate groups.
• This energy helps cells perform
– Mechanical work
– Transport work
– Chemical work
ATP
ATP
ATP
ADP
ADP
ADP
P
P
P
ADP P
P P
P
PX X Y
Y
(a) Motor protein performing mechanical work
(b) Transport protein performing transport work
(c) Chemical reactants performing chemical work
Solute
Solute transported
Protein moved
Product madeReactants
Transportprotein
Motorprotein
Figure 5.5
Cellular respiration:chemical energyharvested fromfuel molecules
Energy forcellular work
ATP
ADP P
Figure 5.6
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Activation Energy• Activation energy
– Activates the reactants
– Triggers a chemical reaction
• Enzymes lower the activation energy for chemical reactions.
• Watch this: http://youtu.be/ok9esggzN18
(a) Without enzyme (b) With enzyme
Reactant Reactant
Products Products
Activationenergy barrier Activation
energy barrierreduced byenzyme
Enzyme
En
erg
y le
vel
En
erg
y le
vel
Figure 5.7
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Induced Fit• Every enzyme is very selective, catalyzing a specific reaction.
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• Each enzyme recognizes a substrate, a specific reactant molecule.
– The active site fits to the substrate, and the enzyme changes shape slightly.
– This interaction is called induced fit.
• Enzymes can function over and over again, a key characteristic of enzymes.
Figure 5.9-1
Active site
Enzyme(sucrase)
Sucrase can accept amolecule of its substrate.
Active site
Enzyme(sucrase)
Sucrase can accept amolecule of its substrate.
Substrate (sucrose)
Substrate bindsto the enzyme.
Figure 5.9-2
Active site
Enzyme(sucrase)
Sucrase can accept amolecule of its substrate.
Substrate (sucrose)
Substrate bindsto the enzyme.
The enzymecatalyzes thechemical reaction.
H2O
Figure 5.9-3
Active site
Enzyme(sucrase)
Sucrase can accept amolecule of its substrate.
Substrate (sucrose)
Substrate bindsto the enzyme.
The enzymecatalyzes thechemical reaction.
H2O
Fructose
Glucose
The productsare released.
Figure 5.9-4
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Enzyme Inhibitors• Enzyme inhibitors can prevent metabolic reactions by binding to
the active site.
• An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. They are also used in pesticides.
(a) Enzyme and substratebinding normally
(b) Enzyme inhibition bya substrate imposter
(c) Enzyme inhibition bya molecule that causesthe active site to changeshape
Substrate
Substrate
Substrate
Active site
Active site
Active site
Inhibitor
Inhibitor
Enzyme
Enzyme
EnzymeFigure 5.10
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• Other enzyme inhibitors
– Bind at a remote site
– Change the enzyme’s shape
– Prevent the enzyme from binding to its substrate
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MEMBRANE FUNCTION• Working cells must control the flow of materials to and from the
environment.
• Membrane proteins perform many functions.
• Transport proteins
– Are located in membranes
– Regulate the passage of materials into and out of the cell
Cell signaling
Attachment tothe cytoskeletonand extracellular
matrix
Enzymatic activity
Cytoskeleton
Cytoplasm
Cytoplasm
Transport
Fibers ofextracellularmatrix
Intercellularjoining
Cell-cellrecognition
Figure 5.11
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Passive Transport: Diffusion across Membranes• Molecules contain heat energy that causes them to vibrate and
wander randomly.
• Diffusion is the tendency for molecules of any substance to spread out into the available space.
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• Passive transport is the diffusion of a substance across a membrane without the input of energy.
• Diffusion is an example of passive transport.
• Substances diffuse down their concentration gradient, a region in which the substance’s density changes.
• Watch This: http://youtu.be/LeS2-6zHn6M
Molecules of dye Membrane
(a) Passive transport of one type of molecule
(b) Passive transport of two types of molecules
Net diffusion Net diffusion Equilibrium
Net diffusion Net diffusion Equilibrium
Net diffusion Net diffusion Equilibrium
Figure 5.12
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• Some substances do not cross membranes spontaneously.
– These substances can be transported via facilitated diffusion.
– Specific transport proteins act as selective corridors.
– No energy input is needed.
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Osmosis and Water Balance
• The diffusion of water across a selectively permeable membrane is osmosis.
• If diffusion is the movement of a solute, osmosis is the movement of water (solvent)
Hypotonic solution Hypertonic solution
Sugarmolecule
Selectivelypermeablemembrane Osmosis
Figure 5.13-1
Hypotonic solution Hypertonic solution
Sugarmolecule
Selectivelypermeablemembrane Osmosis
Isotonic solutions
Osmosis
Figure 5.13-2
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• A hypertonic solution has a higher concentration of solute.
• A hypotonic solution has a lower concentration of solute.
• An isotonic solution has an equal concentration of solute.
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• Osmoregulation is the control of water balance within a cell or organism.
• Most animal cells require an isotonic environment.
Water Balance in Animal Cells
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• Plant have rigid cell walls.
• Plant cells require a hypotonic environment, which keeps these walled cells turgid.
• Watch this: http://youtu.be/rMGH1-mpp8g
Water Balance in Plant Cells
Animal cell
Plant cell
Normal
Flaccid (wilts)
Lysing
Turgid
Shriveled
Shriveled
Plasmamembrane
H2OH2O H2O H2O
H2OH2OH2O H2O
(a) Isotonicsolution
(b) Hypotonicsolution
(c) Hypertonicsolution Figure 5.14
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• As a plant cell loses water,
– It shrivels.
– Its plasma membrane may pull away from the cell wall in the process of plasmolysis, which usually kills the cell.
Figure 5.15
Active Transport: The Pumping of Molecules Across Membranes
• Active transport requires energy to move molecules across a membrane.
• Watch this: http://youtu.be/RPAZvs4hvGA
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Lower solute concentration
Higher solute concentration
ATP
Solute
Figure 5.16-1
Lower solute concentration
Higher solute concentration
ATP
Solute
Figure 5.16-2
Exocytosis and Endocytosis: Traffic of Large Molecules
• Exocytosis is the secretion of large molecules within vesicles.
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Outside of cell
Cytoplasm
Plasmamembrane
Figure 5.17
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• Endocytosis takes material into a cell within vesicles that bud inward from the plasma membrane.
Figure 5.18
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• There are three types of endocytosis:
– Phagocytosis (“cellular eating”); a cell engulfs a particle and packages it within a food vacuole. Ex: the act of a white blood cell engulfing a bacteria is phagocytosis
– Pinocytosis (“cellular drinking”); a cell “gulps” droplets of fluid by forming tiny vesicles
– Receptor-mediated endocytosis; a cell takes in very specific molecules
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The Role of Membranes in Cell Signaling• The plasma membrane helps convey signals between
– Cells – Cells and their environment
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• Receptors on a cell surface trigger signal transduction pathways that
– Relay the signal – Convert it to chemical forms that can function within the cell– Watch this: http://youtu.be/qOVkedxDqQo
Outside of cell Cytoplasm
Reception Transduction ResponseReceptorprotein
Epinephrine(adrenaline)from adrenalglands
Plasma membrane
Proteins of signal transduction pathway
Hydrolysisof glycogenreleasesglucose forenergy
Figure 5.19
Evolution Connection: The Origin of Membranes
• Phospholipids– Are key ingredients of membranes
– Were probably among the first organic compounds that formed before life emerged
– Self-assemble into simple membranes
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Passive Transport(requires no energy)
Active Transport(requires energy)
Diffusion Facilitated diffusion Osmosis
Higher solute concentration
Lower solute concentration
Higher water concentration(lower solute concentration)
Lower water concentration(higher solute concentration)
Solute
Higher soluteconcentration
Lower soluteconcentration
ATP
So
lute
So
lute
Wat
er
So
lute
MEMBRANE TRANSPORT
Figure 5.UN03
Exocytosis Endocytosis
Figure 5.UN04