© 2010 pearson education, inc. functions of cells the sum total of all chemical reactions that...

© 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


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.


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


• 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.


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?


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


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


• 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


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.


• 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


• 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!


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


ATP AND CELLULAR WORK• Chemical energy is

– Released by the breakdown of organic molecules during cellular respiration

– Used to generate molecules of ATP


• 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


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

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


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


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

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


Induced Fit• Every enzyme is very selective, catalyzing a specific reaction.


• 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)


Substrate (sucrose)

Substrate bindsto the enzyme.

Figure 5.9-2

Active site

Enzyme(sucrase)


Substrate (sucrose)


The enzymecatalyzes thechemical reaction.

H2O

Figure 5.9-3

Active site

Enzyme(sucrase)


Substrate (sucrose)


The enzymecatalyzes thechemical reaction.

H2O

Fructose

Glucose

The productsare released.

Figure 5.9-4


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


• Other enzyme inhibitors

– Bind at a remote site

– Change the enzyme’s shape

– Prevent the enzyme from binding to its substrate


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


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.


• 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

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



Figure 5.12


• 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.


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


• 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.


• Osmoregulation is the control of water balance within a cell or organism.

• Most animal cells require an isotonic environment.

Water Balance in Animal Cells


• 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

http://youtu.be/rMGH1-mpp8g

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


• 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


http://youtu.be/RPAZvs4hvGA

Lower solute concentration

Higher solute concentration

ATP

Solute

Figure 5.16-1



ATP

Solute

Figure 5.16-2

Exocytosis and Endocytosis: Traffic of Large Molecules

• Exocytosis is the secretion of large molecules within vesicles.


Outside of cell

Cytoplasm

Plasmamembrane

Figure 5.17


• Endocytosis takes material into a cell within vesicles that bud inward from the plasma membrane.

Figure 5.18


• 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


The Role of Membranes in Cell Signaling• The plasma membrane helps convey signals between

– Cells – Cells and their environment


• 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

http://youtu.be/qOVkedxDqQo

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


Passive Transport(requires no energy)

Active Transport(requires energy)

Diffusion Facilitated diffusion Osmosis



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

© 2010 pearson education, inc. functions of cells the sum total of all chemical reactions that...

Documents