Table 5-1, p. 80

Energy In, Energy Out

• Chemical reactions– Reactants (molecules in)– Products (molecules out)

• Endergonic reactions (energy-requiring)– Photosynthesis

• Exergonic reactions (energy-releasing)– Aerobic respiration

Fig. 5-3, p. 74

Exergonic reactions, such asaerobic respiration, end with a netoutput of energy. Such reactionshelp cells access energy storedin chemical bonds of reactants.

glucose (C6H12O6) + 6 O2

6 CO2 + 6 H2O

energy in energy out

Endergonic reactions, suchas photosynthesis, proceedonly with a net input of energy.Cells can store energy in theproducts of such reactions.

Fig. 5-4, p. 75

ENERGY OUTWith each conversion,there is a one-way flow ofa bit of energy back to theenvironment. Nutrientscycle between producersand consumers.

NUTRIENTCYCLING

producers

consumers

ENERGY OUTEnergy continuallyflows from the sun.

ENERGY INSunlight energy reachesenvironments on Earth.Producers of nearly allecosystems secure someand convert it to storedforms of energy. Theyand all other organismsconvert stored energyto forms that can drivecellular work.

Fig. 5-12, p. 80

Enzymes in Metabolism

• Activation energy – Minimum energy needed to start a reaction

• Enzymes are catalysts – Speed reaction rates by lowering activation

energy– Most are proteins

Fig. 5-6, p. 76

activation energywith enzyme

Time

En

erg

y

starting substances:glucose and phosphate

activation energywithout enzyme

product:glucose-6-phosphate

Fig. 5-27, p. 89

Enzyme Action

• How enzymes lower activation energy – By concentrating substrate molecules – By orienting substrates to favor reaction – By inducing fit between substrate and active

site– By excluding water from active site

Fig. 5-8, p. 78

active site altered,substrate can bind

allosteric activator

allosteric binding site vacant

enzyme active site

substrate cannot bind

X

X

active sitealtered, can’tbind substrate

allostericbindingsite vacant;active sitecan bindsubstrate

allosteric inhibitor

Fig. 5-10, p. 79

Fig. 5-11, p. 79

Diffusion

• Diffusion – Net movement of molecules to a region where

they are less concentrated

• Diffusion rates are influenced by:– Temperature – Molecular size– Gradients of pressure, charge, and

concentration

Fig. 5-16, p. 82

waterdye

dye

Fig. 5-17, p. 83

Glucose and other large,polar, water-soluble molecules,and ions (e.g., H+, Na+, K+, Cl–,

Ca++) cannot cross on their own.

lipidbilayer

Oxygen, carbon dioxide,small nonpolar molecules, andsome molecules of water crossa lipid bilayer freely.

Fig. 5-18, p. 84

Working With and Against Gradients

• Many solutes cross membranes through transport proteins (open or gated channels)

• Facilitated diffusion (passive transport) does not require energy input– Solute diffuses down its concentration gradient

through a transporter – Example: Glucose transporters

Fig. 5-19, p. 85

Fig. 5-21, p. 86

The fluid volume rises in thesecond compartment as waterfollows its concentration gradientand diffuses into it.

hypotonicsolution in firstcompartment

hypertonic solutionin secondcompartment

Initially, the volumes of the twocompartments are equal, but thesolute concentration across themembrane differs.

Which Way Will Water Move?

• Osmosis – The diffusion of water across a selectively

permeable membrane– Water molecules follow their concentration

gradient, influenced by solute concentration

Tonicity

• Relative concentrations of two solutes separated by a semipermeable membrane– Hypertonic fluid (higher solute concentration)– Hypotonic fluid (lower solute concentration)– Isotonic solutions (two solutions with the same

tonicity)

Fig. 5-22, p. 87

1 liter of 10%sucrose solution

2% sucrosesolution

1 liter ofdistilled water

1 liter of 2%sucrose solution

Fig. 5-23, p. 87

Active Transport

• Active transporters require ATP energy to move a solute against its concentration gradient – Maintain gradients across cell membranes– Example: Calcium pumps

Fig. 5-20, p. 86

An ATP molecule bindsto a calcium pump.

higher concentrationof calcium ions outsidecell compared to inside

calcium pump

The shape of the pumpreturns to its resting position.

Membrane Traffic To and From the Cell Surface

• Exocytosis– Cytoplasmic vesicle fuses with plasma

membrane– Contents are released outside

• Endocytosis– Part of plasma membrane forms a vesicle that

sinks into the cytoplasm

Endocytosis and Exocytosis

Phagocytosis