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