Energy and Energy and MetabolismMetabolismChapter 8Chapter 8

Energy and Energy and MetabolismMetabolismChapter 8Chapter 8

Energy

Energy

Energy

Metabolism• All the chemical reactions carried

out by the cell

Metabolism• Catabolic reactions: • Break down large molecules into

smaller substances• Exergonic:• Releases energy

Metabolism• Anabolic reactions: • Synthesis of large molecules from

smaller substances• Endergonic:• Requires energy

Metabolism• Biochemical pathways: • Reactions in a cell• Occur in sequence• Product of one reaction • Becomes substrate in the next• Pathways are highly regulated and coordinated• Feedback inhibition:• End product of a reaction blocks the pathway

from producing more.

Energy

Energy• Bioenergetics: • Analysis of how energy powers

activities of living systems • Growth, order, reproduction,

responsiveness & regulation

Energy• Energy: • The capacity to do work • Kinetic energy:• Energy of motion• Potential energy:• Energy of position or stored energy

Energy• Kinetic energy:

• Potential energy:

Energy• Thermodynamics:  • Study of energy “heat changes”• Most work done by living

organisms• Transformation of PE to KE

Energy• Sun main source of energy• Energy from sun• Combine smaller molecules to

make larger molecules• Energy is stored in the chemical

bond

Energy• Redox(oxidation-reduction)

reactions: • Transfer of an electron or electrons• Play a key role in the flow of energy in

biological systems• An electron is passed from one atom to

another energy is passed

Law of thermodynamics

• Laws of thermodynamics govern all energy changes in the universe.

•  First law of thermodynamics: • Energy cannot be created or destroyed • Change from one form to another.

(potential to kinetic) • Total amount of energy stays the same

First law• In living organisms:• Eating transfers energy from the

bonds in food to organism• PE is transferred to KE

First Law• Heat: • Random motion of molecules • Heat can be lost in the system

during conversions• Sun replaces energy lost as heat

Second law• Second law of

thermodynamics:• Transformation of PE to heat

(random motion of molecules). • Entropy (disorder) in the universe

is increasing

Second law• Energy transformations tend to

proceed spontaneously • Convert matter from a more

ordered state to a less ordered or more stable state.

Second law• Entropy(s): • Disorder in a system• Enthalpy (H): • Heat content• Free energy(G): • Amount of energy available to do work in any

system.• Amount of energy available to break and then

make other chemical bonds

Second law• G=Gibbs free energy G = H - TS (T=Kelvin temp) G is positive • Products have more energy than

reactants• Due to more energy in the bonds or less

randomness • Endergonic reaction

Endergonic reaction

Second lawG is negative• Products have less energy than

reactants• H is lower (bond energy) or

S is greater- more randomness• Exergonic:• Reaction that releases energy

Exergonic reaction

Exergonic reactions

Activation Energy• Energy needed to initiate a

reaction • All reactions require activation

energy.• Reactions with higher AE tend to

move forward more slowly

Enzymes• Catalyst in living organisms• Large three-dimensional globular

protein• Ribozymes:• RNA catalysts are specific & speed

up reactions

Enzymes• Substrate: • Molecule that is going to undergo the reaction• Active sites: • Specific spots on the enzyme that substrates binds• Enzyme-substrate complex:• Enzymes are bound to substrates with a precise fit.• Induced fit: • When the substrate causes the enzyme to adjust to

make a better fit• E+S ES E + P

Fig. 8-17Fig. 8-17Fig. 8-17Fig. 8-17

Substrates

Enzyme

Products arereleased.

Products

Substrates areconverted toproducts.

Active site can lower EA

and speed up a reaction.

Substrates held in active site by weakinteractions, such as hydrogen bonds andionic bonds.

Substrates enter active site; enzyme changes shape such that its active siteenfolds the substrates (induced fit).

Activesite is

availablefor two new

substratemolecules.

Enzyme-substratecomplex

5

3

21

6

4

Enzymes• Only small amounts are necessary• Can be recycled• Specific• Speeds up the reactions• Different types of cells have different

enzymes• Determine the course of chemical

reactions in the cell

Enzyme examples• Lipase, protease• Carbonic anhydrase

– CO2 + H2O H2CO3

• Lactate dehydrogenase– Lactate to pyruvate

• Pyruvate dehydrogenase– Enzyme that starts the Kreb cycle

Enzymes• Factors that affect the rate of enzyme• 1. Concentration of enzyme & substrate• 2. Factors that affect 3-D shape of the

enzyme • Temperature, pH, salt concentration

and regulatory molecules

Enzymes• Inhibitor: • Binds the enzyme• Prevents it from working• Occurs at the end of a pathway to stop

the reactions• Two types of inhibitors• Competitive• Noncompetitive

Fig. 8-19Fig. 8-19Fig. 8-19Fig. 8-19

(a) Normal binding (c) Noncompetitive inhibition(b) Competitive inhibition

Noncompetitive inhibitor

Active siteCompetitive inhibitor

Substrate

Enzyme

Enzymes• Allosteric site: • On/off switch for the enzyme• Usually at different location than the active

site• Allosteric inhibitor:• Binds at the allosteric site • Stops the enzyme activity• Activators: • Binds & increases the activity

Enzymes• Cofactor:• Assists enzyme function such as Zn, Mg, Cu• Coenzymes:• Cofactors that are not proteins but are organic

molecules • Help transfer electrons & energy associated

with the electrons• Vitamins are coenzymes • NAD+ important coenzyme

Energy

ATP• ATP powers the energy requiring

processes in the cell• 1. Chemical work (making

polymers)• 2. Transporting substances• 3. Mechanical work • Muscle movement, cilia

ATP• Structure of ATP• Ribose sugar• Adenine• 3 phosphate attached in a row

ATP

ATP• ATP • ADP • Losses a inorganic phosphate • Hydrolysis • 7.3kcal/mole of energy is released.