Metabolism

•Chemical reactions in life

•Convert Energy – Store Energy – Use Energy

•Enzymes*****

•Controls

Latin

• Allo• Ana• Cata• Endo• Exo• Kine• Lyse• Thermo -

Terms

• Allosteric• Anabolic• Catabolic • Endergonic• Entropy • Exergonic• Free energy• Gibb’s Free Energy

Organisms and Energy

• Three types of energy organisms use:– Light – photons, waves– Electrons – potential energy in chemical bonds– Gradients – ‘push’ protons across a membrane and

let them flow back

Learning Objectives:

• 1.B.1.a – Organisms share many conserved core processes and features and are widely distributed among organisms today.– Metabolic pathways are conserved across all

Domains• Interpreted as evidence of evolution (descent with

modification)

Shared Metabolic Processes and Features

• All cells:– Break and form chemical bonds– Use ATP– Many prokaryotes and all eukaryotes possess

cytochrome c– Almost all cells do aerobic respiration w/ETC– Have similar enzymes for metabolism

2.A.1 – All Living Systems Require Constant Input of Free Energy.

Life Requires a Highly Ordered System

• Order is maintained by constant input of free energy

• Loss of order or free energy results in death• Increased disorder and entropy are offset by

biological processes that maintain or increase order

• Living systems do not violate the Second Law of Thermodynamics which states that entropy increases over time.– Order is maintained by coupling reactions that

increase entropy (and so have negative changes in free energy) with those that decrease entropy (and so have positive changes in free energy)

– Energy input must exceed free energy lost to entropy to maintain order and power cellular processes

– Energetically favorable exergonic reactions such as ATP-ADP, have a negative change in free energy can be used to maintain or increase order in a system by being coupled with reactions that have positive free-energy change.

Thermodynamics

• 1st law – energy cannot be created or destroyed.– Can be transformed, but does not go away

• 2nd law – Entropy; energy becomes less usable as it is transformed.– Lost as unusable heat.– Entropy increases as energy is transferred.– Stuff goes from order to disorder.

Thermodynamics – ‘Free’ Energy

• ‘Free’ = ‘usable’• Organisms absorb usable energy

(free energy) from light.• They convert light (kinetic

energy) to potential energy in chemical bonds (C-H); entropy of the environment increases.

• Cells maintain their organization by increasing the entropy of the universe (Earth).

Thermodynamics

10% law2nd Law of Thermodynamics

Gibbs “Free” Energy

Δ G = ΔH – TΔS•G - Gibbs “free” energy•H – Enthalpy (the amount of usable energy in

the system)•T – Temperature in Kelvin (273 + C )⁰•S - Entropy (disorder created by something

being broken down)

Usable energy = total energy – T x ‘lost’ energyYoutube – Gibbs free energy; Bozeman

Unstable (Capable of work)vs.

Stable (no work)

G = 0

A closed hydroelectric system

G < 0

Catabolism(Hydrolysis Reaction)

Reactants

EnergyProducts

Progress of the reaction

Amount ofenergyreleased(G < 0)

Fre

e en

erg

y

Exergonic reaction: energy released

Anabolism(Dehydration Synthesis)

ReactantsEnergy

Products

Progress of the reaction

Amount ofenergyrequired(G > 0)

Fre

e en

erg

y

Endergonic reaction: energy required

Practice, Practice, Practice• An experiment determined that when a protein

unfolds to its denatured (D) state from the original folded(F) state, the change in Enthalpy is ΔH = H(D) – H(F) = 56,000 joules/mol. Also the change in Entropy is ΔS = S(D) – S(F) = 178 joules/mol. At a temperature of 20 C, ⁰calculate the change in Free Energy ΔG, in j/mol, when the protein unfolds from its folded state. Show all your work and circle your final answer.

• Is this a spontaneous or non-spontaneous reaction?

ATP***

• Phosphate bond is easily broken/formed

Energy Coupling

• To maintain organization, energy input must be greater than the free energy lost to entropy.

• Energy coupling – couple reactions that increase entropy (exergonic; negative changes in free energy) with those that decrease entropy (endergonic; positive changes in free energy)• Ex. ADP-ATP cycle

G < 0 G > 0

Potential vs Kinetic Energy

• Potential energy - stored– Chemical bonds of electrons (C-H)– Identify potential and kinetic energy in the picture

Short polymer Unlinked monomer

Dehydration removes a watermolecule, forming a new bond

Dehydration reaction in the synthesis of a polymer

Longer polymer

Chemical Reactions

• Two kinds of reactions:– Exergonic – net release of energy

• Fire, respiration– Endergonic – net absorption of energy

• Photosynthesis

Hydrolysis Dehydration synthesis

Metabolism – Types of Reactions

• Anabolism - build up– Store energy by

assembling macromolecules (photosynthesis)

– Endergonic

• Catabolism - break down– Release energy by

breaking down molecules (digestion, respiration)

– Exergonic

Activation Energy

• Reactions are random collisions

• Spontaneous, exergonic reaction; ΔG < 0

• Most reactions require activation energy

Activation Energy

• Cells can only tolerate certain conditions– Not too hot, low electrical charge (why?)

• Cells need chemical reactions to be at low activation energy– Catalyst – lowers activation energy

• Enzymes – biological catalysts

Rate of Reactions in Cells

• Three factors affect rate of reaction in cells:– Temperature – affects the speed at which

molecules can collide (fast or slowly)– Energy provided by the cell – Enzymes - catalysts

Enzymes

• Catalysts – reduce activation energy**• Globular proteins (700)

– Specific conformational shape**• Only catalyze one specific

reaction

• Anabolic or catabolic • Catalase catalyzes 40 million reactions per second

• Transition state - reactants absorb energy

******

??

Endergonic or exergonic?

.

Course ofreactionwithoutenzyme

EA

without enzyme

G is unaffectedby enzyme

Progress of the reaction

Fre

e en

erg

y

EA withenzymeis lower

Course ofreactionwith enzyme

Reactants

Products

Enzymes

• Substrate – reactant enzyme acts upon• Active site - area on the enzyme where the

substrate attaches – Groove or pocket created by the

specific folding of proteins• Secondary, tertiary and/or quaternary

• ‘Lock and Key’ = specificity• Induced fit model - enzyme changes shape

when the substrate attaches to the active site making it easier for bonds to form or break

How Enzymes Work

Factors That Affect Enzyme Activity

• Correct environmental conditions– pH, heat

• Cofactors• Inhibitors

Correct Environmental Factors

• Denature the enzyme (protein)– Heat, pH, salinity– Why?

Competitive Inhibition

• Competitive inhibitors - resemble substrate, block active site– Cyanide is a competitive

inhibitor for catalase

Allosteric Control

• Allosteric control – the shape of an enzyme’s active site is controlled at another place on the enzyme

• Allosteric site has to be activated, (may be inhibited)

Feedback Inhibition

• Feedback Inhibition - end product of the pathway inhibits the pathway****– Prevents cells from wasting

resources

Isoleucine – allosteric inhibitor

Structure and Metabolism

• Cells are organized • Multi-enzyme complex - enzymes are positioned

in a membrane– Inner membrane of mitochondria, chloroplasts

• Cooperativity - one substrate molecule can activate all other subunits of an enzyme

• Only requires a small concentration of substrate to activate enzyme– Phosphofructokinase – Hemoglobin

Enzyme Cooperativity

• Organisms use free energy to maintain organization, grow and reproduce:– Use various strategies to regulate temperature.

• Endothermy – use thermal energy to maintain homeostasis.

• Ectothermy – use external temperature to regulate and maintain temperature

• Elevated floral temperatures in some plants.

• Relationship between metabolic rate per unit body mass and the size of multicellular organisms • Generally, the smaller the organisms, the higher the

metabolic rate.

• Reproduction and rearing of offspring requires more free energy than just maintenance and growth.

– Different strategies in response to energy availability.• Seasonal reproduction in animals and plants• Life-history strategy (annuals, biennials, etc.)

– Diapause – eggs and/or development stop due to adverse conditions (insects, plants)

Energy Changes Affect Populations

• Changes in free energy availability can result in changes in population size and or disruptions to an ecosystem– Change in the producer level can affect the size and

number of other trophic levels

– Change in energy resource (sunlight) can affect all trophic levels