ENERGY & ENZYMESChapter 6 Biology in Focus

AP Bio 2014

Ms. Eggers

Chapter 6 vocabulary terms6.1-6.3 Energetics• Metabolism• Catabolic pathways• Anabolic pathways• Bioenergetics• Kinetic energy• Thermal energy• Potential energy• Chemical energy• Thermodynamics• First law of thermodynamics• Entropy• Second law of thermodynamics• Spontaneous reaction• Free energy• Exergonic• Endergonic• Energy coupling• ATP/phosphorylated intermediate

6.4-6.5 Enzymes• Enzyme• Catalyst• Activation energy• Substrate• Enzyme-substrate complex• Active site• Induced fit• Cofactors• Coenzyme• Competitive inhibitors• Noncompetitive inhibitors• Allosteric regulation• Cooperativity• Feedback inhibition

Part 1: Metabolism & EnergeticsSections 6.1 - 6.3

Metabolism, anabolic and catabolic defined

Examples of metabolic pathways

Metabolism is WICKED COMPLEX - these are just the reactions involved in starch and sucrose metabolism

Forms of Energy• Kinetic energy

• Energy of motion• Thermal energy

• Potential energy• Chemical energy• Stored in the covalent

bonds of organic molecules such as carbohydrates and fats

The Laws of Thermodynamics• 1st Law of Thermodynamics

• Energy can be transferred but it can neither be created nor destroyed

• 2nd Law of Thermodynamics• Every energy transfer increases the entropy of the universe

• Entropy: a measure of the disorder or randomness

• Heat is the most randomly ordered form of energy so in terms of biology, the second law really means that no conversion of chemical energy is perfect – heat is always generated and lost.

A SPONTANEOUS process occurs without any input of energy AND always results in an INCREASE in ENTROPY

Free-energy• Measures the portion of

a system’s energy that is available to do work

• DG is the change in free energy between the final state and the initial state

• DG = negative value = can occur spontaneously

• DG = positive value = can NOT occur spontaneously

DG = Gfinal – Ginitial

• A system must LOSE free energy from its initial state to its final state in order for it to occur spontaneously

More on Free-energy (G)• Free energy is also a measure of the “instability” of a

system – losing free energy makes a system more stable

• A system at maximum stability is at EQUILIBRIUM• If a system is moving TOWARD equilibrium, it will

occur spontaneously (ie diffusion) AND can do work• At equilibrium, DG = 0

Exergonic versus endergonic reactions

• An exergonic reaction RELEASES free energy• DG is negative• Can occur spontaneously• Makes things LESS ordered• Catabolic reactions

• An endergonic reaction requires an input of energy• DG is positive• Will not occur spontaneously• Makes things MORE

ordered Anabolic reactions

Endergonic ExergonicPlants use an input of the sun’s energy

to assemble glucose from CO2 and H2O

Plant and animal cells break down glucose and convert the

energy to usable ATP

ATP: the cell’s battery

• Pushing endergonic reactions – those that build molecules (anabolic reactions) – requires chemical work

• An endergonic reaction MUST be coupled to an exergonic reaction

ATP = adenosine triphosphate

Coupling ATP hydrolysis to an endergonic process

• Coupling ATP to an endergonic reaction can involve a phosphorylated intermediate (a)

• Or can be indirect as in (b)

Part 2: EnzymesSections 6.4 & 6.5

In chemistry, a “spontaneous” reaction doesn’t necessarily occur readily…

• Example: a log – the log contains A LOT of chemical potential energy and once the log is lit it will burn and release that energy in the form of heat and light energy BUT without the small input of energy from a match, that log would sit there NOT burning for a LONG time

Exergonic reactions often require…

• Activation energy = free energy of activation, or EA

• The breakdown of glucose releases energy – and is therefore considered “spontaneous”, but those covalent bonds are quite stable…

Enzymes are chemical catalysts

• Enzymes speed up the occurrence of chemical reactions by reducing the “height” of the activation energy barrier

• Enzymes reduce EA

The name game…what is the name of the enzyme that breaks down lactose?

• Proteases- A protease is any enzyme that can break down a long protein into smaller chains called peptides (a peptide is simply a short amino acid chain).

• Peptidases - Peptidases break peptides down into individual amino acids. Proteases and peptidases are often found in laundry detergents -- they help remove things like blood stains from cloth by breaking down the proteins.

• Amylases - Amylases break down starch chains into smaller sugar molecules. Your saliva contains amylase and so does your small intestine. Maltase, lactase, and sucrase finish breaking the simple sugars down into individual glucose molecules.

• Lipases - Lipases break down fats.• Hydrolases – Hydrolases catalyze hydrolysis reactions.• Transferases – Transferases transfer different functional groups on a

molecule.• Nucleases – The various nucleases act on nucleic acids.

You get the picture… add –ase to the end

Another enzyme example: maltase• Maltose is made of two glucose molecules bonded together.• The maltase enzyme is a protein that is perfectly shaped to

accept a maltose molecule and break the bond. Then the two glucose molecules are released.

• A single maltase enzyme can break in excess of 1,000 maltose bonds per second, and will only accept maltose molecules.

Substrate specificity

• The molecule that an enzyme acts on is called its substrate (sometimes the term ligand will be used)

• When the enzyme binds the substrate, it is called an enzyme-substrate complex.

• The substrate is bound by the enzyme in a specific region called the active site.

Reaction rates – effect of varying enzyme concentration and substrate concentration

Enzymes have a unique 3-dimensional shape that is held together primarily by ionic and hydrogen bonds: Many factors can affect enzyme function

• Temperature• pH• Cofactors• Enzyme inhibitors• Regulators – negative

feedback

Reaction rates – the effect of temperature

At low temperatures things are moving too slow, some temperature is “just right”, and at high temperatures, the enzyme denatures

Reaction rates – the effect of pH

Other factors affecting enzyme activity

• Cofactors = non-protein helpers• Metals such as iron, zinc

& copper

• Coenzymes = organic molecule ‘helpers’ – many vitamins are coenzymes

• The protein portion of an enzyme is called the apoenzyme. A cofactor is the non-protein part of an enzyme. The complete enzyme (apoprotein + cofactor) is termed the holoenzyme.

Enzyme inhibitors

• Competitive inhibitors block the substrates from entering the active sites

• Noncompetitive inhibitors bind at spots away from the active site but change the shape of the protein so it can no longer bind the substrate

Enzyme Inhibitors

How are enzymes regulated?

• Allosteric regulation is kind of like noncompetitive inhibition – but purposeful…

Another kind of allosteric regulation -- cooperativity

• Cooperativity can amplify the response of an enzyme to a substrate (eg hemoglobin)

Feedback inhibition – shutting enzymes off

Animated tutorials & resources• http://www.northland.cc.mn.us/biology/Biology1111/animat

ions/enzyme.html