Chapter 6: Energy and Enzymes AP BIO

6.1 Metabolism

What is Metabolism?

6.1 Metabolism

What is Metabolism?

• total of an organism’s chemical reactions

  ex/ food converting into energy is a chemical reaction. that’s why so many people say “i want high metabolism” because if you have that high metabolism that means there is more reactions and therefore more food gets converted into energy instead of fat

Metabolic Pathways

• molecules altered via defined steps, catalyzed by specific enzymes

BARF

Break = Absorb

Release = Form

Catabolic Pathways

• net release of energy = exergonic

• digestive, breaks down complex molecules into simpler ones

• ex/ hydrolysis

Anabolic Pathways

• net absorption/

  gain of energy = endergonic

• synthesis, combine smaller molecules into more complex ones

Kinetic Energy

• movement

• thermal, heat

• light

Potential Energy

• stored

• chemical energy: potential energy available for release in a chemical reaction

First Law of Energy Transformation (Thermodynamics)

• energy cannot be created or destroyed, it can only be transformed

Second Law of Energy Transformation (Thermodynamics)

• during energy transformation, some energy is converted into heat

  • ex/ lightbulbs are hot because the light energy transferred into the bulb and some is loss to heat —> which means lightbulbs are less efficient and wastes more energy

• Universe is always trying to expand —> everything naturally increases in entropy

  • therefore, to decrease entropy, energy is necessary

    • this “reverses” it

    • Entropy = randomness, chaos

6.2

Gibb’s Free Energy

• available energy that can perform work

• net energy absorbed/released by reaction pathway

ΔG is less than 0

• negative, energy released aka exergonic

• exergonic = spontaneous —> increase of entropy

• Catabolic Pathways

  • ex/ breakdown of glucose into CO2 and H2O has ΔG of -686k cal

ΔG is greater than 0

• positive, energy gained/absorbed aka endergonic

• entropy decreases —> not spontaneous

• anabolic pathways

ΔG = 0

• cellular death :(

• chemical equilibrium - no work is being done

6.3

Energy Coupling

• use energy released from exergonic rxn to drive an endergonic rxn

ATP

• structure: adenine, ribose, 3 phosphate groups

• ATP —> ADP + P

Phosphorylation

• transfer of phosphate group from ATP to some other molecule/reactant, which is more reactive (less stable) than original molecule (changes shape)

• ex/ when phosphorylation occurs in the sodium-potassium pump, the pump receptors change shape to fit the potassium atoms and will then release the sodium in and potassium out if ykyk

ATP regenerated by addition of phosphate to ADP; requires energy

6.4 ENZYMES

So… what are enzymes

organic catalysts

Catalyst

• speed up chemical reactions

• ex/ Catalase breaks down hydrogen peroxide (H2O2) into H2O and O2 and the catalase is the enzyme that catalyzes the breakdown

• ex/ Hydrolysis (breakdown of compound due to reaction with water) can happen fast due to the enzyme SUCRASE

Activation Energy

• initial investment of energy for starting a reaction (energy requited to contort reactant molecules so bonds can break)

• often supplied by heat (thermal energy) absorbed from surroundings —> reactant molecules accelerate and collide more often and more forcefully

• enzymes lower activation energy barrier

Enzymes in Activation Energy

• provide template on which reactants (substrates) can come together in proper orientation

• stretch substrate molecules, stressing/bending chemical bonds

• provide conducive microenvironment for reaction (ex/ proper pH)

  • microenvironment = just in active site at enzyme, the bit gets altered, NOWHERE ELSE

Enzyme-Substrate Specificity

• most enzymes names end in

• active site of enzyme binds to substrate (pocket/groove enzyme surface) - complementary fit between shape of active site and shape of substrate

• Induced fit - enzyme slightly changes shape to “hug” the substrate so it fits snug in active site.

  • analogy: changing your cupped hand up to catch a speeding ball towards you

Enzyme-Substrate Specificity (continued)

• substrate held in active site by weak interactions between R-groups of enzyme and substrate (H bonds and ionic bonds)

• Single enzyme can act on about a thousand substrates per second

• Enzymes can usually catalyze either forward or reverse reaction

Enzyme Saturation

• think of the toothpick activity

• enzyme saturation = max rxn rate

• overcome by just adding more concentration aka bring in a friend

Temperature and pH

• thermal agitation of enzyme molecule disrupts weak interactions that stabilize active shape of enzyme = denaturation

• Most human enzymes have optimal temps of 37°C

  • temperature decreases, slow down enzyme molecule

  • temperature increases, denatures molecule

  • pH increases or decreases, denatures molecule

Cofactors

• nonprotein helpers that bind to enzyme

• May be inorganic - Zn, Fe, Cu ions (trace elements)

• May be organic - coenzymes

Enzyme Inhibitors

• inhibit (stop) action of specific enzymes by binding to them

Competitive Inhibitor

• fit into active site, blocking ability of substrate to bind

• competes with substrate

Noncompetitive Inhibitor

• allosteric inhibitors —> bind to the allosteric site —> this causes the enzymes active site to change shape and halt of its function (not denatured, just stop functioning) once it is removed its function resumes

Irreversible Inhibitors

• inhibitor that makes it so the enzyme cannot return to its original shape

• toxins and poisons (sarin, pesticides, penicillin, parathion, etc)

• sarin —> inhibits muscular relaxation and tells diaphragm to contract and not relax

• Toxins bind permanently to the allosteric site and this causes the enzymes shape to be permanently altered

• Antibiotics inhibit bacterial growth, so that the immune system can turn them off more easily

Allosteric Regulation

• enzyme’s function at active site affected by binding of a regulatory molecule to a separate site (allosteric site)

• Activator: stabilizes shape with functional active sites (cofactor)

• Inhibitor: stabilizes inactive form of enzyme (non competitive inhibitor)

Other regulation of Enzyme Activity

• binding to one subunit of multi-subunit enzyme affects all subunits

  • A single activator or inhibitor molecule that binds to one regulatory site will affect the active sites of all subunits

  • Only need one activator/inhibitor to regulate all active sites

Feedback Inhibition

• metabolic pathway switched off by inhibitory binding of its end product to an enzyme that acts early in the pathway