Bio HL1 Test 3 - Kim

enzymes

biological catalysts made of proteins (sometimes RNA)

increase biochemical reactions without being consumed or changed

allow rapid metabolic reactions to sustain life

enables homeostasis under changing environmental conditions

prevents accumulation of toxic intermediates

metabolism

complex network of interdependent and interacting chemical reactions in living organisms

consists of anabolism and catabolism

enzymes provide ________

specificity; one catalyzes only one specific type of reaction or a specific substrate

each metabolic pathway consists of

many different enzymes—differences in enzymes determines which pathway occurs and how each is regulated

most enzyme produces only _______ changes

small

significant transformations occur via

a sequence of many enzymatic steps

linear pathway (chain)

proceeds in a single direction with distinct starting and ending molecules—e.g. glycolysis converting glucose into pyruvates  

cyclical pathway (more common)

regenerates starting molecule at end of process, allowing cycle to repeat—e.g. Calvin and Krebs cycle

enzymatic reactions can occur

both inside and outside of the cell

intracellular enzymes

made by free ribosomes and used within cytoplasm—glycolysis—some are used inside organelles—Krebs cycle in mitochondrial matrix

extracellular enzymes

made by bound ribosomes on ER and released from cell—break down larger macromolecules in the gut of digestive syste

anabolic reactions

synthesis of complex molecules—monomers → polymers via condensation reaction—e.g. protein synthesis, glycogen formation, photosynthesis—endergonic

endergonic

requires energy, usually from ATP, reactants have less energy then products, more free energy after rxn

catabolic reactions

breakdown of complex molecules into simpler ones—polymers → monomers via hydrolysis—e.g. digestion, cellular respiration—exergonic

exergonic

releases energy that can be captured as ATP, reactants have more energy than products, spontaneous, less free energy after reaction

enzymes are _____ proteins whose ______ arises from folding polypeptides into compact forms

globular; shape

active site

region where substrates bind and reactions occur

enzymes and active sites are

complimentary in shape and chemical property

active sites consist of ____ amino acids

few

three dimensional conformation of entire enzymes

determines active site’s shape and chemical properties

AA interactions distant from active site in primary structure maintain

correct folding necessary for catalytic activity

if any part of an enzyme changes

overall shape and active site may change, and enzyme may lose function

induced fit model

proposes that both enzyme’s active site and substrate undergo slight conformational changes upon bonding, with adjustment increasing surface area and precision of fit, ensuring greater catalytic efficiency by positioning substrate in optimal orientation, lowering activation energy and increasing reaction potential

Brownian motion

molecules move randomly in cell environments (aqueous) due to kinetic energy, substrate and active site must collide with correct orientation and sufficient energy for binding and reaction to occur, some larger substrates are immobilized, or fixed, so enzymes must approach them, sometimes enzymes are immobilized due to membrane attachment so substrates must diffuse towards them

metabolic reactions convert energy from food

into ATP, but transfer of energy is never fully efficient, and some energy is lost in the form of heat (in mitochondria during respiration)

mammals and birds (endotherms) use heat

to maintain constant body temp—essential for homeostasis, ensuring optimal conditions for enzymatic activity and survival; if not enough is produced, metabolic rate increases

some enzymes are absolutely _____, while others are less _____.

specific and bind to only one substrate; specific and bind to a group of substrates

denaturation

loss of enzyme’s specific structure due to environmental factors like temp, pH, or concentration; its usually irreversible and results in loss of function

increase in thermal energy leads to

increased kinetic NRG → increased particle motion → increased collisions → increased reaction rate

lower temperatures on enzymes

lowers reaction rate but doesn’t denature

increasing substrate concentration

results in an increase in enzyme activity and therefore reaction rate, because increasing substrates allows for more frequent collision with enzymes, at some point the reactions plateau because all active sites are occupied or “saturated,” and the reaction has reached Vmax of maximum rate

activation energy

minimum energy required to break bonds in a reactant and initiate a chemical reaction—enzymes increase reaction rate by increasing activation energy, temporarily binding to substrate to stress and destabilize bonds, less overall energy is required, increasing reaction rate, net amount of free energy in reaction stays the same

enzymes work as templates by

allowing substrates to reach optimal orientation and place stress on necessary bonds, functioning as suitable microenvironments by maintaining optimal pH

non-competitive inhibitor

binds to allosteric site that is separate from active site—only specific molecules (allosteric regulators) can bind here, changes overall shape of enzyme and therefore its active site—increasing concentration does not overcome inhibition, binding is mostly reversible

competitive inhibitor

substrate and inhibitor are structurally and chemically similar and compete for the same active site, increasing substrate [] reduces or overcomes inhibition because substrates outcompete for active site, normally reversible, covalently bonded inhibitors are not

statins

drug that acts as a competitive inhibitor of HMG-CoA reductase (enzyme involved in cholesterol synthesis), resembles HMG-CoA and binds to active site, decreases cholesterol production in liver cells—higher [HMG-CoA] can partially overcome inhibition

end product inhibition

control mechanism in which end product of a metabolic pathway inhibits an earlier enzyme by binding to its allosteric site, preventing overproduction of end product and conserving energy—once product levels decrease, inhibitor dislodges and pathway resumes

example of end product inhibition

isoleucine as inhibitor for threonine—threonine→intermediate compounds→ isoleucine—isoleucine is a noncompetitive inhibitor for threonine deaminase

mechanisms based inhibition

inhibitor permanently binds to active site with covalent bond, rendering it irreversibly inactive—e.g. penicilin—antibiotic that targets transpeptidase enzyme, responsible for cell wall synthesis, some bacteria have evolved mutations in the gene that codes for transpeptidase, causing structural changes in the active site, and penicillin can’t bind effectively, preventing covalent bonds (how resistance develops)