concept 8.4: enzymes speed up metabolic reactions by lowering energy barriers

describe spontaneous reaction

does not need added energy but can be slow enough to be inperceptible

catalyst

a chemical agent that speeds up a reaction without being consumed by the reaction

enzyme

a macromolecule- typically protein- that acts as a catalyst to speed up a reaction

what is activation energy (free energy of activation)

the initial energy needed to break the bonds of the reactants

what is the transition state

when molecules become unstable when enough energy is absorbed to break bonds

where does the energy come from that supplies activation energy

heat in the form of thermal energy absorbed from the surroundings

where does energy go in a exergonic reaction

the formation of new bonds releases more energy than was used to break the old bonds

what does it mean to have a low activation energy

the reaction could occur at low temperatures such as room temp

what does it mean to have a high activation energy

need a lot of heat to occur

why is heat not a useful way to speed reactions

too much heat can cause proteins to denature and it could speed up undesired reactions accidentally

how to organisms speed up their reactions

a catalyst selectively speeds up a reaction without being consumed

what is an enzyme able to change

enzyme cannot change delta G it can only lower to the activation energy

can an enzyme turn an endergonic reaction into an exergonic reaction

no

enzyme substrate

the reactant that an enzyme acts on

how do most enzymes end

-ase

enzyme substrate complex

the enzyme bound to its substrate

what does the enzyme turn the substrate into

the enzymes converts the substrate into product

the active site

the region on the enzyme, often a pocket or groove, that binds to the substrate

how does the active site react to a substrate

it changes its shape slightly when the substrate enters, induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction

what in the active site is binding to the substrate

R groups

what is responsible for enzyme specificity

the complementary fit between the shape of the active site and the shape of the substrate

what does maltase catalyze

maltose to two glucose subunits

what does lactase catalyze

lactose to glucose and galactose

what holds the substrate in the active site

weak bonds like hydrogen bonds

**what mechanisms do enzymes use to lower activation energy

1- substrates may be orientated to facilitate the reaction

2- substrates may be stretched to strain the substrates covalent bonds to make these bonds easier to break

3- the active site may provide a microenvironment that factors the reaction

4- amino acids in the active site may participate in the reaction, in some instances, covalent bonds can be briefly made between the enzyme and substrate during the catalysis reaction, these covalent bonds are usually quickly broken to restore the enzymes normal bond positions

what can enzymes activity be affected by

temperature and Ph or chemicals that specifically influence the enzyme

what can the speed of an enzyme be affected by

the concentration of the substrate and the concentration of the enzyme

what is true about enzymes regarding temperature

all enzymes have an optimal temperature for the enzyme to occur and before and beyond that point the rate of reaction drops

what is true about enzymes regarding pH

all enzymes have optimal pH that depends on its environment

what specifically does pH and temperature have an effect on with enzymes

pH and temperature both effect the 3D shape of the enzyme

cofactors

non- protein helpers that bind to the enzyme permanently or reversibly with the substrate

organic vs inorganic cofactors

inorganic cofactors include metals like zinc and copper and organic cofactors are called coenzymes and include vitamins

enzyme inhibitor

a chemical that will selectively bind to an enzyme and change the active site

describe the reversibility of enzyme inhibitors

many inhibitors bind to the enzymes with weak attractions allowing it to be reversible, but some will bind with covalent bonds and this is irreversible

competitive inhibitors

closely resemble the substrate and bind to the active site of an enzyme, competing with the substrate for the active site

what does a competitive inhibitor do to an enzyme

reduces the productivity because it is blocking the substrate from accessing the active site

what is a way to overcome a competitive inhibitor

increase the substrate concentration

example of competitive inhibitors

many antibiotics inhibit bacteria, sarin nerve gas blocks some neurotransmitters, methanol is converted to formaldehyde by alcohol and treatment is an iv of ethanol because they are competitive, toxins like pesticides or poisons

noncompetitive inhibitors

bind to a part of the enzyme that is not the active site and causes the enzyme to change its shape and makes the active site less effective in substrate binding

example of noncompetitive inhibitors

heavy metals like mercury, lead and silver

central dogma of biology

enzymes are proteins encoded by genes

what happens when genes become mutated

it can lead to the amino acid composition of the enzymeand result in novel enzyme activity