BMCB 658A EXAM 2

The ΔG0‡ of the reaction

As an exergonic reaction, it releases energy to spare.

Spontaneous exergonic

Nonspontaneous endergonic

Free energy

decreases, increases

Equilibrium

Free energy change can be used to predict spontaneity of reaction under the conditions of constant TEMPERATURE and PRESSURE

∆G = ∆H - T∆S

reaction is spontaneous

Standard set of conditions used for comparisons of chemical reactions

pH=0

[H+] = 10-7 M and pH = 7.0

∆G°ʹ

added energy

Couple endergonic reaction to an exergonic reaction

speed up reactions that would eventually occur without them

Difference between energies of reactants and products \n under standard conditions

activation energy (ΔG°‡),which is the energy input required to initiate a reaction

Substrate binds to that portion of the enzyme with a \n complementary shape

Binding of the substrate induces a change in the conformation of the enzyme that results in a complementary fit

speed up the reaction

catalysis can occur

• Orienting substrates correctly

• Straining substrate bonds

• Providing a favorable microenvironment

• Non-covalent bonding to the substrate

Increasing the substrate concentration

all enzyme molecules in a solution are bonded with substrate

\n Decrease in enzymatic activity caused by binding of \n a substrate analogue to the active (catalytic) site \n

Inhibitor competes with the substrate for the active \n site on the enzyme

Form of enzyme inactivation in which a substance binds \n to a site other than the active site but distorts the \n active site to inhibit reaction

Involves two distinct binding sites, one for the substrate \n and one for the inhibitor

overcome noncompetitive inhibition

Inhibitor can bind to the ES complex but not to the free E

Oligomer whose biological activity is affected by other substances binding to it

Substance that modifies the behavior of an allosteric enzyme by binding to it

positive cooperativity

catalysis

globular proteins

ES complex

E + S -→ ES

Description of a reaction whose rate depends on the first power of the concentration of a single reactant

Description of a reaction whose rate depends on the product of the concentrations of TWO reactants

rate of reaction does NOT depend on concentration of substrate, it instead relies on the presence of catalysts

Condition in which the [ES] remains constant in spite of continuous turnover

describes the affinity of enzyme for substrate

maximum velocity of reaction

• First-order kinetics \n • Double [S], Vinit doubles

Vinit = Vmax/2

Vinit= Vmax \n • enzyme is saturated with substrate \n • Zero-order kinetics

substances that decrease the rate of an enzyme-catalyzed reaction

Substances that bind to an enzyme and subsequently are released

Substances that react with enzymes to produce proteins that are not enzymatically active and from which original enzymes cannot be regenerated

Decrease in enzymatic activity caused by binding of a substrate analogue to the active (catalytic) site DOESNT AFFECT CATALYSIS

• Vmax is unchanged

• apparent increase in KM

Because substrate and inhibitor are competing for the same location, a sufficiently high amount of substrate will outcompete inhibitor

Form of enzyme inactivation in which a substance binds to a site other than the active site but distorts the active site to inhibit a reaction

Involves two distinct binding sites: one for the substrate and one for the inhibitor

overcome noncompetitive inhibition causing the Vmax to decrease and the value of kM to stay unchanged

The compound is a competitive inhibitor

remains constant

KM

Alter enzyme concentration \n

-rate of synthesis \n -rate of degradation \n

Alter enzyme activity \n

-allostery (activation, inhibition) \n -phosphorylation \n -post-translational processing \n -sequestration

sigmoidal curve

K systems

V systems

K 0.5

Enzyme for which the substrate concentration that yields \n one-half Vmax is altered by the presence of inhibitors or activators

Enzyme in which the presence of inhibitor/activator \n changes the maximal velocity of the enzyme but not the substrate level that yields one-half Vmax

Substrate level at one-half Vmax in a K system

Allosteric effects that occur when several IDENTICAL molecules are bound to a protein

Allosteric effects that occur when DIFFERENT substances are bound to a protein

positive cooperativity

Description of allosteric activity in which the conformations of all subunits change simultaneously

Inactive protein that can be activated by specific hydrolysis of peptide bonds

Cooperative effect whereby binding of the first ligand \n to an enzyme or protein causes the affinity for the next ligand to be lower

Synthesized compounds that mimic the form \n of the transition state of an enzyme reaction

Antibodies that are produced against a transition-state analog and that have catalytic activity similar to that of a naturally occurring enzyme

Nonprotein substances that take part in enzymatic reactions and are regenerated at the end of the reaction

Molecule that has one end with a polar or charged, water-soluble group and another end with a nonpolar hydrocarbon group that is insoluble in water

Unbranched chain carboxylic acids

• Amphipathic compounds

• 12–20 carbons long

• Unsaturated fatty acids - Contain \n carbon–carbon double bonds

• Saturated fatty acids - Contain only \n single bonds

Lipids formed by the esterification of \n three fatty acids to glycerol

Ester groups form the polar part of the molecule, and the tails are nonpolar

Compound in which two fatty acids and phosphoric acid are esterified to the three hydroxyl groups of glycerol

•Polar head group is charged \n

•Phosphate group is ionized at \n neutral pH \n

•Positively charged amino group is \n contributed by an amino alcohol \n esterified to the phosphoric acid

•Complex mixtures of esters of long-chain carboxylic acids and long- \n chain alcohols \n

•Serve as protective coatings for plants and animals

•Contain sphingosine, a long- \n chain amino alcohol \n

•Found in plants and animals and \n are abundant in the nervous \n system

•Lipid to which a sugar moiety is bonded

•Lipids with a characteristic fused-ring structure •Three six-membered rings (the A, B, and C rings) \n •One five-membered ring (the D ring)

Four fused rings in total

Cholesterol is an important steroid, it acts as a precursor for other steroids

membrane function

Aggregate of a lipid molecule in which the polar head groups are in contact with water and the hydrophobic parts are not that is held together by noncovalent interactions (van der waals and hydrophobic interactions)

That the hydrocarbon interior of saturated and unsaturated fatty acid chains and the fused-ring system of cholesterol

triacylglycerols

Sphingolipids, gangliosides, cerebrosides have larger hydrophilic groups and are more likely to be found on the outer layer of a curved bilayer

phosphoacylglycerols with smaller hydrophilic groups are more common on the inner layer.

phosphoacylglycerols such as phosphatidylethanolamine and phosphatidylcholine

Saturated fatty acids have a LINEAR arrangement of hydrocarbon chains leading rigidity

Unsaturated fatty acids have a KINKY arrangement that causes disorder in its packing and leads to greater fluidity

The presence of cholesterol can enhance order and rigidity due to the fused ring structure of cholesterol

detect extracellular signals and trigger intracellular signaling pathway

Loosely bound to the outside of a membrane