Exam 2 Flashcards
A reactant species that is electron rich and attacks another reactant deficient in electrons is termed an electrophile.
False.
When a carbon-carbon bond is split such that one carbon atom loses both electrons, that carbon atom becomes a carbocation.
True.
A transition state proposed to form as part of a reaction mechanism is a transient species that cannot be trapped and studied.
True.
The interior of a globular protein is generally a hydrophobic region. The active site of an enzyme is usually a cleft or pit in the globular protein. All the amino acid residues in the active site, therefore, have hydrophobic side chains.
False.
Ping-pong kinetics are a hallmark of enzymes that catalyze reactions involving covalent catalysis.
True.
Relatively strong binding of reactants in the enzyme active site is necessary for efficient catalysis.
False.
Entropy of reactants increases as reactants are bound by enzymes.
False.
An enzyme active site binds more tightly to a transition-state analog than to its substrate.
True.
Chymotrypsin is a proteolytic enzyme with three alpha-amino termini (N-termini).
True.
Serine proteases contain the same amino acid residues in the catalytic triad that are part of their active sites.
True.
Enzymes typically have an optimal pH range that is based on the protonation state of ionizable groups within the active site.
True.
A free radical is a transient species that results from C-C bond cleavage that leaves a C with an unpaired electron.
True.
A/an ______________ is the species formed when bond cleavage leaves a carbon with both electrons.
carbanion
The ____________ is a description of the bond-breaking and bond-forming events in a chemical reaction.
mechanism
The ________________ is the term for a highly energetic chemical species in which bonds are being formed and broken prior to product formation in an enzyme-catalyzed reaction.
transition state
The energy required for reactants to reach the transition state from their group state is called the ___________ of the reaction.
Ea
In a ______________ reaction, every collision between reactant molecules gives rise to product.
diffusion controlled
Rate enhancement by the binding of reactants close to each other in the enzyme active site is called the _______________.
proximity effect
For a substrate with a positive charge, _______________ or _________________ might be present near the binding site on an enzyme to aid in substrate binding.
aspartate
glutamate
Very strong hydrogen bonds that form when the electronegative atoms are less than 0.25 nm apart are termed _____________________.
low barrier hydrogen bonds
In the catalytic triad of serine proteases, the side chain of a __________ residue acts as a covalent catalyst.
serine
___________________ is the term applied to the catalytic mode that involves increased binding of transition states to enzymes as compared with binding of substrates or products.
Transition state stabilization
The four major modes of enzymic catalysis are ____________, _____________, ____________, and___________.
acid-base catalysis
proximity effects
covalent catalysis
transition state stabilization
Activation of an enzyme by a substrate-initiated conformation change is called ______________.
induced fit
The most frequently found catalytic residue in the active site of enzymes is ______________.
histidine
_______________ are inactive enzyme precursors activated by removal of one or more portions of the precursor molecule.
Zymogens
Iron-sulfur clusters are modified forms of heme groups involved in certain electron transfer processes.
False.
Some coenzymes are made by an organism for its own use and are called metabolite coenzymes.
True.
One should not take vitamin supplements that contain water-soluble vitamins, since an excess might lead to hypervitaminosis.
False.
Pellagra is a disease characterized by dermatitis, impaired digestion, and diarrhea. Pellagra is associated with a deficiency of vitamin C.
False.
A deficiency of vitamin B1, or thiamine, is associated with the disease beriberi, which is characterized by rapid weight loss, muscle atrophy, and weakness.
True.
Tetrahydrofolate, a coenzyme with a polyglutamate tail, is derived from the water-soluble vitamin folic acid.
True.
Vitamin K is a lipid vitamin with antioxidant activity.
False.
NAD+ is a 2 electron oxidizing agent while NADH can serve as 1 or 2 electron reducing agent.
False.
Cytochromes are heme-containing protein coenzymes in which the iron (III) ions of the heme undergo reversible one-electron reduction.
True.
The four fat-soluble vitamins (A, D, E, and K) all function as coenzymes.
False.
Both NAD+ and NADH absorb light at 340 nm.
False
The active portion of the coenzyme A molecule is a thiol group.
True.
Biotin is involved in decarboxylation reactions that require ATP (or an ATP equivalent).
False.
The conversion of an alpha-amino acid to an alpha-keto acid occurs with the conversion of pyridoxamine 5’-phosphate to pyridoxal 5’-phosphate.
False.
Cofactors can be classified in one of two major categories, which are ____________ and _____________.
coenzymes
essential inorganic ions
Some enzymes do not require cofactors to be active. For those that do, the inactive protein itself, without its cofactor, is called the _____________.
apoenzyme
When the inactive protein is combined with its specific cofactor, an active form is created called the ____________.
holoenzyme
The function of coenzymes is to act as ____________.
reagents w/ chemical properties unlike those of any amino acid side chains
The two reducing agents derived from niacin are _____________ and ______________.
NADH
NADPH
Mobile metabolic groups transferred by coenzymes are temporarily attached to the _______________ of the coenzyme.
reactive center
A coenzyme that is chemically altered during an enzyme-catalyzed reaction and that dissociates from the active site is called a/an ____________.
cosubstrate
A coenzyme that does not dissociate from the active site but remains firmly bound to the enzyme is called a/an _______________.
prosthetic group
The reaction of pyruvate decarboxylase takes advantage of the acidity of the proton C-2 of thiamine diphosphate. In this reaction, the enzyme, via the R-group of an amino acid, acts as a __________ to remove the proton on C-2. With a negative charge, C-2 is now a good ____________ which can attack the carbonyl of pyruvate.
base
nucleophile
The two main categories of vitamins are the _______________ vitamins and the _______________ vitamins.
water soluble
lipid soluble
The _________________ are proteins that acts as coenzymes. They usually contain such reaction centers _______________, _______________, and _______________.
protein coenzymes
metal ions
iron sulfur clusters
heme groups
The formation of UDP-glucose from UTP and glucose 1-phosphate results in the release of ______________ which is further hydrolyzed to 2 phosphates.
pyrophosphate
___________ and ___________ almost always act as cosubstrates for dehydrogenases.
NAD+
NADP+
The _______________ form results from a single electron reduction of FAD or a single electron oxidation of FADH2.
semiquinone or FADH
Dihydroxyactetone could be described as a ketotetrose.
False.
The naturally occurring sugars, like the natural amino acids, have a stereochemistry that places them in the L-series of sugars.
False.
