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.
Epimers are two carbohydrates that differ only in the configuration of groups at a single chiral center.
True.
Monosaccharides that form six-membered rings are called pyranoses.
True.
The complete hydrolysis of starch, glycogen, and cellulose would yield only D-glucose.
True.
Amylopectin is an entirely linear polymer of D-glucose units found in natural starch.
False.
Lactose is a disaccharide that contains a beta 1-4 type linkage.
True.
Maltose, lactose, sucrose, and cellobiose are all reducing sugars.
False.
Glycogen is like the amylopectin of starch except that glycogen has beta 1-4 linkages between D-glucose units.
False.
Fructose forms a cyclic structure that is a hemiketal.
True.
D-Glucose and D-Galactose are epimers.
True.
The anomeric carbon of an aldose is always carbon 1.
True.
Glycerol is a sugar alcohol.
True.
The Gram stain procedure for bacteria involves interaction of a purple dye with peptidoglycans of the bacterial cell walls.
True.
Most glycoproteins are found in the cytoplasm of cells.
False.
A carbohydrate that is made by joining five monosaccharides is called a/an ______________.
oligosaccharide
The new chiral center formed when a monosaccharide such as D-galactose assumes a cyclic form is called the ______________.
anomeric carbon
The two different forms of D-fructose that exist in solution, which differ in the -OH group orientation at the number 2 carbon, are called ____________.
anomers
The C-3 epimer of D-glucose iscalled the _________.
D-allose
The digestion of starch by amylase produces an amylase-resistant core called a/an ______________.
limit dextrin
The reaction of a monosaccharide with an alcohol produces a/an ____________.
glycoside
The homoglycan ____________, composed of ____________ units in beta 1-4 type linkages, is found in the exoskeleton of insects and crustaceans.
chitin
N-acetyl-D-glucosamine
Bacterial cell walls contain a combination of small peptides and carbohydrates. This is referred to as the _____________ layer of the cell wall.
peptidoglycan
Large glycoproteins found in mucus, which contain O-linked oligosaccharides, are called ____________.
mucins
When fructose cyclizes, it most commonly forms a _________.
furanose
Sorbitol is an example of a type of compound called a/an _____________.
sugar alcohol
In the ABO blood type system, the addition of _________________ to the H antigen converts the H antigen into the A antigen.
N-acetylgalactoseamine
Double bonds in polyunsaturated fatty acids are conjugated.
False
Phosphatidyl choline (also called lecithin) is a type of phospholipid found in biological membranes.
True.
Of the three types of membrane lipids mentioned in the text, all are charged.
False.
Plasmalogens are sphingosine derivatives.
False.
All phospholipases catalyze the specific hydrolysis of phosphoester bonds of phospholipids.
False.
The fatty acid component of a ceramide is attached to sphingosine via an ester bond.
False.
Gangliosides contain N-acetylneuraminic acid group.
True.
Micelles are aggregates of cholesterol.
False.
Membrane lipid bilayers are permeable to water.
True.
Triacylglycerols are neutral lipids.
True.
Membrane proteins are associated only with the surfaces of biological membranes.
False.
The two surfaces of a biological membrane differ from each other.
True.
Integral proteins can move within the lipid bilayer of the membrane.
True.
A wax is an ester made from a long chain alcohol and a long chain fatty acid.
True.
A triacylglycerol that contains 3 saturated fatty acids will have a higher melting point than one containing 3 unsaturated fatty acids.
True.
_________ and __________ are essential fatty acids for mammas.
lineoleate
linolenate
Three major types of lipids in animal membranes are ________, _________, and _________.
glycerophospholipid
sphingolipids
cholesterol
A moiety common in the head group of all phosphatidates is ___________.
phosphate
Three common amino alcohols found in phosphatidates are ___________, ___________, and ___________.
serine
choline
ethanolamine
___________ are glycosphingolipids that provide cells with distinctive surface markers such as those that provide the basis of ABO blood grouping.
Gangliosides
During the process of partial hydrogenation, _____________ fatty acids are converted to _____________ fatty acids with small amounts of _____________ fatty acids produced as a by-product.
unsaturated
saturated
trans
The type of enzyme that catalyzes formation of phosphatidates from glycerophospholipids is _____________.
phospholipase D
_____________, which are abundant in nerve tissue, contain sphingosine, a fatty acid, and a carbohydrate such as glucose, galactose, or an oligosaccharide.
Cerebrosides
____________ is an ATP-dependent protein that moves phospholipids from the outer to the inner leaflet of a membrane.
Flippase
The more fluid phase of membranes is called the ___________, and less fluid phase is called the ___________.
liquid crystalline phase
gel phase
The movement of a phospholipid from one monolayer to the other in a membrane is called _______________.
transverse diffusion
The two types of proteins associated with membranes are the _____________ and ____________ proteins.
peripheral
integral
Specific peripheral proteins on the inner surfaces of membranes that have GTPase activity and function as signal transducers are called _____________.
G proteins
The movement of a molecule with its concentration gradient using a protein transported is referred to as _______________.
facilitated diffusion
The movement of sodium across a membrane, against its concentration gradient using the hydrolysis of ATP as energy source represents __________ active transport. The use of those sodium ions to move glucose across a membrane against its concentration gradient represents _________ active transport.
primary
secondary
Metabolism is an inclusive term used to indicate all reactions carried out by living cells.
True.
The enzymes of the glycolytic pathway are found in the cell cytoplasm. Since they are not compartmentalized, glycolysis is always “on” and will convert glucose to pyruvate as long as any glucose is available.
False.
Cells are very efficient at capturing the stored energy in a molecule such as glucose; thus, the efficiency of energy conversion approaches 100%.
False.
One gram of NaCl dissolved in a test tube of water has a greater entropy than does a gram of NaCl in the form of a crystalline solid.
True.
The Gibbs free energy change is a measure of the energy available in a reaction.
True.
For a reaction to be spontaneous, the change in free energy, delta G, must be negative.
True.
Processes that result in an increase of the entropy of the system are always spontaneous.
False.
The free energy change, delta G, in a system is dictated only by the absolute temperature and the change in heat content (enthalpy), delta H, of the system.
False.
Cellular reactions tend to reach equilibrium so that delta G becomes zero.
False.
Cellular reactions for which the steady state ratio of products to reactants, Q, is numerically not close to the normal equilibrium constant, Keq, are known as metabolically irreversible reactions.
True.
For a reaction of the type A + B C + D with a Keq = 0.125, one could say that the reaction proceeds nearly to completion.
False.
In biological systems, ATP plays a central role in energy transfer since it has an intermediate phosphoryl transfer potential.
True.
Glycolysis is an example of a linear metabolic pathway.
True.
Most chemoautotrophs are eukaryotic organisms that oxidize inorganic molecules and use CO2 as a carbon source.
False.
ATP contains 3 high energy phosphoanhydride bonds.
False.
In a reaction where NAD+ is converted to NADH, NAD+ is said to be the oxidizing agent.
True.
_________ reactions are those by which the cell synthesizes needed materials such as proteins and nucleic acids, while ________ reactions are those by which the cell degrades materials for energy and building blocks.
Anabolic
catabolic
Three “forms” of metabolic pathways are ________, ______, and _________.
linear
cyclic
spiral
The flow of metabolites through a pathway is called ________.
flux
Two event that increase the likelihood of a spontaneous process are a large __________ in the entropy of the system and a/the __________ of heat by the system.
increase
release
The multistep catabolism of glucose to pyruvate is called _____________.
glycolysis
The type of bond in ATP or ADP that has the highest free energy of hydrolysis is called a/an _________________.
phosphoanhydride bond
A molecule or species that loses one or more electrons in a reaction is called a/an ___________ agent and becomes ____________.
reducing
oxidized
Energy from catabolic pathways is most often conserved in the form of ________.
ATP
Energy-rich phosphate-storage molecules that occur in muscle tissue are called __________. The best example is __________.
phosphagens
phosphocreatine
Phosphorylated compounds with phosphoryl-group transfer potentials equal to or higher than that of ATP are termed ____________.
energy rich compounds
Metabolic pathways are controlled by the modulation of allosteric enzymes. When the rate of the pathway is slowed by the action of a product of the pathway, we say that the pathway is controlled by __________ inhibition. If the rate of the pathway is increased by the action of a substrate within the pathway, we say that the pathway is controlled by _________ activation.
feedback
feedforward
Individual enzymes in a pathway are regulated by _______________ or by reversible ______________.
allosteric modulation
covalent modification
The relative tendency, in an oxidation-reduction reaction, for one species to accept electrons from another species (be reduced) is termed the ______________.
reduction potential
A nonphotosynthetic organism that requires an organic carbon source such as glucose is called a/an _______________.
chemoheterotroph
Two biological processes that are entropy driven are ____________ and ___________.
protein folding
lipid bilayer formation
