In a bacterial cell, the DNA is in the:
A) cell envelope.
B) cell membrane.
C) nucleoid.
D) nucleus.
E) ribosomes.
C) nucleoid.
A major change occurring in the evolution of eukaryotes from prokaryotes was the development of:
A) DNA.
B) photosynthetic capability.
C) plasma membranes.
D) ribosomes.
E) the nucleus.
E) the nucleus.
In eukaryotes, the nucleus is enclosed by a double membrane called the:
A) cell membrane.
B) nuclear envelope.
C) nucleolus.
D) nucleoplasm.
E) nucleosome.
B) nuclear envelope.
The dimensions of living cells are limited, on the lower end by the minimum number of biomolecules
necessary for function, and on the upper end by the rate of diffusion of solutes such as oxygen.
Except for highly elongated cells, they usually have length
C) 0.3 �m to 100 �m.
The bacterium E. coli requires simple organic molecules for growth and energy�it is therefore a:
A) chemoautotroph.
B) chemoheterotroph.
C) lithotroph.
D) photoautotroph.
E) photoheterotroph.
B) chemoheterotroph.
Which one of the following has the cellular components arranged in order of increasing size?
A) Amino acid < protein < mitochondrion < ribosome
B) Amino acid < protein < ribosome < mitochondrion
C) Amino acid < ribosome < protein < mitochondrion
D) Protei
B) Amino acid < protein < ribosome < mitochondrion
The three-dimensional structure of macromolecules is formed and maintained primarily through
noncovalent interactions. Which one of the following is not considered a noncovalent interaction?
A) carbon-carbon bonds
B) hydrogen bonds
C) hydrophobic interact
A) carbon-carbon bonds
Which one of the following is not among the four most abundant elements in living organisms?
A) Carbon
B) Hydrogen
C) Nitrogen
D) Oxygen
E) Phosphorus
E) Phosphorus
The four covalent bonds in methane (CH4) are arranged around carbon to give which one of the
following geometries?
A) linear
B) tetrahedral
C) trigonal bipyramidal
D) trigonal planar
E) trigonal pyramidal
B) tetrahedral
The macromolecules that serve in the storage and transmission of genetic information are:
A) carbohydrates.
B) lipids.
C) membranes.
D) nucleic acids.
E) proteins.
D) nucleic acids.
Stereoisomers that are nonsuperimposable mirror images of each other are known as:
A) anomers.
B) cis-trans isomers.
C) diastereoisomers.
D) enantiomers.
E) geometric isomers
D) enantiomers.
The enzyme fumarase catalyzes the reversible hydration of fumaric acid to l-malate, but it will not
catalyze the hydration of maleic acid, the cis isomer of fumaric acid. This is an example of:
A) biological activity.
B) chiral activity.
C) racemization.
E) stereospecificity.
Humans maintain a nearly constant level of hemoglobin by continually synthesizing and degrading it.
This is an example of a(n):
A) dynamic steady state.
B) equilibrium state.
C) exergonic change.
D) free-energy change.
E) waste of energy.
A) dynamic steady state.
If heat energy is absorbed by the system during a chemical reaction, the reaction is said to be:
A) at equilibrium.
B) endergonic.
C) endothermic.
D) exergonic.
E) exothermic.
C) endothermic.
If the free energy change ?G for a reaction is -46.11 kJ/mol, the reaction is:
A) at equilibrium.
B) endergonic.
C) endothermic.
D) exergonic.
E) exothermic.
D) exergonic.
The major carrier of chemical energy in all cells is:
A) acetyl triphosphate.
B) adenosine monophosphate.
C) adenosine triphosphate.
D) cytosine tetraphosphate.
E) uridine diphosphate.
C) adenosine triphosphate.
Enzymes are biological catalysts that enhance the rate of a reaction by:
A) decreasing the activation energy.
B) decreasing the amount of free energy released.
C) increasing the activation energy.
D) increasing the amount of free energy released.
E) incre
A) decreasing the activation energy.
Energy requiring metabolic pathways that yield complex molecules from simpler precursors are:
A) amphibolic.
B) anabolic.
C) autotrophic.
D) catabolic.
E) heterotrophic.
B) anabolic.
Hereditary information (with the exception of some viruses) is preserved in:
A) deoxyribonucleic acid.
B) membrane structures.
C) nuclei.
D) polysaccharides.
E) ribonucleic acid.
A) deoxyribonucleic acid.
When a region of DNA must be repaired by removing and replacing some of the nucleotides, what
ensures that the new nucleotides are in the correct sequence?
A) DNA cannot be repaired and this explains why mutations occur.
B) Specific enzymes bind the corre
C) The new nucleotides basepair accurately with those on the complementary strand.
The three-dimensional structure of a protein is determined primarily by:
A) electrostatic guidance from nucleic acid structure.
B) how many amino acids are in the protein.
C) hydrophobic interaction with lipids that provide a folding framework.
D) modific
E) the sequence of amino acids in the protein.
According to Oparin's theory for the origin of life, the prebiotic atmosphere:
A) already contained some primitive RNA molecules.
B) basically was very similar to the atmosphere of today.
C) contained many amino acids.
D) had an abundance of methane, ammo
D) had an abundance of methane, ammonia, and water.
What six characteristics distinguish living organisms from inanimate objects?
(1) are chemically complex and highly organized;
(2) extract, transform, and
use energy from their environment;
(3) have the capacity to precisely self-replicate and self-assemble;
(4) exploit a chemical interplay with their environment;
(5) possess progr
All cells are surrounded by a plasma membrane composed of lipid and protein molecules. What is the function of the plasma membrane?
The plasma membrane acts as a barrier to the free passage of inorganic ions and most other
charged or polar compounds into or out of the cell. It contains proteins that can transport specific ions or molecules. Other membrane proteins act as receptors tha
E. coli is known as a gram-negative bacterial species. (a) How is this determined? (b) How do gramnegative bacteria differ structurally from gram-positive bacteria?
(a) Gram-negative bacteria have little affinity for the dye gentian violet used in Gram's stain, but
gram-positive bacteria retain Gram's stain.
(b) Gram-negative bacteria have an outer membrane and a peptidoglycan layer; gram-positive bacteria lack an ou
Most cells of higher plants have a cell wall outside the plasma membrane. What is the function of the cell wall?
The cell wall provides a rigid, protective shell for the cell. It is porous, allowing water and
small molecules to pass readily, but it is rigid enough to resist the swelling of the cell caused by the accumulation of water.
(a) List the types of noncovalent interactions that are important in providing stability to the threedimensional structures of macromolecules. (b) Why is it important that these interactions be
noncovalent, rather than covalent, bonds?
(a) Noncovalent interactions include hydrogen bonds, ionic interactions between charged
groups, van der Waals interactions, and hydrophobic interactions.
(b) Because noncovalent interactions are weak, they can form, break, and re-form more rapidly and wit
What is the underlying, organizing biochemical principle that results in the chemical similarity of virtually all living things? Given this biochemical similarity, how is the structural and functional
diversity of living things possible?
Living things are composed primarily of macromolecules, polymers of simple compounds of just a few different types. The properties of these polymers are determined by their sequence of monomers and these can be combined in many different ways. Diversity i
Name two functions of (a) proteins, (b) nucleic acids, (c) polysaccharides, (d) lipids.
Many answers are possible including:
(a) proteins function as enzymes, structural elements, signal carriers, transporters;
(b) nucleic acids store and transmit genetic information and act as both structural and catalytic elements;
(c) polysaccharides serv
Why is an asymmetric carbon atom called a chiral center?
An asymmetric carbon has four different substituents attached, and cannot be superimposed on its mirror image�as a right hand cannot fit into a left glove. Thus a molecule with one chiral carbon will have two stereoisomers, which may be distinguishable fr
Differentiate between configuration and conformation.
Configuration denotes the spatial arrangement of the atoms of a molecule that is conferred by
the presence of either double bonds, around which there is no freedom of rotation, or chiral centers, which give rise to stereoisomers. Configurational isomers c
(a) What is optical activity? (b) How did Louis Pasteur arrive at an explanation for the phenomenon of optical activity?
(a) Optical activity is the capacity of a substance to rotate the plane of plane-polarized light. (b)
Using fine forceps, he was able to separate the two types of crystals found in tartaric acid (racemic acid) that are identical in shape, but mirror image
A chemist working in a pharmaceutical lab synthesized a new drug as a racemic mixture. Why is it important that she separate the two enantiomers and test each for its biological activity?
Biomolecules such as receptors for drugs are stereospecific, so each of the two enantiomers of the drug may have very different effects on an organism. One may be beneficial, the other toxic; or one enantiomer may be ineffective and its presence could red
Proteins are constantly being synthesized in a living cell. Why doesn't the number of protein molecules become too great for the cell to contain, leading to cell destruction?
The proteins in a cell are continuously being synthesized and degraded. The cell maintains a
dynamic steady state in which the amount of each protein remains fairly constant at the level required under given conditions.
Describe the relationship between a living organism and its surroundings in terms of both matter and
energy.
Living organisms are open systems and exchange both matter and energy with their
surroundings. They are not at equilibrium with their surroundings; that is, the concentrations of
molecules inside the cells of the organism are not the same as their concent
The free-energy change for the formation of a protein from the individual amino acids is positive and is thus an endergonic reaction. How, then, do cells accomplish this process?
The endergonic (thermodynamically unfavorable) reaction is coupled to an exergonic
(thermodynamically favorable) reaction through a shared intermediate, so that the overall free-energy change of the coupled reactions is negative (the overall reaction is e
What is meant by feedback inhibition and why is it important in a living organism?
Feedback inhibition is the regulation of a biochemical pathway in which a reaction product
inhibits an earlier (usually the first) step in the pathway. It is an important type of regulation because it ensures that energy is not wasted by an organism produ
How is the genetic information encoded in DNA and how is a new copy of DNA synthesized?
The genetic information is encoded in the linear sequence (order) of the four different
deoxyribonucleotides in the DNA. When a new copy of DNA is needed, the two strands of the DNA unwind and each strand serves as a template on which a new strand is synt
Hereditary transmission of genetic information can be viewed as a balance between stability and change. Explain.
Hereditary transmission of genetic information occurs via replication of DNA, the information containing molecule. This process is very accurate and thus results in relatively few changes in genetic information. This stability is important to maintain ind
Discuss how a mutation in DNA could be harmful or beneficial to an organism.
Some mutations lead to the synthesis of an inactive or defective enzyme or other protein that
can no longer carry out its proper function, which is thus harmful to the organism. However, other
mutations may lead to a more stable enzyme or to a protein tha
Describe Stanley Miller's experiment (1953) and its relevance.
Miller subjected a gaseous mixture of ammonia, methane, water vapor, and hydrogen to
electrical sparks for periods of a week or more. When he analyzed the contents of the closed reaction vessel, the gas phase contained CO and CO2, as well as unreacted sta
Describe the "RNA world" hypothesis.
Initially, RNA molecules were both genes and catalysts. Self-replication of these molecules
over long periods of time produced variants that were able to catalyze polymerization of amino acids to form peptides that assumed the function of catalysts. Event
Describe how the rise of O2-producing bacteria might have led to the eventual predominance of aerobic organisms on earth.
The rise of O2-producing bacteria would result in an increase in the levels of O2 in the earth's
atmosphere. This would give a selective advantage to aerobic organisms (which utilized O2 as electron acceptor) over anaerobic organisms for which O2 was toxi
What is meant by endosymbiotic association? How can this concept explain the evolution of eukaryotic cells that are capable of carrying out photosynthesis and/or aerobic metabolism?
An endosymbiotic association is the envelopment of one organism by another to form a relationship that is beneficial to both organisms. It is believed that primitive eukaryotic cells, which were incapable of photosynthesis or aerobic metabolism, formed en
The chirality of an amino acid results from the fact that its ? carbon:
A) has no net charge.
B) is a carboxylic acid.
C) is bonded to four different chemical groups.
D) is in the L absolute configuration in naturally occurring proteins.
E) is symmetric.
C) is bonded to four different chemical groups.
Of the 20 standard amino acids, only ___________ is not optically active. The reason is that its side chain ___________.
A) alanine; is a simple methyl group
B) glycine; is a hydrogen atom
C) glycine; is unbranched
D) lysine; contains only nitrogen
E) pro
B) glycine; is a hydrogen atom
Two amino acids of the standard 20 contain sulfur atoms. They are:
A) cysteine and serine.
B) cysteine and threonine.
C) methionine and cysteine
D) methionine and serine
E) threonine and serine.
C) methionine and cysteine
All of the amino acids that are found in proteins, except for proline, contain a(n):
A) amino group.
B) carbonyl group.
C) carboxyl group.
D) ester group.
E) thiol group.
A) amino group.
Which of the following statements about aromatic amino acids is correct?
A) All are strongly hydrophilic.
B) Histidine's ring structure results in its being categorized as aromatic or basic, depending on pH.
C) On a molar basis, tryptophan absorbs more ul
C) On a molar basis, tryptophan absorbs more ultraviolet light than tyrosine.
Which of the following statements about cysteine is correct?
A) Cysteine forms when the �CH2�SH R group is oxidized to form a �CH2�S�S�CH2� disulfide bridge between two cysteines.
B) Cysteine is an example of a nonstandard amino acid, derived by linking t
A) Cystine forms when the �CH2�SH R group is oxidized to form a �CH2�S�S�CH2�
disulfide bridge between two cysteines.
The uncommon amino acid selenocysteine has an R group with the structure �CH2�SeH (pKa ? 5).
In an aqueous solution, pH = 7.0, selenocysteine would:
A) be a fully ionized zwitterion with no net charge.
B) be found in proteins as D-selenocysteine.
C) never
A) be a fully ionized zwitterion with no net charge.
Amino acids are ampholytes because they can function as either a(n):
A) acid or a base.
B) neutral molecule or an ion.
C) polar or a nonpolar molecule.
D) standard or a nonstandard monomer in proteins.
E) transparent or a light-absorbing compound.
A) acid or a base.
Titration of valine by a strong base, for example NaOH, reveals two pK's. The titration reaction occurring at pK2 (pK2 = 9.62) is:
A) �COOH + OH? ? �COO? + H2O.
B) �COOH + �NH2 ? �COO? + �NH2+.
C) �COO? + �NH2+ ? �COOH + �NH2.
D) �NH3+ + OH? ? �NH2 + H2O.
D) �NH3+ + OH? ? �NH2 + H2O.
In a highly basic solution, pH = 13, the dominant form of glycine is:
A) NH2�CH2�COOH.
B) NH2�CH2�COO?.
C) NH2�CH3+�COO?.
D) NH3+�CH2�COOH.
E) NH3+�CH2�COO?.
C) NH2�CH3+�COO?
For amino acids with neutral R groups, at any pH below the pI of the amino acid, the population of amino acids in solution will have:
A) a net negative charge.
B) a net positive charge.
C) no charged groups.
D) no net charge.
E) positive and negative char
B) a net positive charge.
What is the approximate charge difference between glutamic acid and ?-ketoglutarate at pH 9.5?
A) 0
B) �
C) 1
D) 1�
E) 2
B) �
The formation of a peptide bond between two amino acids is an example of a(n) ______________reaction.
A) cleavage
B) condensation
C) group transfer
D) isomerization
E) oxidation reduction
B) condensation
Thepeptide alanylglutamylglycylalanylleucine has:
A) a disulfide bridge.
B) five peptide bonds.
C) four peptide bonds.
D) no free carboxyl group.
E) two free amino groups.
C) four peptide bonds.
An octapeptide composed of four repeating glycylalanyl units has:
A) one free amino group on an alanyl residue.
B) one free amino group on an alanyl residue and one free carboxyl group on a glycyl residue.
C) one free amino group on a glycyl residue and o
C) one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue.
At the isoelectric pH of a tetrapeptide:
A) only the amino and carboxyl termini contribute charge.
B) the amino and carboxyl termini are not charged.
C) the total net charge is zero.
D) there are four ionic charges.
E) two internal amino acids of the tetr
C) the total net charge is zero.
Which of the following is correct with respect to the amino acid composition of proteins?
A) Larger proteins have a more uniform distribution of amino acids than smaller proteins.
B) Proteins contain at least one each of the 20 different standard amino ac
C) Proteins with different functions usually differ significantly in their amino acid composition.
The average molecular weight of the 20 standard amino acids is 138, but biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight. Why?
A) The number 110 is based on the fact that the average molecular weight of
B) The number 110 reflects the higher proportion of small amino acids in proteins, as well as the
loss of water when the peptide bond forms.
In a conjugated protein, a prosthetic group is:
A) a fibrous region of a globular protein.
B) a nonidentical subunit of a protein with many identical subunits.
C) a part of the protein that is not composed of amino acids.
D) a subunit of an oligomeric pro
D) a subunit of an oligomeric protein.
Prosthetic groups in the class of proteins known as glycoproteins are composed of:
A) carbohydrates.
B) flavin nucleotides.
C) lipids.
D) metals .
E) phosphates.
A) carbohydrates.
Which of the following refers to particularly stable arrangements of amino acid residues in a protein
that give rise to recurring patterns?
A) Primary structure
B) Secondary structure
C) Tertiary structure
D) Quaternary structure
E) None of the above
B) Secondary structure
Which of the following describes the overall three-dimensional folding of a polypeptide?
A) Primary structure
B) Secondary structure
C) Tertiary structure
D) Quaternary structure
E) None of the above
C) Tertiary structure
For the study of a protein in detail, an effort is usually made to first:
A) conjugate the protein to a known molecule.
B) determine its amino acid composition.
C) determine its amino acid sequence.
D) determine its molecular weight.
E) purify the protein
E) purify the protein.
By adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to:
A) determine a protein's isoelectric point.
B) determine an enzyme's specific activity.
C) determine the amino acid composition of the protein.
D) preserve a
E) separate proteins exclusively on the basis of molecular weight.
To determine the isoelectric point of a protein, first establish that a gel:
A) contains a denaturing detergent that can distribute uniform negative charges over the protein's surface.
B) exhibits a stable pH gradient when ampholytes become distributed in
B) exhibits a stable pH gradient when ampholytes become distributed in an electric field.
The term specific activity differs from the term activity in that specific activity:
A) is measured only under optimal conditions.
B) is the activity (enzyme units) in a milligram of protein.
C) is the activity (enzyme units) of a specific protein.
D) ref
B) is the activity (enzyme units) in a milligram of protein.
The functional differences, as well as differences in three-dimensional structures, between two different enzymes from E. coli result directly from their different:
A) affinities for ATP.
B) amino acid sequences.
C) roles in DNA metabolism.
D) roles in th
B) amino acid sequences.
One method used to prevent disulfide bond interference with protein sequencing procedures is:
A) cleaving proteins with proteases that specifically recognize disulfide bonds.
B) protecting the disulfide bridge against spontaneous reduction to cysteinyl su
C) reducing disulfide bridges and preventing their re-formation by further modifying the �SH
groups.
A nonapeptide was determined to have the following amino acid composition: (Lys)2, (Gly) 2, (Phe) 2, His, Leu, Met. The native peptide was incubated with 1-fluoro-2,4-dinitrobenzene (FDNB) and then hydrolyzed; 2,4 dinitrophenylhistidine was identified by
C) His-Leu-Phe-Gly-Lys-Lys-Phe-Met-Gly.
Even when a gene is available and its sequence of nucleotides is known, chemical studies of the protein are still required to determine:
A) molecular weight of the protein.
B) the amino-terminal amino acid.
C) the location of disulfide bonds.
D) the numbe
C) the location of disulfide bonds.